Anaerobic digestion of brewing “waste”.

L.S. Nkadimeng, S.T.L. Harrison

Energy Postgraduate Conference 2013

Background

Picture from : http://www.sabmiller.in/know-beer_brewing.html

Effluents• Beer• Spent grain• Spent yeast• Wastewater

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AD(wastewater treatment)

Anaerobic digestion (AD)

Proteins

Carbohydrates

Lipids

sugars

Amino acids

Fatty acids

Organic acids,

alcohols

H2, CO2, NH4

Acetate,H2, CO2

Biogas (CH4, CO2)

Hydrolysis Acidogenesis Acetogenesis Methanogenesis td : 30 minutes 1,4 to 5 days 2 to 3 days

Water

Steam to brewery CO2

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(Mosey 1983; Lawrence & McCarty 1989; Gerber & Span 2008)

Spent grain

• Mechanical pre-treatment to promote hydrolysis: grinding

Only 15% reduction in COD over 19 days of digestion

Digestibility:(Aliyu & Bala, 2011, Mussatto & Teixeira, 2010)

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Spent yeast: Effect of non-acclimated system on pH

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Spent yeast: Slow incremental feeding

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Highest removal rate: 962 mg-COD/L.day

Removal efficiency: 69% in 1 day

97% in 3 days99% in 9 days

•

Spent yeast: Continuous feed and draw

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• 25 day HRT, SCOD/TCOD of feed ~ 60%

Spent yeast: Comparisons to SAB reactor

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  HRT Average COD reduction rate

COD reduction efficiency

Substrate

  days mg-COD/L.day 

Lab reactors 25 3390 91% Spent yeast

WTP at current op.

1.8 1260 73 - 91% Wastewater

WTP design spec. 1(min)

4500(max)

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• Aim to reduce the HRT on lab reactors.

• Suggested strategies: recycling and continuous flow.

• 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.

Conclusions

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Acknowledgements

Prof. S T L Harrison

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