Effect of ζ-Potential of Influent Particles on Initial Filter Coefficient for Rapid Sand Filters

Abstract

Simultaneous experimental study was carried out on down-flow (DF) and up-flow (UF) sand filters using artificial influent replicating settled surface water in order to assess dependence of initial filter coefficient (λ₀, m⁻¹) on ζ-potential of influent particles (ζ_p, mV). The ζ_p for various filter runs was varied by using poly-aluminum chloride (PAC) for coagulation of artificial raw water. In order to improve performance of UF filter, it was conditioned by down-flushing with PAC modified wash water subsequent to fluidized wash. An attempt is made to correlate ζ_p and λ₀ using observations through various runs with different rates of filtration for both filters. System constants proposed in the nonlinear relationship were computed for the different rates of filtration, using method of least-square fit. It was evident from the computation of coefficient of determination for the regression that the hypothesized nonlinear relationship provided an excellent fit for each case. The ζ_p is found to be dominant parameter and so, worth of continuous monitoring for operational control in order to avail consistent filter performance. Effect of influent with less negative ζp on DF and UF filter was evaluated by conducting full length filter runs; and it was observed that surface removal was aggravated in DF filter whereas better removal and less incremental increase in head-loss were witnessed for UF filter.