Phosphorus removal from spiked municipal wastewater using either electrochemical coagulation or chemical coagulation as tertiary treatment

Abstract

Effluents from municipal wastewater treatment plants (WTP) can contain residual phosphorus concentration above the recommended limiting values and it could have a high environmental impact (e.g. eutrophication as a result of excess nutrients). In order to produce an effluent suitable for stream discharge, electrochemical techniques have been explored at the laboratory pilot scale, for total phosphorus (Ptot) removal from spiked municipal wastewater (MWW). The MWW was an effluent provided from a biofiltration process installed at the Quebec Urban Community WTP. The effects of current density, retention time and initial Ptot concentration were investigated using a bipolar electrolytic cell made of mild steel electrodes. Effectiveness was measured in terms of Ptot reduction. The amount of residual sludge produced and energy consumed have been also considered. Results showed that the best performances of Ptot removal from MWW were obtained while combining electrocoagulation with flocculation. Under optimal conditions, electrolysis was operated at a current density of 38.2mA/cm2 through 20min of treatment and then, the electrocoagulated-effluent was flocculated using a cationic polymer (10mg/l) before filtration. At least, 97% of Ptot was removed regardless of the initial Ptot concentration imposed (5.0–50mg/l) in MWW. The optimal conditions determined for Ptot removal, including energy consumption, electrode consumption and metallic sludge disposal, involved a total cost varying from 0.24 to 0.35$CAN per cubic meter of treated MWW in continue mode operation.