Constant-current electro-dewatering of sewage sludge: Effect of anthracite modification on dehydration performance and economic benefit

Electro-dewatering (EDW) is a sludge reduction technology with considerable potential. However, its application is limited by low economic benefit, partially due to energy spent on heating sludge. When the mode of EDW with constant current (C-EDW) is chosen, a substantial amount of energy is wasted to heat the poorly-conductive dry sludge in the late stage of C-EDW. Reducing the sludge electrical resistance can weaken the ohmic heating effect in this process. Therefore, anthracite, a material with good electrical conductivity, was used to modify sewage sludge for C-EDW (constant current at 1 A) in this study, with different dosages (0% 12% mass of dry sludge (DS)) tested and compared. The results show that all anthracite-conditioned groups, with 2% 12% DS of anthracite added to sludge, had lower energy consumption than the blank group when the moisture content was all reduced to 60%. The economic benefit, quantified by an evaluation indicator KsiEDW, was improved by anthracite conditioning comparing all conditioned groups to the blank group. The optimal addition was 6% DS in the study, as the group had the lowest energy consumption (0.128 kWh/kgDS) and KsiEDW (1.71 (kWh/kgDS)center dot(h/ kgDS)). Anthracite also improved the dehydration performance of C-EDW- all conditioned groups had lower final moisture content than the blank group at the same final voltage (60 V), with 51.5% being the lowest (6%DS group).