ORGANIC WASTE
- A RENEWABLE ENERGY SOURCE
Process solutions for production and use of biogas
and digestate resulting from organic waste
in the Pomeranian voivodeship
The research presented in this publication was conducted within the framework of the Project entitled
"Pomeranian Biogas Model" [POM-BIOGAS] co-funded by the Norwegian Financial Mechanism under
the Polish-Norwegian Research Cooperation Programme, which is operated by the National Centre
for Research and Development.
Bjarne Paulsrud, Beata Szatkowska, Aquateam COWI AS, Oslo, Norway
Jan Hupka, Robert Aranowski, Gdansk University of Technology
Adam Cenian, Tadeusz Zimiński, The Szewalski Institute of Fluid-Flow Machinery
of Polish Academy of Sciences in Gdańsk
Katarzyna Dembowska, Katarzyna Pontus, InnoBaltica Ltd.
Gdańsk, October 2016
Research leading to the results presented in the publication
received funding from the Polish-Norwegian Co-operation Programme
operated by National Centre for Research and Development,
as part of the Norwegian Financial Mechanism for the period 2009-2014
under the framework of the project entitled "Pomeranian Biogas Model" [POM-BIOGAS],
Agreement No. Pol-Nor/202919/57/2013.
Research Team:
Robert ARANOWSKI, Żaneta BARGAŃSKA, Adam CENIAN, Witold CENIAN,
Mateusz CIROCKI, Krzysztof CZERWIONKA, Olga DENYSIUK, Aleksandra GŁOGOWSKA,
Hussein Al-HAZMI, Jan HUPKA, Przemysław KOWAL, Iwona KOPCZYŃSKA-CICHOWSKA,
Aleksandra KORKOSZ, Joanna LELIWA, Joanna MAJTACZ, Jacek MĄKINIA,
Katarzyna PONTUS, Bjarne PAULSRUD, Grażyna RABCZUK,
Adam STRZELCZYK, Katarzyna RONEWICZ, Beata SZATKOWSKA, Nikola ŚNIADECKA,
Andrzej TONDERSKI, Agnieszka TUSZYŃSKA, Tadeusz ZIMIŃSKI
Editors:
Jan Hupka, Adam Cenian, Bjarne Paulsrud,
Beata Szatkowska, Robert Aranowski, Katarzyna Dembowska
Table of Content
ABSTRACT ........................................................................................................................................................... 5
INTRODUCTION ................................................................................................................................................. 7
1. SUBSTRATES ................................................................................................................................................... 8
1.1. BIO-WASTE RESOURCES IN THE REGION .......................................................................................... 8
1.2. MAPPING AND CHARACTERISTICS OF ORGANIC WASTE ............................................................. 9
1.3. SUMMARY .............................................................................................................................................. 17
1.4. REFERENCES .............................................................................................................................................. 17
2. BIOGAS POTENTIAL OF THE ORGANIC FRACTION OF MUNICIPAL WASTE .......................... 19
2.1. MUNICIPAL ORGANIC WASTE...................................................................................................................... 19
2.2. COMPOSITION OF THE ORGANIC FRACTION OF MUNICIPAL WASTE .............................................................. 20
2.2.1. Variability of the composition - difficult to predict ........................................................................... 20
2.2.2. Need for research on the model batch ............................................................................................... 21
2.2.3. Model batch composition................................................................................................................... 21
TABLE 1. COMPOSITION OF 'MODEL' WASTE ...................................................................................................... 22
2.2.4. Organic fraction of separately collected municipal waste - 'wet' ...................................................... 22
2.3. METHANE GENERATION POTENTIAL FOR ORGANIC MUNICIPAL WASTE RESULTING FROM THE CHEMICAL
COMPOSITION - "MODEL" FRACTION AND SEPARATELY COLLECTED .................................................................. 24
2.4. SUMMARY .................................................................................................................................................. 30
2.5. LITERATURE: .............................................................................................................................................. 30
3. PILOT PLANT AND LABORATORY PLANT .......................................................................................... 31
3.1. PROCESS SCALE .......................................................................................................................................... 31
3.2. LABORATORY PLANT .................................................................................................................................. 31
3.3. PILOT PLANT .............................................................................................................................................. 33
3.4. SUMMARY .................................................................................................................................................. 40
4. USE OF BIOGAS ............................................................................................................................................ 41
4.1. ORIGIN AND COMPOSITION OF BIOGAS........................................................................................................ 41
4.2. FEASIBILITY STUDY OF SELECTED BIOGAS APPLICATIONS .......................................................................... 42
4.2.1. Use of biogas and biomethane ........................................................................................................... 42
4.2.2. Combined heat and power (CHP) ..................................................................................................... 42
4.2.3. Injection of biomethane into the gas grid .......................................................................................... 43
4.2.4. Biomethane as a transport fuel .......................................................................................................... 44
4.3. COMPARISON OF BIOGAS USES - STUDY OF SELECTED CASES ...................................................................... 45
4.4. BIOGAS ENRICHMENT ................................................................................................................................. 46
4.5. ECONOMICS OF BIOGAS ENRICHMENT TECHNOLOGY .................................................................................. 49
4.6. RESULTS FOR SELECTED ENRICHMENT TECHNOLOGIES .............................................................................. 50
4.6.1. SFR technology .................................................................................................................................. 50
4.6.2. Polyamide membrane technology ...................................................................................................... 51
4.6.3. Technology for removal of H2S/NH3 in a system with a fixed bed ..................................................... 53
4.7. SOCIO-ECONOMIC ASPECTS OF BIOGAS USE IN POLAND .............................................................................. 53
4.7.1. Farm biogas plant with a biogas enrichment system - biomethane use ............................................ 54
4.7.2. Biomethane in urban transport in Poland ......................................................................................... 55
4.8. CONCLUSIONS REGARDING THE USE OF BIOGAS ......................................................................................... 56
5. SOCIO-ECONOMIC ANALYSIS OF BIOGAS PRODUCTION FROM ORGANIC WASTE ............. 57
6. UTILISATION OF DIGESTATE ................................................................................................................. 61
6.1. FERTILISATION USING DIGESTATE .............................................................................................................. 61
6.2. NON-AGRICULTURAL USE OF DIGESTATE ................................................................................................... 62
6.2.1. Burning pellets from digestate ........................................................................................................... 62
6.2.2. Nutritional value ................................................................................................................................ 62
6.2.3. Ash composition................................................................................................................................. 63
6.2.4. Calorific value ................................................................................................................................... 64
6.3. AGRICULTURAL USE ................................................................................................................................... 64
6.4. DIGESTATE USE - OWN RESEARCH .............................................................................................................. 68
6.4.1. Studies of nitrification and denitrification in an SBR (sequential batch reactor).............................. 70
6.4.2. Research of soil application of digestate .......................................................................................... 71
6.5. LITERATURE ............................................................................................................................................... 74
Abstract
The main objective of the project entitled "Pomeranian Biogas Model" (acronym:
POM-BIOGAS; www.pom-biogas.eu) was to investigate the possibility of using the organic
fraction of municipal and industrial waste for an environmental friendly production of biogas
as one of the sources of renewable energy. The methane fermentation process is well managed
for agricultural substrates, while still being a challenge for municipal waste due to technical,
economic and social barriers. local, regional and global scale.
Anaerobic digestion of the organic fraction separated from municipal and industrial waste
reduces the volume of waste sent to landfills, produces biogas and contributes to a reduction of
methane emissions into the atmosphere. An important aspect of the developed process
was the recovery of nutrients from digestate, which is an additional advantage, in addition
to the use of dewatered digestate as a fertiliser easy for distribution.
As a result of research and analysis activities lasting more than three years, performed
by means of co-operation between scientists and experts from Poland and Norway, solutions
have been developed for efficient ecological waste management, aimed at using them
to produce energy, respecting the environmental, social and economic factors, which have been
summarised in this publication.
The main objectives of the project included:

optimising the composition of the substrate in order to achieve the highest quality
of the biogas

biogas production process optimisation, in a deliberately constructed and built pilot
plant

new approach to the processing and use of biogas and digestate.
These objectives have been grouped into four thematic areas:

Waste substrates

Biogas installations and technology

Use of biogas

Use of digestate.
Conducted studies have shown that the Pomorskie voivodeship features significant sources
of organic waste (municipal and industrial), available for methane fermentation.
The identified biomass amount and conducted AMPTS tests support co-fermentation of biowaste.
The heterogeneous nature of municipal waste could hinder the implementation
of the technological process due to the presence of undesirable substances, as well as
the varying nutrient content, with the nutrients supporting micro-organisms in anaerobic
processes. Organic waste tends to putrefy quickly, which increases the likelihood
of the development of pathogens representing an epidemiological threat. The choice
of appropriate process conditions that would render the digestate more hygienic is
an important issue in preventing the spread of pathogenic micro-organisms. The hygienisation
effect is obtained by applying the thermophilic methane fermentation (55 °C) process
and/or biomass thermolysis.
The efficiency of methane fermentation was tested in reactors of three sizes:
1) a laboratory multi-reactor device (0.5 dm3 each) from Bioprocess Control, Sweden
2) a large laboratory plant of two bioreactors (10 dm3 each) and
3) a pilot plant with two bioreactors (1000 dm3 each).
Both bioreactor plants were designed and manufactured in the Department of Chemical
Technology of the Gdańsk University of Technology. Reactors of all sizes were equipped with
a stirrer.
Research carried out on model waste batches has made it possible to develop methods
and collect experience, which allowed the process parameters for waste fermentation
to be determined. The process remained stable throughout the experiments, i.e. 180 days,
despite the high volatility of the substrates. The thermophilic process conditions have made
it possible to use a short retention time and a high load, while ensuring a high degree
of biomass hygienisation, which means that further use of the resulting digestate, virtually
odourless, is not burdensome.
The results show the potential for applying the activated sludge process in the treatment
of fermentation sludge liquor from dewatering of the digestate, which is both an effective
and economical method of removing biogenic elements or its further treatment for recovery
of nutrients. A gradual adaptation of the activated sludge was observed in relation
to the applied fermentation liquid, which confirmed the possibility of processing continuously
higher doses of the medium undergoing purification.
In the case of small biogas plants, co-generation using the heat at near-by consumers
is the most effective way for utilising biogas. For large biogasproducers, a better option
is to enrich and supply methane to the grid or use it as a transport fuel. A key factor
in the economic aspects of a biogas plant investment is the cost of biogas production,
in particular the selection of a substrate mix. The cost of dedicated crops, such as maize
or wheat, accounts for up to 50% of the production cost. On the other hand, municipal waste or
slurry may even have a negative price, constituting an additional revenue stream
for the biogas plant.
Modestly, we hope that information contained in this publication based upon our research
results will inspire the reader to cooperate in the implementation of waste management plans
using a biogas plant, especially at the level of a municipality (gmina).
Introduction
The Pomeranian Biogas Model (acronym: POM-BIOGAS) project was implemented
by a Project Consortium consisting of four Partners - three from Poland and one from Norway,
and was a response to the demand for knowledge in the area of producing biogas from biomass
coming from municipal waste. In the Pomeranian voivodeship a number
of initiatives for the construction of energy islands has been created and there is also interest in
energy clusters - biogas plants (economically viable) are a key source of renewable energy for
both innovative programmes.
Among organic wastes used for the production of biogas, the organic fraction recovered from
municipal waste is the most difficult substrate, with the greatest component and biomass quality
variability, as well as significant uncertainty about the presence of components interfering in
the process, such as pathogenic bacterial flora, mycoflora, chemical substances or xenobiotics.
At the core of the research covered by the Project (taking into account the market and social
needs and conditions) is the co-operation between science and the economy, with a strong
emphasis on the protection of industrial property and commercialisation of the results. These
are undoubtedly key elements of the region's development policy.
This publication summarises the Project and discusses selected issues. These consist of four
thematic areas: inventory of fermentable biomass resources in the region; process aspects
of these studies, conducted for three biogas performance scales; assessment of biogas use,
as well as general issues of digestate utilisation. Research leading to the results presented
in this document has received funding from the Polish-Norwegian Research Cooperation
Programme, which is operated by the National Research and Development Centre, as part
of the Norwegian Financial Mechanism 2009-2014.
Jan Hupka
Project Scientific Leader
Gdańsk University of Technology
1. SUBSTRATES
Beata SZATKOWSKA, Bjarne PAULSRUD
1.1. BIO-WASTE RESOURCES IN THE REGION
Growth in the EU is still accompanied by increasing amounts of waste, causing unnecessary
losses of materials and energy, environmental damage and negative effects on health
and quality of life. It is a strategic goal of the EU to reduce these negative impacts, turning
the EU into a resource efficient "Recycling Society". Resource efficiency and waste
management are key elements of EU environmental policy and the Europe 2020 strategy.
Bio-waste is an important waste stream. It is estimated that it constitutes about 20 - 40%
of municipal solid waste (MSW). The potential of bio-waste in Europe equals to 80 M tpa
(million tonnes per annum), while presently recycling of bio-waste in Europe is 24 M tpa,
that means more than 50 M tonnes of bio-waste is wasted every year! Meanwhile, bio-waste
has a potential to contribute to targets of the Renewable Energy Source (RES) Directive
(2009/28/EC).
Anaerobic digestion (AD) naturally occurs in the nature. Its potential to generate methane has
been recognized by engineers as an advantage, and nowadays it is widely applied around
the word as an environmentally sustainable technology to manage organic waste (e.g. food,
agricultural, industrial wastes).
This concept is not yet widely used in Poland due to a number of economic, social
and technical barriers. Here, there are only about 210 biogas plants treating sewage sludge,
animal manure and organic wastes, while in neighboring countries (e.g. Germany) these figures
are given in thousands. The total installed electrical power from biogas in 2013
in Poland was about 136 MW, whereas according to the adopted strategic documents
this number should reach 802 MW in 2020. Therefore it is desired to map and characterize
the available organic substartes.
Moreover, in regards to municipal waste and according to the National Waste Management
Plan covering the years 2011-2014 and the outlook for the years 2015-2022 there is a need
to reduce by 2020 the amount of municipal biodegradable waste that presently is landfilled,
to 35% by weight of wastes generated in 1995. Additionally, the revised EU Waste Framework
Directive (2008) includes a new 50 % recycling target for waste from households, to be fulfilled
by 2020. Therefore, more efforts should be made in Poland to map
and characterize available organic waste substrates, and to further develop anaerobic digestion
technology as one of the solutions which can contribute to solving many environmental
problems linked to organic waste management.
The Pomeranian Biogas Model project (POM-BIOGAS), funded by the Polish-Norwegian
Research Programme with the main objective to provide innovative technological solutions
for production and utilization of biogas generated from municipal and industrial organic waste,
is one of the actions taken towards this development.
The project focuses on the area of The Pomeranian Voivodeship which is situated in northcentral Poland at the Baltic Sea and is one of three coastal provinces in Poland. It covers
the area of 18,293 km2 (5.9% of the surface of Poland) and is an integral part of the Polish
and European Baltic Sea Region. The administrative center is Gdańsk. Traditionally, a strong
position in the Pomeranian Region is held by the food industry, which produces about 11%
of total industrial production in the Pomeranian region and employs about 20 thousand people.
For several years, in food processing industry, the biggest turnover was generated
by the fish processing industry, which revenues represent approximately 30% of the sales value
of the local sector of industry.
Another important part in the turnover of the regional food sector is occupied by meat
processing and production of oils and fats.
1.2. MAPPING AND CHARACTERISTICS OF ORGANIC WASTE
Assessment of available organic substrates in the Pomeranian region in Task 1.1 was mainly
based on statistical data acquired from Marshal’s Office in Gdańsk, Polish Central Statistical
Office, Waste Management Plan for the Pomeranian Voivodeship 2018 (“Plan Gospodarki
Odpadami dla Województwa Pomorskiego 2018” PGO 2018) and Agency for Restructuring
and Modernization of Agriculture (ARMA). Collected data were subjected to graphics analysis
using GIS. As a result of task the following sources of waste have been identified
as important in the Pomeranian Voivodeship:

Organic waste from industrial sources;

Sludge from industrial and municipal wastewater treatment plants;

