Reuse of greywater: effect of coagulant

The objective of the present study was to (1) examine the effect of coagulants on greywater (GW) characteristics and (2) assess the potential of treated GW for reuse. Since the pH plays an important role in the amount of coagulant required, the effect of coagulants was studied under different pH conditions (pH 5.5, 6.5, 7.5 and 8.5) with the help of jar tests. Ferric chloride (FeCl3) and polyaluminium chloride (PAC) coagulants were tested on light GW. Study revealed that, the optimum coagulant dose was decreased with a decrease in GW pH, indicating high coagulant demand at high pH. Turbidity removal was between 93 and 98% in FeCl3 treatment and 97–98% in PAC treatment. In FeCl3 treatment, mean biochemical oxygen demand (BOD5) removal ranged from 50 to 59%, and Escherichia coli removal was above 91%. In the PAC treatment, mean BOD5 removal ranged from 42 to 62%, and E. coli removal was above 92%. Total coliforms and faecal coliforms removal was above 99% in both the coagulant treatments. The present study shows that both (FeCl3 and PAC) treatments satisfy almost all the reuse standards for discharge into land for irrigation, and industrial cooling in India.