[Effect of magnesium ion content on the biological phosphorus removal system in SBR]

This study investigated the effect of magnesium iron content on the enhanced biological phosphorus removal system, which performed differently at magnesium content of 0 mg/L, 8 mg/L and 24 mg/L (R1-R3). The results indicated appropriate Mg addition could enrich phosphorus accumulating organisms and keep stable running. During the steady state period, phosphorus removal rate declined to below 50% gradually, moreover, the system tended to deteriorate with the shortage of magnesium in R1. However, the system with appropriate magnesium kept the higher phosphorus removal rate (more than 90%). The statistical analysis of the experimental data also showed a strong correlation between Mg and phosphorus concentrations in R2 and R3, the ratios of Mg and P were 0.29-0.59 and 0.25-0.54 in two reactors respectively. In the anaerobic phase of EBPR, the magnesium content, the absolute value of ORP and the phosphates release had a correlation. Meanwhile, magnesium was released together with phosphates in the anaerobic phase, and that would uptake under aerobic conditions. Thus it was obvious that magnesium played a key role on the biological phosphorus removal system.