Effect of Impeller Rotating Speed of Sludge Recirculation Clarifier on Turbidity Removal Efficiency for Water Treatment Plant

Abstract

This paper aims to study the turbidity removal efficiency of sludge recirculation clarifier when changing impeller rotating speed. The alum dosing rates of 13, 17 and 21 mg/l and production rates of 2.2, 2.4 and 2.6 cubic meter per second (cms) were applied in the study. The effect of optimized impeller rotating speeds corresponded to the best turbidity removal efficiency. Experimental results found that the relationship between the impeller rotating speeds and turbidity removal efficiency tended to in the third order polynomial equation. In the range of 1.3-1.6 rpm of impeller rotating speeds, the turbidity removal efficiencies were relatively low. In the range of 1.6-2.0 of impeller rotating speeds, the turbidity removal efficiencies were increased with impeller rotating speeds. The increased impeller rotating speeds from 2.0 to 2.2 rpm resulted in relatively low of turbidity removal efficiencies. The increased impeller rotating speeds could possibly induce the sludge collision, thus decreasing sludge size. In addition, the alum dosing rates and production rates were also affected with turbidity removal efficiencies. The optimum conditions caused by 17 mg/l of alum dosing rate, 2.4 cms of production rate and 1.9-2.1 rpm of Impeller rotating speeds provided high turbidity removal efficiencies of 89.4±1.18%.