To reduce the residual organic matter and phosphorus contained in secondary effluent, a biofiltration system combined with electrocoagulation using bipolar iron elegctrodes was evaluated as a supplementary treatment to existing small-community sewage treatment. Based on the results of batch tests, bipolar electrocoagulation (BEC) was found to be more effective on phosphorus removal than monopolar electrocoagulation (MEC) but energy consumption was less in monopolar electrocoagulation. Optimum conditions of BEC to treat the secondary effluent were current density 15 A/m2, electrode spacing 1 cm and pH < 8. The removals of CODCr and phosphorus by biofiltration system without BEC were 69.1% and 9.6%, respectively. However, biofiltration system combined with BEC showed 76.6–83.7% and 70.7–93.0% removal for CODCr and phosphorus respectively. Extraordinary increase in phosphorus could be achieved by introducing electrocoagulation to biofiltration, and BEC/biofiltration system was evaluated to be applicable to existing small-community sewage treatment plants as a supplementary process.

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