Course 2 Unit 6
Part a
Introduction to composting
Teacher Mariska Ronteltap
[email protected]
Course 2 Unit 6
Introduction to composting
Part A – Fundamentals and design considerations
Part B – Vermicomposting (in separate file)
Part C – Engineered composting toilets (in separate file)
Part D – Examples and case studies (in separate file)
This unit deals with which part of the sanitation
system?
Crop grown with ecosan products as fertiliser (closing the loop)
Part A
Household
toilet
Household
toilets, but can
also include
showers, bath
tubs, sinks
Part B
Part C
Part D
Treatment
& storage
Collection &
transport
Urine, faeces,
greywater
transport
(road-based
vehicles in
combination
with pipes)
Part E
Re-use in
Agriculture
Transport
Treatment
for faeces
and
greywater,
storage for
urine
Transport of
sanitised urine and
faeces by truck;
treated greywater
transport by pipes
Sale of fertiliser
(sanitised human
excreta); irrigation
with treated
greywater
 The composting process is used to sanitise faeces (either in composting toilets or in a
centralised composting system) with the aim to produce an end product suitable for reuse
in agriculture
 Pathogen kill is achieved through the raised temperatures in the compost heap, which
are sustained for a certain period of time
Preamble about composting in Europe
 Composting is widely used in Europe (Germany being the
leader*) to treat organic solid waste, which is collected
separately from households in many municipalities – see next
slide
 There is a vast amount of know-how on composting as a
secondary treatment process (semi-centralised or
centralised), with using organic solid waste or sewage sludge
as an input material
 Challenges for “us ecosan people”:
- We have to harness this knowledge and apply it to faecal
matter as an input material
- Devise simple low-cost processes that can be used at
community level
* In Germany there are currently 485 composting plants with RAL quality assurance, and in total about
800 composting plants which treat organic solid waste (no faeces) - data from Annette Ochs, 23 April 2007
Extent of separate biowaste collection in
Europe
Mt
20,000
18,000
16,000
Potential of source separated biowaste and green waste
EU 25 + NO [ 113 Mio tons ]
Biowaste and green waste separetly collected in 2005
EU 25 + NO [ 24 Mio tons = 21% ]
14,000
12,000
10,000
8,000
Germany (DE) has the highest collection level in
Europe (“EU 25 + NO” means 25 European member
states plus Norway (now there are 27)).
Treatment predominantly by composting or anaerobic
digestion
6,000
4,000
2,000
0
IT DE FR UK PL ES NL HU BE CZ SE AT PT EE SK DK FIN NO GR IE LT LV SL CY LU MT
How is the “biowaste” (organic kitchen and
garden waste) collected?
(remember this picture from Course 2 Unit 3 Storage and Transport)
For example at my
house in Ede, the
Netherlands: kerbside
collection (fortnightly
for the brown bin)
Paper
Bin for biowaste (for composting)
Other waste
Course 2 Unit 6
Amount of biowaste treated in Germany in
composting plants (in million tons)
6
5
4
3
2
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
199
199
199
199
199
199
199
199
200
200
200
200
200
200
200
0
Source: Bundesgütegemeinschaft Kompost e.V., 19. Kasseler Abfallforum, April 2007
(obtained via Annette Ochs)
Development of
source separation
and composting in
Europe
Source: European Compost
Network (ECN),
http://www.compostnetwor
k.info/index.php?id=10
Note: the article did not
state for which year this
situation was (it might have
changed by now)
Course 2 Unit 6
Course 2 Unit 6
Part A: Fundamentals and design considerations
Note: “compost” is a
popular term which is
used for all sorts of
materials even if they are
not really true compost
(e.g. Faeces that have
been just air-dried) – be
careful.
Compost (from www.wikipedia.org)
What is “compost” and “composting”?
 Compost is the aerobically decomposed remnants of organic
materials (those with plant and animal origins). Compost is
used in gardening and agriculture as a soil amendment, and
commercially by the landscaping and container nursery
industries. It is also used for erosion control, land/stream
reclamation, wetland construction, and as landfill cover (see
compost uses). Compost is also used as a seed starting
medium generally mixed with a small portion of sand for
improved drainage.