Biodegradable municipal waste

Biodegradable agricultural waste (manure)
Collected data showed that Gdańsk and Gdynia are not the municipalities with the highest
amount of organic waste potentially available for biogas production, despite their high
population density.
Information regarding the closest and most abundant types of organic waste around Gdańsk has
been analyzed for two circles with the radius 50 and 25 km, respectively. Within
a distance of 50 km from Gdańsk, the total amount of organic waste is 3 280 923 t/a, divided
among the different sources: 446 676 t/a Industrial waste, 28 192 t/a Sludge, 2 270 772 t/a
Agricultural waste (livestock manure), and 535 333 t/a Municipal organic waste.
Within a radius of 25 km from Gdańsk, the total amount of organic waste is 1555 470 t/a,
divided among the different sources: 224 153 t/a Industrial waste, 21 602 t/a Sludge,
901 843 t/a Agricultural waste (livestock manure), and 407 872 t/a Municipal organic waste.
Figures 1 and 2 show GIS analysis of data collected for industrial and biodegradable municipal
waste, while Table 1 shows all main organic substrates, which were identified
in the radius of 50 km from Gdańsk being a center of the region.
Figure 1. Location of landfills and waste treatment utilities in Pomerania, and the amount of biodegradable
municipal waste handled annually.
Figure 2. Location of industries generating biodegradable waste and their annual amount (t/a)..
Table 1. Amounts of potentially available organic waste within a distance of 50 km from Gdańsk.
Waste type
Sludge (industrial
and municipal)
(100% total
solids)
Agricultural
waste (livestock
manure)
28 192
2 270 722
Amount [t/a]
Biodegradable
industrial waste
Biodegradable
municipal waste
446 676
535 333
Norway has come a long way with the biological treatment and energy recovery from organic
waste up to the level where it is now one of the leading countries in the world
with comprehensive knowledge and advanced technology in the waste management sector.
With its great experience with organic waste handling and biomass utilisation, it can act
as a role model for other countries.
Poland became a member of EU in 2004. Since then, it took many efforts to adjust its standards
to the European levels. This also includes the waste management sector. Even though many
improvements have been done in the last 10 years, Poland still faces many challenges.
Norway has developed the source separation system that allows for direct use of organic
municipal waste in biogas plants. Only less than 20% of municipal waste consists of bio-waste
(Table 2 and 2a). In Poland, separate collection system is still under development.
The bio-waste share in municipal solid waste in Poland varies between 40-50%.
Also other recycling parameters, saying about municipal solid waste quality, indicate
considerably lower values for Poland. A comparison of recycling of municipal solid waste in
Poland and Norway is presented in the Table 2.
Table 2. Recycling of municipal solid waste in Poland and Norway
Poland
Municipal waste generation per capita in 2010
Bio-waste share in municipal solid waste in years 2008-2010
Recycling of municipal solid waste in 2009
Material recycling rate
Bio-waste recycling
(1) Entire Poland – 293; Pomeranian - 305; GUS 2013 r.
(2) 496; GUS 2013 r.
(3) 21%; EUROSTAT 2014 r.
(4) 26%; EUROSTAT 2014 r.
(5) 11%; EUROSTAT 2014 r.
(6) 16%; EUROSTAT 2014 r.
Norwey
(1)
330
(331,6 in Pomeranian
Region in 2010)
40-50%
(58% in the Pomeranian
region in 2010)
21%
(28.7 % in the
Pomeranian region in
2010)
480
(2)
less than 20%
42%
14%
(3)
27%
(4)
7%
(5)
14%
(6)
Table 2a. Amounts of wastes in Norway after handling, in 1000 tones (Statistisk Sentralbyrå, 2014,
https://www.ssb.no/natur-og-miljo/statistikker/avfregno/aar/2016-0525?fane=tabell&sort=nummer&tabell=266995)
total
wet organic
waste
green
waste
wood
sludgey
paper
glass
metal
electric
concrete
No.
1
2
3
4
5
6
7
8
9
10
Total
11 937
688
179
1 347
236
769
97
811
153
979
Recycling
4 244
218
1
143
28
734
84
800
117
38
Biogas
production
81
79
0
0
0
0
0
0
0
0
Composting
408
190
160
6
1
0
0
0
0
0
Polimers
and gums
616
0
0
4
5
0
0
0
0
569
Combustion
4 220
188
9
1 177
6
34
0
1
119
2
Storage
1 502
0
0
0
21
1
7
0
16
324
Other
467
3
8
8
4
0
3
0
1
46
Unkown
399
9
0
8
171
0
3
10
0
0
Slag, dust,
ashes
Plastic
Gum
Fabrics
Discarded Radioactive
vehicles
waste
Hazardous
waste
Mixed
waste
other
16
17
18
19
Lightly
contaminated
soil
20
No.
11
12
13
14
15
Total
handling
781
211
54
2
223
0
1 392
2 804
1 212
1 481
Recycling
378
98
98
2
178
0
304
84
1 003
0
Biogas
production
0
0
0
0
0
0
0
2
0
0
Composting
0
0
0
0
0
0
0
51
1
0
Polymers and
gumy
30
0
0
0
0
0
0
2
6
7
Combustion
18
109
109
0
32
0
332
2 254
35
0
Storage
355
2
2
0
13
0
432
195
133
1 474
Other
0
0
0
0
0
0
325
37
13
0
Unknown
0
2
2
0
0
0
0
179
17
0
Poland, having a high share of bio-waste in its municipal solid waste, still recycles only
a limited amount of bio-waste, resulting in a relatively marginal effect of bio-waste recycling
on total municipal waste recycling rates. This is a clear indication that a stronger focus on biowaste recycling is needed. There is a great potential for improving the overall recycling rate
of municipal waste through increasing bio-waste recycling.
For Poland to fulfil the 50% recycling target by 2020, it is necessary to obtain a very high yearly
increase in recycling, from 2010 to 2020. According to EUROSTAT, there was
a significant increase in the recovery of biomass in years 2010-2014 in Poland,
from 7 to 11%. In the same time in Norway, recovery of biomas from waste increased from 14
to 16%. The necessary increase in recycling will require a tremendous effort from
the Polish government, the local authorities and a good cooperation between the public
and private sector, in order to secure sufficient treatment capacity. Up to now, bio-wastes
handling relied mainly on composting, while in Norway – most of biomass goes under
anaerobic digestion.
Still, the basic method of municipal waste utilization in the Pomeranian region is landfilling
while the increased use of bio-wastes as resources in the Pomeranian region can bring tangible
benefits as: increase in local energy security, improvement of the environment, reduction of
unemployment and activation of local entrepreneurship, a significant reduction
in the cost of heating and electricity. The use of large amounts of organic wastes has a longterm and multi-step character. The implementation of such a vison is a complex and difficult
undertaking in terms of financial, technical and organizational means. But it is worth to face
this challenge, because the benefits to municipalities from the wider use of organic wastes
create unique opportunities for socio-economic development, which can be described
as a "jump" of civilization and technology.
Learning from the experience of other countries, cooperating with the private sector and using
EU funding, the Pomeranian region has a chance to implement the new system efficiently,
following the model solutions and avoiding the mistakes made by others.
The availability of EU funding as well as the interest of technology suppliers, construction
companies, installation operators, investors and financial markets in infrastructure projects,
create a unique opportunity for Polish regions and cities to make up for the decades
of backwardness in developing modern waste management systems.
In the Pomeranian region, the following obstacles with the greatest impact on the waste
management sector were identified:

scarcely effective separate collection of wastes at the source, especially biodegradable
wastes

low purity of organic fraction of municipal waste

lack of education and awareness of society about the benefits of waste separate
collection system

problems with determination of the actual amount of municipal waste generated.
The short comparison of legal status, collection systems and processing of the wastes between
Pomeranian region and Norway is presented in table 3.
Table 3. Comparison of waste management in the Pomeranian Region and in Norway.
Regulations
Collection
Processing
Pomeranian Region
Since 2004 following EU policy.
New commitments to the EU include reduction
of waste sent to landfill, including
biodegradable waste and increasing the level of
recycling and preparation for re-use of selected
fractions
of municipal waste (paper, plastics, metals and
glass).
In 2012 EU targets reflected in the Polish law –
new act on maintaining cleanliness and order in
municipalities changing the existing model of
municipal waste management, communities
become responsible for wastes.
Having about 38 municipal waste landfills.
Developing separate collection system. Still big
stream of municipal wastes in category of
“mixed” = not subjected to segregation.
Dominating handling method – landfilling.
Focus on the construction of additional new
RIPOKs (regional plants for treatment of
municipal waste) and construction of
incineration plants.
Norway
Since 90’ policy aimed at waste recovery.
Not being an EU member, but follows EU
regulations. Frontrunner of waste recycling
and energy recovery.
Well-developed separate collection system.
Bio-wastes collected at the source.
Dominating handling method – biological
treatment. All new plans for biological
treatment involve anaerobic treatment and
the production of biogas. Well-developed
technologies
for
enhanced
biogas
production.
Mapping of available substrates showed that in Pomerania region there is a vast potential
of organic waste, which could be digested. Sludge represents the smallest but important amount
of wastes, however especially municipal sludge is usually utilized at the Wastewater Treatment
Plants (WWPT) where they are produced. Agricultural wastes represent the largest amount of
analysed wastes, and the construction of biogas plants based on agriculture substrate is the most
common and well known technology used around the world, as well
in Poland. Therefore, these wastes (municipal sludge and agricultural waste) were considered
the least interesting for further investigation.
In particular, important is evaluation of specific biomethane potential (SBP) of organic fraction
of municipal solid waste (OFMSW) and various streams of organic industrial waste,
such as: slaughter, food, distillery processing wastes.
For this purpose Automatic Methane Potential Test System (AMPTS) devise was used. AMPTS
determines the biogas potential of particular substrates or mixture of substrates (Figure 3.). The
system is based upon batch operation and is nearly fully automatic – requires only careful setup of the machine. The simple operation makes it easy to compare several substrates (or
mixtures) at once with exactly the same conditions.
The apparatus was developed by the company Bioprocess Control from Lund in Sweden.
It consists of 15 digestion bottles/reactors (shown on the left), that can be run simultaneously.
Each digestion reactor is connected via tubes to the CO2 absorption bottles (shown
in the centre), which are filled with a 3M NaOH solution and an indicator (saturated solution
in the presence of indicator changes the colour). These are connected to the gas measurement
or flow cell array (shown on the right), where gas is collected under levers submerged
in water – the buoyancy of the gas lifts the lever, the gas is released and metered.
The digestion bottles are submerged in a water bath, which is held at a constant temperature,
and each digestion bottle has an attached motorized stirring rod which stirs each reactor.
Each digestion bottle will experience exactly the same conditions, so theoretically
the differences in measured methane volumes are due solely to the different substrates used.
Figure 3. Photo of AMPTS (II) apparatus (II).
According to the European Commission report, the total yearly production of bio-waste
(defined in the Waste Framework Directive (WFD) as "biodegradable garden and park waste,
food and kitchen waste from households, restaurants, caterers and retail premises,
and comparable waste from food processing plants") in the EU amounts to 118 -138 Mt/a.
Around 88 Mt of this amount originate from municipal waste and between 30 to 50 Mt/a from
industrial sources such as food processing (Saveyn & Eder, 2014). The data for
the Pomeranian region allows us drawing a similar conclusion for that region. Both, industrial
and municipal wastes, seem to be important and so far neglected sources of potential organic
material suitable for biogas production. Therefore it was decided to run the following tests:
Test no 1:
Biodegradable municipal wastes from municipal waste landfill:

mixed raw – municipal wastes without selective collection

mixed after sieving - municipal wastes without selective collection after sieving (100
mm)

wet from selective collection - municipal organic wastes from selective collection

green wastes - grass, branches, leaves, etc.
Test no 2:
Biodegradable industrial wastes from:

