Study On The Control Of Chloral Hydrate And Its Precursors By Oxidation Technology

As we all know,Chlorination disinfection has the advantages of economy and good bactericidal effect,but at the same time,it will also cause the formation of disinfection by-products（DBPs）.Chloral hydrate（CH）is the DBPs that content and harmfulness second only to trihalomethanes（THMs）and haloacetic acids（HAAs）.The tap water of water plants in the south of China had the risk of exceeding the standard of the CH content,because of the high temperature and rain,the frequent eruption of algae in summer,the deterioration of seasonal water quality of the water source,and the limited conventional processing capacity of the water plants.The main purpose of this paper is to put forward the control CH method,which is economical,effective and suitable for the water quality in the south,to provide technical support for the control of CH in small and medium water works.The paper first evaluated the control effect of CH in a water plant in southern China,and analyzed the change characteristics of dissolved organic matter（DOM）and chloral hydrate formation potential（CHFP）in each process section by 3D-EEM method.The results showed as follow:the raw water in the water plant is mainly aromatic protein,fulvic acid and microorganism metabolite.The DOC,CHFP and DOM are gradually reduced along the conventional process section of the water plant,and the removal rate of CH precursor in the enhanced coagulation sedimentation process section is higher than that of other process sections,the removal rates were21.67%,68.55%and 56.65%,respectively,and the fluorescence removal rate of the fluorescence region II and IV was higher than that of other fluorescent regions,and the aromatic protein and microbial metabolites might be the precursors of CH.The study of pre-oxidation coagulation sedimentation process on CH precursor showed that ClO₂,KMnO₄,H₂O₂ and K₂FeO₄ combined coagulation sedimentation could achieve better CHFP control effect.The optimum dosage of each oxidant were0.9,0.2,1.5,1mg·L^-1,respectively,and the removal rates of CHFP were 86.35%,70.15%,93.66%,76%,respectively.At the pre-oxidant dosage range,the removal rate of CHFP by ClO₂,H₂O₂,and K₂FeO₄ combining with coagulation sedimentation process increased with the increase of pre-oxidant dosage and at the low dosage of KMnO₄,KMnO₄ combining with coagulation sedimentation process acquired obvious control effect,while the removal rate of CHFP decreased with the increase of pre-oxidant dosage.ClO₂,H₂O₂ and K₂FeO₄ combined with coagulation sedimentation made further removal on DOM than only coagulation sedimentation,by the way,the removal efficiency of soluble microbial product（SMP）-like characterized by fluorescence region IV is better than that of other regions,but KMnO₄ combined coagulation sedimentation leaded to an increase of total fluorescence volume of the water after sedimentation.The study on the control of CH precursors by UV and its combined with coagulation sedimentation process showed that UV has a certain removal effect on the CHFP on the raw water.The removal rate of CHFP increased with the increased of UV dose and at the UV dose of 1400mJ·cm^-2,the removal rate of CHFP reached the maximum and the removal rate of CHFP were 33.61%.When the UV dose reached a certain extent,the algae cells could be broken up.Pre-UV achieved great effect on DOM control and the removal rate of SMP-like was highest by40.64%.When UV combined with coagulation sedimentation,UV pretreatment were conducive to coagulation sedimentation,and the removal rate of CHFP increased with the increased of UV dose and at the UV dose of 1400mJ·cm^-2,the removal rate of CHFP reached the maximum and the removal rate of CHFP were 81.56%.The pre-UV/coagulation precipitation process also has a good removal effect on the fluorescent Region IV,this indicated that pre-UV/coagulation sedimentation has a better removal effect on SMP-like.The control of CH and its precursors by UV/H₂O₂ process showed that UV/H₂O₂process had a good removal rate for CH,but the control effect of CHFP by UV/H₂O₂process was affected by UV dose and the concentration of hydrogen peroxide.When the UV dose was 1000 mJ·cm^-2,the CHFP decreased first and then increased with the increasing concentration of hydrogen peroxide,at the same time,when the concentration of hydrogen peroxide was 10 mg·L^-1,CHFP largest were 6.31μg·L^-1.By the way,when the concentration of hydrogen peroxide is too high or too low,CHFP were lower than the settled water,which was due to the content of·OH.When the concentration of hydrogen peroxide was 10 mg·L^-1,CHFP decreased with the UV dose increasing,When the UV dose was 1000 mJ·cm^-2,CHFP decreased slowly.The results of 3D-EEM show that fulvic acid-like substance and aromatic protein-like substances were main components of dissolved organic matter（DOM）of this settled water.In addition,the trend of unsaturated aromatic proteins and microbial metabolites were consistent with CHFP.This suggested that the mechanism of UV/H₂O₂ process remove CH precursors was that unsaturated aromatic proteins and microbial metabolites were degraded oxidatively or converted to other non-CH precursors to reduce the formation of CH.The CH removal rate increased first and then decreased with the increasing concentration of hydrogen peroxide when the UV dose was 1400 mJ·cm^-2,at the same time,when the concentration of hydrogen peroxide was 12 mg·L^-1,the removal rate of CH largest were 99.85%.When the concentration of hydrogen peroxide was 12 mg·L^-1,the removal rate of CH increased with the UV dose increasing,When the UV dose was higher than 1400 mJ·cm^-2,the removal rate of CH increased slowly.