Combined electrooxidation and electrocoagulation processes for the treatment of municipal wastewater

Abstract

A study was conducted to investigate the effectiveness of combined processes of electrooxidation and electrocoagulation using stainless steel electrodes for the removal of BOD, ammonia, coliform, turbidity and total suspended solids. In addition to total organics, removal of soluble and particulate organics was also investigated. Experiments were also conducted with filtered samples to study the effect of suspended solids on the electrooxidation of soluble BOD and ammonia. Comparative jar test experiments were conducted with FeCl₃ coagulant, to compare the sludge production by electrocoagulation with chemical addition process.

Combined processes were proved effective for the removal of BOD. Most of the removal of BOD was contributed by the removal of particulate organics by electrocoagulation. Significant effect of current and contact time was observed on the removal of the above contaminants. BOD removal increased with the increase in current and contact time up to 0.2 A, beyond which, further increase in current (i.e. at 0.4 and 0.8 A) resulted in the decrease in the removal efficiency. The maximum removal of 84.82% was observed at 0.2 A and 50 minutes contact time. Ammonia removal on stainless steel electrodes was not efficient. Maximum removal of only 18.13% was observed at 0.2 A and 50 minutes contact time. Coliform removal was observed to be directly dependent on applied current and contact time. Maximum removal of 5.05 log scale removal was observed at 0.8 A and 30 minutes contact time. High removal of turbidity and total suspended solids (93.33 and 95.38%) was achieved by the combined processes. Experiments with filtered samples resulted in the increase in the removal of soluble BOD and ammonia thus shows that there is an effect of suspended solids on the electrooxidation of contaiminants. Sludge production by electrochemical process was observed to be 2.45 less than the conventional coagulation process. However, when the sample pH was altered from 7.07 to 9.11, marked decrease in the optimum dosage was observed, and the sludge production was observed to be 2.95 times less than the electrocoagulation process.