distillery

slaughterhouse

malt production

supermarket – overdue milk products and vegetables.
Test no 3 was based on results from test 1 and 2, and included two mixtures of municipal
and industrial substrates: mixed after sieving + supermarket waste and wet from selective
collection + malt waste.
Performed AMPTS tests showed that both industrial and municipal waste have a high specific
biomethane potential (SBP) varying in the range of 300-520 Nml/gVS (Figure 4).
The addition of industrial wastes to organic fractions of municipal solid waste (MSW) increases
the overall biogas production.
600
Nml/gVS
500
524
404
400
415
393
334
404
464
441
357
337
295
300
200
mixed after siev+superm.
wet from sel col.+malt
supermarket
malt
slaughterhouse
distillery
green
mixed after siev.
wet from sel col.
wet from sel col
0
mixed raw
100
Figure 4. Summary of all AMPTS results.
Obtained values of SBPs for mixtures of municipal and industrial substrates were
in agreement with both theoretical calculations and values given in the literature (Table 4).
Table 4. Specific biomethane potential of different substrates.
Waste (substrate)
Methane yield
(ml CH4/g VS)
Literature reference
MSW, unsorted
MSW, sorted
organic fraction
Green wastes
400-500
400
Slaughterhouse
waste
300- 700
Fish waste
Food waste
400-550
472
Overdue dairy
products
Distillery waste
Malt waste
100-300
520
150-400
350
Angelidaki and Ellegard, 2003
Angelidaki and Ellegaard, 2003
Hartmann and Ahring, 2005
Angelidaki and Ellegaard, 2003
Carlsson and Uldal, 2009
Deublein and Steinhauser, 2008
Carlsson and Uldal, 2009
Schnürer and Jarvis, 2009
Ahring et al., 1992
Ward et al., 2008
Carlsson and Uldal, 2009
Carlsson and Uldal, 2009
Willkie et al., 2000
Schnürer and Jarvis, 2009
Tshiteya, 1985
1.3. SUMMARY
The EU Landfill Directive requires Member States to set up a national strategy
for the implementation of the reduction of biodegradable waste going to landfills. Moreover,
the EU's updated Waste Framework Directive (2008) includes a new 50% recycling target
for waste from households, to be fulfilled by 2020. Poland, as one of the member states,
must follow the rules and obligations imposed by EU.
Performed studies in WP1 showed that Pomeranian region has a big potential of organic waste
available for anaerobic digestion. This process, if applied in the region, can provide sustainable
solutions for the reduction of biodegradable wastes, the generation of renewable energy
and the conversion of waste to resources, and therefore its application to organic wastes can be
a solution which will allow fulfilling of above EU requirements.
Identified a big volume of industrial waste and performed AMPTS tests, indicate that anaerobic
digestion of municipal bio-waste can be supplemented or enriched by industrial biodegradable
waste and this seems to be the very promising solution for organic waste handling
and renewable energy production in Pomeranian region.
1.4. References
Angelidaki, I. and Ellegaard, L., 2003. Co-digestion of manure and organic wastes
in centralized biogas plants. Status and future trends. Applied Biochemistry and Biotechnology
95:109, 95-105.
Ahring, B. K., Angelidaki, I., Johansen, K., 1992. Anaerobic treatment of manure together
with industrial waste. Water Science and Technology 25:7, 311-18.
Berglund, M. and Börjesson, P., 2003. Energianalys av biogassystem. Report no. 44. Dept.
teknik och samhälle, Lund University (in Swedish).
Carlsson, M. and Uldal, M., 2009. Substrathandbok för biogasproduktion. Report SGC 200,
Svenskt Gastekniskt Center (SGC) (in Swedish).
Deublein, D.; Steinhauser, A., 2008. Biogas from waste and renewable resources,
an introduction. WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany.
Hartmann, H., Ahring, B. K., 2005. Anaerobic digestion of the organic fraction of municipal
solid waste: Influence of co-digestion with manure. Water Research 39, 1543–52.
Saveyn H. & Eder P., 2014. End-of-waste criteria for biodegradable waste subjected
to biological treatment (compost & digestate): Technical proposals. European Commission
Joint Research Centre Institute for Prospective Technological Studies. Report EUR 26425 EN.
ISBN 978-92-79-35062-7.
Schnürer, A., Jarvis, Å., 2009. Micorbiological Handbook for Biogas Plants, Rapport
U2009:03. Avfall Sverige, Svenskt Gastekniskt Center (SGC).
Tshiteya, M., 1985. Fuel production from a brewery residue. Energy Volume 10:12, 1299-1306.
Ward, A. J., Hobbs, P. J., Holliman, P. J., Jones, D. L, 2008. Optimisation of the anaerobic
digestion of agricultural resources. Bioresource Technology 99, 7928–40.
Wilkie, A. C., Riedesel, K. J., Owens, J. M., 2000. Stillage characterization and anaerobic
treatment of ethanol stillage from conventional and cellulosic substrates. Biomass
and Bioenergy 19, 63-102.
2. BIOGAS POTENTIAL OF THE ORGANIC FRACTION OF MUNICIPAL WASTE
Nikola ŚNIADECKA, Aleksandra KORKOSZ, Jan HUPKA
2.1. Municipal organic waste
Establishing the characteristics of biomass destined for fermentation, an analysis of the organic
fraction of municipal waste has been conducted. In the first stage of analysis, studies
on the composition of raw waste have been conducted aimed at planning the methodology
of marking and treating the selected fraction in biological decomposition processes. The study
used two fractions of organic wasteas substrates for a process of thermophilic methane
fermentation. The first fraction was "model" waste. The determination of the composition
of "model" waste was conducted based on the results of many months of analysis
of the composition of the organic fraction of waste selected from mixed municipal waste
(not specified in the study). "Model" waste consisted of pure raw food, free of undesirable
inorganic contaminants. The second source of biomass was the organic fraction of municipal
biomass derived from a dual system, i.e. separate collection of biodegradable waste.
In the following text, this fraction will be referred to as "wet" waste. "Wet" waste was taken
directly from Zakład Utylizacyjny Sp. z o.o. in Gdańsk (ZUT).
Organic municipal waste is a stream that comes from private households (kitchen waste)
and urban green areas (green waste). Such waste is collected under two separate systems:
separate and mixed. Figure 1 presents a general diagram of handling organic waste in ZUT
in Gdansk, where mechanical-biological processing is employed. The organic waste delivered
and processed in the processing plant is divided into two streams: 1) organic waste
collectedseparately, called "wet", and 2) organic waste present in the mixed waste fraction,
called the "biofraction." These streams are processed independently through biological
stabilisation during intensive composting in a closed hall, combined with maturation in an open
space. The "wet" waste stream is treated as a source of pure raw material used for biological
processes and immediately after being deposited in the delivery hall, it is transported
to the composting hall, where, following the addition of a structural component, it remains
for about 3 weeks. Ultimately, "wet" waste is meant to produce compost, which is suitable
for agricultural use.
In turn, the "biofraction" stream is an organic fraction separated from a stream of mixed
municipal waste, with no division into "wet" and "dry" waste. The "dry" waste stream
is subjected to manual and mechanical separation aimed at recovering recyclable materials
and the energy fraction. The "biofraction" remaining after the mechanical process is subjected
to composting. The final product is referred to as "wastes not otherwise specified", which
is waste that due to a high degree of pollution (mainly inert substances, i.e. glass, foil, etc.)
does not meet the requirements for organic fertilisers.
tworzywa sztuczne
metal
szkło
papier
pozostałe
odzysk materiałów wtórnych
zmieszane odpady komunalne - „suche”
odpady organiczne komunalne - „mokre”
Hala wyładowcza „nadawa”
odpady zmieszane
Hala sortownicza
frakcja organiczna
Hala kompostowania
stabilizat
Plac dojrzewania kompostu
kompost
plastics
metal
glass
paper
other
recycling
mixed municipal waste - "dry"
organic municipal waste - "wet"
Delivery hall
mixed waste
Sorting hall
organic fraction
Composting hall
waste not otherwise specified
Composting yard
compost
Figure 1. Block diagram of mechanical-biological processing of municipal waste.
2.2. Composition of the organic fraction of municipal waste
2.2.1. Variability of the composition - difficult to predict
Municipal waste treatment by means of thermophilic methane fermentation has been
implemented (see Chapter 3). Over the three subsequent steps, conducted continuously,
methane fermentation of municipal waste with certain compositions was conducted:
Step 1 - model organic waste; Step 2 - model organic waste + food products past their sell-by
date; Step3 - the organic fraction of "wet" municipal waste from the waste disposal plant.
Research conducted on both organic fractions of municipal waste has made it possible
to establish their composition (Figure 2). The analysis of the "biofraction's" composition was
carried out at monthly intervals, while the outcome, a mean of the composition of several
analyses, was the basis for proposing the composition of the model municipal waste batch (step
1). The "biofraction" consists of about 50% inorganic impurities, which is a technological
impediment to the processing of this fraction, as well as an obstacle in its use due to the presence
of inert substances. The content of individual organic components, as well as those that are not
the biofraction, is varied and the analysis did not indicate specific percentage dependencies due
to waste seasonality. Municipal waste is characterised by significant variability in composition
and subject to seasonal fluctuations. The composition of waste depends on, among others: the
season, the degree of urbanisation (rural/urban area), the type of buildings (single- and multifamily housing), the influence of society, the place of sampling waste for analysis.
zielone i kuchenne
zwierzęce
pozostałe nieorganiczne
papier i tektura
maj 2015
kwiecień 2015
marzec 2015
luty 2015
styczeń 2015
grudzień 2014
listopad 2014
0%
10%
20%
30%
40%
zielone i kuchenne
zwierzęce
papier i tektura
pozostałe nieorganiczne
maj 2015
kwiecień 2015
marzec 2015
luty 2015
styczeń 2015
grudzień 2014
listopad 2014
50%
60%
70%
80%
90%
100%
green and kitchen
animal
paper and cardboard
other inorganic
May 2015
April 2015
March 2015
February 2015
January 2015
December 2014
November 2014
Figure 2. "Biofraction" composition - seasonality of the composition [3].
2.2.2. Need for research on the model batch
Due to the large fluctuations in raw material composition of municipal waste, an attempt was
made to compose a model batch intended for biological processing. The "model" composition
was based on analyses performed for the organic fraction selected from mixed municipal waste.
The main advantage of using "model" waste is its fixed and unchanging composition, which
makes it possible to plan and anticipate the effects of the process. Moreover, model waste is
devoid of toxic substances that can disrupt or even stop the process. Using waste with an
unchanging composition makes it possible to perform analyses with any number of repetitions
and allows optimisation of the process, whose results can be applied to real samples of
municipal waste in subsequent processes.
2.2.3. Model batch composition
The composition of "model" waste includes all typical biodegradable components and those
most common in the organic fraction of municipal waste. According to the presented Table 1,
the organic fraction was divided into three groups of waste: kitchen (including animal), green
(from gardens and green areas), as well as paper and cardboard. Each group has been divided
into waste materials with a specified percentage composition. All components included in the
"models" are composed of fresh raw materials according to the established composition and
proportions.
Table 1. Composition of 'model' waste
Type of waste
[%]
Fraction composition
[%]
Model 1
Kitchen
(including animal)
70
Green
10
Paper and
paperboard
Model 2
20
Dairy
Animal
30
15
Kitchen
30
Fruit juices
Breads
other
5
10
10
Vegetable and fruit peelings (potatoes, citrus, apple,
carrots, etc.).
Whole fruits and vegetables
Animal bones and skins, including fish
Other (tea bags, husks, bread, rice, pasta, etc.).
Tree leaves
Small tree branches
Kitchen towels, handkerchiefs
Office paper
Butter, cream, milk, cottage cheese, yoghurt, eggs
Animal meat, processed meat, fish
Apples, potatoes, bananas with skin, citrus fruit, tomatoes,
lettuce
Apple juice, orange juice and other
Yeast-raised cakes and wheat bread
Cut flowers, office paper
60%
20%
10%
10%
50%
50%
50%
50%
5%
of each
subcomponent
2.2.4. Organic fraction of separately collected municipal waste - 'wet'
The "wet" fraction is characterised by its quick putrification and nauseous smell, so the
frequency of sampling was decided by the conditions and the possibility of storing waste under
appropriate conditions, while avoiding partial decomposition of biomass.
During the process, from March to the end of August, 11 separate samples were collected,
which after thorough removal of fractions other than biomass (usually plastics, textiles, rubber,
glass and others), was subjected to grinding, thermolysis and methane fermentation.
The "wet" fraction should by definition include only pure biomass. However,
analyses show that the organic fraction is in the range of between 35 and 95% (Figure 3)
depending on the month or circumstances of sampling (holidays). Each of the batches was
subjected to a detailed analysis of raw materials, during which waste was divided into four
groups and their percentage determined (Figure 4).
9 10 11
10.08.16.
8
07.07.16.
7
20.06.16.
6
09.06.16.
5
31.05.16.
4
23.05.16.
3
06.05.16.
2
06.04.16.
28.07.16.
14.07.16.
0%
10%
20%
30%
40%
50%
60%
70%
80%
90% 100%
niebędące biomasą
biomasa
niebędące biomasą
biomasa
non-biomass
biomass
9 10 11
10.08.16.
8
07.07.16.
7
20.06.16.
6
09.06.16.
5
31.05.16.
4
23.05.16.
3
06.05.16.
2
Figure 3. Composition of the organic fraction of municipal waste for batches 2-11
06.04.16.
28.07.16.
14.07.16.
0%
10%
kuchenne
kuchenne
zielone
zwierzęce
papier
20%
30%
40%
zielone
50%
60%
70%
zwierzęce
80%
90%
100%
papier
kitchen
green
animal
paper
Figure 4. Detailed composition of the organic fraction of municipal waste for batches 2-11.
The differences in the content of individual components is visible in subsequent samples.
For the total content of organic waste with respect to inorganic residues, there is an upwards
trend, which can be affected by an increase in the amount of grass clippings and garden plants
in spring and summer. During early summer dry leaves and branches dominated, and kitchen
waste accounted for a high percentage of the fraction's composition.
In the "wet" fraction the composition fluctuations are greater than in the case
of the "biofraction", which does not help in forecasting the use of waste in anaerobic processes.
2.3. Methane generation potential for organic municipal waste resulting from
the chemical composition - "model" fraction and separately collected
The theoretical potential for methane generation of two organic fractions of municipal waste
was calculated. The aforementioned calculation of this potential used information
on the elemental CHN-O composition of analysed waste samples. The calculation results are
presented in Table 2 and
Table 3. Calculations and analyses were based on appropriate literature: Buswell and Mueller
(1952), Sobotka et al. (1983), Klimiuk et al. (2010), Cho et al. (2012).
The calculations are based on two equations describing the stoichiometry of methane generation
(CH4). The first was the equation by Buswell and Mueller (1):
(1)
This formula does not take into account the content of nitrogen compounds, which have
a negative effect on the anaerobic process when in excess. The amount of nitrogen bound
in the waste is, in fact, large and variable, and its increase causes a fall in the efficiency
coefficient YCH4/g of the substrate. The above balance should be supplemented with a nitrogen
component and other elements [5]. Nitrogen content is included in the equation proposed
by O'Rourke (1968) (2), which is an extension of the above-described equation by Buswell
and Mueller (1952)
(2
)
Boyle (1976) extended the equation by another element - sulphur (3).
(3
)
where,
C, H, N, S, O
- chemical elements,
n, a, b, z
- atomic number of the elements;
In this document the calculation is limited to the first two equations.
Electron equilibrium for a substrate redox conversion with a general formula CnHaObNz
has been described using the formula 4n+1a-2b-3z, which has been referenced for 1 carbon
atom. The formula is referred to as the, so-called, substrate reducibility degree "ɤ " or the
equivalent of free electrons in the organic material with respect to 1 g of carbon atoms.
ɤ = 𝟒 +
𝒂
𝒃
𝒛
− 𝟐 − 𝟑
𝒏
𝒏
𝒏
The following have also been calculated and listed in the table:

formula based on the stoichiometry of the equation, calculated for 1 C atom (CHaObNz)

the degree of reducibility of the substrate within the range of 0 to 8 (ɤ of the substrate)

the ratio of carbon mass to the rest of the substrate's components (δ of the substrate)

theoretical coefficient of methane efficiency (YCH4)

methane percentage (%CH4)

calorific value (Q)

