Optimization of Polymer Dose Based on Residual Polymer Concentration in Dewatering Supernatant

Abstract

Optimization of sludge conditioning and dewatering is a continuing challenge for wastewater treatment plants. This study investigated the use of an in-line UV–vis spectrophotometer to optimize the polymer dose during sludge dewatering. The study established a relationship between the optimum polymer dose and residual polymer concentration in filtrate using UV–vis absorbance measurements at 191.5 nm. Experiments were carried out with four different polymers (FloPolymer CA 475, CAB 4500, FloPolymer CB 4350, and FloPolymer CA 4600), and similar results were obtained from all polymers. Detection limits of the polymers ranged from 0.35 to 0.95 mg/L in centrate. The optimum polymer dose was determined based on capillary suction time (CST) and filtration tests, and a relationship between the filtrate absorbance at 191.5 nm and optimum polymer dose was established. In the under-dose range, increasing the polymer dose resulted in a decrease in filtrate absorbance due to improvement in filtrate quality. The optimum polymer dose corresponded to the minimum filtrate absorbance at 191.5 nm. When the optimum dose was exceeded, absorbance values started to increase corresponding to the increase in the residual polymer concentration in filtrate in the over-dose range. These results indicate that real-time optimization of polymer dose can potentially be achieved at wastewater treatment plants using an in-line UV–vis spectrophotometer based on the absorbance of centrate or filtrate samples at 191.5 nm.