Transcript Nkadimeng_L_final - Energy Postgraduate Conference 2013

Anaerobic
digestion of
brewing “waste”.
L.S. Nkadimeng, S.T.L. Harrison
Energy Postgraduate Conference 2013
Background
Effluents
• Beer
• Spent grain
• Spent yeast
• Wastewater
AD
(wastewater treatment)
Picture from : http://www.sabmiller.in/know-beer_brewing.html
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Anaerobic digestion (AD)
Steam to brewery
Water
Carbohydrates
sugars
Proteins
Amino
acids
Hydrolysis
td :
Boiler
Organic
acids,
alcohols
Acetate,
H2, CO2
Biogas
(CH4, CO2)
H2, CO2,
NH4
Fatty
acids
Lipids
CO2
Acidogenesis
30 minutes
Acetogenesis
1,4 to 5 days
Methanogenesis
2 to 3 days
(Mosey 1983; Lawrence & McCarty 1989; Gerber & Span 2008)
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Spent grain
(Aliyu & Bala, 2011, Mussatto & Teixeira, 2010)
Digestibility:
Only 15%
reduction in
COD over
19 days of
digestion
•
Mechanical pre-treatment to promote hydrolysis: grinding
40
Soluble COD (mg-COD/gdBGS)
Soluble COD (mg-COD/g-dBGS)
1300
1100
900
700
500
300
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25
20
15
10
5
0
100
-100 0
35
0
50
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100
Time (s)
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150
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50
200
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Time (s)
150
200
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Spent yeast: Effect of non-acclimated system on pH
5000
10000
4000
8000
3000
6000
2000
4000
1000
2000
0
COD fed (mg-COD)
Reactor COD (mg-COD/L)
12000
TCOD in reactor
SCOD in reactor
TCOD fed to 1L reactor
SCOD fed to 1L reactor
0
0
1
2
3
4
5
0
1
2
3
4
5
6
7
8 9 10 11 12 13 14 15 16 17 18
Time (days)
7.8
7.6
7.4
pH
7.2
7
6.8
6.6
6.4
6.2
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Time (days)
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8000
5000
7000
4500
4000
6000
3500
5000
3000
4000
2500
3000
2000
1500
2000
COD fed (mg-COD)
Reactor COD (mg-COD/L)
Spent yeast: Slow incremental feeding
1000
1000
TCOD in reactor
SCOD in reactor
TCOD fed to 1L reactor
SCOD fed to 1L reactor
500
0
0
0
5
10
20
Time (days)
25
COD removal rate
(mg-COD/L-reactor.day)
pH
1200
7.8
15
1000
7.6
30
35
Highest removal rate: 962 mg-COD/L.day
7.4
800
7.2
6007
6.8
400
6.6
200
6.4
6.2
0 0
0
40
500
5
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15
20
25
1000 1500 2000 2500 3000
Time (days)
Substrate COD (mg-COD/L-reactor)
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30
35
3500 4000
Removal efficiency:
69% in 1 day
97% in 3 days
99% in 9 days
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Spent yeast: Continuous feed and draw
• 25 day HRT,
SCOD/TCOD of feed ~ 60%
TCOD in reactor 1
TCOD in reactor 2
TCOD in reactor 2
TCOD if no digestion
SCOD in reactor 1
SCOD if no digestion
45000
40000
Reactor COD (mg-COD/L)
35000
30000
25000
20000
15000
10000
5000
0
27
28
29
30
31
32
33
34
Time (day)
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Spent yeast: Comparisons to SAB reactor
Lab reactors
WTP at current op.
WTP design spec.
HRT
Average COD COD reduction
reduction rate
efficiency
Substrate
days
mg-COD/L.day
25
3390
91%
Spent yeast
1.8
1
(min)
1260
4500
(max)
73 - 91%
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Wastewater
-
• Aim to reduce the HRT on lab reactors.
• Suggested strategies: recycling and continuous flow.
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Conclusions
• Degradation efficiency on spent grain was poor and not
enhanced by mechanical pre-treatment. Spent grain is
not viable as substrate in in the WTP.
• Acclimation of the system to yeast feed is important for
auto-regulation of pH.
• Yeast is promising as substrate in the WTP.
Future work
• Optimisation of yeast digestion on lab reactors.
• Anaerobic digestion experiment to mimic large scale
digester (including biogas production measurements)
• Possibly, implementation of results on the WTP.
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Acknowledgements
Prof. S T L Harrison
University of Cape Town
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