 Composting is the process of producing compost through
aerobic decomposition of biodegradable organic matter. The
decomposition is performed primarily by aerobes, although
larger creatures such as ants, nematodes, and oligochaete
worms also contribute.
 Source: www.wikipedia.org
Which materials can be a substrate (input
material) for composting?
(in order of importance for ecosan concept)
1. Dried faeces (from UDD
toilets)*
2. Faecal sludge
3. Organic solid waste (kitchen
residue)
4. Animal waste / agricultural
waste
5. Sludges from centralised
wastewater treatment plants
(i.e. this includes faeces)
Materials 3 – 5 are already widely
composted; materials 1 and 2
are “ new”
Compost samples from Romanian UDD toilets with
secondary composting (displayed by Margriet Samwel
from WECF at Ecosan Seminar in Bulgaria, April
2007)
* Moisture content and C/N ratio may have to be adjusted
by adding water or wet kitchen waste
Composting and anaerobic digestion (AD)
can be competing processes to treat organic
solid waste
Composting may be preferred over AD in the following cases:
For dry solid input materials, e.g. > 50% d.s.
 Some organic matter is more amenable to composting than to AD,
e.g. garden clippings, leaves (high lignin content)
When a higher quality soil conditioner is desired
 fewer pathogens in compost compared to digester residue
 drier product  can be transported more easily; easier to sell
 but less nitrogen content (nitrogen losses during aeration)
When there is no need or use for biogas (energy)
 E.G. in Germany, anaerobic digestion appears to be gaining the
upper hand compared to composting because of the desire to
produce green energy (climate change issues)
When a system with lower investment costs is desired (less know-how
required for construction of composting processes compared to AD)
When some odour emissions are acceptable (population density low) –
composting processes are usually not enclosed, although a building
could be constructed around it
Course 2 Unit 6
Applications of composting process in ecosan
concept
1. Thermophilic composting (55-65°C) as secondary treatment
of faeces (in semi-centralised composting plants)
 E.g. Co-composting of faeces or faecal sludge with organic
solid waste at semi-centralised level
2. Mesophilic composting (35°C) in composting toilets (for
primary treatment of faeces) - see Part C for more details on
composting toilets
 Most of the traditional composting toilets have no urine
diversion (in recent times, urine diversion has been added)
 Careful: Some people call dehydration toilets also
composting toilets, which can be confusing
most
important
See debate on Ecosanres Discussion Forum end of September 2006: Some experts
say that composting and dehydration are both occurring at the same time when ash is
added as a carbon source to a UDD toilet. Paul Culvert (ecosan pioneer in India) calls
his toilet design a “dry composting toilet” (with urine-diversion).
Reminder from Course 2 Unit 1 Part C:
2 levels of excreta treatment: primary, secondary
Urine;
faeces
primary
treatment
Sanitised urine;
partially sanitised
faeces
PRIMARY TREATMENT

Treatment integrated into individual toilet

Usually sufficient when households can
reuse their own products
Examples:

Storage and drying in the toilet (double-pit
collection is preferred)

Alkaline treatment (addition of ash and lime;
pH >9 during >6 months)

Composting (not recommended except for
dedicated users)
secondary
treatment
Sanitised urine;
sanitised faeces
SECONDARY TREATMENT

Treatment at community / block
level (outside of household)

Necessary if project is at
community level, particularly for
faeces
Examples:

See next slide
Reminder from Course 2 Unit 1 Part C:
Secondary treatment options for faeces
Type of
process
Description
Is it
common?
Storage
One year under tropical conditions (2830 ºC)
Very common
Composting
Thermophilic preferred (> Common
50 ºC for > 1 week)
Anaerobic digestion
Works well in conjunction with animal
manure (household biogas plants), but
incomplete pathogen removal
Common in some
countries (e.g.
