MIEX® treatment of an effluent‐impacted stream

A case study was conducted to examine the magnetic ion exchange (MIEX®) process for treating water impacted by wastewater treatment plant effluent and removing disinfection by‐product precursors. The plant effluent increased dissolved organic carbon, ultraviolet absorbance at 254 nm (UV254), anions, and disinfection by‐product precursors at the discharge and downstream locations. The MIEX 1 process reduced dissolved organic carbon by 42–47%, UV254 absorbance by 61–68%, and trihalomethane and haloacetic acid formation potential (FP) by 50–70% at different downstream locations. On the other hand, halonitromethane FP was reduced by only 10–15% and N‐nitrosodimethylamine (NDMA) FP increased as a result of chloramination after MIEX treatment. Uniform formation condition experiments showed that NDMA concentrations remained below 10 ng/L when chlorine alone or 40 min of chlorine contact time before ammonia addition were used for postdisinfection. However, use of preformed chloramine resulted in 36 ng/L of NDMA formation. Because MIEX substantially removes trihalomethane and haloacetic acid precursors, it may allow the use of more chlorine for longer contact time, which can lead to less NDMA formation.