Chemical Oxygen Demand (COD).
Table 2. describes the methane potential for the "model" fraction. This includes the potential
of the individual components, as well as the batch as a whole. Table 3,Table 4 andTable 5 refer
to the fraction collectedseparately. The calculations used the methane potential values for the
four main groups of waste in batches (Table 3), taking into account their percentage. The table
shows the division into batches from 2 to 11. During the process of methane fermentation a
significant decrease in the production of biogas was noted, which is why a decision was made
to
add
an extra portion of fish waste. Calculations with an additional portion of fish concern batches
8-11 (Table 4 andTable 5). The addition of source-separated waste improved productivity of
the batch and made it possible to achieve better biogas productivity.
Table 2. Methane potential for the organic fraction of municipal waste with a "model" composition
Ln.
Substrate
Formula
Y CH4
[g CH4/ g substr.]
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
carrot peelings
tangerine peels
bananas
bread
sprigs of flowers
small tree branches
bones
tree leaves
grapefruit peels
apple peels
potato peelings
office paper
sanitary paper
fish
eggshells
potatoes
orange peels
flower leaves
kitchen paper
CH0,14O0,72N0,05
CH0,14O0,04N0,07
CH0,14O0,82N0,09
CH0,15O0,56N0,09
CH0,12O0,73N0,08
CH0,13O0,73N0,07
CH0,19O0,56N0,30
CH0,14O0,71N0,10
CH0,15O0,85N0,10
CH0,17O0,59N0,10
CH0,15O0,27N0,14
CH0,13O1,31N0,04
CH0,14O0,98N0,09
CH0,12O0,28N0,18
CH0,05O1,14N0,20
CH0,17O0,77N0,14
CH0,14O1,02N0,03
CH0,13O0,83N0,06
CH0,15O1,31N0,10
(1)
0.23
0.64
0.2
0.29
0.22
0.23
0.29
0.29
0.19
0.28
0.44
0.09
0.16
0.43
0.12
0.21
0.12
0.12
0.12
Ʃ
Batch total
CH0,14O0,77N0,1
0.25
Y CH4
[dm CH4/kg substr.]
%CH4
[%]
3
COD
[gO2 / g substr.]
(2)
0.21
0.56
0.17
0.24
0.19
0.2
0.17
0.2
0.16
0.24
0.34
0.08
0.13
0.32
0.07
0.17
0.07
0.07
0.07
(1)
322.0
896.0
280.0
406.0
308.0
322.0
406.0
406.0
266.0
392.0
616.0
126.0
224.0
602.0
168.0
294.0
168.0
168.0
168.0
(2)
294.0
784.0
238.0
336.0
266.0
280.0
238.0
280.0
224.0
336.0
476.0
112.0
182.0
448.0
98.0
238.0
98.0
98.0
98.0
(1)
33.68
50.82
31.13
37.83
33.22
33.48
38.47
34.04
30.68
37.47
45.11
18.9
27.26
44.46
22.18
32.91
22.18
22.18
22.18
(2)
31.76
48.23
27.89
34.38
30.27
30.93
27.34
30.33
27.04
33.86
39.8
17.49
23.97
37.77
14.83
27.73
14.83
14.83
14.83
(1)
0.49
0.17
0.56
0.39
0.5
0.49
0.38
0.48
0.58
0.4
0.25
1.22
0.71
0.26
0.95
0.52
0.75
0.57
1.2
(2)
0.53
0.2
0.66
0.45
0.57
0.56
0.64
0.57
0.7
0.47
0.32
1.33
0.84
0.35
1.55
0.66
0.79
0.64
1.53
0.20
350.0
280.0
32.32
27.93
0.60
0.72
Table 3. Methane generation potential for organic municipal waste resulting from the chemical composition (data for batches 2 - 11)
Ln. Substrate
1
2
3
4
5
kitchen
green
animal
paper
fish (additional)
1
2
3
4
Formula
ɤ of the substrate
[1]
δ of the substrate
[1]
Y CH4
[g CH4/ g substr.]
5
Y CH4
[dm3 CH4/kg substr.]
5
6
7
%CH4
[%]
Q
[kJ/g substr.]
COD
[gO2 / g substr.]
CH0,13O0,6N0,05
CH0,13O0,54N0,04
CH0,15O0,35N0,17
CH0,14O1,14N0,06
CH0,12O0,28N0,18
(1)
2.93
3.05
3.45
1.86
3.56
(2)
2.77
2.92
2.93
1.67
3.02
(1)
0.55
0.58
0.67
0.396
0.72
(2)
0.53
0.56
0.59
0.384
0.63
(1)
0.270
0.295
0.388
0.123
0.43
(2)
0.246
0.274
0.289
0.107
0.32
(1)
378.0
413.0
543.2
172.2
602.0
(2)
344.4
383.6
404.6
149.8
448.0
(1)
36.62
38.17
43.13
23.283
44.46
(2)
34.59
36.53
36.58
20.889
37.77
(1)
15.23
16.65
21.93
6.94
24.14
(2)
13.90
15.48
16.35
6.05
17.83
(1)
0.41
0.38
0.29
0.905
0.26
(2)
0.45
0.41
0.38
1.038
0.35
CH0,13O0,62N0,05
CH0,13O0,57N0,04
CH0,13O0,58N0,05
CH0,13O0,58N0,05
CH0,13O0,59N0,05
CH0,13O0,66N0,05
CH0,13O0,59N0,05
CH0,13O0,57N0,05
CH0,14O0,85N0,06
CH0,13O0,60N0,05
2.90
2.99
2.97
2.97
2.94
2.81
2.95
2.98
2.43
2.94
2.73
2.37
2.82
2.82
2.79
2.66
2.80
6.44
2.96
2.87
0.55
0.50
0.56
0.56
0.56
0.54
0.56
0.57
0.90
0.61
0.53
0.47
0.55
0.55
0.54
0.52
0.54
1.24
0.51
0.55
0.270
0.261
0.280
0.281
0.274
0.257
0.279
0.283
0.172
0.273
0.246
0.222
0.258
0.258
0.252
0.236
0.256
0.598
0.131
0.246
378.0
365.4
392.0
393.4
383.6
359.8
390.6
396.2
240.8
382.2
344.4
310.8
361.2
361.2
352.8
330.4
358.4
837.2
183.4
344.4
36.25
32.49
37.10
37.10
36.78
35.18
36.93
37.29
18.83
35.27
34.18
29.67
35.21
35.22
34.86
33.24
35.03
35.38
19.12
33.62
15.26
14.73
15.84
15.89
15.49
14.52
15.74
15.97
18.56
16.55
13.89
12.52
14.56
14.60
14.22
13.32
14.45
33.79
70.78
22.10
0.44
0.31
0.41
0.41
0.41
0.47
0.42
0.40
57.67
7.78
0.48
0.36
0.45
0.45
0.45
0.52
0.46
0.94
59.87
8.09
"Wet" waste batch
5
6
7
8
9
10
11
12
13
14
2 – 06.04.16.
3 – 06.05.16.
4 – 23.05.16.
5 – 31.05.16.
6 – 09.06.16.
7 – 20.06.16.
8 – 07.07.16.
9 –14.07.16.
10 – 28.07.16.
11 – 10.08.16.
Table 4. Methane generation potential for organic municipal waste resulting from the chemical composition (data for batches 8 - 11 enriched with fish)
1
Ln.
1
2
3
4
Substrate
8 – 07.07.16.
9 –14.07.16.
10 – 28.07.16.
11 – 10.08.16.
2
ɤ of the substrate
[1]
(1)
(2)
2.99
2.81
3.13
2.88
2.80
2.93
3.15
2.86
Formula
CH0,13O0,59N0,05
CH0,13O0,57N0,05
CH0,14O0,85N0,06
CH0,13O0,60N0,05
3
δ of the substrate
[1]
(1)
(2)
0.57
0.55
0.60
0.57
2.59
0.59
0.61
0.57
4
Y CH4
[g CH4/ g substr.]
(1)
(2)
0.287
0.259
0.320
0.275
0.540
0.304
0.329
0.276
5
%CH4
[%]
(1)
(2)
37.32
35.17
39.10
35.98
0.243
36.65
39.39
35.79
6
Q
[kJ/g substr.]
(1)
(2)
16.18
14.63
18.03
15.45
32.37
17.13
18.54
15.49
7
COD
[gO2 / g substr.]
(1)
(2)
0.41
0.45
0.37
0.42
13.63
0.48
0.37
0.42
Table 5. Comparison of changes in methane yield after the introduction of an additional portion of fish (batches 8-11)
Without the addition of fish
Ln.
Y CH4
Y CH4
[g CH4/ g substr.]
[dm3 CH4/kg substr.]
Y CH4
Y CH4
[g CH4/ g substr.]
[dm3 CH4/kg substr.]
Substrate
Formula
1
2
3
4
With the addition of fish
8 – 07.07.16.
9 –14.07.16.
10 – 28.07.16.
11 – 10.08.16.
CH0,13O0,60N0,04
CH0,13O0,58N0,05
CH0,15O0,98N0,03
CH0,13O0,61N0,05
(1)
(2)
(1)
(2)
0.279
0.283
0.172
0.273
0.256
0.598
0.131
0.246
390.6
396.2
240.8
382.2
358.4
837.2
183.4
344.4
Formula
CH0,13O0,59N0,05
CH0,13O0,51N0,08
CH0,13O0,67N0,10
CH0,13O0,50N0,09
(1)
(2)
(1)
(2)
0.287
0.320
0.540
0.329
0.259
0.275
0.304
0.276
401.8
448.0
756.0
460.6
362.6
385.0
425.6
386.4
2.4. Summary
Conducted analyses of the composition of municipal waste, and the following research
on methane potential indicates that the organic fraction of municipal waste is a good raw
material for processing in anaerobic processes combined with energy recovery (methane
production). The heterogeneous nature of municipal waste could hinder the implementation
of the technological process due to the presence of undesirable substances, as well as
the varying nutrient content, as the nutrients support micro-organisms in anaerobic processes.
Organic waste tends to putrefy quickly, which increases the likelihood of the development
of pathogens, which are an epidemiological threat. The choice of appropriate process conditions
that would render the batch more hygienic is an important issue in preventing the spread
of pathogenic micro-organisms. The hygienisation effect is obtained by applying
the thermophilic methane fermentation (55 °C) process and thermolysis (> 70°C for 1 hour)
for lower temperature processes.
In order to properly plan the experiment and assess the methane potential of the substrate,
empirical calculations are used. The methane potential estimated on the basis of the substrate's
chemical formula allows for proper selection of batch components and, if necessary,
co-fermentation, resulting in a higher biogas yield.
Availability of the organic fraction of municipal waste as a clean fraction intended for methane
fermentation can be increased following the principles of separate collection of waste
"at source". The experiences of Western EU countries show that separate collection is the most
effective way to achieve clean raw material waste.
2.5. Literature:
[1]
J. Sikora, “Badanie efektywności produkcji biogazu z frakcji organicznej odpadów
komunalnych zmieszanej z biomasą pochodzenia rolniczego,” Infrastrukt. i Ekol. Teren. Wiej.,
vol. 2, no. IV, pp. 89–98, 2012.
[2]
S. Myszograj, “Produkcja metanu wskaźnikiem oceny biodegradowalności
substratów,” Rocz. Ochr. Środowiska, vol. 13, no. 77, pp. 1245–1260, 2011.
[3]
N. Śniadecka, A. Tonderski, A. Hanel, J. Wojda-Gburek, and J. Hupka, “Mineral matter
in municipal solid waste,” Physicochem. Probl. Miner. Process., vol. 52, no. 2, pp. 973–990,
2016.
[4]
M. Buswell and H. F. Mueller, “Mechanism of Methane Fermentation,” Ind. Eng.
Chem., vol. 44, no. 3, pp. 550–552, 1952.
[5]
M. Sobotka, J. Votruba, I. Havlík, and I. G. Minkevich, “The mass—Energy balance
of anaerobic methane production,” Folia Microbiol. (Praha)., vol. 28, pp. 195–204, 1983.
[6]
E. Klimiuk, T. Pokój, W. Budzyński, and B. Dubis, “Theoretical and observed biogas
production from plant biomass of different fibre contents.,” Bioresour. Technol., vol. 101,
no. 24, pp. 9527–35, Dec. 2010.
[7]
H. S. Cho, H. S. Moon, and J. Y. Kim, “Effect of quantity and composition of waste
on the prediction of annual methane potential from landfills.,” Bioresour. Technol., vol. 109,
pp. 86–92, Apr. 2012.
3. PILOT PLANT AND LABORATORY PLANT
Robert ARANOWSKI, Katarzyna RONEWICZ, Jan HUPKA
3.1. Process scale
Two research systems have been designed for conducting methane fermentation research,
at a laboratory and pilot scale. In order to assure adequate statistical evaluation of the studies,
the measuring systems had a similar structure and the differences were only in ancillary
elements with no significant impact on the research process. Both plants were equipped with
geometrically similar reactors, so as to scale the processes. The methane fermentation process
was performed at thermophilic conditions. Dry organic matter was maintained within a 3-8%
range. Figure 5 presents the core operations and individual processes used in the research.
Figure 5. Main operations and individual processes
3.2. Laboratory plant
The laboratory installation consisted of twin bioreactors with a capacity of 10 dm3 each.
In addition to two fermentation chambers, an additional thermal treatment tank was used.
Its total volume was 1.5 dm3. The bioreactors were heated using heating jackets. Process
parameters for the fermentation in the laboratory plant are shown in Table 6.
Table 6. Basic process parameters of a laboratory plant
Parameter
Process temperature
Hydraulic retention time
Daily organic load
Organic load
Biogas efficiency from t of DOM (for a standard mixture)
Dry matter content
Active volume of fermentation chamber (digester)
Diameter of fermentation chamber
Height of fermentation chamber
Value
55
14
4·10-2
5.7
Unit
°C
Day
kg DOM / day
kg DOM / day m3
150
3-8
6
0.29
0.3
Nm3/t of DOM
% by weight
dm3
m
m
The plant consists of several key elements (Figure 6). Due to the small amount of supplied
biomass, the batch dosing system and digestate receipt system was designed as dosing pistons
with a variable stroke. The heating of bioreactors is conducted in a similar manner to the pilot
plant, through heating jackets with isopropyl glycol as the heating medium.
A)
B)
Figure 6. Laboratory biogas production plant: A. Schematic: 1) frame, 2) fresh biomass dispenser, 3) bioreactor,
4) fresh biomass storage tank, 5) pipeline, 6) dispensing cylinder limiters, 7) electrical box, 8) circulation pump 9)
heater of heating medium; B. Installation photography.
Figure 3. Methane fermentation installation control panel: process visualisation
3.3. Pilot plant
The plant has been designed in order to conduct research on methane fermentation
of the organic fraction of municipal waste in a thermophilic fermentation process on
a fractional-process scale. The size of the plant has been chosen, so as to avoid measurement
errors resulting from batch heterogeneity (organic fraction of municipal waste). In essence,
the system consists of three modules. A biological and thermal processing system for the input,
twin bioreactors for methane fermentation and a dehydrating and digestate processing system.
A schematic diagram of the plant is shown in Figure 4. The reactors were constructed from
AISI 316L stainless steel, while the fittings are made of PP pipes reinforced with an aluminium
cover. The system consists of a thermolysis tank with a total capacity of 800 dm3 equipped
with a stirrer and a heating jacket, and two twin bioreactors with a total capacity of 1000 dm 3
equipped with a stirrer, heating jacket and a strain gauge system used to measure the weight
of the bioreactors. The reactors are heated using a jacket filled with isopropyl glycol using
electric heaters, with a phase power regulator equipped with a PID module. This solution
guarantees highly accurate temperature control in bioreactors, to within 0.2C. The weighing
system provides accurate mass measurement, to within 1 kg. The whole is equipped with flow
meters to measure the biogas flow rate and gas meters counting the amount of produced gas.
A screw pump has been used for loading the hydrolysis unit and bioreactors, and unloading
bioreactors, as well as loading digestate to the centrifuge. Figure 5 shows the general
appearance of the pilot plant for biogas production.
Table 2. Basic technological parameters of the pilot installation
Parameter
Process temperature
Hydraulic retention time
Daily load
Chamber biomass load
Biogas efficiency from t of DOM (for a standard mixture)
Dry matter content
Active volume of fermentation chamber (digester)
Diameter of fermentation chamber
Height of fermentation chamber
Value
55
14
4.5
5.7
Unit
°C
Day
kg DOM / day
kg DOM / day m3
150
3-8
600
0.9
1.1
Nm3/t of DOM
% by weight
dm3
m
m
The plant has been equipped with a surveillance and data archiving system. It makes it possible
to control the fermentation process (set temperature, stirrer speed, loading and unloading
of bioreactors) and registers all measured and pre-set parameters. The control panel is shown
in Figure 6.
Figure 4. Diagram of the pilot installation
Hydrolysis
unit
Bioreactor II
Bioreactor I
Figure 5. General appearance of the pilot installation: a) picture b) visualisation of the plant
Figure 6. Methane fermentation plant control panel: a) process visualisation b) device settings and calibration card
3.4. Study of methane fermentation of the organic fraction of municipal waste on a pilot scale
Studies of methane fermentation of the organic fraction of municipal waste on a laboratory
scale have been conducted in bioreactors with a capacity of 0.5 dm3, reactors with a capacity
of 10 dm3 and pilot scale bioreactors with a capacity of 1000 dm3. The scale increase was aimed
at determining the possibility of scaling the methane fermentation process, as well as identifying
potential hazards that may occur during industrial methane fermentation using the organic
fraction of municipal waste with a variable and non-homogeneous composition. In laboratory
scale tests it is difficult to predict problems that may arise in the hydraulic, grinding and input
composition systems, as well as the operation of bioreactors. Therefore, results obtained in the
experiments performed at a pilot scale.
Biomass obtained from municipal and industrial waste and used in the studies was characterised
in chapter 2. Research on the pilot plant, which was conducted continuously for close to 180
days, can be divided into five periods, which were characterised by variable load
on the bioreactors with the same remaining process parameters maintained. As input for the
methane fermentation process, a properly composed organic fraction of municipal waste was
used to obtain the "model" composition with a similar dry matter content. Such an approach
was aimed at reducing the impact of the variability of the substrate on the process.
Research at the pilot scale started with the introduction of inoculum derived from thermophilic
fermentation of pig slurry to the bioreactors, in the amount of half their working volume. Dry
matter and dry organic matter in the inoculum amounted to 10.3% and 9.4%, respectively.
The intensity of mixing was set at 70 rpm on the basis of experiments, to ensure uniformity
of the biomass. Initially, the dry mass content was maintained at a constant level for about 90
days, in order to stabilise the process and avoid overload with proteins and fermentation
inhibitors. Next, the dry matter content and dry organic matter content was increased regularly
(as shown in Figure 7 and 8), while the hydraulic retention time was reduced (Table 3).
15
Bioreaktor
BioreactorI I
Bioreaktor
BioreactorIIII
Hydrolizer
Hydrolysis unit
Sucha
(%)
mass (%)
Dry mass
10
5
0
0
30
60
90
120
Dzień
fermentacji
Day after
start-up
Figure 7. Changes in dry matter content during the experiment
150
180
15
matter (%)
organic
Drymasa
(%)
organiczna
Sucha
Bioreaktor
BioreactorII
Bioreaktor
BioreactorIIII
Hydrolizer
Hydrolysis unit
10
5
0
0
30
60
90
120
150
180
Dzień
fermentacji
Day
after
start-up
Figure 8. Changes in dry organic matter content during the experiment
Table 3. Hydraulic retention time in the respective periods of the experiment
Stage
I
II
III
IV
V
Duration [days]
6
96
23
20
Hydraulic retention time
up to the present
30 days
20 days
15 days
12 days
11 days
Due to the increasing amount of the input stream and the dry matter content, the daily load
increased simultaneously. Organic load on reactors is shown in Table 4.
Table 4. Organic load on reactors
Period
I
II
III
IV
V
Daily organic load
[kg DOM/d]
1.14
1.89
2.82
4.88
6.27
Organic load
[kg DOM/m3d]
1.90
3.15
4.70
8.13
10.45
In order to achieve high efficiency methane fermentation in the methanogenic phase, it is
important for the pH of the fermentation mixture to be maintained near neutral. After about 45
days of the process, the pH level stabilised and the process remained stable until the end of the
experiment reported here. The average pH value in the last research period was about 7.46 in
the two fermenting reactors (Figure 9). In the preliminary treatment reactor (hydrolysis unit)
fluctuations in pH were observed, resulting from the volatility of the substrates used, but in the
last measurement period the pH remained at a constant level of 5.4, which in relation to the
optimal pH value for bacteria participating in the acid-generation phase being within the range
of 5.2 to 6.3, indicates that the changes are correct.
10
Odczyn
pH (pH)
8
6
4
Bioreactor
I I
Bioreaktor
Bioreactor
II II
Bioreaktor
Hydrolysis
unit
Hydrolizer
2
0
30
60
90
120
150
180
Dzień
fermentacji
Day
after
start-up
Figure 9. pH level during the process
Figure 10 presents daily biogas production and the moments new biomass batches were added
have been marked. In the second stage of the process, i.e. from day 7 to day 103, when the dry
matter content was about 3.5%, the average amount of biogas produced per day was 0.542 m3
in R1 and 0.766 in R2. An increase in the dry matter content brought about an increase in biogas
production at the final stage of the process, up to 2.5 m3.
3,0
Bioreactor
I I
Bioreaktor
Bioreactor
II
Bioreaktor II
3
3
(m/d)
Biogas production
/d)
biogazu (m
Produkcja
2,5
2,0
1,5
1,0
0,5
0,0
0
30
60
90
120
150
180
Dzieńafter
fermentacji
Day
start-up
Figure 10. Daily biogas production
A)
B)
100
60
Bioreaktor I
Bioreaktor II
Stężenie dwutlenku węgla (% v/v)
Stężenie metanu (% v/v)
90
80
70
60
50
40
0
30
60
90
Dzień fermentacji
Bioreaktor I
Bioreaktor II
Stężenie metanu (% v/v)
Stężenie dwutlenku węgla (% v/v)
Dzień fermentacji
120
150
180
Bioreaktor I
Bioreaktor II
50
40
30
20
0
30
60
90
120
Dzień fermentacji
Bioreactor I
Bioreactor II
Methane concentration (% v/v)
Carbon dioxide concentration (% v/v)
Fermentation day
Figure 11. Biogas stream composition: a) methane content, b) carbon dioxide concentration
150
180
The main product of the fermentation process - biogas exhibited the desired quality due to the
high methane content in the stream - the average was 70% (Figure 11).
Table 5. Average values of selected fermentation parameters
Parameter (mean value)
Degree of biomass decomposition
C/N ratio
Biogas yield
Volatile fatty acids
N-NH4+
Volatile fatty acids/alkalinity ratio
Bioreactor I
66%
18.05
0.35 m3/kg DOM
7078 mg/dm3
733 mg/dm3
0.24
Bioreactor II
64%
17.66
0.42 m3/kg DOM
6792 mg/dm3
690 mg/dm3
0.23
As has been shown in table 5., during the whole process duration, the amount of volatile fatty
acids was relatively high, higher that the values suggested as optimal in literature on the subject.
However, at a pH above 7.4, the inhibitory effect of volatile fatty acids does not occur1,
so despite the high volatile fatty content the process remained stable.
A carbon to nitrogen ratio near 18, respectively in bioreactor I and II, was high enough to obtain
a satisfactory efficiency of the fermentation process, reaching even 0.42m3/kg DOM,
comparable to that obtained in agricultural biogas plants.
3.4. Summary
Studies have shown that with appropriate control of the fermentation process it is possible
to use the organic fraction of municipal waste for continuous and stable production of high
quality biogas. Experiments carried out on model batches have made it possible to develop
methods and gather experience, which has enabled the process parameters for the fermentation
of municipal organic waste to be assessed. The process remained stable for the entire duration
of the experiment, i.e. 180 days, despite the high variability of the substrate. The thermophilic
process conditions allowed a short retention time and high organic loads, all the while providing
a high degree of biomass hygienisation, which rendered subsequent use of the resulting
digestate, virtually odourless, not burdensome. As a result, the amount of solid waste requiring
management, is also reduced,. Furthermore, taking into account the production of biogas
and its quality, the obtained results might form the basis for industrial scale implementation.
1
A. Jędrczak, Biologiczne przetwarzanie odpadów, PWN, Warszawa 2007
4. USE OF BIOGAS
Adam CENIAN, Witold CENIAN, Grażyna RABCZUK
4.1. Origin and composition of biogas
The word 'biogas' usually specifies a gas produced in the process of biological decomposition
of biodegradable material in an anaerobic atmosphere. There are three main sources of biogas:

