INTEGRATED ANAEROBIC AND AEROBIC TREATMENT OF DAIRY WASTEWATER WITH SEQUENCING BATCH REACTORS

Abstract

Integrated biological treatment of dairy wastewater using anaerobic and aerobic sequencing batch reactors wasstudied in the laboratory. An anaerobic sequencing batch reactor (ASBR) was used as the first-stage reactor and tested atthree organic loading rates (2, 3, and 4 g VS/L/d). The loading rate of 3 g VS/L/d resulted in the highest biogas production,solids removal, and chemical oxygen demand (COD) removal from the wastewater. An aerobic sequencing batch reactor(SBR) was used as the second-stage reactor and tested with different feeding and aeration schemes, either to achievenitrification only or to achieve sequential nitrification-denitrification. Two alternative designs (I and II) for the ASBR-SBRsystem were evaluated. In system design I, an intermittently aerated SBR was used to treat the effluent of the ASBR to achievenitrification only. When treating dairy wastewater of 12,600 mg/L TS and 1,240 mg/L TKN, system design I achieved thefollowing removals: 54% for COD, 39% for TS, 43% for VS, and 95% for NH3 -N based on total effluent (solids and liquid);and 90% for COD, 70% for TS, 80% for VS, and 95% for NH3 -N based on the liquid effluent alone after part of the suspendedsolids was removed by gravity settling. The concentrations of NO2 -N and NO3 -N in the effluent were 354 and 168 mg/L,respectively. In system design II, an intermittently aerated SBR was used to achieve nitrification and denitrification. Whentreating the same dairy wastewater as used in system design I, the removals of COD, TS, and VS were similar to the removalsachieved by system design I. No NH3 -N was detectable in the effluent, giving 100% NH3 -N removal. Furthermore, lowconcentrations of NO2 -N and NO3 -N (15 and 22 mg/L, respectively) were found in the effluent, indicating that effectivedenitrification was achieved in the SBR.