Effects of Mixing Duration on Biogas Production and Methanogen Distribution in Dairy Manure...
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Transcript of Effects of Mixing Duration on Biogas Production and Methanogen Distribution in Dairy Manure...
Effects of Mixing Duration on Biogas
Production and Methanogen Distribution
in Dairy Manure Anaerobic Digesters
Prepared by: Hui Wang, Rebecca A. Larson
March 31, 20151
Mixing and its Role in AD
Mechanical Mixer
Gas Recirculation
Start: Heukelekian, 1931, Shaking
Contact: Biomass and substrate
Particle size
Diffusion limitation
Stratification
Temperature
Sedimentation
Scum
Inhibitory substance
Source: Chapman, 1989; Parkin and Owen, 1986; Lema et al., 1991, Stenstrom et al., 1983 2
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Why Study Mixing Duration?
Intensity
Duration
Location
Diameter
Energy consumption =
~ 54% to run the biogas plants
5-10% of the energy produced from biogas
Source: Dachs Rehm 2006, FAL 2005
Less energy consumption
More biogas production
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Previous Studies on Mixing Duration
No decrease in gas production with discontinued mixing,
1979
Continuously mixing produced 8-10% higher CH4 than
2h/d mixing,1982
2h/3h and 1h/28h mixing produced ~20% more biogas
than continuously mixing, 2013
Coppinger, 1979, Hruska, 1982, Kowalczyk 2013 4
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Hypothesis and Objective
Loading rate: Mixing duration is not critical at low TS
< 10%, Karim 2005
Retention time (RT): Discontinued mixing causes solids
accumulation which impacts RT
Microbial community structure
How does mixing duration impact biogas production,
solids and methanogens distribution?
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Experimental Design (completely random)
I fixed factor (Mixing)
3 levels
30 min/hour (CON): 2*15 min
15 min/hour (INT): 1* 15 min
0 min/hour (NO): 0
Carried out in triplicates
• Test:
o Gas quantity, Gas quality
o Temperature, pH, TS,VS, VFA, COD, C/N, methanogens
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Fig.1 Design of the pilot-scale digester
Feed tank
Effluent
Pump
F
Sample ports
Heating band
Daily FeedingMixing
Temperature
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Operation Parameters
• Manure source: Local diary farm (Madison, WI)
• Total Solid content: 5.5 ± 0.5 %
• Feed amount: 8 kg of manure per day
• Retention time: 21 days
• Temperature: 33.5 ±0.8 °C
• Mixing rate: 400RPM (safe rate for feeding while mixing)
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Cumulative Biogas Production
0
2000
4000
6000
8000
10000
12000
14000
16000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
Bio
gas
Pro
du
ctio
n p
er k
g T
S f
eed
(L)
Time (Days)
NO CON INT
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80
Fig. 2 Cumulative Biogas Production with 3 Mixing Durations
Biogas Production
b
aa
b
a
ab
0
200
400
600
800
1000
1200
NO INT CON
Bio
gas
pro
du
ctio
n (
L)
Mixing Duration
L biogas per kg VS in digester L biogas per kg TS in digester
10
9
Fig. 3 Biogas production per kg of VS and TS in digester
Specific Biogas Yield
aa
b
0.0
0.5
1.0
1.5
2.0
2.5
NO INT CON
Sp
ecif
ic g
as
pro
du
ctio
n (
L M
eth
an
e
per
kg V
S d
estr
oy
ed)
Mixing Duration
L Methane per kg VS destroyed
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10
Fig. 4 L methane per kg of VS destroyed with different mixing duration
Solids Sedimentation over Time
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
1T-15 1M-15 1B-15 2T-15 2M-15 2B-15 3T-15 3M-15 3B-15
TS (
%)
Fig. 5 Total Solids of 3 digesters at different location after 15 min settling
1211
Solids Sedimentation
0
1
2
3
4
5
6
7
8
TS (
%)
Sampling time (min)
Top Middle Bottom
Fig. 6 Total Solids at top, middle and bottom of the digester in 2 hrs
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12
Total Solids Percentage in AD
14
13
Fig. 7 Total solids percentage for AD with NO, INT and NO mixing in 4 weeks
0 7 14 21 0 7 14 21 0 7 14 21
Solids, Methanogens and Biogas Production
a a a
a a a
b a aa a a
b
a a
0
200
400
600
800
1,000
1,200
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
NO INT CON
Bio
ga
s p
rod
uct
ion
(L)
Mixing DurationVS % in the digester TS % in the digester
logSUMm (log, base=10) Archaea (log,base=10)
L biogas per kg TS in digesterTS
(%),
V
S(%
), S
um
M&
Arc
haea
(lo
g,
base
=10)
15
14
Fig. 8 Compare of solids, methanogens and biogas production
Methanogens in AD
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15
Fig. 9 Archaea and sum of 5 tested Methanogens
Archaea
Sum M5
Sample time( day)
Summary
• No mixing has a higher biogas production when TS =
5.5%, compared with INT and CON mixing.
• No mixing will result in low specific gas production
• Recommendation: Operate the mixer to prevent
settling and other operational issues.
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Methanogens in AD
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Fig. 10 Methanogens changes in the digester
Limitations
• This study does not take the whole range of mixing
duration: 0,1/4,2/4 . might also need ¾ and 4/4
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