ASBR treatment of low strength industrial wastewater at psychrophilic temperatures

Anaerobic treatment of dilute wastewater was studied using three laboratory-scale anaerobic sequencing batch reactors (ASBR), each with an active volume of six (6) liters. The reactors were fed a synthetic substrate made from non-fat dry milk supplemented with nutrients and trace metals. The COD and BOD5 of the feed was 600 mg/l and 285 mg/l, respectively. Steady-state performance data were collected at reaction temperatures of 25, 20, 17.5, 15, 12.5, 10, 7.5 and 5 degrees C over a period of two years; Hydraulic retention times (HRT) were maintained at 24, 16, 12, 8 and 6 hours. Results showed that the ASBR process was capable of achieving in excess of 90% soluble COD and BOD5 removal at temperatures of 25 degrees C and 20 degrees C at all HRTs. At the low temperature of 5 degrees C and the six hour HRT, soluble COD and BOD5 removals were 62% and 75%, respectively. At the intermediate temperatures from 20 degrees C down to 5 degrees C and HRTs between 24 and 6 hours, removal of soluble organics ranged between 62 and 90% for COD and 75 and 90% for BOD5. In all cases, SRT were high enough to maintain good performance. Substrate utilization rates and half-velocity constants were also determined at all temperatures. The temperature correction coefficient was found to be 1.08 in the temperature range from 25 degrees C to 7.5 degrees C which follows the Q(10) or Van't Hoff's rule. (C) 1997 IAWQ. Published by Elsevier Science Ltd.