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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