Chemical Conditioning for Removal of Water and Phosphate from Enhanced Sludge

Abstract

The chemical conditioning required to improve water removal from waste activated sludge and phosphorus from the filtrate was examined in this study. The sludge, collected from a local municipal wastewater treatment plant, was adjusted to 10 g/L total solids (TS) before testing. The conditioning chemicals were ferric chloride (FeC1₃) and cation polymer (T-3086). The free water content in the sludge was determined by measuring the capillary suction time (CST) and specific resistance filtration (SRF). Experimental results indicated that CST had a large correlation coefficient of 0.92 with SRF. Also, adding either FeCl₃ or T-3086 alone did not simultaneously improve both sludge dewatering and phosphorus removal. A combined addition of FeC1₃ (750 mg/L) and T-3086 (20 mg/L) resulted in significant improvement in sludge dewatering as well as phosphorus removal from the filtrate. The optimum process to condition sludge was proposed as follows: the waste activated sludge was mixed with FeC1₃ (750 mg/L) at 200 rpm for 1 min, then immediately mixed with T-3086 (20 mg/L) for 3 min, and then slowly mixed at 30 rpm for 10 min. Under such conditions, the minimum values of CST (6 s) and supernatant turbidity (1 NTU) were achieved. Moreover, combined dosages of FeC1₃ and T-3086 also produced phosphorus removal in either supernatant or filtrate up to 90%.