Laboratory scale experiments operated by the EBPR (enhanced biological phosphorus removal) process with coagulant addition were carried out to clarify the effects of coagulant on phosphorus uptake and release as well as the stabilization of phosphorus removal efficiency in the EBPR process using sequencing batch reactors. Phosphorus was removed without Fe addition, however, standard deviation of effluent PO4-P concentration was high and the phosphorus removal performance was generally unstable. Phosphorus removal was stable with the Fe addition. The PO4-P concentrations at the end of the anaerobic phase with Fe addition were lower than those concentrations without Fe addition. The phosphorus uptake rates at the aerobic phase with Fe addition were higher than those concentrations without Fe addition. These indicated that coagulant addition could decrease the phosphorus concentration at the end of anaerobic phase and enhance the phosphorus uptake rate during aerobic phase. These contributed to the stabilization of the phosphorus removal in the EBPR process. Addition of Fe with Fe/P molar ratio of 0.2 was enough to stabilize the phosphorus removal efficiency. The molar ratio was extremely small compared to the usual amount of the coagulant added in the activated sludge process.
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