municipal and industrial sewage treatment plants

landfill biogas installations

biogas plants using various biodegradable waste (mainly the organic fraction
of municipal waste, from the production of food and agricultural technology operations,
agricultural waste and animal husbandry).
Depending on the source of the biogas, it contains different concentrations of methane and
carbon dioxide, and a small admixture of hydrogen sulphide and other sulphur compounds,
ammonia, oxygen and nitrogen (Table 4.1.). Biogas is normally saturated with water vapour,
contains dust particles and organic silicon compounds (e.g. siloxanes).
Table 4.1. Composition of biogas produced in different plants; as per [ 2.3]
Components
3
Landfill
Sewage
treatment plant
Natural gas
Methane
[vol.%]
6070
4555
55 65
28.8-97.8
Carbon dioxide
[vol.%]
3040
3040
3545
0.01-42
Nitrogen
[vol.%]
<1
515
<1
0.3-47.8
Oxygen
[% vol.]
<0.2
<0.5
<0.4
0
104000
502000
10-500
1.5-424,000
Hydrocarbons
[Mg/m3]
0
503000
0
0.06-43.6%
Wobbe index
[MJ/m3]
24-33
20-25
25-30
14.5-55
Hydrogen
sulphide
[ppm]
2
Biogas plant
E.H. Dirkse, Biogas upgrading using the DMT Carborex® PWS Technology, 2009
http://fluid.wme.pwr.wroc.pl/~spalanie/dydaktyka /spalanie_wyklad_energetyka/PALIWA/PALIWA
_GAZOWE.PDF
4.2. Feasibility study of selected biogas applications
The energy value of biogas is mainly dependent on the methane content. The removal of carbon
dioxide from biogas increases this value, thus often determining its use. It is possible to use raw
biogas (without removing CO2) and its purified version (biomethane). Biomethane has
properties almost identical to natural gas, so it can be used interchangeably.
The way biogas is used depends on technical, economic and regulatory factors, as well as
on local conditions and needs. If biogas is used in the place of its production, typically only
30-50% of its energy is converted into electricity. The remainder of the energy is converted into
heat and lost when there is no demand. However, when the biogas is transported by means
of a pipeline and burned in a co-generation system, even over 90% of the energy can be used.
The energy market in Europe is dominated by co-generators, producing electricity and heat.
Such production is supported by support schemes, such as certificates and investment grants.
4.2.1. Use of biogas and biomethane
Main uses of biogas (Fig. 4.1.):

heat and/or steam production

co-generation (combined production of heat and power - CHP) or poly-generation
(heat and/or steam and/or energy and/or cold and/or fuel)

enrichment and injection into the gas grid

enrichment and direct use as a fuel.
Electricity
CHP
Heat
Biogas
enrichment
Biogas facility
CHP
Gas grid
Heat
Biofuel
Heating
Fig. 4.1. Main options for biogas use 4
4.2.2. Combined heat and power (CHP)
Biogas is mostly used in the combined production of electricity and heatproduction stimulated
by various forms of support for renewable energy sources (RES). CHP systems consisting
4
www.fnr.de, Biogas – An introduction, 2013
of a biogas-powered motor driving the biogas-powered electric power generator. Many
different technologies are employed [5]. Reciprocating engines are the most common
technology. Other technologies, such as turbines, Stirling engines and fuel cells, all providing
similar performance, are also used.
The investment costs for CHP systems depend on the size, which for smaller power (approx.
50 kWe) amount to ~ €1000/kWe and €600/kWe for engines with a power of 500 kWe (prices
as of 2015).
Electricity generated in CHP systems can be transferred entirely to the grid or used on-site.
The overall efficiency of the CHP plant depends on the efficiency of the electric generator
and the possibility of using heat. The amount of fuel and energy contained therein transformed
into electricity generally increases with the size of the system and is in the range of 30%
for small CHP systems and 40% for larger ones. Thermal energy accounts for 45 - 60%, while
the resulting overall efficiency of the CHP system reaches 90%.
Using heat generated in the CHP system is a key challenge for the economic success of a biogas
plant and the importance of environmental protection. Optimum use of heat depends on many
factors, such as the location of the biogas plant and its potential consumers, as well as
the demand for heat. Heat can be used for heating, drying and production of cold, as well as
additional production of electricity (eg. in an Organic Rankine Cycle (ORC) system 6). In this
system, heat from co-generation allows evaporation of the organic medium, e.g. silicone oil.
The working substance's vapour moves the turbine, resulting in the production of electricity
in the associated generator. Combined production of electricity and heat from biogas can be
profitable for large farms or producer groups, provided that there is a sufficient source of slurry
or other biomass waste and it is possible to sell excess heat and electricity to external consumers.
4.2.3. Injection of biomethane into the gas grid
Biomethane can act as a substitute for natural gas, after being pumped into the gas grid. It can
still be used by households, industrial recipients and CHP plants, as well as CNG fuel. In order
to inject biogas into the grid, it must be enriched (e.g. to 95% biomethane), conditioned,
measured and compressed. Conditioning consists of odourisation and increasing the calorific
value by adding propane to meet technical standards (including a calorific value above
18 MJ/m3)7.
Bio-methane is introduced into the network at pumping stations which have systems
for measuring and adjusting the gas pressure, a compressor and a gas volume measurement
system. The gas composition is determined there and adapted to local network conditions.
Many EU countries have national standards for the injection of biomethane into the gas grid [8],
[9]. The standards define parameters, such as: energy density, Wobbe index and the permissible
5
O.Razbani et. al, Literature review and road map for using biogas in internal combustion engines, Third Int.
Conf. on Applied Energy 2011, Perugia, Italy
6
D. Rutz, Sustainable Heat Use of Biogas Plants, A handbook, 2012 by WIP Renewable Energies, Munich,
Germany
Rozporządzenie Ministra Gospodarki z 24 sierpnia 2011, Dz. U. 187, poz. 1117.
L. Bailón Allegue ,J. Hinge, Biogas and bio-syngas upgrading, Report of Danish Technological Institute, 2012
9
M. Svenson, Biomethane standards, European wokshop Biomethane, Brussel,2014, GreenGasGrids, SGC
7
8
concentrations of pollutants: sulphur, oxygen molecules; as well as the dew point for water
vapour. These parameters are achieved in the biogas enrichment process. The energy density
and the Wobbe index are determined for a given gas and, if necessary, increased by the addition
of propane. Subsequently, odourants are added and the pressure raised to a level adapted to
the level at the point of injection into the grid.
One of the important benefits of using the gas grid for distribution of biomethane is the fact that
its place of production, usually located in areas with low population density, is connected
to areas of high population density. As a result, the gas can be delivered to a greater number
of consumers. Injection of biomethane into the network improves local gas supply security.
The main barriers for biomethane injection are the high costs of biogas enrichment and access
to the grid. This process is also limited by the location of biogas plants and enrichment
installations, which should be located in close proximity to the gas grid.
The costs of biomethane injection into the gas grid include:

transport from the enrichment system to the gas grid

compressing biomethane to the necessary pressure level

conditioning (matching the caloric value to quality standards by adding propane, butane
or air)

odourisation

measurement of the gas' quality and its flow.
An exact determination of the costs of biomethane injection into the grid is difficult because
they depend on a number of parameters specific to the location, including soil conditions,
engineering, as well as installed monitoring and measuring means. The most expensive part
of the technology is the pipe connection to the gas grid; cost of approx. 150,000 €/km [ 10]
depending on the material and size of the connection pipes, the operating pressure
and the necessary compression.
Data available in the literature confirm that the cost of biomethane injection into the network
is a small part of the cost of biomethane. According to ref. [11] the injection cost is estimated
at 0.1-0.3 ct/kWh.
4.2.4. Biomethane as a transport fuel
Biogas can be used as a fuel for cars, buses and trucks, after enrichment (removal of CO2, water
and hydrogen sulphide). The gas must be odourised and compressed to 200 bar before it can
be used as a fuel [12].
10
B. Balkenhoff et al., Upgraded Biogas as Renewable Energy, SLR consulting, www.iswa.org/uploads/
tx_iswaknowledgebase/5-325paper_long.pdf
11
F. Van Foreest, Perspectives for Biogas in Europe, Oxford Institute for Energy Studies, 2012
12
M. Persson et al., Biogas Upgrading to Vehicle Fuel Standards and Grid Injection, IEA, 2006
Biomethane as a transport fuel is used in the same engines as natural gas, so its quality must
meet similar quality requirements:

a calorific value high enough to increase the maximum distance on a single tank

consistent gas quality for stable engine working conditions

low concentrations of corrosive compounds, including H2S, NH3 and water.
Biomethane produced from agricultural or landfill biogas can be used as a transport fuel
in the following forms:

LBM - liquefied biomethane

CBM - compressed biomethane, used locally or at off-site stations after transport

conditioned and injected into the gas network.
For the production of the liquid fraction of bio-methane the gas is cooled and stored at
a temperature of -160 °C. Then, cars can be filled with LBM using pumps for cryogenic liquids.
The advantage of LBM is its higher density than CBM and the possibility of limiting the size
of tanks. On the other hand, the fuel is less stable and requires great care in filling the tanks.
Vehicles powered by biomethane have significant advantages compared to those equipped
with gasoline or diesel [13] engines. While vehicles using CNG exhibit emission approx. 17%
lower than petrol, the use of biomethane produced from waste reduces greenhouse gas (GHG)
emissions by over 80%. Biomethane produced from dedicated crops allows a smaller reduction
in GHG emissions, at a level of 71 - 76%. The use of biomethane as a fuel will make it possible
to reduce fuel consumption by more than 100 million litres of diesel and limit GHG emissions
by approx. 335,000 tonnes per year.
There are many factors influencing the price of production and distribution of biomethane
as a fuel, including, the current market prices of different transport fuels, the price
of biomethane production, the price of equipment required to use biomethane as a fuel
and the cost of upgrading or buying a new vehicle.
4.3. Comparison of biogas uses - study of selected cases
Usage of biogas should be selected for each of the use cases. Availability and prices
of substrates for biogas production, local energy prices and market availability of gas
and electrical infrastructure, subsidy schemes as well as investment support are the key factors.
There are several studies on determining the optimal conditions for the production of biogas
and its use. Unfortunately, these studies use different optimisation criteria, making them
difficult to compare. Some of them examine the technical criteria, including energy efficiency,
others define the GHG emissions associated with production and use of biogas; still others take
Electrigaz Technologies inc. (2007) Feasibility study – Anaerobic digester and gas processing facility in the
Fraser Valley, British Columbia. Prepared for BC Bioproducts Association, submitted December 2007
13
into account the economic criteria (profitability) of different systems. For example, in [14], [15]
the authors examine different ways of production and utilisation of biogas in Germany from the
point of view of energy efficiency. The results show that biogas plants using different substrates
and processes (e.g. fermentation versus co-fermentation), conversion technologies and the use
of digestate are characterised by different levels of energy efficiency.
In order to minimise environmental damage associated with the type of substrate while
maintaining a positive energy balance, co-fermentation of waste from agriculture, the food
industry and municipal waste, is the most appropriate, both for small scale (<500 kWe)
and large scale (>500 kWe) plants. The most effective way to use biogas in small co-generation
plants is to use the heat in the vicinity of the biogas plant (up to 2 km); for larger biogas plants
it seems advantageous to enrich and inject into the grid. Options for biogas utilisation
in the perspective of reducing GHG emissions were studied in Ref. [16]. In the study's
conclusion it was decided that the sustainable option is to use biogas for transport (after
enrichment) and co-generation on a small scale on-site.
In [17] the authors studied the economic efficiency of biogas use under specific conditions
in the Västra Götaland region in Sweden. Two options are compared: the use of biogas
in transport and co-generation within the district heating network. The impact of the different
support schemes on the cost-effectiveness of biogas use has also been considered. The main
conclusion of the study was that, from the technical and economic standpoint, it is more
advantageous to use biogas as a transport fuel than in co-generation.
4.4. Biogas enrichment
Depending on the place of generation, biogas can contain different amounts of methane,
CO2 and water vapour, as well as small additions: nitrogen, hydrogen sulphide, ammonia,
siloxanes and oxygen. Biogas can be enriched by removing water vapour, CO2 and most
of the impurities. Enriched biogas (biomethane) has a much wider field of applications,
but the enrichment facility significantly increases investment costs, which must be taken into
account during the planning of investments.
Technologies for biogas enrichment contain both:

processes for removal of impurities (H2S, H2O and others), which are harmful to the gas
network and end users' devices

full enrichment processes, including the removal of CO2 from biogas in order to increase
the methane content and calorific value.
14
M. Poschl et al., Evaluation of energy efficiency of various biogas production and utilization pathways,
Applied Energy 87 (2010) 3305–3321
15
M. Poschl et al., Prospects for expanded utilization of biogas in Germany, Renewable and Sustainable Energy
Reviews 14 (2010) 1782–1797
16
J.D. Murphy et al., Technical/economic/environmental analysis of biogas utilisation, Applied Energy 77 (2004)
407–427
M. Börjesson, E. Ahlgren, Cost-effective biogas utilisation e - A modelling assessment of gas infrastructural
options in a regional energy system, Energy 48 (2012) 212-226
17
After enrichment, the properties and quality of biomethane are similar to natural gas, so it can
be used as its supplement in all applications. Enrichment techniques allow biogas to be cleaned
up to a methane level of 99.9%.
Several methods of biogas enrichment are commercially available and widely described in
the referenced literature. [18, 19, 20]. The main enrichment technologies are:

absorption in water (water scrubbing) - CO2 is dissolved in water at elevated pressure
in an absorption column and is then released in a desorption column after the addition
of air at atmospheric pressure

pressure swing adsorption (PSA) - biogas is compressed, so that CO2 is adsorbed in
an adsorber unit; once lowered, it is released

physical absorption in an organic solvent (organic physical scrubbing); CO2 from biogas
is absorbed in an organic solvent (e.g. a mixture of dimethyl ethers of polyethylene
glycol), similar to absorption in water

absorption in an amine (amine scrubbing) - CO2 is chemically absorbed an amine
(dissolved in water) and then released in a desorption column once temperature is raised

