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Biological Waste Treatment – Aerobic and Anaerobic
Tobias Bahr, Sept. 2010 – Hong Kong Baptist University
Waste Compositions
%
Germany
avarage
China
Brazil
Thailand
India
Java solo
Paper /
Cardboard
15.7
15,0
10.2
7.7
1.5
3.5
Glass
6.4
2.0
2.0
2.0
0.2
1.7
Organic
46.9
63,9
67.1
62.0
75.2
78.5
Plastic
9.8
16,9
8.7
12.0
0.9
2.6
Textiles
4.0
1,4
3.1
1.0
Metal
4.6
0,7
3.2
0.5
0.1
Rest
16.8
3.2
8.8
16
19.0
13,7
35 - 45
42 - 60
46- 58
41 - 53
42 - 60
49 - 63
8 - 9.000
4 - 7.300
< 4.000
< 4.000
Water
content
Calorific V
kJ/ kg
3 - 6.900 4 - 7.500
Waste with a calorific value lower 3.500 - 4.000 kJ/kg needs
additional fuel for combustion
Collection Systems
- Germany
Rest
Waste
MBT or
Incineration
+
Organics
+
Anaerobic digestion /
Composting Facility
Paper
+
+
Packaging
Sorting Facility
3
Glas
Collection Systems (Formal Sector)
2 Bin System
Dry
Waste
Sorting Facility
MBT
Incineartion
Wet
Waste
Anaerobic digestion and
Composting Facility
Collection Systems (Formal Sector)
2 Bin System
Rest
Waste
Sorting Facility
MBT
Incineration
Organics
Anaerobic digestion and
Composting Facility
Utilisation of Biomass from MSW
material
Composting
ca. 880
Composting facilities
material/energetic
energetic
Fermentation
Combustion Incineration,
Gasification (Pyrolysis)
ca. 85
Fermentation facilities
ca. 100
Incineration facilities
Technical options for biowaste treatment
Biowaste and
Other organic
green waste
wastes
Coarse fraction
Mechanical pretreatment
Anaerobic
Composting
Aerobic drying
digestion
(aerobic)
Biomass
Biogas
Organic
combustion
fertilizer
Substrates for anaerobic digestion
Anaerobic digestion
Combustion
Tree clippings
Green waste (winter/summer)
Biowaste (rural/urban)
Industrial org. waste
Kitchen waste
Food waste
Manure
Increasing water content
Increasing structure (lingnin)
Resource Management by closing the natural circle of life
Aerobic Treatment
Composting is the biological decomposition of biodegradable solid waste under
controlled aerobic conditions to a state that ist sufficiently stable for storage and
handling .
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O +
energy (heat and ATP)
• Biological Decomposition of
• biodregradable solid waste
• under controlled aerobic conditions
Steps Composting Process
The aerobic decomposition
process can be described as
follows:
Organic Compounds + Oxygen
→ Carbon Dioxide + Water +
Energy
Aerobic decomposition can be
shown by the decomposition of
glucose:
C6 H12 O6 + 6 O2
→ 6 CO2 + 6 H2O + Energy (Heat
and ATP)
Steps Composting process
Entrance, weighting,
controlling ,
Storage greenwaste and
bio waste
Pre condition: Screening,
homogenisation, splitting
Composting, Aeration,
Irrigation
Refining, Screening 8 to
20 mm
Compost storage and
packing
12
Pre condition: Material Flow Splitting
Aerobic
digestion/
Small particles (~ 70 %)
Green Waste
Screen
Shredder
Garden
Organics
Large particles (~ 30 %)
Composting
Fuel
e.g. Fertilisers and Renewable Fuels from Bio Waste
Pre condition: Removal Undesired Components
Composition of undesiredplastic
components
film
49,4%
textiles
1,8%
glass
3,0%
others
3,1%
Various plastics
4,0%
packaging
24,5%
metals
4,9%
compounds
9,4%
< 4,5Vol.% Störst. Sichtung HD 43+44 KW 1997 Vol.%
Content of undesired components up to 10 %
Waste Quality - Grain-size distribution: undesirable components
in Bio Waste
mass %
Undesirable components
Gew.-% (Bioabf鄟le und St顤stoffe auf je 100% normiert)
80
74
70
60
50
Bio Waste
40
36
35
30
20
16
13 13
12
10
6
8
12
0
< 25 mm
25-50 mm
Bio
Bio Waste
Waste
51-80 mm
Undesirables
Bioabfall St顤stoffe
> 80 mm
Examples for a drum screen
Manufacturing of a HORSTMANN drum screen
Hand sorting –
negative sorting of the Course fraction
Technical systems of composting
low-tech-approach: open windrow composting
Triangle
Trapezoid
high-tech-approach: fully enclosed technicaly advanced system, emission controlled
Bio-waste delivery – open area
Witzenhausen (Germany)
Low standard of air - emissions control (odour)
Bio-waste delivery – closed bunker
Composting Process – open windrow composting <10.000 t/a
general process of building windrows
1. Chop/shred the waste
