Anaerobic Sequencing Batch Reactor Treatment of Dilute Wastewater at Psychrophilic Temperatures

Anaerobic treatment of dilute wastewater was studied using three laboratory-scale anaerobic sequencing batch reactors (ASBRs), each with an active volume of 6 L. The reactors were fed a synthetic substrate made from nonfat dry milk supplemented with nutrients and trace metals. The chemical oxygen demand (COD) and 5-day biochemical oxygen demand$({\rm BOD}_{5})$of the feed were 600 mg/L and 285 mg/L, respectively. Steady-state performance data were collected over a time period of 2 years at reactor temperatures of 5, 7.5, 10, 12.5, 15, 17.5, 20, and 25°C. Hydraulic retention times (HRTs) were maintained at 24, 16, 12, 8, and 6 hours. Steady-state process kinetics and removal efficiencies were evaluated for the various conditions. Results showed that the ASBR process was capable of achieving more than 90% soluble COD (SCOD) and${\rm BOD}_{5}$removal at temperatures of 20°C and 25°C at all HRTs. At a temperature of 5°C and a 6-hour HRT, SCOD and${\rm BOD}_{5}$removals were 62% and 75%, respectively. At intermediate temperatures ranging from 5 to 25°C and HRTs between 24 and 6 hours, removal of soluble organic matter ranged from 62 to 90% for COD and from 75 to 90% for${\rm BOD}_{5}$. In all cases, solids retention times were high enough to maintain good performance. Substrate removal rates and half-saturation coefficients were also determined at all temperatures. The temperature correction coefficient was determined to be 1.08 in the temperature range of 7.5 to 25°C. It is concluded that the ASBR has unique characteristics that enable efficient removal of organics during treatment of dilute wastewaters at low temperatures.