Evaluation of Performance of a Sludge Blanket Clarifier

Abstract

Maintaining a stable blanket is essential for operation of a Sludge Blanket Clarifier. However, operators have to use their judgement to assess the stability and performance of the blanket, due to lack of information about their performance indicators. Main objective of this study was to observe the effect of the coagulant dose on the stability and performance of the sludge blanket. The characteristic ‘Sludge Cohesion Co-efficient’ (SCC) defined as the upward velocity needed to expand the sludge blanket to double its initial volume was selected as a suitable indicator of the stability of the sludge blanket. Tests were done on 33 sludge samples prepared with a Bentonite suspension and PACL as the coagulant. Raw water turbidity, PACL dose, supernatant turbidity and SCC of each sample were recorded. Results showed that there is an optimum coagulant dose that produces the highest SCC, which varies with raw water turbidity. With increasing raw water turbidity, optimum coagulant dose for SCC is the same as the Jar Test optimum, up to approximately 300NTU. Thereafter the optimum dosage for SCC is lower than the Jar Test optimum. A correlation can be established between the Jar Test and SCC optimum PACL doses.