Effect of feed characteristics and operational conditions on treatment of dairy farm wastewater in a coupled anoxic-upflow and aerobic system

This study investigated the removal of nitrogen and organic matter from dairy farm wastewater (DFW) in a hybrid anoxic-upflow bioreactor and aerobic (UBR-A) system. Due to variable and complex composition of real DFW, system performance and behaviour was compared with synthetic wastewater (SWW) in two identical pilot-scale UBR-A systems. Both systems were operated for 334 days first under internal recycle ratios (R) of 2, 3 and 4 and then at solids retention times (SRT) of 140-150, 65-75 and 30-40 days at uniform R of 3. Performance with both wastewaters was comparable with higher nitrification efficiencies ( > 90%) and COD removal (>80%) under all conditions, and lower denitrification efficiencies at R > 3. DFW exhibited significantly lower nitrification/denitrification rates, biomass yield, VSS/TSS ratio and a higher inert COD fraction showing that kinetics, sludge characteristics and organic matter degradation were not analogous. The optimum internal recycle ratio was found as R of 3 at a total hydraulic retention time (HRT) of 4 days whereas at different SRTs, performance efficiencies were mostly comparable however nitrification and denitrification rates significantly increased at lower SRT of 30-40 days.