Study On Removal Methods And Influencing Factors Of Haloacetonitriles In Water

The purpose of disinfection is to guarantee the safety of drinking water biologically.However,disinfection by-products will be produced from the reaction of disinfectants and organic matters in the water while disinfectants kill pathogenic microorganisms.Disinfection by-products are poisonous compounds with”three induced effects",and the most frequently detected disinfection by-products around the world are halo methanes and halo acetic acids.Haloacetonitrile is a new type of nitrogenous disinfection by-products.Although the content of haloacetonitrile is lower than regular disinfection by-products,it is orders of magnitude more cytotoxic and genotoxic than regulated disinfection by-products.Therefore,it is necessary to study the stability and removal methods of haloacetonitriles.Nowadays,removing disinfection by-product precursors and applying alternative disinfectants are the two major approaches to reduce disinfection by-product risks from drinking water.However,these methods can not eliminate disinfection by-products due to the inevitable presence of disinfectant and organic matter.So,this paper considered treatment of existing haloacetonitriles after their formation.It investigated the stability of haloacetonitrile in water environment,and the main factors that has been studied are hydrolysis and oxidation.The next part is to evaluate the removals of haloacetonitrile by household devices,including ultraviolet photolysis,adsorption,reverse osmosis filtration volatilization,ultrasonic degradation.The results of this study is expected to enrich the information about the stability of haloacetonitrile in aqueous environment,and to safeguard drinking water safety by providing reasonable suggestions for consumers.The results of hydrolysis and oxidation of haloacetonitrile sta showed that the hydrolysis of haloacetonitrile generally followed first-order kinetics,and the reaction rate constants increased significantly with pH value changing from acidic to basic.Highly halogenated compounds appeared more labile than lowly halogenated compounds,and low molecular weight haloacetonitriles were more amenable than high molecular weight species.Free chlorine is able to oxidize di-and tri-haloacetonitriles,and the oxidation ability of chlorine increases with increasing content of free chlorine.In contrast,chloramine can not oxidize halo ac eto nitrile s.The results of the haloacetonitrile removal by household facilities showed that adsorption had certain effect on haloacetonitrile removal.the adsorption effect of three adsorbents in descending order was:granular activated carbon,carbon block filter,PP cotton,and flowrate had enormous effect on the adsorption of haloacetonitriles,with the efficiency increasing with the decrease of flowrate of water.Reverse osmosis had high removal efficiencies for six haloacetonitriles(average removal efficiency is 83%).Ultraviolet photolysis of haloacetonitriles generally followed first-order kinetics and dehalogenation is the main reaction pathway that occurs during the photolytic process.As for the influencing factors,chloride and initial concentration had no obvious effect on the photolysis rates,while nitrate had silight enhancement effect.The photolysis effect of haloacetonitriles in ultrapure water is better than that in tap water.The experimental results indicated that the substances that have absorption in 254 nm will interfere the photolysis effect of haloacetonitriles.Mainly driven by its volality,stirring had notable effect on haloacetonitrile removal,the average removal efficienvy is 50%,and the removal efficiency increased with the increase of stirring speed and stirring time.Boiler heating and microwave oven irradiation are efficient and convenient ways in removing haloacetonitriles too,and the removal may be attributed to volatilization and thermal hydrolysis.The removal trends of haloacetonitriles can be well captured by a quantitative structure activity relationship model.The mechanism of ultrasonic in haloacetonitrile removal was volatilization as a result of water turbulence.