Predicting the efficiency of deposit removal during filter backwash

Abstract

The long-term performance of granular media filters used in drinking water treatment is ultimately limited by the efficiency of the backwash process. This paper demonstrates that it is possible to develop quantitative predictions of backwash efficiency based on filter operating conditions. An experimental investigation into the effect of backwash rate, type of coagulant, degree of clogging and accumulation of residual deposits (not removed by backwash) on the efficiency of fluidised bed filter back wash in laboratory scale filters is described. A natural raw water was used and small variations in the raw water character istics (manifested as variations in raw water turbidity, temperature, pH, rate of head loss development and turbidity removal efficiency) within each set of experiments appeared to affect the efficiency of backwash in addition to the parameters varied deliberately. Stepwise linear regression and statistical analysis of model significance were used to determine which of several possible filtration and backwash parameters were the best predictors of backwash performance.

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