Electrocoagulation of wastewater using aluminum, iron, and magnesium electrodes.

Abstract

Primary influent from a municipal wastewater treatment plant was electrochemically treated with sacrificial aluminum, iron, and magnesium electrodes. The influence of sacrificial anodes on the removal of chemical oxygen demand, total nitrogen, total phosphorus, and orthophosphate during sedimentation was investigated. Nitrification kinetics were assessed on treated supernatant and biogas production was monitored on settled solids. Changes in alkalinity, conductivity, and pH were also recorded. Aluminum and iron electrodes provided high rates of orthophosphate removal (i.e., 6.8 mg-P/mmol-e). Aluminum and iron electrodes also provided similar treatment to equivalent doses of alum and ferric salts (i.e., 38-68% chemical oxygen demand, 10-13% total nitrogen, and 67-93% total phosphorus). The estimated stochiometric ratio of aluminum and iron dosed to orthophosphate removed was approximately 1.3:1 and 4.1:1, respectively. Magnesium electrodes, on the other hand, removed orthophosphate at rates 8-9 times slower than aluminum and iron (i.e., 0.9 mg-P/mmol-e). Magnesium had to be dosed at a ratio of 13.5:1 orthophosphate for phosphorus removal. Orthophosphate removal by magnesium electrodes was most likely limited by electrolysis reactions responsible for increases in pH (i.e., 0.52 pH units/mmol-e). Magnesium electrodes removed 49% chemical oxygen demand and 21% total nitrogen at the high molar ratios required for orthophosphate removal.