A Research Of Household Methods For Halomethane Treatmen In Drinking Water

Chlorination is a vital process widely used in drinking water disinfection since the early 20 th century. However, the process can also lead to formation of a series of harmful disinfection by-products(DBPs) during the reaction of disinfectant with natural organic matter. Halomethanes(HMs) are one of the major DBPs detected in water.However, the control of HMs after formation is not well-studied before, especially the endpoint treatment. Household water treatment(HWT) device is perhaps as important as water treatment plant in controlling DBPs precursor. In this study, we made a systematic evaluation of the treatability of a series of common HWT facilities on the removal of seven types of HMs by several types of HWT facilities, including water purifier, boiler, microwave oven, juice mixer, UV light sterilizer and ultrasonic cleaner, under conditions simulative of normal family operation. These target compounds include Cl-, Br-, and I- HMs.The evaluation results of water purifier showed that granular activated carbon had greater potentials(60%~90%) than polypropylene cotton(10%~40%) and compressed activated carbon(10%~40%) with a range of flow rate, water type and different initial concentration.When the three cartridge were used together, 80%~ 100% HMs can be reduced. Reverse osmosis cartridge alone eliminated >(95%~10%) of HMs regardless of operating pressure, water type and initial HMs concentration. The treated water by reverse osmosis contain < 10 μg/L HMs. HMs of higher molecular weight tended to obtaine better removal efficiency. Ultrafiltration showed a poor ablity to remove HMs with a reduction of 9%~33%.Br- and I- HMs can be removed effectively by ultraviolet light of 254 nm, five of which obtained a 78%~100% removal within 4 min, while bromodichloromethane and trichloromethane with a removal of 20%, 0%. Initial concentration and water type had negligible effect on HMs photolysis. The removal rates increased with higher power. The presence of carbonate and free chlorine within the concentration ranges also had negligible effect on HMs photolysis. Direct photolysis have poor effect on bromodichloromethane and trichloromethane, while in the presence of iodide, the removal rates of Cl-HMs increased. Residual chlorine was also reduced significantly by photolysis.The evaluation results of kitchen devices showed that boiling is a robust way to remove HMs. When the boiled water was cooling down naturally without a cap, HMs can be removed by 80%~98%, of which, iodoform was the most difficult to dispose(62%~78%). However, when the boiled water was cooling down with a cap, the removal efficiency of HMs fell down by 20%. Although higher initial HMs concentration obtained better removal efficiency, the same level of HMs were achieved in the treated water. In ultrapure water, HMs exhibited higher removal than tap water by boiling. Volatilization is important mechanism for HMs removal during boiling.48%~81% HMs in a uncapped water sample can be reduced within 4 min by microwave, while in capped condition, only 10%~26% HMs can be removed.Stirring for 20 min with 2 500 r/min speed can remove HMs from water by(65%~90%) except for CHI3(20%). The removal rates increased with higher stiring speed.Ultrasonic cleaner can also degrade HMs. When the power is 30 W, HMs can be removed 60% in uncapped condition within 40 minutes, and All HMs in uncapped condition degraded much higher than those in capped condition. The removal rates also increased with higher power.Overall, boiling water is a convenient and effective way to remove HMs, and reverse osmosis can obtain better removal of HMs than boiling. Heating water is beneficial for reducing HMs, but uncap cooling is crucial before drinking. Photolysis can not only remove HMs, but also free chlorine.These findings may help common people deal with challenges from polluted water and may assist in better understanding the relations of DBP intake and health risks.