The development of effective simultaneous removal processes of nitrogen and phosphorus have been desired, since environmental standards for nitrogen and phosphorus in lakes were set in December, 1982. In Hamamatsu City, attempts have been made to remove nitrogen and phosphorus simultaneously from wastewater at two smaller-sized sewage treatment plants in order to prevent entrophication as well as to conserve water quality in Lake Hamana. These treatment plants are operated with alternative simultaneous nutrients removal processes by making use of the existing treatment facilities designed as the extended aeration system. In these processes, internal carbon sources and / or endogenous respiration is exploited to achieve dissimilatory reduction of nitrate to nitrogen gas, and phosphorus removal can be accomplished by biological excessive uptake of phosphate. The following conclusions were derived from full-scale operations at Kotoh sewage treatment plants. At higher water temperature, excellent treatment pertormances in terms of organic substances and nutrient salts were obtained consistently. On the other hand, it was required sophisticated SRT (sludge retention time) control to achieve satisfactory nutrionts removal at lower water temperature: longer SRT was required for complete nitrification- denitrification reaction, whereas excessive SRT might have adverse effects on the biological phosphorus removal.

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