Influence of solid residence time on the phosphorus adsorption of extracellular polymer substances

Influence of solid residence time (SRT) on phosphorus (P) adsorption of extracellular polymer substances (EPS) was investigated from the perspectives of the contents, compositions and properties of loosely bound and tightly bound extracellular polymers (i.e., LB-EPS and TB-EPS) and microbial community structure. The TP contents of EPS were 59.6±6.0 - 87.4±4.4 mg·g-1 VSS and 63.7% - 68.1% of those of sludge, which was still underestimated due to the residual TB-EPS protecting cell membrane integrity. The influences of SRT on the yield and compositions of TB-EPS were obviously greater than those of LB-EPS. Compared with the SRTs of 12 d and 18 d, the significant P storage enhancement of biological P removal (BPR) sludge with the SRT of 25 d was related with the increases of TB-EPS yield, polyP content and average chain length in TB-EPS. The P adsorption property of TB-EPS was slightly increased through increasing SRT, while the K, Mg and Ca adsorption properties were markedly reduced. Increasing extracellular P content could kept good BPR efficiency at longer SRTs, but the loss risk of phosphorus accumulating organism dominance was increased. Additionally, adding Mg and Ca salts might improve extracellular P adsorption at longer SRTs.