membrane separation - the components of biogas are separated by a dense molecular
filter, which has different values of selectivity for methane and CO2.
Table 4.2. Characteristics of biogas enrichment technologies [17]
Parameter
Water
PSA
scrubbing
Membranes
Chemical
scrubbing
(2-4 degrees)
Organic
scrubbing
physical
(amines)
Methane
[vol.%]
96-98%
96-98%
96-98%
96-99%
96-98%
2-3%
2-3%
3-4%
2-3%
2-3%
Removal of H2S
Yes
Ext.
Ext.
Ext./Yes
Ext.
Removal of H2O
Ext.
Yes
Yes
Ext.
Ext.
Annual cost of
operation
[% of investment cost]
L. Bailón Allegue, J. Hinge, Biogas and bio-syngas upgrading, Report of Danish Technological Institute, 2012
F. Bauer, et al., Biogas upgrading – Review of commercial technologies, Biogas upgrading – Review of
commercial technologies’, SGC Rapport 2013: 270
20
D. Thrän et al., Biomethane Status and factors affecting market development and trade’, IEA Bioenergy: Task
40 and Task 37,2014
18
19
N2 and O2
separation
No
No/part
Part of O2
No
No
0.2-0.3
0.2-0.3
0.2-0.3
0.1-0.15
0.2-0.3
Heat
(kWh/Nm3
biogas)
0
0
0
0.5-0.6
Internal
Clean CO2
No
Yes
Yes
Yes
No
Electricity
consumption
(kWh/Nm3
biogas)
Economic and environmental characteristics of biogas enrichment technology are determined
by energy/material requirements (i.e. energy and water consumption) and methane losses
(Table 4.2). Each of these methods has its advantages and disadvantages [21]. The selection
of the optimal enrichment process depends on the sources and quality (e.g. landfill gas,
fermentation of slurry or sewage treatment plants), the desired quality of the output biogas (gas
grid or fuel) and local conditions: availability of heat, power, and space. Most enrichment
systems are located at major biogas production plants and are optimised for maximum biogas
yield and energy efficiency. Data from Table 4.2. shows that the consumption of energy
in different technologies is similar, typically approx. 0.2 - 0.3 kWh/Nm3 of biogas, except
for amine absorption, for which it is 0.10-0.15 kWh/Nm3.
According to ref. [22], there were 17240 biogas plants in Europe in 2014 (with an installed
capacity of 8339 MWe) and 368 biogas enrichment plants with a production capacity of 310000
m3/h. The number of enrichment plants in different EU countries is shown in Fig. 4.2. Germany
is the European leader in terms of the number of installed biogas and enrichment plants.
The main substrate for biogas plants are dedicated harvests and agricultural waste, such
as slurry and manure. In most cases the bio-methane is injected to the gas grid, to be later used
in CHP systems elsewhere. German investors are in a favourable position due to a welldeveloped gas pipeline network, especially in relation to their Swedish colleagues (the second
largest producer of biomethane), where such a network is virtually non-existent. That is why
biomethane is used as a transport fuel in Sweden. There, 78% of biogas from a total of 1303
GWh of produced methane is dedicated to the purpose of powering 50000 vehicles [19].
21
22
M. Persson, Evaluation of upgrading techniques for biogas, Report SGC 142, 2003
] http://european-biogas.eu/2015/12/16/biogasreport 2015/
Fig. 4.2. Number of enrichment plants in different EU countries (31.12. 2014, Source: [19])
4.5. Economics of biogas enrichment technology
The investment costs of different types and capacities of biogas enrichment plants were
estimated in the SGC Report (2013) [16]. As shown in Fig. 4.3, the specific investment costs
for the enrichment plant decrease with its size. For plants enriching 500 Nm3 biogas/h specific
investment costs vary between 1000 and 3000 €/Nm3 [16].
Annual operational costs usually amount to approx. 2-4% of the investment costs.
In Europe, the majority of biogas is produced in small-scale biogas plants (50-200 Nm3/h) [23].
Small scale enrichment systems can be used for the purification of biogas for a local CHP
system and/or the production of fuel for local vehicles (e.g. on a farm). In the case of smaller
plants, the profit from 1 Nm3 of enriched biogas should amount to € 0.35-0.45 for the return
on investment time to be approx. 5 years. This means that the cost of biogas enrichment
for small biogas plants should be below € 0.2-0.3 / Nm3[24].
23
VALORGAS, D5.1, Evaluation of potential technologies and operational scales reflecting market needs for lowcost gas upgrading systems, 2010
24
K.Warren, Techno-economic comparison of biogas upgrading technologies in Europe, MSc University
of Jyväskylä, 2012
PSA
Physical absorption
Membrane separation
Chemical absorption
Water scrubbing
Fig. 4.3. Investment costs of different biogas enrichment installations (Source: [16])
4.6. Results for selected enrichment technologies
As part of the POMBiogas project, 3 biogas purification technologies were tested: SFR
developed at the Technical University of Gdansk, membrane separation and a fixed bed process
for the removal of H2S/NH3.
4.6.1. SFR technology
The Spinning Fluids Reactor - SFR - biogas enrichment module was
developed within the NCBR Strategic Programme: Advanced technologies for energy
generation, Task 4. Development of Integrated Technologies for Fuel and Energy Production
from Biomass, Agricultural Waste and others. The transportable plant prototype
(Fig. 4.4.) operating at a biogas plant in Międzyrzec Podlaski allows the removal of acidic
biogas components (CO2 and H2S). A modular design allows easy scalability, with a single
module capable of enriching 200 m3/h of biogas with an initial 45% CO2 content and less than
2000 ppm H2S.
The produced biomethane contains less than 10% CO2 and 50 ppm H2S.
Both, chemical and physical absorption can be used for the separation of gases in an SFR.
The commissioned plant uses chemical absorption with an aqueous amine solution as an active
agent. The absorption of CO2 takes place in the SFR and then in the CO2 desorption chamber
it is released upon heating of the amine above 100 °C. The heat from the co-generation unit
in the biogas plant can be used to heat the amine. The heat released during the amine's cooling
can be used for other purposes (e.g. heating the fermentation chamber). The carbon dioxide
released in the desorption chamber can be used for other processes. The system does not require
high pressure conditions (ΔP < 25 kPa).
Fig. 4.4. Modular transportable prototype biogas enrichment plant commissioned on the site of a biogas plant
in Międzyrzec Podlaski.
The SFR module is characterised by its small dimensions - in comparison to a water scrubber,
an absorption chamber of similar performance is 7 times smaller, i.e. the SFR can be placed
in a 40-foot container [an additional container is needed for the installation of control
and measurement systems. This means a substantial reduction in the device's price and ROI
time (in the order of several years)].
4.6.2. Polyamide membrane technology
Biogas enrichment methods based on membrane technologies have been studied for several
years. The latest achievements make the process technically and economically accessible.
A very popular solution uses so-called hollow fibres.
Fig. 4.5. UMS-A2 module with membranes with hollow-fibre from UBE
Membrane technologies have some key advantages:

long life at temperatures up to 100 °C; in the case of membrane modules from UBE
and PermSelect the nominal temperatures are in the 40 - 60 °C range

compactness and simplicity of design

simultaneous removal of CO2, H2O and H2S

significant selectivity for various gases

technical reliability, no moving parts, limited energy and maintenance requirements

high flexibility in module working conditions: flow and pressure.
Fig. 4.6. Laboratory measuring system for the performance of membrane modules in a single
and multi-stage system
As part of the project a module with "hollow fibres" from UBE (Fig. 4.5.) and its ability
to separate CO2 from biogas with different content of this gas were studied. Single- and multistage UMS-A2 module systems were used. A purpose-built rig that allows the filter to be tested
in various configurations was used for this purpose - see Fig. 4.6. Gas mixtures at a pressure
of 4 - 7 bar and a flow of 30 - 150 Ndcm3/h were studied. The gas temperature was in the
24 - 25 °C range and equal to the ambient temperature. The system was tested for various
mixtures of CH4/CO2 with a 29%, 52% and 60% methane concentration.
Since the composition of the retentate and the permeate varies depending on the biogas
flow rate and pressure, rotameters were used to measure air flow, making flow calibration
necessary. As the gas analyser, a biogas analyser from Geotech, model GA5000, was used,
which measures CH4 and CO2 content with an accuracy of ± 0.5%.
The measurements indicate a high efficiency of the membrane system for the separation of lean
methane mixtures. For a system with three membranes arranged in a series, an increase
in methane concentration of approx. 60% (for a flow of 145 dcm3/h) was achieved.
In the entire measurement range for a lean methane mixture of CH4/CO2= 29%/71% (flows
70-410 dcm3/h), methane concentrations increased from 34 to 60%. In a single-stage system,
the increase in methane concentration was up to 43% for a flow rate of 82 dm 3/h. Along
with an increase in methane concentration on the supply side, the methane losses grow as well,
and for a mixture of CH4/CO2= 63%/27% methane concentrations in the permeate increased
from 6 - 16%. Losses for lean methane mixtures do not exceed 3%.
4.6.3. Technology for removal of H2S/NH3 in a system with a fixed bed
Module built by Pexpool for the removal of H2S/NH3 in a fixed bed (Fig. 4.7.) was used
in a micro-scale biogas plant located in Pomorski Ośrodek Doradztwa Rolniczego [Pomeranian
Centre for Agricultural Consultancy] in Lubań. The fixed bed was made of a mineral called
halloysite. Due to the large active surface, the mineral is a good candidate for a H2S and NH3
adsorbent. The catalytic process on the adsorbent's surface leads to the surface of the halloysite
being covered with an atomic layer of sulphur, which gradually limits the process of hydrogen
sulphide removal. The filter's regeneration occurs after it is cleaned with a stream of air, which
leads to intensive heating (due to sulphur oxidation)
and should be controlled by the control system. A microscale biogas plant is equipped with two filter columns
with a fixed bed, so as to ensure consistent operations,
even when one column is being regenerated. The design
of the filter allows periodic replacement of the halloysite
bed. The system allows up to 1000 ppm H2S to be
removed at a biogas flow rate of 10 m3/h.
More information about the results of biogas enrichment
can be found in the reports of the POMBiogaz project
(see www.pom-biogas.eu/pl/publikacje-i-wydarzenia).
4.7. Socio-economic aspects of biogas use in Poland
In 2014 there were 278 biogas plants in Poland [25] with
a total capacity of approx. 212.5 MWe. These comprised
97 plants using landfill biogas (with a capacity of 59.7
MWe), 79 biogas plants located on-site at sewage
treatment plants (with a total capacity of 42.3 MWe)
Fig. 4.7. A fixed bed module for the
and 32 agricultural biogas plants (87 in mid-2016 - 92.7
removal of H2S/N3 from biogas placed in
MWe). Production of renewable energy sources is
a micro-scale biogas plant in Lubań
supported through various support schemes, investment
grants and certificates of origin. In Poland, there are
a number of certificates [26] (green, yellow, red, purple and brown) issued by the Energy
Regulatory Office (ERO; pl. URE) for renewable energy generated in a variety of sources [27,
28
].
Currently in Poland, biogas is mainly used for the production of electricity and heat
in highly efficient co-generation units. This was promoted by a support system of (yellow and
purple) certificates of origin. Gas co-generation units with a capacity below 1 MW, irrespective
of the fuel's origin, received support in the form of yellow certificates. Units using biogas
as a fuel can also receive support in the form of purple certificates.
A budget for a biogas plant should include revenue from the sale of the following products:
25
http://www.ure.gov.pl, 2015
Z. Muras, Rainbow vertigo” – or a description of Polish support schemes for renewable and cogeneration
sources, Clean Energy 2011, No. 5.
27
Journal of Laws of the Republic of Poland, 2010., No 21, item 104
28
Z. Muras, Polish support schemes for renewable and cogeneration sources, ERO
26

electricity with appropriate certificates of origin

excess heat

digestate as a fertiliser and

a fee for the disposal of more or less burdensome organic waste.
The possibility of injecting biogas into the gas grid appeared in Poland in 2010
as an amendment to the Energy Law. According to it, a brown certificate of origin may be
acquired for agricultural biogas injected into the grid. This right is not given to producers
of landfill biogas and biogas from sewage treatment plants. The gas grid operator is obliged
to accept agricultural biogas, provided it meets certain quality parameters.
However, enrichment and injection of biogas into the network still encounters difficulties,
such as:

lack of sufficient financial and legal support for produsers of biogas

lack of legislative support for the technology of injecting biomethane into the grid

constantly changing and unclear system of support for biogas production and use

no national standards for biomethane

high investment costs for biogas enrichment units

no support system for using biogas in transport

limited knowledge of investors about available enrichment technologies.
Despite the legal and economic problems of biogas manufacturers in Poland, there are many
studies regarding biogas (technical, economic and environmental).
4.7.1. Farm biogas plant with a biogas enrichment system - biomethane use
A preliminary feasibility study for a biogas plant with a biogas enrichment system
was developed by the Automotive Industry Institute (PIMOT) in Warsaw [29]. A simplified
economic analysis of biogas enrichment has been prepared for two options:

injecting biogas into the gas grid

use of compressed biomethane as a transport fuel.
For the enrichment of biogas, water scrubber technology with a capacity of 1200 Nm3 /h
was chosen. The potential for biomethane production (98% CH4) was estimated at 5.26 million
Nm3/year. Although costs vary depending on the technology used, the specific cost
Ł. Kowalski, B. Smerkowska, A Polish case study for biogas to biomethane upgrading Combustion Engines,
No. 1/2012 (148)
29
of enrichment is assumed to be 0.29-0.33 and 0.19-0.26 PLN/Nm3 for a capacity of 500
and 1200 Nm3/h, respectively.
Biogas plants using two types of substrates were analysed: (1) 30% slurry and 70% corn silage;
(2) 30% slurry, 50% corn silage and 20% bio-waste. The selling price of biomethane
(to the network operator) was set at 0.85 PLN/Nm3. Brown certificates 275 PLN/MWh.
The main results of the analysis are summarised in Table 4.3.
Table 4.3. Results of the economic analysis for the injection of biogas into the gas grid [26]
Substrate type
Net profit
[k PLN/year]
Return
on investment
[%]
Simple payback
SPP taking
period (SPP)
into account
[years]
subsidies [years]
slurry/ silage 3/7
1.114
4.03
24.83
9.70
slurry/silage/
waste 3/5/2
2.089
7.55
13.24
6.18
The results in Table 4.3. show the effect of substrate selection on profits from the investment.
The second substrate option provides a much better investment result (much shorter SPP) than
option 1. The authors explain that this is due to the much lower cost
of substrates 2 (reducing the amount of silage, whose cost has the largest share in the plant's
operating costs).
4.7.2. Biomethane in urban transport in Poland
As part of the EU project (2013-2014) 'More Baltic Biogas Bus', a prototype mobile biogas
enrichment plant was built by PIMOT and the Poznań University of Technology [30]. It was
installed at an inactive landfill in Niepołomice, near Cracow. The landfill's area is 4.31 ha.
The potential for biogas production is estimated at approx. 47 million m3, while the average
biogas yield was about 94 Nm3/h. The methane concentration was 65%.
Biomethane obtained by enrichment was tested in urban buses, which usually use CNG.
The tests showed that a bus using biomethane as a fuel experienced no technical problems,
which reassured the researchers as to the good quality of the biomethane.
The economic aspects of switching standard fuel for biomethane from a landfill were analysed
for different numbers of buses powered by biomethane [31]: two or three buses use bio-methane.
The average cost of 1 Nm3 of biomethane was set at 2.09 and 1.60 PLN/Nm3 for enriched
landfill biomethane for options 1 and 2, respectively. The purchase cost of biogas is included
in the analysis. The average cost of biomethane is lower than CNG (at 2.89 PLN/Nm3 at the
end of 2014).
30
W. Gis et. al. Upgrading landfill gas to biomethane and use of it in urban bus transport in Poland,
www.balticbiogasbus.eu,
J. Waśkiewicz et al. Preliminary economic evaluation of the use of biomethane in the urban bus transport system.
case study
31
As for the environmental aspect, the average cost of GHG emissions in the case of biomethane
is significantly lower (even if the purchase price of biogas is included) than the cost of emissions
of buses using diesel fuel.
4.8. Conclusions regarding the use of biogas
There are many different uses of biogas: co-generation, production of biomethane,
injection of biomethane into the gas grid and using biomethane as a transport fuel.
As is commonly known, a national strategy and regulations in the form of various support
and taxation systems, as well as standards are key factors that determine the economic viability
of each biogas investment (production and use). An appropriate level of support is necessary
for the successful implementation of a business venture. The level of support determines
the profitability of biogas projects.
It has been shown that a key factor in the economies of a biogas plant investment is the cost
of biogas production, with this being primarily the choice of substrate mixture. The cost
of dedicated crops such as corn and wheat can account for up to 50% of the production cost.
On the other hand, substrates such as municipal waste or slurry may even have a negative price,
acting as an additional income stream for a biogas plant. Other important factors are the size
of the plant (economies of scale), type of technology and distance from energy infrastructure.
Co-generation is favourable, due to the large potential for CO2 reduction. The level to which
heat produced in CHP is used has a significant effect on the profitability of a biogas plant.
In the case of small biogas plants co-generation with the heat being used in the vicinity is
the most effective way for utilising biogas. For large manufacturers of biogas, enrichment
and injection of biomethane into the network or use as a transport fuel, is the better option.
The support system significantly affects the revenue (and profit).
5. SOCIO-ECONOMIC ANALYSIS OF BIOGAS PRODUCTION FROM ORGANIC WASTE
Katarzyna RONEWICZ
Waste management should be highlighted among the many environmental problems emerging
with the development of civilisation. Methods used within the context of waste management
should be a full system solution that comprises limiting the amount of waste, energy recovery,
as well as management. Therefore, the European Union puts a strong emphasis on this aspect
of environmental protection and introduces priority actions within this framework.
Taking into account the effects of waste on human health, finances and the environment
at different stages of waste management, i.e. collection, transport, storage, recovery
and disposal, it is possible to determine the optimal methods of waste management using life
cycle assessment. This makes it possible to evaluate potential risks and match the most
appropriate technological solutions.
In respect of social concerns, the waste management system can be divided into the following
primary impact categories:

