Effect of coagulant in greywater treatment for reuse: selection of optimal coagulation condition using Analytic Hierarchy Process

摘要

The objective of the present study was to (i) examine the effect of the coagulants on greywater (GW) characteristics under variable pH conditions, (ii) assess the potential of treated GW for reuse, and (iii) select optimal coagulation condition (pH and optimum dose) using Analytic Hierarchy Process (AHP). The effect of coagulants (alum and lime) was studied under four different pH conditions (8.5, 7.5, 6.5 and 5.5). Multiple linear regression models were built with optimum coagulant dose (OD) vs. pH, turbidity removal and alkalinity consumed. R-2 values ranged from 0.771 to 0.852 in case of alum and from 0.778 to 0.949 in lime treatment. In alum treatment, turbidity removal was above 88%, biochemical oxygen demand removal was in the range 53-77%, and Escherichia coli removal was 95-99% under the pH conditions examined. It was observed that alum-treated GW satisfied most of the reuse standards for the discharge of effluents into land for irrigation and industrial cooling in India. Total eight alternatives were ranked using AHP, considering nine criteria/sub-criteria. Using AHP, the optimal alternative selected was alum treatment at pH 5.5 with OD 204mg/L and the worst was lime treatment at pH 8.5.