2. Mix different types of waste
thoroughly and spread hindhigh
3. Spray additives (mostly not
required)
4. Moisten if necessary
5. Add further layers of waste in
the same way
6. Finished compost heap
(windrow)
aeration systems
• passive aeration systems
natural aeration (diffusion),
because of gradients of CO2concentration and heat
only < 80 cm,
can be supported by chimney
effect and turning
• forced aeration systems
ventilation-systems (sucking or
blowing systems)
Before
turning
After turning
process factors – 1
• kind of substrate:
content of biodegradable components
interstices volume (structure material)
moisture content
particle size of input material
• temperature
Active organisms producing thermal energy
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy (heat and ATP)
Should never rise over 65°C
process factors – 2
• moisture
micro-organisms need water to survive and for metabolic process
problem: very close relation between moisture and aeration
both needs interstices which can only be filled with free water or air depends on input material
Particle
Interstices
process factors – 3
• aeration (passive or forced) has many different functions
supply with oxygen, removal of CO2
reduction of water to dry the material
leading away the heat to prevent temperatures over 65°C
• pH-level
Activity of micro-organisms is related to pH-level, good for biological
activity are levels between 7-11
pH < 7 reduction of speed in decomposting process
pH < 5 strong inhibition
low ph-levels can be caused by uncontrolled anaerobic cond.
process factors – 4
• C/N – ratio
ratio betwen carbon and nitrate atoms in input material has a close
relation to speed of the composting process
Optimum: 1:20 to 1:35
< 1:10 growing inhibition
> 1:40 less nitrates are available
out of this range micro-organsim-populations are not able to grow
Adequate oxygen supply
waste-water effluent (discharge)
Aeration aggregat
Pile
Skizze Versuchsaufbau Kessler & Luch
Compost pile
Suking canal
Collecting
(Sucking) pipe
Folie
Temperature
Appropriate temperature
Duration (time)
self heating cause of low warmth conductivity
KKK..Appropriate temperature < 60-65° C,
cause of protein denaturation
29
Rotting degree of compost
Defines the required composting process time
(market-dependent)
Process
Time
(Weeks)
2 -3
fresh compost
3 -6
6-10
finished compost
8-16
Bio waste composting plant > 10.000 t/a
Completely encapsulated composting systems
(emission control)
Treatment of bio waste prior to composting
> 10.000 t/a
Turning device – table composting system
Schematic cross section
of an intensive
composting facility (e.g.
table composting System)
33
Turning device
Tunnel Composting System
35
Aeration systems
Sucking
System
Combination of
Sucking and
Blowing
System
36
Biological Treatment of Gaseous Emissions
Air Transport to the Biofilter
Air Purification - Biofilter System
clean gas
dirty gas
ventilator
moistener
container
Biofilter in Operation
Refining Process
Compoststorage
Mass Balance Composting Process Biowaste
Organic Waste Entry
100 %
65 % Water
23 % TSbio*
12 % TSmin**
up to 5%
Pre Conditioning
Undesirables
5 % Störstoffe
Air, Water
Composting
Aerob Process
up to 65%
Waste Water
11 % Biogas
CO2
29 % Abwasser
bio
Fine Conditioning
Sieving
Foreign Material Removal
Compost
29 %
10,2 % Water
8,2 % OTSbio **
10,7 % Tsmin **
up to 5%
Foreign
Mat.
2 % Störstoffe
* Burn Res. t/OTSbio 65 %
** Water Content 35 % i. d. TS
Loss TS
bio 43 %
Anaerobic Processes - Digestion
Stoichiometric formula for the conversion from Glucose:
C6H12O6 3CO2 + 3CH4 + Energy
The majority of the energy is stored in the decomposition product
methane.
Barcelona / Spain
300.000 t/y
Procedure and Mass Balance of Organic Waste Fermentation and
Coposting
Organic Waste Entry
100 %
65 % Water
23 % TSbio*
12 % TSmin**
Coarse Conditioning
Process
Water
Prozesswasser
Sieving
Foreign Material Removal
Pulper **
55 %
% Undesirables
Störstoffe
Fermentation Entry
95 %
Process
Water
Prozesswasser
Degradation of the Organic
Substance
Fermentation Discharge
55 %
Air
Luft
Post-composting
11
11 %
% Biogas
Biogas
29
Water
29 %
% Waste
Abwasser
24
Losses
24 %
% Matur.
