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.