China, India,
Nepal)
Chemical treatment
Mixing with urea to achieve pH increase
Experimental
stage
Incineration
Burning, reuse of ash; complete
pathogen kill
Not common
This elevated temperature for an extended time period will achieve pathogen kill (not
complete pathogen kill but sufficient to make it safe for reuse (see also Course 3 Unit 1))
based on Schönning and Stenström (2004)
Reminder of terms (1): “Indicator organisms”
 Microorganisms which are easy to quantify and
which exhibit same or greater survival
characteristics in the environment as the target
pathogen organism for which they are a surrogate
 Should be present when faecal contamination is
present
 Examples: helminth eggs, total coliforms, faecal
coliforms, E. coli, Enterococci, MS2 coliphage
o Helminth eggs (e.g. Ascaris) is now becoming the norm
as an indicator organism for treatment of faeces in
composting since they are very resilient
o Unfortunately, helminth eggs are also expensive to
measure
Note: Ova = eggs
Course 2 Unit 6
Reminder of terms (2): what is “organic”?
 An organic compound is any member of a large class of
chemical compounds whose molecules contain carbon and
hydrogen; therefore, carbides, carbonates, carbon oxides and
elementary carbon are not organic (see below for more on the
definition controversy for this word). The study of organic
compounds is termed organic chemistry, and since it is a vast
collection of chemicals (over half of all known chemical
compounds), systems have been devised to classify organic
compounds.
 The name "organic" is a historical name, dating back to 19th
century, when it was believed that organic compounds could
only be synthesised in living organisms through vitalis - the
"life-force". The theory that organic compounds were
fundamentally different from those that were "inorganic", that is,
not synthesized through a life-force, was disproved with the
synthesis of urea, an "organic" compound by definition of its
known occurrence only in the urine of living organisms, from
potassium cyanate and ammonium sulfate by Friedrich Wöhler
in the Wöhler synthesis.
(Source: www.wikipedia.org)
Course 2 Unit 6
Reminder of terms (3): what is “humic acid”?
 Humic acid is one of the major components of humic
substances which are dark brown and major constituents of
soil organic matter humus that contributes to soil chemical
and physical quality and are also precursors of some fossil
fuels. They can also be found in peat, coal, many upland
streams and ocean water.
 Humic substances make up a large portion of the dark matter
in humus and are complex colloidal supramolecular mixtures
(Piccolo, 1996, 2001; MacCarthy, 2001) that have never been
separated into pure components.
Source: www.wikipedia.org
Compost during curing phase after active composting period
Substrate: organic solid waste
Composting fundamentals overview
 Organic material undergoes biological degradation to
a stable end product (the compost)
 During the decomposition process, the compost heap
heats itself up to temperatures in the pasteurisation
range of 50 to 70°C (=self-heating) and enteric
pathogenic organisms are destroyed
-Note no external heating needs to be applied!
- Sometimes an insulation is used (in composting toilets)
 Composting is usually carried out under mostly
aerobic conditions
 When composting is used to treat faecal matter, the
recommended indicator organism to measure extent
of pathogen kill is helminth eggs
Note: the temperatures in vermi-composting are much lower (under 25ºC –
see Part B)
Composting process microbiology
 Complex destruction of organic material coupled with the
production of humic acid* to produce a stabilised end product
 The micro-organisms involved are bacteria, actinomycetes
and fungi
 Interrelationships between microbial populations are not fully
understood
 Three stages of activity and associated temperatures:
 Stage 1: Initial mesophilic stage (40°C) – self-heating
 Stage 2: Thermophilic range 40-70°C – self-heating
 Stage 3: Cooling period (stabilisation of pH, completion of
humic acid formation)
* see definition on next slide
Phases during composting as measured by
carbon dioxide respiration and temperature
Stage 1
Stage 2
Stage 3
Temperature in °C
(or CO2 respiration)
High-rate
composting
Typical values for
aerated static pile
composting:
Curing
Thermophilic
temperatures
Mesophilic
temperatures
3-4 weeks
Stable and
mature compost
1 month or longer
Source: Metcalf & Eddy (2003), page 1547
Course 2 Unit 6
Isothermal lines in a cross-section of a 14-dayold compost heap
(= in stage 2 of the composting process)
If your compost pile is not heating itself up, then you know
that something is wrong!
1.
2.
3.
4.
5.
