Proceedings

Previously, a model was set-up to investigate the effects of sludge type on anaerobic digestion and subsequent dewatering at a municipal sewage treatment works based on data collected from full-scale anaerobic digestion plants up to 900,000 population equivalents in size. Other than sludge type, the model investigated the effects of various parameters such as: plant size; sludge thickness; volatile solids content; value of renewable energy credits etc on overall processing costs. Subsequently, the model has been further developed to investigate the effects of co-digestion (with biodegradable municipal waste, for example) on mass and energy balances.

The model also investigates the effects of anaerobic digestion (with or without codigestion) on several downstream options – namely sludge drying with and without the option for co-firing and agricultural recycling with lime addition. The model also evaluates the quantity and value of “lost” biogas energy generated from secondary digestion storage. Finally, comparisons are made between anaerobic digestion and raw sludge processing on dewatering performance and sizing of downstream equipment.

KEY WORDS: Anaerobic digestion; Biogas; Cost analysis; Dewatering; Renewable Energy; Sludge quality.