Simultaneous sludge minimization and nutrients removal in activated sludge process

Simultaneous biological phosphorus and nitrogen removal along with sludge minimization in an anaerobic-aerobic-anoxic sequencing batch reactor was investigated. One control-SBR in nutrient removal mode and one SBR in nutrient removal along with sludge minimization mode (modified-SBR) were run for more than 10 months. The waste activated sludge from the control-SBR was subjected to conventional anaerobic digestion at 10 day HRT whereas the sludge reduction in the modified-SBR was achieved by subjecting the recycled sludge to fasting and feasting with the aid of a sludge holding tank that was attached top the modified-SBR. The NH3-N removal efficiencies in both the SBRs were consistent at an average influent NH3-N concentration of 25.3 mg N/L and NH3-N concentrations in the effluents of both reactors were below detection limits. The average removal efficiencies of dissolved phosphorus in the control-SBR and the modified-SBR were 86.5% and 83.6%, respectively, under anaerobic-aerobic-anoxic mode of operation. When the time cycle in both the reactors was changed to anaerobic-aerobic-anoxic-aerobic for the betterment of EBPR activity, the EBPR activity improved in the control-SBR, giving an average effluent P concentration of 3.2 mg/L. On the contrary, the EBPR activity in the modified-SBR deteriorated due to this change. The biomass yield in the modified-SBR was estimated to be 0.166 mg TSS/mg COD, which represented a 61.4 % reduction in solids reduction compared to the control-SBR.