Household wastewater treatment plants have been rapidly promoted in recent years as part of the measures for reducing the pollution loading discharge from private households in Japan. The authors have developed a high-efficiency household wastewater treatment plant employing a flow equalisation anoxic-oxic recirculation biofilm process removing organic matter as well as nitrogen which causes eutrophication. A full-scale experiment has been conducted for one year by leading actual grey water (cooking, bathing, washing effluents) from a private household into the experimental apparatus. The results obtained in this study are summarised as follows: effective flow equalisation and excellent effluent quality were achieved, the maximum effluent flow rate was 100 l/h (the peak coefficient 1.5) when the maximum influent flow rate was 415 l/h (the peak coefficient 6.2), the average values of BOD5, CODMn, SS, T-N and T-P of the treated water were 7.8 mg/l, 11.1 mg/l, 5.9 mg/l, 6.4 mg/l and 1.2 mg/l, respectively BOD5 and T-N of the treated water were less than 10 mg/l during the experimental period.

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