Integration of electrochemical and calcium hypochlorite oxidation for simultaneous sludge deep dewatering, stabilization and phosphorus fixation

Highlights: • A method for sludge dewatering, stabilization and phosphorus fixation was proposed. • Optimum condition at 15 V and 150 mg/g VS Ca(ClO)₂ was obtained. • Both extra- and intra- cellular oxidation were critical for the excellent results. • The conversion of Fe(II) to Fe(III) was facilitated with the addition of Ca(ClO)₂. • Electrocoagulation process enhanced sludge deep dewatering and phosphorus fixation. A hybrid electrochemical process with Ca(ClO)₂ addition for simultaneous sludge dewaterability, stabilization and phosphorus fixation was proposed. Under optimal conditions (150 mg/g VS Ca(ClO)₂, 15 V), the capillary suction time (CST) and specific resistance to filtration (SRF) were decreased by 88% and 92%, respectively. Efficient sludge stabilization with E. coli colonies of less than 1000 MPN/g TS was achieved. Phosphorus of 99% was removed from the filtrate and successfully fixed in the sludge cake and on the electrode surface. The integration of electrochemical and hypochlorite oxidation could effectively degrade the tightly bound extracellular polymeric substances (TB-EPS) structure with a total organic carbon (TOC) reduction of 52%. Besides, the disintegration of microbial cell envelopes was also achieved, with a reduction of living cell fraction of 98%. Furthermore, system pH could be maintained at near neutral (7.45) and the conversion of Fe(II) to Fe(III) was also facilitated with the addition of Ca(ClO)₂, resulting in improved electrocoagulation process for enhanced sludge dewatering and phosphorus fixation. The multifunctional effects were achieved with the cooperated extracellular electrooxidation for EPS destruction and the active chlorine for intracellular microbial cell disintegration. This research provides a promising strategy for integrated sludge treatment and recycling for possible land utilization.