Rotteverluste
18,4
18,4 OTS
OTSbio
bio
220,4
220,4 Water
Wasser
Fine Conditioning
Sieving
Foreign Material Removal
Compost
29 %
10,2 % Water
8,2 % OTSbio **
10,7 % Tsmin **
22 %
Mat.
% Foreign
Störstoffe
* Burn Res. t/OTSbio 65 %
** Water Content 35 % i. d. TS
Loss TS
bio 43 %
Biogas-Production and Quality by Mechanical-Biological Waste
Treatment
Biogas Production
Gas Amount
Waste Input
(plant) fresh matter
60 – 110 m3/t
Waste Input
(plant) dry matter
113 – 160 m3/t
Biogas Quality
CH4-Content
Energy Content
57 – 68%
5.8 – 6.8 (KWh/Nm3)
Biogas quality from different substrates
Substrate
Biogas composition
Source
CH4
CO2
H2S
[Vol.-%]
[Vol.-%]
[Vol. -%]
57 – 65
k.A.
< 0,05
Bio waste
Fricke et al., 2002
62 – 741)
k.A.
k.A.
Residual waste
57 – 65
k.A.
(0,07–0,09)1) 0,40–0,45
Liquid manure
53 – 69
(80)2)
(15)2) 30 - 46
0,05 – 1,0
Sewage sludge
55 - 65
35 – 45
0,001 – 0,0043)
Tentscher, 2002
Landfill gas
45 - 55
30 - 40
0,005 – 0,03
Tentscher, 2002
Fricke et al.,1993 u.
2002
Hüttner, 1997
Heating value of different gases
Gas
Heating value Hu
[MJ/m3]
Natural gas
30,2
Bio-gas
23,3
Town gas
19,9
coal gasification
Quality of Biogas
Component
Raw gas
Clean gas
CH4
65 %
> 96 %
CO2
35 %
<4%
H2S
max. 200 ppm
max. 5 mg/Nm3
H2O
variable
< 10 mg/Nm3
Anaerobic digestion
Suitable organic substrates
One-stage, two-stage
process
Mesophilic,
thermophilic operation
Wet or dry anaerobic
digestion
Biogas
Conditioning
Desulfurization
Refining
Compression
Pressurized storage
Gas heating
boiler
CHP
Heat
Fuel
cell
Electricity
Motor fuel
Energetic equivalent of biowaste as car fuel
Energetic Equivalent of bio-waste
(approximated values)
10 kg Kitchen waste
1,5 m3 Bio-gas
1 m3 Clean-gas
10 Km Car drive
1 kg waste = 1 Km car drive
Comparison anaerobic an aerobic Process
• Energy
• Air Emissions
• Leachate Emissions
• Required area
• Ecological evaluation
• Potential for further
development
• Operation stability
• Costs
anaerob
++
+
aerob
+
++
++
++
+
+
The Future belongs to Anaerobic
Treatment
Mass flow MSW- Germany - 2006
reuse + recycle +
energetic recovery
19 Mio [t/y]
avoidance
??
48%
municipal solid
waste
40 Mio [t/y]
waste Disposal
21 Mio [t/y]
Landfill???
52
Treatment Before Landfilling – Aims:
Minimizing volume and mass of waste delivered to the landfill
Inactivation of biological and chemical processes thus preventing
landfill gas production and settlement
Immobilizing contaminants of the waste in order to reduce leachate
emissions
Separation of recyclable materials, Fe- and non-Fe-metals, fuels, biogas
etc.
Limit values for the landfilling of waste according to the
German AbfAblV (2001)
Respiration activity in 4 days (AT4)
Gas formation in 21 days (GB 21)
Upper heating value Ho
Unit
% of dry matter
% of dry matter
mg/l eluate
mg O 2/g dry
matter
l/kg dry matter
kJ/kg dry matter
Mechanical–biological
pre-treatment (MBT)
Parameter
Organic matter, determined as loss on
ignition
TOC in solid matter
TOC in eluate
Incineration (IP)
German Ordinance for Environmentally Safe Landfilling of MSW stipulates criteria for waste to be
landfilled. Main requirements are:
Landfill
Class I
Landfill
Class II
MBT-Waste
3
1
20
5
3
100
18
300
-
-
5
20
6.000
*)
Treatment capacities for municipal solid waste
in Germany (2006)
MBS
8,7%
MT
2.9%
mi.
