Abstract  

The high performance sedimentation tank (HPST) is an efficient water treatment  technology, which accelerates the settling rate of flocculates by adding sludge, so as  to increase the water treatment load of coagulation sedimentation tank. Its sewage  treatment effect is affected by many factors such as sludge dosage, wastewater pH,  flocculant dosage, stirring time, settling time, etc. This paper was to study the optimal  conditions of HPST, first, some single-factor tests were conducted to preliminarily  explore the optimal range of influencing factors, and then response surface method ology (RSM) tests were performed to accurately determine the optimums of signifi cant factors.The results showed that adding sludge can not improve the water quality of coagulation treatment, but it can significantly accelerate the coagulation settlement  process, the sludge dosage, the coagulant dosage and sewage pH all impacted significantly on its coagulation effect, and existed inflection points. A model that could  guide HPST was obtained by RSM tests. The model optimization and experimental  validation showed that the optimal HPST conditions for treating domestic sewage  were as follows: the dosage of polyaluminum chloride (PAC) was 1.70 g/L, cationic  polyacrylamide (CPAM) dosage was 2.35 mg/L, sewage pH was maintained at 8.0,  sludge dosage was 10 mL/L, stirring time lasted for 5 minutes, and settling time lasted  for 30 minutes. As a result of these optimized conditions, the turbidity of treated sew age decreased to 1.19 NTU.