Anaerobic sequencing batch reactor treatment of dilute wastewater at psychrophilic temperatures

Abstract

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 (BOD5) 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 BOD5, 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 BOD5, 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 BOD5. 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.