Impact of process parameters of thermal alkaline pretreatment on biogas yield and dewaterability of waste activated sludge.

Abstract Thermal alkaline pretreatment (TAP) of waste activated sludge (WAS) before anaerobic digestion (AD) was reviewed. Focus of the review was on impact of TAP process parameters on biomethane yield (BY) and kinetics of AD and downstream dewatering. With higher initial biodegradability of untreated WAS, effect of TAP on BY decreases. Depending on initial biodegradability, BY increase of 22–97% is expected. Treatment temperatures below 100 °C showed to be as effective as temperatures higher than 100 °C in terms of BY increase. Alkali dosage and resulting initial pH have a significant effect on BY increase and showed to have an optimum range of 40–60 mg NaOH per g total solids (TS) of sludge. It is advised that alkali is dosed based on solids content in WAS and monitored by pH. Treatment time of 1.5–5 h is sufficient for an effective low temperature TAP (T