To reduce the residual organic matter and phosphorus contained in secondary effluent, a biofiltration system combined with electrocoagulation using bipolar iron electrodes 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 COD(Cr) 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 COD(Cr) 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.

Biological Oxygen Demand (BOD), nitrogen, and phosphorus were treated with the use of an intermittently aerating bioreactor combined with electrocoagulation. Experiments consisting of batch reactor tests were conducted to identify the most efficient electrode material and the best condition for electrolysis so that the current density would not impede the biological treatment. The operating conditions needed when using an intermittently aerating bioreactor combined with electrocoagulation to enhance phosphorus removal were also identified. Iron was found to be more efficient than aluminum as an electrode material in terms of electricity requirement. When electrocoagulation was conducted and an intermittently aerating bioreactor was used, the electrolysis of the iron electrode in the aerobic stage was observed to be more favorable compared to continuous electrolysis. Sludge rise occurred at the current density of 5.7 mA cm(-2), and lysis of cell at 11.2 mA cm(-2). The applicable current density was found to be less than 4 mA cm(-2). Based on the results of this study, it can be concluded that the use of an intermittently aerating bioreactor combined with electrocoagulation enhances phosphorus removal in sewage treatment plants.

An existing SBR plant in a rural area was retrofitted from a conventional fill-and-draw system to an intermittent-aeration system for additional nitrogen removal. This study indicated that organic and nitrogen removal efficiency was improved over that before the retrofitting. But effluent phosphorus concentration was increased gradually with the operating time. In the latter period of investigation, phosphorus concentration in effluent was higher than influent. It was regarded that an excessively accumulated phosphorus was released again under the anaerobic conditions of the sludge storage tank. The application of the electro-coagulation process was investigated as an alternative method in order to prevent phosphorus from re-releasing. A laboratory test for electro-coagulation indicated that T-P removal was more stable than the biological method only. In addition, it was confirmed that T-N and organic materials as well as T-P were removed simultaneously by the electrochemical reaction in the bioreactor combined with electrolysis by more than the bioreactor only.

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