Human life and health - climate change, emissions, odours, microbiological risks

Environment - acidification, eutrophication, land development, climate change

Natural resources - fossil fuels.
In addition, the system's economics also take into account the costs of possible solutions.
The agri-food industry and livestock farms produce significant amounts of waste. If organic
municipal waste is added, the potential of renewable energy and nutrients is significant, and has
so far remained untapped. In this regard, methane fermentation is a promising solution for the
management of organic waste, economically more favourable than alternative methods like
composting, incineration or storage, which is also a nuisance to local communities due to odours
carried over long distances, involves a large surface area, which reduces the aesthetic value
of the environment. Figure 1 shows an example flow diagram in a waste management system.
Figure 7 Example waste stream flow diagram
Prevention of waste
generation
People
Biodegradable
waste
Other
waste
Pre-selected waste
Preparation for
reuse
Waste
collection
Product
Waste sorting
Selected waste
Biodegradable
waste
Recycling
Management of
biodegradable waste
Mixed
waste
Processing
Storage
Projekt ‘Pomeranian Biogas Model’ [POM-BIOGAS]
Umowa o dofinansowanie nr Pol-Nor/202919/57/2013
The processing of organic waste through methane fermentation methods is the source of a smell
generally regarded as unpleasant.
The main source of the nauseous odour in this process is the arriving substrate and, with proper
effort, it can be minimised through proper collection and storage of waste. A possible solution
is to preserve waste food and waste biomass in the form of silage.
The fermentation process takes place in closed tanks, without oxygen, while the source
of the process odour can either be the main product of the process, biogas, or the resulting
by-product - digestate. Biogas, in addition to its main components, i.e. methane and carbon dioxide,
also contains small amounts of compounds such as hydrogen sulphide, ammonia, mercaptans,
volatile organic compounds, thiols, amines and others. Due to the relatively low threshold for these
compounds to be perceived by humans, even a negligible quantity of them in the waste stream can
cause unpleasant sensations. With a properly designed system smells do not escape from
the reactors, as the process takes place without oxygen and the installation must be tight. The places
most vulnerable to leaks are subject to periodic checks with increased frequency.
Other concerns related to the odour nuisance of the process stem from the necessity to manage
post-fermentation slurry. It should be noted, however, that the odour creating properties
of the digestate are inversely related to the length of the fermentation phase proper, so as to ensure
full compound dissolution. A worthwhile option is methane fermentation performed
in thermophilic conditions. This stems from the fact that higher temperatures lower viscosity, which
leads to faster exchanges of mass and therefore increases the reaction speed. Moreover,
thermophilic conditions assure a high degree of biomass hygienisation, thus reducing the risk
of spreading pathogenic organisms such as Escherichia coli.
It is in effect the utilisation of digestate that raises the greatest concerns of society, while digestate
from a properly operated and controlled process can be a valuable product rich in nutrients. Good
quality digestate should not be treated as waste - low in heavy metals it can be used in agriculture.
There are many methods of utilising digestate, among them incineration, storage, agricultural use
in unchanged form, agricultural use after processing, dewatering and recovery of nutrients from
the effluent.
The digestate's potential is best used in agriculture. In addition, its prior dewatering significantly
reduces transport costs to the place of use, contributing to improved economic aspects
of fertilisation. In addition, it is reasonable to utilise the resulting effluent in the nutrient recovery
process. The Annamox process is an example of such a solution, one that allows for the removal
of nitrogen from sewage and, in comparison to the standard denitrification process, is characterised
by a positive energy balance. Furthermore, because of the low growth rate of bacteria involved in
the process, the problem of excessive sludge formation is eliminated, which can be, if necessary,
directed to the methane co-fermentation process.
Public concerns associated with the production and use of biogas are largely based on the possible
impacts on the environment and their effects. These include climate change due to greenhouse gas
emissions. Losses of methane could have the biggest impact on these changes, but a properly
designed process is characterised by marginal emissions when compared to, for example, emissions
from agricultural livestock and minimal explosion risk. It should also be noted that the deliberate
use of organic matter in the fermentation process reduces the risk of uncontrolled decomposition
of biomass, in a landfill for example, and associated greenhouse gas emissions. It is, therefore,
‘Pomeranian Biogas Model’ Project [POM-BIOGAS]
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a constant component of the atmosphere, present in a concentration of 1.8 ppm, and at the same
time in equilibrium with methane dissolved in seawater.
In addition, the carbon dioxide released to the environment or further enrichment of biogas, is taken
up by plants through photosynthesis, so the total balance of this component is equal to 0.
Further on, purified biogas can be used as a transport fuel and to produce heat or electricity in CHP
plants, which contributes to a reduction in the use of non-renewable energy sources and makes
it possible to cover own energy needs. This makes it possible to become independent of external
energy sources or, depending on the amount of gas produced, generate additional economic benefits
from the sale of its surplus, as well as certificates and grants.
Others discuss acidification and eutrophication. Using digestate as an agricultural fertiliser helps
to reduce the amount of synthetically obtained fertilisers, whose production is associated with high
energy inputs and therefore the use of fossil fuels and pollutant emissions. Digestate is therefore,
in and of itself a natural fertiliser, whose production does not require chemical synthesis or use
of non-renewable energy sources.
The tightening of legal requirements within the scope of environmental protection and the use
of renewable energy sources result in the need to search for new and develop existing waste
management methods, so as to reduce their negative environmental impact. However, in the chain
of activities related to waste management, individual people are the most important link,
immediately after the producers of packaging and entities that put them on the market, in taking
actions aimed at reducing the amount of produced waste. The fact that the consumer understands
the local waste management system and his or her key position in the structure is a very important
element of this system. In addition, any feedback defining the influence of the consumer caring
for appropriate and accurate waste segregation on the local environment, will affect social
integration in this area.
‘Pomeranian Biogas Model’ Project [POM-BIOGAS]
Grant Agreement no. Pol-Nor/202919/57/2013
6. UTILISATION OF DIGESTATE
Katarzyna RONEWICZ, Katarzyna PONTUS, Jan HUPKA, Jacek MĄKINIA
6.1. Fertilisation using digestate
Digestate is the material remaining after the process of anaerobic decomposition of organic matter.
It is rich in nutrients. This is due to the fact that during anaerobic digestion of organic matter, plant
nutrients are subject to a process of mineralisation. Nitrogen and phosphorus are mineralised
to NH4+ and PO43-, and in this form they are much more absorbable for the plants than before
the fermentation process. Reduction of pathogens is another important aspect of the fermentation
process, especially when the process is operated at thermophilic temperatures (> 55 C). It consists
of the residue of a non-fermentable mass and dead micro-organisms.
Natural fertilisers used in agriculture improve soil properties, its structure, and subsequently
the air-water balance, creating better conditions for the development of micro-organisms in
the soil. They also contribute to maintaining a constant level of humus in the soil and prevent its
reduction. They are characterised by a high amount of beneficialnutrients: i.e. nitrogen, phosphorus
or potassium. According to Council Regulation (EC) No. 834/2007 on organic vegetable crops,
it is unacceptable to use mineral-based fertilisers derived from chemical synthesis. Therefore, new
solutions are sought that would allow organic farming to achieve similar results to those obtained
using conventional methods, while maintaining all standards and requirements for healthy eating.
One of the methods that allow soil fertility to be maintained is crop rotation with legumes
and maximum utilisation of mineral-based fertilisers constituting waste from agricultural
production. Organic fertilisers that constitute waste from agricultural production are: manure,
slurry, liquid manure, straw, bird droppings and various composts. The primary products obtained
from the operation of a biogas plant are biogas and digestate, which after limited processing can
also be used to fertilise soil. Digestate can be a valuable organic fertiliser, rich in nutrients,
so returning it to the environment can reduce the consumption of mineral-based fertilisers and
improve soil properties. This is due to the fact that the components of digestate, especially
containing cellulose and lignin, are not completely biodegradable, so that organic carbon
is introduced to the soil. This justifies further research aimed at assessing the suitability and
application methods of digestate, examining its nutrient content, as well as a comparison of plant
growth with and without digestate.
Digestate can be exploited in various ways. As a rule, it can be divided into agricultural use, thermal
utilisation and storage in a landfill. The graph below (Figure 1) shows the percentage of each
of these methods in general digestate use [1]:
Figure 1. Digestate uses
‘Pomeranian Biogas Model’ Project [POM-BIOGAS]
Grant Agreement no. Pol-Nor/202919/57/2013
The most common method of using digestate is its thermal utilisation and employment
in agriculture.
6.2. Non-agricultural use of digestate
6.2.1. Burning pellets from digestate
A biogas plant with a capacity of 500 kW produces more than 10000 tonnes of post-fermentation
sludge (digestate) per year. Such a large amount of sludge cannot be used completely locally
because of the limitations on the agricultural use of digestate.
One of these limitations is the amount of sludge that can be used on one square metre of soil.
Furthermore, there are many other restrictions on agricultural use of sludge as a natural fertiliser.
Excess material remaining after fermentation is difficult to use and its storage is associated with
a number of difficulties e.g. it requires a large surface area and causes inconvenience related
to odours. In addition, the storage location of such material should be covered from the outside
in order to reduce losses of minerals and limit pollution caused by the emission of ammonia
and methane [2].
Digestate destined to be used as a fertiliser in another location can be transported, but this is not
an economically viable undertaking. If the distance is greater than 5-10 km, the cost
of transportation exceeds the value of the fertiliser. Therefore, other methods of its use are
constantly sought. One promising idea for using sludge is to convert it into pellets constituting fuel.
In this form it can be transported and stored at reasonably low cost.
A concise comparison of wood pellets and those made from digestate was prepared in 2010
by M. Kratzeisen. This work aimed to show the advantages and disadvantages of digestate-derived
pellets [3].
6.2.2. Nutritional value
First of all, pellets from digestate contain a lot of elements associated with the emission
of poisonous substances. Concentrations of nitrogen, sulphur and chlorine repeatedly exceed limits.
The zinc content slightly exceeds the permitted value, while the values for arsenic, mercury
and cadmium are close to the limits.
The high content of some of them (sulphur and nitrogen) leads to difficulties in incineration.
Gas emissions are higher than in the case of wood pellets and for many parameters the limits
are exceeded (dust, CO and NOx).
The following table presents an analysis of heating pellets obtained from digestate in comparison
with pine pellets and limits.
‘Pomeranian Biogas Model’ Project [POM-BIOGAS]
Grant Agreement no. Pol-Nor/202919/57/2013
Table 1. Analysis results of heating pellets obtained from digestate and pine
Element
Heating pellet
from digestate
% dry matter
C
N
O
H
P
S
K
Cl
[mg/kg] dry
weight
As
Cd
Cr
Cu
Pb
Hg
Zn
Heating pellet
from wood
Permissible
value
45.3
2.9
28.4
5.2
1.3
0.9
1.4
0.84
49.7
0.13
43.3
6.3
0.03
0.02
0.1
0.01
0.3
0.08
0.03
0.93
0.29
13.2
58.8
4.4
0.07
0.48
0.23
6.8
3.5
2.17
0.04
0.8
0.5
8
5
10
0.05
304
35
100
6.2.3. Ash composition
The ash content is much higher than in the case of wood pellets. Meanwhile, the heavy metal
content in the ash is lower. Just the concentrations of nickel and chromium are three times higher
than the reference value. An analysis of the concentration of mineral elements (high concentrations
of phosphorus and potassium) and heavy metals in the ash shows that this material can be used
as a fertiliser on arable land, following an earlier reduction in nickel and chromium content.
In order to reduce these concentrations various methods are employed, such as scrubbing and heat
treatment.
Table 2. Comparison of ash composition of pellets from digestate with pellets from wood
Oxides
of elements [%]
P
K
Mg
Na
Ca
Si
S
Fe
Al
[mg/kg]
As
Pb
Cd
Cr
Ni
Hg
Ash from a pellet
from digestate
26.7
15.5
8.4
0.8
13.6
30.4
0.9
1.8
1.2
Ash from a pellet
from wood
2.6
6.4
6
0.7
41.7
25
1.9
2.3
4.6
1.1
2.3
< 0.5
184
285
< 0.1
4.1
13.6
1.2
325.5
66
0.01
Permissible value
40
150
1.5
2
80
1
‘Pomeranian Biogas Model’ Project [POM-BIOGAS]
Grant Agreement no. Pol-Nor/202919/57/2013
6.2.4. Calorific value
Pellets obtained from heat drying of digestate have a high calorific value of 15 MJ/kg, with a water
content of 9.9%. For comparison, this value for a wood pellet is 16.3 MJ/kg, with a water content
of 12%. This parameter for the two given types of pellets has a similar value, but the production
of pellets from digestate is associated with many problems relating to dewatering and drying
processes for the material. Only after dewatering and drying the digestate (whose water content
should be reduced to 15-20%) can be used to produce a heating pellet.
6.3. Agricultural use
Digestate is considered an extremely valuable natural fertiliser. Currently, it is increasingly often
used as a substitute for mineral fertilisers. Many positive effects resulting from the agricultural use
of sludge are noted, but there are also many opponents of that method. They justify their point
of view with the fear of bacteria and pathogens present in digestate. Another argument against
the use of sludge for fertilisation is the odour resulting from the distribution of sludge on the field.
The following table lists the physico-chemical properties of the soil in relation to other used
fertilisers. Four samples were taken and for each different results obtained [4].
Table 3. Physico-chemical properties of the soil in relation to the fertilisers used
Parameter
pH
EC (dS/m)
TN (g/kg)
Reference
Bovine slurry
Digestate
Mineral-based
fertiliser
7.9
7.8
7.7
n. d.
8
7.9
7.9
7.9
8.1
8
8
8.1
7.8
7.8
7.8
7.7
8.1
8
8
8
0.12
0.14
0.16
n. d.
0.16
0.25
0.23
0.24
0.13
0.14
0.14
0.13
0.23
0.24
0.22
0.31
0.12
0.14
0.14
0.14
1.7
2.1
2
n.f.
1.5
1.8
1.3
1.3
1.5
1.3
1.2
1.1
1.6
1.8
1.3
1.5
1.3
0.9
1
1.1
‘Pomeranian Biogas Model’ Project [POM-BIOGAS]
NH4- N
(mg/kg)
NO3- N
(mg/kg)
Available P (mg/kg)
Grant Agreement no. Pol-Nor/202919/57/2013
1.5
1.4
1.7
n. d.
0.1
3
3.2
0.2
15.4
14
7.5
14
1.8
1.1
1.3
1.5
5
4.3
3.4
3.8
14.5
25.1
64.7
n. d.
2.8
2.9
3.2
7.2
1.4
1.6
1.5
1.7
6.9
9.2
8.9
11.3
2.4
2.8
4.4
3.8
28.5
36.3
36.7
n.f.
24.2
37.4
48.2
32.2
24.8
42.4
54.8
32.9
39.7
53.5
75.8
59.4
38.3
27.8
34.6
46.4
n.f. - not found
This table provides a brief comparison of the differences between fertilisers: bovine slurry,
digestate and mineral-based fertiliser. The properties of such soil are compared to a control soil
not containing any fertiliser.
The digestate slightly affected the pH of the soil, presumably due to the high buffer capacity
of the soil used. It is clear that the addition of bovine slurry and digestate are the cause the greatest
total concentration of nitrogen after the first application of fertiliser. In subsequent applications
the differences were already small and insignificant.
The concentration of NH4-N in soil fertilised using slurry, as well as digestate was higher than
in the case of a mineral-based fertiliser or the reference soil. In general, these values were low.
Only in sample number three were they high, which means that the nitrification process occurred
only partially and the nitrate level was the lowest of all the samples. Inhibition of the nitrification
process could have been stopped by substances contained in the sample that were toxic to bacteria
