Enhanced dewaterability of waste activated sludge with Fe(II)-activated hypochlorite treatment

A novel method was explored to improve the waste-activated sludge (WAS) dewaterability using Fe(II) combined with calcium hypochlorite, and the possible mechanisms were investigated simultaneously. Capillary suction time (CST), specific resistance to filtration (SRF) of sludge, and water content (WC) of dewatered sludge cake were selected as the factors to evaluate the sludge dewaterability. The maximum reduction of WC (30.76%) was achieved under the optimal conditions of Ca(ClO)2 0.04 g/g total suspended solids (TSS), FeSO4·7H2O 0.097 g/g TSS, and pH 7.3, while the reduction of CST and SRF reached 91.24 and 99.47%, respectively. Three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy of extracellular polymeric substances (EPSs) showed that sludge dewaterability was mainly related to the degradation of tryptophan and tyrosine protein-like substances in sludge EPS. Economic analysis suggested Fe(II) combined with calcium hypochlorite treatment had greater potential on enhancing WAS dewaterability compared with the traditional sludge treatment.