Biological Excess-Sludge Reduction and Sludge Settleability Improvement Using a New Modified IFAS-OSA Process by Adding an Anoxic Sludge-Holding Tank to the Return Activated Sludge Line of the System

Abstract

Integrated fixed film activated sludge-oxic settling anoxic system (IFAS-OSA) is a new, modified system for excess-sludge reduction. In this research, the efficiency of the IFAS-OSA system in biological excess-sludge reduction with the addition of an anoxic sludge-holding tank to the return line of the system was studied. The results showed that the average oxidation reduction potentials (ORPs) in the IFASAerobic, IFASRAS, IFAS-OSA2 h, and IFAS-OSA4 h processes were +80±15, −62±22,–102±8, and −140±13 mV, respectively. The average values of Yobs in the IFAS, IFAS-OSA2 h, and IFAS-OSA4 h processes were 0.43±0.01, 0.31±0.02, and 0.23±0.01 g MLSS/g COD, respectively. Accordingly, in the IFAS-OSA2 h and IFAS-OSA4 h processes, the sludge production was reduced by 27.9% and 46.5%, and the excess sludge was reduced by 13.65% and 22%, respectively, compared with the control system. Furthermore, as the average SVIs reached 95±12,63±6, and 49±4 mL/g, the TSS values in the effluents of the IFAS, IFAS-OSA2 h, and IFAS-OSA4 h processes reached 16.5±3, 7.2±1.5, and 5.5±1.2 mg/L, respectively. The average percentages of total nitrogen (TN) removal efficiency in the IFAS, IFAS-OSA2 h, and IFAS-OSA4 h processes were 78.56±2.46, 83.60±0.92, and 85.03±1.69, respectively, whereas the percentages of phosphorus removal efficiency in these processes were 32.69±8.25, 36.35±6.73, and 39.87±3.61, respectively. This study revealed that the modified IFAS-OSA system had a more efficient performance than the IFAS system.