ANAEROBIC SEQUENCING BATCH REACTOR TREATMENT OF DILUTE WASTE-WATER ATPSYCHROPHILIC TEMPERATURES

Anaerobic treatment of dilute wastewater was studied using three labor atory-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. Th e chemical oxygen demand (COD) and 5-day biochemical oxygen demand (BO D5) 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 reac tor temperatures of 5, 7.5, 10, 12.5, 15, 17.5, 20, and 25 degrees 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 pro cess was capable of achieving more than 90% soluble COD (SCOD) and BOD 5 removal at temperatures of 20 degrees C and 25 degrees C at all HRTs . At a temperature of 5 degrees C and a 6-hour HRT, SCOD and BOD5 remo vals were 62% and 75%, respectively. At intermediate temperatures rang ing from 5 to 25 degrees C and HRTs between 24 and 6 hours, removal of soluble organic matter ranged from 62 to 90% for COD and from 75 to 9 0% 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 temperatur e correction coefficient was determined to be 1.08 in the temperature range of 7.5 to 25 degrees C. It is concluded that the ASBR has unique characteristics that enable efficient removal of organics during trea tment of dilute wastewaters at low temperatures.