Research On Enhanced Removal Methods For The Precursors Of Chloral Hydrate In Conventional Drinking Water Treatment Process

Halogenated aldehydes are the third category of disinfection by-products other than trihalomethanes(THMs)and haloacetic acids(HAAs)in drinking water,and the halogenated aldehydes are significantly more harmful to the human body than THMs and HAAs.Chloral hydrate(CH)is the most widely studied halogenated aldehyde disinfection by-product.The content of CH precursors in the southern algal water is high,but the conventional water treatment process has a limited control effect on CH,and is facing a higher seasonal risk of CH exceeding the standard.In view of the above problems,the pretreatment and enhanced coagulation process were empolyed to strengthen the removal of CH precursors in conventional drinking water treatment process,and CH control effect was analyzed through the characterization means of three-dimensional fluorescence spectra,molecular weight distribution and polarity separation,and organic matter primarily removed during the control of CH formation was identified,in order to lay the foundation for the research on the control mechanism of CH.Pretreatment studies showed that: adsorption pretreatment on CH control effect was better than chemical pretreatment and biological pretreatment,and when the dosage of powdered charcoal was 80 mg/L,the chloral hydrate formation potential(CHFP)removal rate of raw water reached to 82.5%.The powdered charcoal adsorption process controlled the formation of CH by removing aromatic substances and microbial metabolites,MW<1 KDa and MW>10 KDa organic matter.Conventional enhanced coagulation studies showed that: under the condition that the p H value was 7.5 and the dosage of PAC was 6 mg/L,the removal rate of CHFP was the highest,namely,52.9%;PAM enhanced coagulation on CH control effect was better than chitosan,activation of silicate enhanced coagulation,and when PAM dosage was 0.12 mg/L,CHFP removal rate increased maximally by 19.6%.At the same time,PAM enhanced coagulation also had a good enhanced removal effect on the CHFP of the specific precursor in the chlorination process under above dosages.Although the PAM enhanced coagulation process had a certain enhanced removal effect on the fluorescent substances in each region,the removal of organic matter from aromatic proteins and microbial metabolites contributed significantly to the further reduction of CH formation,and improving the removal of MW>10 KDa organic matter was the main way to further reduce CH formation.Pretreatment combined with coagulation studies showed that: powder charcoal adsorption enhanced coagulation on CH control effect was better than preoxidation enhanced coagulation;When the amount of powdered carbon added was 80 mg/L,the removal rate of CHFP in the coagulation process was maximally enhanced,the removal rate increased by 33.3%,and CHFP was below the national standard.In addition,the powdered charcoal adsorption also had a good effect on the enhanced removal of specific precursors CHFP.Although the powdered charcoal adsorption combined with the enhanced coagulation process had a certain effect on the removal of the fluorescent substances in each region,improving the removal of organic matter from aromatic proteins and microbial metabolites contributed significantly to further reducing CH formation,and improving the removal of MW<1 KDa organic matter was the main way for further reducing CH formation.