Advanced total phosphorus removal approach: system design and combined sewer overflows (CSOs) sludge application

Abstract

Advanced total phosphorus (TP) removal is required to regulate the TP concentrations to less than 0.2 mg/L, as specified by the South Korean policies for the prevention of aquatic eutrophication. In order to meet the standards from 2012, the treatment efficiency of conventional treatment plants should be improved. This study addresses this need by developing a novel TP removal methodology that uses a static mixer for coagulation and a redesigned sedimentation tank incorporated with a guiding baffle. Experiments were carried out during summer, autumn, and winter. Results show that: (1) the phosphorus removal efficiency was relatively higher in summer than in autumn and winter, (2) the inline static mixer increased the efficiency of soluble phosphorus removal to above 95%, and (3) optimal angle determination for the guiding baffle was essential to achieve a stable hydraulic behavior and a low shear rate at the bottom of the sedimentation tank and thus to improve the sedimentation rate. In addition, the application of combined sewer overflows sludge led to stable and high phosphorus removal efficiency (> 90%). These results indicate that the newly designed TP removal plant could serve as a prototype for an advanced treatment of phosphorus in wastewaters.