Estimation of intracellular phosphorus content of phosphorus-accumulating organisms at different P:COD feeding ratios

The intracellular phosphorus content of phosphorus-accumulating organisms (PAO) was determined based on a stoichiometric equation and phosphorus balance for an enhanced biological phosphorus removal system fed with different P:COD ratios. The data indicated that a higher P:COD feeding ratio could significantly promote the growth of PAO. As the P:COD feeding ratio increased from 0.02:1 to 0.04:1 and 0.16:1, the phosphorus in the sludge increased considerably from 0.053 to 0.084 and 0.205 mg P (mg VSSaerobic)−1, respectively, indicating a dynamic condition in the microbial population. From the calculations, the mass fractions of the PAO, glycogen-accumulating organisms, and ordinary heterotrophs changed from 0.10–0.15, 0.83–0.88, and 0.02 at 0.02:1 to 0.19–0.28, 0.70–0.79, and 0.02 at 0.04:1 and to 0.478–0.71, 0.26–0.50, 0.03 at 0.16:1 P:COD feeding ratios, respectively. Despite the variation in microbial diversity, the calculated phosphorus contents of the PAO at all P:COD feeding ratios were consistent between 0.241 and 0.378 mg P (mg VSSPAO)−1. The initial specific phosphorus release and uptake rates were 84.7–167.9 mg P (g VSSPAO)−1 h−1 and 52.8–90.0 mg P (g VSStotal)−1 h−1, respectively.