Formation Of The Halogenated Dbps By Reaction Of Chlorine And Activated Carbon

Activated carbon filter has been more and more applied to drinking water plants in recent years.Na Cl O is one of the most commonly used disinfectants in the process of drinking water treatment.Na Cl O is also often used as a preoxidant to remove algae,pathogenic microorganisms and micro-pollutants in sources water.It is proved in this research that the reaction of activated carbon and Na Cl O will generate a variety of halogenated disinfection by-products(DBPs),in which the yield of chloromethane(TCM)was the highest,followed by bromodichloromethane,chloral hydrate,dichloroacetic acid and trichloroacetic acid.Chlorobromoacetonitrile,dichloroacetonitrile,dichloroacetonitrile,trichloroacetone,and monobromodichloroacetic acid were also produced in small amounts.In addition,the generation of halogenated aromatic DBPs was detected in the system.The influence of pH,chlorine dosage,chlorination time and activated carbon mass on the generation of disinfectant by-products in the reaction process of activated carbon and Na Cl O was further investigated.The results showed that the chlorine consumption first rised and then declined with the rise of pH,and reach the peak under neutral condition.The generation of TCM increased with the increase of pH due to the base-catalyzed reaction,and the amount of TCM at pH=10 increased by 44% compared with that at pH=7.The production amount of other halogenated volatile DBPs and haloacetic acid first rised and then declined with the rise of pH.The yield of DBPs increased with the increase of chlorine dosage.The yield of TCM was 27 μg/L at 2 mg/L chlorine dosage and 50 μg/L at 20 mg/L chlorine dosage.The amount of halogenated DBPs increased with the extension of chlorination time until the third day,indicating that the reaction of Na Cl O and activated carbon ended at the third day.The amount of halogenated DBPs increased with the increase of the amount of activated carbon.The soaking experiment of activated carbon shows that precursor of DBPs can be released when activated carbon is soaked in water,which can react with Na Cl O to produce halogenated DBPs.In order to investigate the reaction of activated carbon and Na Cl O in the actual filtration process of water plant,the process of Na Cl O chlorination and activated carbon filtration were simulated according to the actual parameter of water treatment plant.In the process of pure water prechlorination filtration,chlorinated water reacts with activated carbon during the filtration,generating a variety of halogenated DBPs,including 22.5-41.3 μg/L TCM.In the process of chlorination after filtration of pure water,filtration effluent reacted with Na Cl O and produced a large number of DBPs,where the production amount of TCM reached 22.5～50.8 μg/L.With the extension of filtration time,the production amount of DBPs didn’t decline obviously,indicating that the activated carbon can continuously release the precursor of disinfection by-products into the water during the filtration process.Therefore,both pre-chlorination filtration and post-chlorination after filtration could increase the risk of DBPs generation.This study investigated the rules of DBPs production by the reaction of Na Cl O and activated carbon and proved that the organic matter released in the contact of activated carbon and water is an important precursor of disinfection by-products.To ensure the safety of drinking water,the adsorption efficiency of activated carbon and the risk of releasing the precursor of DBPs should be considered comprehensively.