Energy demand in sludge dewatering

This work investigates the energy required to dewater a suspension, i.e., activated sludge dewatered by centrifugation or consolidation. Total energy input to the suspension from the dewatering device, bond strength between adjacent water and solid surface, and intra-cake friction loss were evaluated for original and flocculated sludges. In centrifugal dewatering, most energy input during the initial stage was consumed by overcoming process irreversibility other than intra-cake friction, and, thereby, had a low energy efficiency. To increase centrifuge speed or to flocculate the sludge at optimal flocculant dosage would yield a high-energy input. In the consolidation test, most energy input at the initial stage was consumed in breaking down the bond strength until the moisture content reduced to less than the critical content. During subsequent dewatering stages, friction loss became the dominant source of energy loss. Dewatering sludge with high-energy efficiency is beneficial to optimally operate a dewatering process. (c) 2005 Elsevier Ltd. All rights reserved.