Five basic process steps of technical
composting operation (at the large scale)
Pre-processing: mixing of faecal matter (or sludge)
with an amendment* and/or a bulking agent
High-rate decomposition: aerating the compost pile
either by addition of air, by mechanical turning, or
by both
Recovery of the bulking agent*
Further curing and storage; cooling
Post-processing; screening
* for explanation see next slide
Amendments and bulking agents
Amendment
 = Organic material added to the feed substrate to reduce
the bulk weight, reduce moisture content and increase the
air voids for proper aeration
 Can be used to increase the quantity of degradable
organics in the mixture
 Examples are sawdust, straw, recycled compost, rice
hulls
Bulking agent
 = Organic or inorganic material that is used to provide
structural support and increase the porosity of the mixture
for effective aeration
 Wood chips are commonly used (can be recovered and
reused)
Main technical methods of large-scale
composting (brief summary)
Agitated (see photo on next slide)
 Periodic agitation to introduce oxygen, control the
temperature and mix the material to obtain uniform
product
 Composting period is about 21 – 28 days
 e.g. windrow method
Static
 Air is blown through the static composting material,
composting period of 21-28 days, and > 30 days for
curing period
 e.g. aerated static pile method
In-vessel composting systems
 Composting is accomplished inside an enclosed container
or vessel
Course 2 Unit 6
Example of an agitated composting process
Composting in rows (agitated by machine), with organic
solid waste as a substrate
Example of home composting (static
process)
In many countries (rich and poor alike), the process of composting kitchen
waste is widely practiced. But not many people add human excreta to their
compost heap, even though this would be possible
Composting of toilet and kitchen waste (outside)
Compost vessel with lid
Worm culture, 24 hours active
Source: Wolfgang Berger (more information on him in Part C)
Design considerations for composting systems
Item
Comment
Carbon to
nitrogen ratio
Initial C/N ratio should be 20:1 to 35:1 by weight*. The ratio
reduces during composting process because of carbon loss and
nitrogen accumulation
Air requirements
Air with at least 50% oxygen remaining should reach all parts of the
composting material
Moisture content
Moisture content of the composting mixture should not be > 60%
for static pile and windrow composting and not > 65% for in-vessel
composting
pH control
pH should be 6 to 9; optimally 7 to 7.5
Temperature
Temperature should be 50 to 55°C for the first few days and 5560°C for the remainder of the active composting period
Control of
pathogens
To kill all pathogens, temperature must be maintained between 60
and 70°C for 24 hours
Mixing and
turning
Material should be mixed or turned on a regular schedule
* See table slide after next for some example C/N values (be aware that it is not so easy to measure
the C/N ratio: you will require access to a laboratory for this)
Source: Metcalf & Eddy (2003), page 1552
Possible reasons for process failure (related to
the table on the previous slide)
C/N ratio too low
 add carbon source
Not enough aeration
 mix more (turn over more)
 use of bulking agent
Too much moisture
 reduce water content of input material
 remove leachate
 use urine diversion if composting toilet is used
Not enough moisture
 add water (rainwater harvesting or recirculate leachate or
add urine)
Example C/N ratios for several waste
types
Human faeces
should be similar
See also Part D for further
C/N ratios
Source: Rothenberger et al. (2006), p. 27
Course 2 Unit 6
Guidelines for
design: space
requirement
This table and many more design
details can be found in the excellent
recent publication by Sandec:
Rothenberger et al. (2006), p. 50
You can also find it under Assigned
Reading
Practical points: the impact of ambient
temperature
“One has to be aware that as composting is a very natureconnected process things might work differently in different
natural environments.
For example in Sweden they say - 'always insulate the composter'.
No one ever thinks of insulation in Bulgaria - the summer is so
hot that the material will decompose until the next growing
season, and who cares to invest money and labor in something
that the nature will do it by itself.
In European climate more or less the composting heap/bin has to
have a volume of ca 1 m3 - something like 1 x 1 x 1 m. With
these dimensions it has good chance to develop enough inside
heat (to kill the pathogenes) and still to be manageable for
turning over relatively easy.”
Source: Diana Iskreva, Bulgaria, former online course participant (May 2007)
Main indicators for composting process
failure
 Odour
 No temperature rise in compost heap (or only
small increase in temperature)
Possible compost prices
€ 7 per ton for compost made from organic solid
waste in Germany (personal communication with
Annette Ochs) – sometimes the compost also has
to be given away for free
€ 22 per ton for compost made from faecal sludge
and organic solid waste in Accra, Ghana –
predicted value (Vodounhessi and von Münch,
2006)
€ 28 per ton for compost made from organic solid
waste (Rothenberger et al., 2006, p. 34 – example
from Bangladesh)
How much does compost sell for in your country?
