Biological phosphorus removal at temperatures from 3 to 10 °C — a full-scale study of a sequencing batch reactor unit

Abstract

Low temperature biological phosphorus removal technology was tested at a small village wastewater treatment plant near the Arctic circle. An aeration basin in a conventional activated sludge step was retrofitted to a sequencing batch reactor with a maximum volume of approximately 27 m3. The study period was November 1989 to June 1991. The wastewater temperature varied between 3 and 10 °C during one full year and was below 5 °C during approximately 240 days of the year. A total sequencing batch reactor cycle time of 6–12 hours produced a phosphorus reduction of 70–80%. During the same time, biochemical oxygen demand (BOD7) reductions varied between 70% and 90%. These reductions were achieved at supernatant suspended solid concentrations of 20–30 mg/L. Effluent soluble phosphorus concentrations were usually lower than 1.0 mg/L at water temperatures down to 5 °C. At 4 °C, a sharp increase to greater than 2.0 mg/L was evident. Supernatant soluble BOD7 was less than 8 mg/L and was found to be independent of temperature. Key words: biological wastewater phosphorus removal, sequencing batch reactor, cold climate.