Supplementing coagulation with powdered activated carbon as a control strategy for trihalomethanes: application to an existing utility

To support a water treatment plant in meeting trihalomethanes (THM) legislation, different THM control strategies using existing treatment processes were investigated. The effectiveness of optimised coagulation and of powdered activated carbon (PAC) (0-25 mg/L) as a mean of supplementing natural organic matter (NOM) removal was assessed. Simultaneous full-scale and bench-scale trials were performed to document THM reductions. At the plant, source and treated water total organic carbon (TOC) was monitored online. At full scale, optimised acidified alum coagulation (3.2 mg/L Al) achieved the maximum NOM removal and the lowest THMFP concentration. Although PAC (11 mg/L) showed a small reduction in TOC (7%) and taste- and odour-causing compounds, results indicated no significant THM reductions. Coagulation and PAC adsorption trials showed a good agreement between bench-scale and plant results.