Comparison of phosphorus removal characteristics between various biological nutrient removal processes

Bench scale experiments were carried out with four biological nutrient removal (BNR) units, A/O, A(2)/O, Phostrip and P/L units, to investigate the behavior of phosphorus in the system and to compare the characteristics of phosphorus removal in four experimental BNR units. The influent COD/T-P ratio was varied from 22 to 64 by changing COD concentration while maintaining phosphorus concentration constant. In general sidestream BNR units such as Phostrip and Pn units outperformed mainstream BNR units such as A/O and A(2)/O units in terms of phosphorus removal. While phosphorus release and uptake in A/O and A(2)/O units became less significant at low influent COD/T-P, the phosphorus release in A(2)/O unit was further influenced by nitrate in return sludge and thus A(2)/O unit required even higher influent COD/T-P ratio for luxury uptake of phosphorus. The luxury uptake of phosphorus in Phostrip and P/L, units were not affected by influent COD/T-P ratio and the adverse effect of nitrate in return sludge on anaerobic phosphorus release in P/L process was not significant due to the sludge blanket in P-stripper. (C) 1997 IAWQ. Published by Elsevier Science Ltd.