3,2%
MBT
15,5%
Incineration
69,7%
Incineration
MBT
75 %
25 %
17.0 Mio t
5,7 Mio t
Source: Prognos 2006
Status quo of MBT Technologies in Germany by June 2005
68 Plants – Treatment capacity 7,2 Mio. t/a
Mechanical
Treatment (MT)
Substance
separation
Mechanicalbiological
Stabilisation (MBS)
• Substance
separation
• Mass reduction
• Biological
stabilisation
mechanically
17 Plants
Mechanicalbiological
drying (MBD)
• Substance separation
• Mass reduction
• Biological drying
Mechanical-physical
drying
(MPD)
• Substance
separation
• Mass reduction
• Thermal drying
aerobic
anaerobic/
aerobic
aerobic
anaerobic/
aerobic
thermal
mechanical
23 plants
13 plants
12 plants
-
3 plants
-
Products and residues
• Refuse Derived Fuel
(RDF)
• Metals
(ferrous and non-ferrous)
• Residues
(for thermal treatment)
• RDF
• Metals
• Residues for landfill
• Bio-gas
• RDF
• Metals (ferrous and non-ferrous)
• mineral secondary building materials
• preliminary products for the production of
„sunfuels“ (gasification)
Characterization of Different Waste Categories
Parameters
Municipal Solid
Waste
Bulky Waste
Commercial
Waste
Dry Matter (dm)
65%
81%
77%
Organic dm (% of dm)
64%
72%
56%
Aerobic biodegradable
organics (% of dm)
44%
52%
23%
Anaerobic
biodegradable
organics (% of dm)
37%
3%
13%
14%
5%
18%
8,300 MJ/t fm
13,200 MJ/t fm
11,400 MJ/t fm
Inerts (% of fm)
Calorific value (l)
MBT- Procedure and
Mass-balance
Municipal solid waste
Shreddering
Sieving 120 mm
> 120 mm
Refuse derived fuel
Fe
25 - 35 %
Hu= 11 – 12,500 MJ/Mg
< 120 mm
Fe
Biological treatment
aerobic
Further mechanical
treatment
Ferrous metals
2-4%
Reduction of
organic matter,
water
25 - 30 %
Refuse derived fuel
5-8%
Hu = 12 – 13,500 MJ/Mg
Filter material
Methane oxidation
layer
Landfill
35 - 45 %
TOC < 18 %
MBT
Municipal solid waste
Shreddering
Sieving 120 mm
> 120 mm
Refuse derived fuel
Fe
25 - 35 %
Hu= 11 – 12,500 MJ/Mg
<120 mm
Fe
Biological treatment
aerobic
Further mechanical
treatment
Ferrous metals
2-4%
Reduction of
organic matter,
water
25 - 30 %
Refuse derived fuel
5-8%
Hu = 12 – 13,500 MJ/Mg
Filter material
Methane oxidation
layer
Landfill
35 - 45 %
TOC< 18 %
MBT
Municipal solid waste
Shreddering
Sieving 120 mm
> 120 mm
Refuse derived fuel
Fe
25 - 35 %
Hu= 11 – 12,500 MJ/Mg
<120 mm
Fe
Biological treatment
aerobic
Further mechanical
treatment
Ferrous metals
2-4%
Reduction of
organic matter,
water
25 - 30 %
Refuse derived fuel
5-8%
Hu = 12 – 13,500 MJ/Mg
Filter material
Methane oxidation
layer
Landfill
35 - 45 %
TOC< 18 %
MBT
Municipal solid waste
Shreddering
Sieving 80 mm
> 120 mm
Refuse derived fuel
Fe
25 - 35 %
Hu= 11 – 12,500 MJ/Mg
<120 mm
Fe
Biological treatment
aerobic
Further mechanical
treatment
Ferrous metals
2-4%
Reduction of
organic matter,
water
25 - 30 %
Refuse derived fuel
5-8%
Hu = 12 – 13,500 MJ/Mg
Filter material
Methane oxidation
layer
Landfill
35 - 45 %
TOC< 18 %
Process Conditions – Aerobic Process
C6 H12 O6 + 6 O2 → 6 CO2 + 6 H2O + Energy (Heat and ATP)
The most important process conditions are:
Adequate oxygen supply
Appropriate temperature
Appropriate water supply and
adequate supply of nutrient substances.
