METHODS FOR INCREASING THE BIOGAS
YIELD IN MANURE BASED BIOGAS
PLANTS
P. KAPARAJU, N. CHRISTENSEN AND I. ANGELIDAKI
ENVIRONMENT & RESOURCES - DTU
TECHNICAL UNIVERSITY OF DENMARK
BIOGAS FORUM
10 DEC 2004
BACKGROUND




Manure - major substrate resource
Large fraction of TS - Particulate matter
One-step CSTR digestion
– Methane yields of 0.2-0.25 m3/kgVS
< theoretical yield of 0.4-0.45 m3/kgVS.
BMP Test – Digested material
– 5-10% additional methane
RESEARCH APPROACH


Focus EFP-04 project on :
1. Reactor configurations
 Serial digestion
2. Operational procedures
 Retain degradable material
3. Methods for degradation of undegraded
material
 Post-treatment
Lab-scale and pilot-scale studies
1. Reactor configuration
15 d HRT
Serial digestion

Conversion eff:
– low - single step digestion



Split total reactor vol between two 12 + 3 d HRT
CSTR connected in series
Two separate methanogenic reactors
On-going projects:
a. Effect of different reactor configuration
90:10, 80:20 & 70:30 Vol.
b. Effect of temperature
1. Reactor configuration
a. Effect of different reactor configuration
80:20 & 90:10
2003
2003
R1
R2
R3
R1
R2
R3
Reactor configuration
100
80
20
100
90
10
Total volume (ml)
3500
3500
1800
3500
3500
1800
Working volume (ml)
3200
3200
800
3200
3200
356
HRT (d)
15
12
3
15
13,5
1,5
Feed rate (ml/d)
213
267
267
213
237
237
Loading rate (gVS/d)
10
13
10
12
Methane production (ml/d)
1922
2726
1979
2485
Methane prod (ml/gVS/d)
184
209
189
214
% increase



12
12
1-10% HIGHER METHANE PRODUCTION COMPARED TO ONESTEP PROCESS
HIGHER (20-40%) METHANE PRODUCTION DURING VARIOUS
PULSES.
PROCESS MORE ROBUST TO DISTURBANCES
a. Effect of different reactor
configuration (contd)
R1
R2+R3
R2
R3
Biogas production (mL/mL feed)
(3 days rolling average)
25
Steady-state period
20
15
10
New batch of manure
5
0
0
5
10
15
20
25
30
Day
35
40
45
50
55
Fig. Daily biogas production from reactor R1 operated in parallel and
reactors R2 and R3 operated in series
60
1. Reactor configuration
b. Effect of temp. on 2-step of serial
digestion

Methanogenesis in second-step of
serial digestion is dependent on temp.
and chemical characteristics of the
incoming digestate.
55 ° C
37 ° C
55°C
20 ° C
b. Effect of temperature (contd):
Gas production
55
Gas produce (mL/mL feed)
7
37
6
20
5
4
3
2
1
0
0
10
20
30
40
50
60
70
80
90
Days
Fig. The effect of temperature (20-55C) on daily biogas production
from reactor R3 operated in series with reactor R2.
2. Operational procedures
Passive solids separation
10°C
Top
60 cm
97 cm
55°C
Top
60 cm
After 1 d
97 cm
2. Operational procedures
Top
Middle
Bottom
Solids (%)
mixed
6
TS
4
2
mixed
12
8
0
6
12
4
VS
2
0
0
0.25 0.5
1.0 2.0
Time (hr)
24 120 240
top
middle
bottom
TS
4
0
Solids (%)
Solids (%)
Solids (%)
Passive solids separation
VS
8
4
0
0
0.25 0.5 1.0
2.0 24 120 240
Time (hr)
Fig. Changes in TS and VS of digested cow manure samples over time
from top, middle (60 cm) and bottom (97 cm) of column
3. Methods for degradation of undegraded
material
Post-treatment

Short-term aerobic/composting as post-treatment
Acknowledgements:
 Chao Pan
 Kanokwan
 Tore & Jacob
 Henar
 Hector