Chemical Enhanced Phosphorus Removal from the Effluent of Micro-Aerobic EGSB System

Chemical precipitation with alum was employed as the post-treatment of a micro-aerobic EGSB system treating domestic wastewater to reduce TP concentration. Effectiveness evaluation focused on the influences of reaction/settling time, pH, coagulant dosage and temperature when original TP ranged in 2-8 mg/L. It was found that 20 min was appropriate for flocculation or sedimentation. Samples with original pH ranged in 6.5-8 had better phosphorus removal. To obtain high efficiency, it was suggested that the pH after precipitator addition ranged in 6-7 was more important than its initial value. In addition, Proper dosage of coagulant increased with the temperature drop. The mole ratio of Al³⁺:P about 1.9 could ensure residual TP below 0.5 mg/L at above 10degC, however, the ratio may increase as temperature dropped below 5degC. The beaker test shows that chemical precipitation was a reliable supplement of micro-aerobic EGSB system.