Air Demand and Energy – MBT
62
MBT Anaerobic-Aerobic
Principle of Biological Stabilisation
Degradation of organic matter in the course of aerobic treatment
process
Reduction of Gas Potential During Aerobic Treatment
220
200
180
lower area
upper area
GB21 (l /kg dm)
160
140
120
100
80
60
40
20
Limit value
0
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19
Duration of treatment (weeks)
exponetial
Reduction of DOC during Aerobic Treatment
4000
3500
DOC-Eluat (mg/l)
DOC
3000
lower area
upper area
2500
2000
1500
1000
Limit Value
500
300
0
0
2
4
6
8
10
12
14
16
18
20
Duration of treatment (weeks)
22
24
26
Stabilisation performance – MBT with anaerobic stabilisation and
aerobic post-treatment
160
Anaerobic
Aerobic post treatment
140
Linde-BRV; 3 W. Fermentation
120
GB21 (l /kg dm)
Valorga, 3 week fermentation
100
80
60
40
German limit
value for open
aerobic curing
20 20
0
0
1
2
3
4
5
6
7
8
9
10 11 12
Duration of treatment (weeks)
13
14
15
16
Stabilisation performance – MBT with anaerobic stabilisation and
aerobic post-treatment
2750
Anaerobic
Aerobic post treatment
2500
Linde-BRV; 3 W. fermentation
2250
Kogas; 2 week fermentation
TOC-Eluat
Eluat (mg/l)
2000
Valorga, 3 week fermentation
1750
1500
1250
1000
750
500
Limit value
300
250
0
0
1
2
3
4
5
6
7
8
9
10
Duration of treatment (weeks)
11
12
13
14
15
16
Landfill gas – Methane
Initial Situation
Water Content (WC) 40 % = 0,40 Mg
Dry Matter (DM) 60 % = 0,60 Mg
1 Mg Municipal
Solid Waste
Lost on Ignition = 80 %
0,80 x 0,60 (Mg DM) = 0,48 Mg organic dry matter (oDM)
Approximative Calculation of methane aerosis in landfill
empirical formula organic matter :
C99 H148O59 N
Buswell-equation for approximative calculation of methane aerosis:
 b c
a b c
a b c
Ca H bOc +  a - − H 2O →  + − CH 4 +  − + CO2
 4 2
2 8 4
 2 8 4
Periodic System
Approximative Calculation of methane aerosis in landfill
empirical formula organic matter :
C99 H148O59 N
Buswell-equation for approximative calculation of methane aerosis:
 b c
a b c
a b c
Ca H bOc +  a - − H 2O →  + − CH 4 +  − + CO2
 4 2
2 8 4
 2 8 4
molar mass C99 = 12 x 99 = 1188 g
oDM = 0.48 Mg = 480.000 g
molar mass H148 = 1 x 148 = 148 g
mol oDM before dagradation:
molar mass O59 = 16 x 59 = 944 g
480.000 g / 2.280 g = 210,5 mol
∑ of molar mass = 2.280 g
Calculation according to Buswell
 99 148 59 
 99 148 59 
→ +
− CH 4 +  +
− CO2 = 53,25 CH 4 + 53,25 CO2
8
4
8
4
 2
 2
molar mass of methane CH4 : 16,04
mass of methane aerosis CH4 : 16,04 x 53,25 x 210,5 = 179.794,4 g
density CH4 : 0,667 g/dm³
Volume CH4 : 179.794,4 g / 0,667 g/dm³ = 269.557 dm³ ≈ 270 m³
Reduction of methane aerosis by composting
organic degradation by composting: approx. 60 % of oDM
=0,60 x 0,48 Mg oDM = 0,288 Mg lost by composting
remained organic compostmass(dry) = 0,48 Mg – 0,288 Mg = 0,192 Mg
= 192.000 g oDM
Mol oDM after composting = 192.000 / 2.280 = 84,2
molar mass CH4 = 16,04 x 53,25 x 84,2 = 71.917,7 g
Volume CH4 = 71.917,7 g / 0,667 g/dm³ = 107,822 dm³ ≈ 108 m³
CH4-Reduction by composting
1 Mg FS 270 m³ CH4
1 Mg FS 108 m³ CH4
Avoidance : 162 m³ CH4
162 * 21 = 3402 m³ CO2-eq
Mass flow MSW- Germany - 2006
reuse + recycle +
energetic recovery
19 Mio [t/y]
CO2, H2O +
energy recovery
13.7 Mio [t/y]
avoidance
??
48%
municipal solid
waste
40 Mio [t/y]
34%
recycle
2.6 Mio
[t/y]
(Fe, Ne,
slag)
6,5%
landfill/
disposal
4,7 Mio [t/y]
waste treatment
21 Mio [t/y]
75% Incin. / 25% MBT
12%
77