of the Nitrosomonas group [5].
The first addition of digestate caused a rapid increase in the concentration of nitrates in the soil,
but there were no major differences in concentration for the remaining samples. Similarly,
the phosphorus levels were higher after the first addition of digestate, but similar at the end of
the experiment. The addition of digestate to the soil did not cause any significant change in
the total organic carbon content in the soil compared to the reference soil, as well as the one
to which artificial fertiliser was applied. On the other hand, the addition of bovine slurry
‘Pomeranian Biogas Model’ Project [POM-BIOGAS]
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is associated with a significant increase in TOC and WSC. Fertilisation with this substance also
increases parameters such as Bc, Bn, and C-CO2 when compared with the reference soil.
The following table shows that the addition of bovine slurry or digestate increases dehydrogenase
activity in the soil by approx. 40%. No significant changes were noted in protease or urease activity
after the administration of slurry or digestate. The influence of fertilising with bovine slurry,
digestate and artificial mineral-based fertiliser was tested also in growing watermelons
and cauliflower. The yields were the indicator of the impact of added fertilisers.
Table 4. Changes in soil parameters after application of various fertilising substances
Parameter
TOC (g/kg)
WSC
(mg/kg)
Bc (µg/g)
Bn (µg/g)
CO2-C
(µg/Cg*d)
Reference
Bovine slurry
Digestate
Mineralbased
fertiliser
9
9.4
9.2
8.8
10.4
9.7
9.8
10.4
9.4
9.4
9.6
8.5
Na
9.1
9.3
9.1
9.4
10.7
9.2
9.3
51
70
55
Na
44
49
46
45
77
93
73
76
78
114
79
89
40
59
49
41
109
149
116
n.f.
98
128
122
126
80
136
107
91
141
176
157
161
123
179
184
175
20.8
26.2
12.3
Na
18.7
25.6
22.1
24.4
16
23.3
19
16.7
17
23.4
18.9
20.2
19.8
29.2
30.4
29.4
8.3
13.4
8.1
Na
6.7
9.9
8.1
7.6
‘Pomeranian Biogas Model’ Project [POM-BIOGAS]
Bc/ TOC
Grant Agreement no. Pol-Nor/202919/57/2013
7.7
11.1
8
7.7
7.6
8.8
8.5
9.3
7.4
11.3
10
9
1.21
1.43
1.24
n.f.
1.05
1.32
1.3
1.39
0.88
1.41
1.11
0.99
1.61
1.7
1.85
1.78
1.34
1.88
1.68
2
(TOC: total organic carbon;
WSC: water soluble organic carbon;
Bc: coal in the microbial biomass in the soil;
Bn: nitrogen in the microbial biomass;
gCO2: biomass respiratory rate)
Yields of watermelon viable for sale after fertilisation using a mineral-based fertiliser, as well as
digestate, were higher than in the case of slurry and the reference soil. The fruit mass was similar
in all cases, but taking into account the lushness, growth uniformity and better coverage, the harvest
was significantly better in the case of a mineral-based fertiliser and the digestate. The differences
in the nutrient content in the leaves of the fruits were also visible. There were no significant
differences between fertilisers, but plants grown on soil fertilised with a mineral-based fertiliser
had the highest nitrogen content and a high level of potassium.
Table 5. Comparison of watermelon yields depending on the used fertiliser
Fertilisation
Harvest viable
for sale (Mg/ha)
Harvest not
viable for sale
(Mg/ha)
Average fruit
weight (kg/fruit)
First year
Reference
32.1
0.6
2.27
Bovine slurry
37.7
1.8
2.34
Digestate
47.9
2.7
2.56
Mineral-based
fertiliser
42.0
2.4
2.10
Reference
31.6
0.6
2.29
Bovine slurry
31.2
1.4
1.90
Digestate
41.9
0.6
2.13
Mineral-based
fertiliser
56.6
0.0
2.2
Second year
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The influence of various fertilisers was also tested on maize and other plants. The following figures
show the results of an experiment conducted on maize (Figure 2) [6].
Figure 2. Maize seedlings
Pots 7 and 11 contained soil fertilised with digestate, 15 was fertilised with raw slurry, while pot
No. 3 was the reference soil. The positive effect of using digestate on the properties of the soil
and thus the growth of plants was very noticeable [6].
The addition of digestate causes rapid nitrification of ammonia. Nitrates can be drawn directly
by plants and embedded in their tissue. That is why nitrates are the best and most easily absorbable
form of nitrogen for plants. On the other hand, however, there is also a high risk of seepage
of nitrates into groundwater, which would cause pollution. Nitrification occurs not only during
winter, when it is caused by low temperature, hampering the process of nitrification, thus the
fertilising properties of digestate are much lower at that point.
Adding digestate was more effective in increasing the concentration of phosphorus than bovine
slurry or mineral-based fertiliser. Consequently, it resulted in better watermelon yields than other
methods of fertilisation. A phosphorus deficiency is one of the most frequent problems since
the high pH and carbonate content in the soil reduce its level of absorbability.
Moreover, fertilising with digestate provides readily available organic matter, quickly degradable,
which means that digestate does not increase the total organic carbon content in the soil, in contrast
to bovine slurry [7].
The organic matter content in the soil depends on microbial and enzymatic activity,
which determines both the release of nutrients, as well as their availability. Therefore, changes
in the soil's enzymatic activity entail changes in soil fertility. An addition of digestate causes
an increase in alkaline phosphatase activity, so that phosphates are readily available to plants.
6.4. Digestate use - own research
Three methods for using digestate were researched:
- direct application to the soil,
‘Pomeranian Biogas Model’ Project [POM-BIOGAS]
Grant Agreement no. Pol-Nor/202919/57/2013
- application of dewatered digestate,
- processing the supernatant (reject water).
Direct use of digestate as a fertiliser is associated with a number of drawbacks, the most important
of them being transport and distribution costs, due to the fact that fertiliser components represent
only a few percent of the suspension's volume. In addition, local over-fertilisation and increased
escape of nutrients in run-off occur. In this regard the focus has been placed on dewatering the
digestate and recovering nutrients, and also using the supernatant. A large-scale system is shown
in Figure 3.
Figure 3. Digestate dewatering diagramme
Dewatering tests were performed using a decanter centrifuge with a capacity of 0.5 m3/h as shown
in Figure 4.
Figure 4. Decanter centrifuge for digestate dewatering
The centrifuge was used with a digestate conditioned with an inorganic coagulant or polymer
flocculant (cationic polyacrylamide), depending on whether the phosphates are to remain in
the sludge or be recovered in later stages of digestate processing in the form of struvite. Ammonium
compounds, 80% of which passed to the supernatant, were removed in the aqueous processing
phase, using activated sludge.
‘Pomeranian Biogas Model’ Project [POM-BIOGAS]
Grant Agreement no. Pol-Nor/202919/57/2013
6.4.1. Studies of nitrification and denitrification in an SBR (sequential batch reactor)
In order to conduct research on activated sludge adaptation, two research units were designed,
a laboratory scale one and a pilot one. Laboratory tests were conducted for 35 days in a sequential
batch reactor (SBR), made of plexiglass and with an active volume of 10 dm3. The laboratory SBR
is shown in Figure 5a.
a)
b)
Figure 5. SBRs used for pre-treatment of post-fermentation liquid (reject water): a) laboratory SBR, b) pilot SBR
At the beginning of the experiment the reactor was inoculated with biomass derived from
the sewage treatment plant Dębogórze. The content of organic suspension (mixed liquor volatile
suspended solids, MLVSS) was in the range of 3.1-3.8 kg/m3. The reactor operated in 12-hour
cycles, which were divided into nitrification and denitrification phases, followed by a one-hour
sedimentation and decanting phase.
For pilot studies batch dosing was used, with a working volume in the range of 0.25 - 0.5 m3. Pilot
reactor is shown in Figure 5b. The reactor with post-fermentation sludge (digestate) was inoculated
with activated sludge derived from a sewage treatment plant in Swarzewo. During the tests,
the concentration of MLVSS ranged between 4.5-4.8 kg/m3.
Nitrogen (NH4-N, NO3N, NO2N), phosphorus (Pog, PO4P) and organic compound concentrations
were determined for a fresh portion of post-fermentation liquid (reject water) once a week. Once
a week the ammonia uptake rate (AUR) and nitrate uptake rate (NUR) were also determined.
In the experiment conducted on a pilot scale, the AUR values were within the range of 1.7-2.9 g
NH4-N / (kg DOM∙ h). NUR values during the laboratory test increased from 2.3 N03-N / (kg
DOM∙h) and after 23 days of testing at a temperature of 25 °C, reached a maximum value of 11.2
NO3-N / (kg DOM∙h). A similar trend was observed during the 33-day pilot scale experiment.
The increase in the NUR value at 20 °C was 1.2-2.8 NO3-N / (kg DOM ∙ h). Results of laboratory
and pilot research for AUR and NUR are shown in Figure 6.
‘Pomeranian Biogas Model’ Project [POM-BIOGAS]
Grant Agreement no. Pol-Nor/202919/57/2013
Figure 6. Results of laboratory and pilot research on the nitrification and denitrification rate:
a) ammonia uptake rate (AUR)
b) nitrate uptake rate (NUR)
Chemical oxygen demand (COD) analyses of the post-fermentation effluent confirm a relatively
high amount of organic compounds – on average a COD of 4000 g/m3. However, these compounds
were not available for micro-organisms, so to ensure the smooth implementation
of the denitrification process, dosing of an external carbon source was used. Differences
in efficiency during the denitrification process may result from the fact that an external,
differentiated carbon source was used (ethanol and fusel oil). The total efficiency of nitrogen
compound removal was in the 80-93% range in both scales.
The obtained results show the potential for applying the activated sludge process in the treatment
ofdigestate or digestate liquor, which is both, an effective and economical method of removing
biogenic elements, as well as a good tool for the preparation of this liquid for further recovery
processes.
6.4.2. Research of soil application of digestate
In order to prepare a feasibility study, as well as methods for using digestate, a series of experiments
were conducted, which were designed to investigate the effect of digestate on the growth of the
plant and the efficiency of fruiting of the Tukan F1 variety of tomato. The study was conducted
on 15 tomato seedlings. The plants were potted in 15 pots with a volume of 9 dm3 filled with soil
based on peat mixed with trace elements, organic matter, mineral particles, humidifier and soil air.
The planted seedlings were placed in a greenhouse. The pH of the soil was in the 5.5 to 6.5 range.
The plants' daily requirements for nutrients and water were determined and the tomatoes watered
in two-day intervals. Additionally, 3 digestate aqueous solutions were prepared, containing 25%,
50% and 100% of the daily requirement of plants for nutrients. Thus prepared nutrient mixtures
were also dispensed in two-day intervals. A series of seedlings were investigated, which consisted
of:
•
a control group, which included tomatoes watered with water only, without any nutritional
supplements.
•
samples with 25%, 50% and 100% of the optimum dosage of nutrients necessary for
proper plant development,
•
a sample watered with digestate, without added water, with an excess of nutrients.
‘Pomeranian Biogas Model’ Project [POM-BIOGAS]
Grant Agreement no. Pol-Nor/202919/57/2013
Periodically, every seven days, the nutrient content in the soil was tested and the growth and fruiting
of plants were monitored. The increase in green mass and the mass, number and size of the obtained
fruits were measured.
Differences in plant growth could already be observed in the first week. Plants from the control
group developed at a much slower pace than the seedlings in the remaining samples. In addition,
after a period of about 3 weeks, growth of the green parts in the control group was greatly
diminished, then ceased, and the still small fruit began to ripen. The best effects were observed in
the case of the group with a 100% dose and excess nutrients in the mixture used for watering.
Figure 7 presents photographs of tomato leaves watered in different ways: with water and with a
mixture containing 100% of the tomatoes' daily requirements after 28 days of plant growth.
Figure 7. Leaves of plants watered (on the left) with water, (on the right)
with a mixture comprising 100% of the daily dose of nutrients
During the experiment, seedlings receiving water began to show a great shortage of nutrients.
The leaves became yellow and began to dry. Meanwhile, the leaves of seedlings watered
with a 100% dose of nutrients showed a healthy appearance and a dark green colour. In addition,
the seedlings receiving water had become susceptible to diseases, moulds and fungi,
which manifested itself by the formation of brown spots on the leaves and fruits (Figure 8).
Figure 8. A tomato seedling leaf (left) and seedling from the control group (right) with visible changes
‘Pomeranian Biogas Model’ Project [POM-BIOGAS]
Grant Agreement no. Pol-Nor/202919/57/2013
Differences were also clearly evident in the size and number of tomatoes obtained. Figure 9
presents an image of fruit trusses, which show that the amount of nutrients supplied to the soil
was crucial in the process of fruit formation and development.
Figure 9. Fruit trusses of samples: (from left) the control group, with a dose of 25% with a dose of 50%,
with a dose of 100%
The tomato trusses differed substantially (Figure 9). A section from the control sample is
characterised by a small number of fruit and of healthy new fruit buds. As the percentage
of nutrients grew, the amount of fruit and healthy fruit buds grew as well. Seedlings watered
with the mixture containing 100% of the nutrient dose were characterised by a large number
of fruits and buds. One truss gave 6 healthy tomatoes on average. It is also worth noting that
tomatoes from the groups with poor nutrients, were much smaller and matured faster. At the same
time, their skin had visible disease changes (Figure 10).
Figure 10. Tomato fruit from the following samples: (from the left) with a dose of 25%, with a dose of 50%, with a
dose of 100%, the control group
The nutrient content in the soil changed as the process of seedling growth proceeded. The biggest
changes were observed in the soil, in which the control group seedlings were growing,
as no nutrients were provided over the course of the study - Figure 11.
‘Pomeranian Biogas Model’ Project [POM-BIOGAS]
Grant Agreement no. Pol-Nor/202919/57/2013
Figure 11. Nutrient content of the control sample soil
An almost constant nutrient content was observed in the case of plants watered with a mixture
containing a 100% dose, which was reflected in normal growth of plants and satisfactory fruiting
efficiency. Average growth of green mass, fruit weight and total yield obtained from growing
tomatoes is presented in Figures 12 and 13.
Figure 12. Average increase
Figure 13. Average increase
of the green part of a tomato
of tomatoes
The values of all studied parameters show a clear increase following a bigger dose of digestate in
a water mixture (increasing nutrient content). This increase in the case of the control sample and
100% dose sample is almost 5-fold. In addition, it can be observed that results achieved for a sample
treated with raw digestate and tests with a 100% dose are comparable. This suggests that nutrient
content is similar in both mixtures.
6.5. Literature
[1] Ocena możliwości zagospodarowania osadów ściekowych i innych odpadów ulegających
biodegradacji w Polsce w świetle propozycji zmian prawa Unii Europejskiej, Politechnika
Częstochowska, Instytut Inżynierii Środowiska, Częstochowa, 2004
‘Pomeranian Biogas Model’ Project [POM-BIOGAS]
Grant Agreement no. Pol-Nor/202919/57/2013
[2] T. Al Seadi, C. Lukehurst, Quality management of digestate from biogas plants used as fertilizer
[Odpowiednie zagospodarowanie pofermentu z biogazowni jako nawozu], IEA Bioenergy pod
adresem www.iea-biogas.net
[3] M. Kratzeisen, N. Starcevic, M. Martinov, J. Muller, Applicability of biogas digestate as solid
fuel [Możliwości zastosowania pofermentu z biogazowni jako paliwa stałego], Fuel, 89, 25442548, 2010
[4] J.A Alburqerque, C. de la Fuente i in., Agricultural use of digestate for horticultural crop
production and improvement of soil properties [Rolnicze wykorzystanie pofermentu w uprawach i
do poprawy właściwości gleby], European Journal of Agronomy, 43, 119- 128, 2012
[5] F. Tambone, B. Scaglia, G. D’Imporzano, A. Schievano, V. Orzi, S. Salati, F. Adani, Assessing
amendment and fertilizing properties of digestates from anaerobic digestion through a comparative
study with digested sludge and compost [Ocena właściwości poprawiających parametry i
użyźniających osadów po fermentacji beztlenowej poprzez analizę porównawczą osadu
przefermentowanego i kompostu], Chemosphere, 81, 577- 583, 2010
[6] Magdalena Szymańska, poferment z biogazowni nawozem dla rolnictwa, Szkoła Główna
Gospodarstwa
Wiejskiego
w
Warszawie,
Kraków
2013
pod
adresem
http://www.biomasterproject.eu/docs/Szyma_aeska.pdf
[7] I. A Łucka, A. U Kołodziej, Rolnicze wykorzystanie masy pofermentacyjnej z biogazowni
rolniczej, Zachodniopomorski Ośrodek Doradztwa Rolniczego w Barzkowicach at
http://www.multichem-eko.pl/uploads/docs/rolnicze-wykorzystanie-masy-pofermentacyjnej-zbiogazowni-rolniczej-technologia-FuelCal.pdf