The potential reuse of drinking water treatment sludge for organics removal and disinfection by-products formation control

Insufficient dissolved organic matter removal results in higher residual organics (measured as dissolved organic carbon, DOC) in the treated water which can act as precursors for disinfection by-products (DBPs) and consequently increases the potential for health risk. This study aims to use drinking water treatment sludge (DWTS) as a coagulant-aid to improve the DOC removal efficiency. The effect of various DWTS doses (between 0.5 and 3 g/L) on the coagulation performance (by alum) to treat natural surface water that has relatively low turbidity and high DOC at optimum pH (similar to 6) was examined using standard jar tests procedure. Although addition of DWTS at doses lower than 1.5 g/L improved the DOC removal efficiency (by 4% and 12% at DWTS dose of 0.5 and 1.0 g/L, respectively), the turbidity levels increased. In comparison to optimum dose of alum without DWTS, the addition of DWTS at 3 g/L led to reduce the alum dose to similar to 50% to achieve similar removal efficiency of organics (70% DOC removal). Further, addition of DWTS improved the floc's characteristics (achieve larger flocs and rapid growth rate; measured by photometric dispersion analyser, PDA) and settling rate significantly, and the produced sludge volume decreased by similar to 50% compared to the figure with no DWTS addition. Trihalomethane formation potential (THMFP) was also reduced (up to similar to 30%) when DWTS used. The results indicate that DWTS reuse as a coagulant-aid has the potential to reduce DOC and control DBPs formation when the organic loads require high coagulant dose exceeding the WTP design limits.

Automated summary

This study aims to use drinking water treatment sludge (DWTS) as a coagulant-aid to improve dissolved organic matter (DOC) removal efficiency and control the formation of disinfection by-products (DBPs). The results indicate that the reuse of DWTS as a coagulant-aid can enhance floc characteristics and settling rate, reduce DOC and trihalomethane formation potential (THMFP).