BIOLOGICAL PHOSPHORUS REMOVAL AT TEMPERATURES FROM 3-DEGREES-C TO 10-DEGREES-C - A FULL-SCALE STUDY OF A SEQUENCING BATCH REACTOR UNIT

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-degrees-C during one full year and was below 5-degrees-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-degrees-C. At 4-degrees-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.