Course 2 Unit 6
Operating costs for semi-centralised
composting processes
 It depends on the composting technology
used and the scale of the process
 In developing countries it may cost only €
15 per ton of input material
 in Germany the costs are around € 60 per
ton (in comparison: anaerobic digestion: ~ €
120 per ton)
 Composting cannot be financed by sale of
product alone (in most cases) but mostly
via a waste disposal fee
Compost marketing hierarchy indicating market
prices (in €/ton or €/m3)
The absolute cost
values in this graph
are not so
important, but note
that different
applications can
result in different
compost prices (and
different quality
requirements)
Source: European
Compost Network
(ECN),
http://www.compostne
twork.info/index.php?i
d=10
Possible compost yields
0.1 ton compost per m3 faecal sludge if faecal sludge
is co-composted with organic solid waste (Source:
Vodounhessi and von Münch (2006))
0.3 ton compost per ton of organic solid waste
(personal communication with Annette Ochs)
Course 2 Unit 6
Types of compost end products according
to German standardisation
• “Fresh compost”
– Hygienised, suitable for further intensive
rotting, separated material for improvement of
soil and fertilisation
• “Complete compost”
– Hygienised, biologically stable and separated
compost for improvement of soil
• “Substrate compost”
– Complete compost with limited content of
soluble plant nutrients and salts, useable as
mixed component for use in public gardens
(soil covering and fertilising)
• “Mulch compost”
Remember: Hygienised = sanitised = minimal pathogens
– Hygienised, separated compost without fine
particles for land covering
The benefits of compost application in agriculture will be dealt with in Course 3 Unit 1
Explanations on different compost types
and effects on plants
“Fresh compost” or “immatured compost”: this compost is not yet
utilisable by the plants (you can test this with the cress test) but you can easily work it in the top layer of the soil as mulch.
Matured compost is compost that can be utilised by plants. This
compost does not have to be soil-like, it can still contain
partially-composted parts of plants (or organic matter).
Matured compost is rich in soil organisms which can
accelerate the decomposition process, and they do not harm
the soil or plants.
Complete compost is compost where the decomposition process
is totally complete - it ist often called "compost soil". This is
the so-called commercial compost - it is less relevant for
enriching the soil life (soil microorganisms); often it is
amended with nutrients to also have a specific fertilising
effect.
These compost names have been translated from the German literature on composting – that’s why
the names in English seem a bit unclear sometimes (at least for me)
Source: Wolfgang Berger (composting specialist) personal communication, May
2007
An experience with compost
“Now I know what went wrong with my basil
seeds when I sow them in fresh compost
substrate; it was probably immature and killed
the poor seeds. I guessed already then that
there was something not right with the
compost. I made another trial with 'older'
compost and the plants grew well.”
Source: Ulrike Lipkow, GTZ Philippines, former online course
participant, May 2007
Course 2 Unit 6
Question: “Is compost a soil conditioner or
a fertiliser?”
Answer:
“The border between soil conditioners and fertiliser is fluid.
Normally, compost is called both. Final clarification about the
fertiliser effect of compost can only be obtained with an
analysis. Either way it is important to know whether the soil
has already an excess of nturients or a shortage of nutrients
and what nutrient requirements the respective plant has.”
Source: Wolfgang Berger (composting specialist) personal
communication, May 2007
Standardised methods for compost
analysis
Standard methods "TMECC (Test Methods for Examination of
Composting and Compost)" jointly published by USDA and US
Composting Council
Swedish Standard method for soil
Methods published in Germany (sorry, in German):
 BGK (1994) Bundesgütegemeinschaft Kompost e.V:
Methodenbuch zur Analyse von Kompost
 LAGA (1995) Qualitätskriterien und
Anwendungsempfehlungen für Kompost aus Müll und
Müllklärschlamm/ Mitteilung der Länderarbeitsgemeinschaft
Abfall 8, Merkblatt 10. Erich-Schmidt- Verlag (Quality criteria
and
application recommendations for compost obtained from
refuse and refuse/sludge, Pamphlet M10). Federal German
Department of Environment.