Research On DOM In-situ Separation Technology And Its Application In The Evaluation Of New Drinking Water Treatment Processes

Dissolved organic matter(DOM)is widely present in drinking water source water,significantly impacting drinking water treatment.The water purification effect will be weakened due to the reduced effectiveness of DOM on oxidants and disinfectants.In addition,DOM will produce disinfection by-products under the action of disinfectants,such as trihalomethanes and haloacetic acids,threatening the safety of drinking water.Therefore,understanding the nature of DOM has always been one of the most important research topics to ensure the safety of drinking water.The structure of DOM is complex and will change with the source water,which affects its reactivity and removal efficiency.To design a drinking water treatment process with the best DOM removal effect,it is necessary to understand the removal characteristics of DOM in the actual drinking water treatment process,and evaluate the effectiveness of the process in ensuring water safety.In recent years,resin fractionation has been widely used in DOM fractionation.By using XAD-8(DAX-8)in series with XAD-4 resin,DOM is fractionated into hydrophobic acid(HPOA)and hydrophobic neutral(HPON),transphilic acid(TPIA),transphilic neutral(TPIN)and hydrophilic(HI)five components.Fractionation of DOM in actual water samples requires transportation and storage of a large amount of water samples.There are problems with the breeding of bacteria,algae and other microorganisms,which will cause the analysis results to be distorted.Therefore,in this research,a DOM grading device based on in-situ separation technology was first developed and applied to the DOM grading of actual water bodies.Secondly,the traditional drinking water process of coagulation,precipitation,filtration,ozone-biological activated carbon,disinfection and biological contact oxidation pretreatment,coagulation,precipitation,ion exchange resin,filtration,and disinfection of the new drinking water process are evaluated,with the exploration of the DOM removal characteristics,mechanism and the generation potential of disinfection byproducts(such as haloacetic acid and trihalomethane)of each process.This research provides theoretical support for the design and optimization of actual drinking water treatment.The main research contents and conclusions are as follows:(1)Development of resin classification device based on DOM in-situ separation technology.The Suwannee river DOM and Tongyu river DOM were selected as targets to test and optimize the in-situ separation technology.This technology can replace traditional methods.The dissolved organic carbon(DOC)error of the components is within 5%,and the characteristic peaks of the ultraviolet-visible absorption spectrum and the three-dimensional fluorescence spectrum of each DOM component are consistent.In addition,it is found that the classification process is greatly affected by the flow rate.The DOC of HPOA at high flow rates decreases by 12.2% at lower flow rates.The composition of DOM in different water sources is different.The content of HPOA in the Suwangni River DOM has the highest DOC accounting for 51.4%,while the HPOA in the Tongyu River DOM accounts for 13.7%.The fulvic and humic acidlike regions in the Suwangni River DOM are characteristic peaks,while Class II aromatic proteins in the Tongyu River DOM.(2)Study on the in-situ separation of DOM removal by the new drinking water purification process.The No.2 Water Plant(traditional process)and Tongyu River Water Plant(new process)with Tongyu River as the main water source,were selected as experimental objects to study the DOM removal characteristics of each process.HPON(27.5%,27.2%,respectively),TPIN(28.5%,27.2%,respectively)and HI(21.0%,24.9%,respectively)in the source water DOM of the two water plants accounted for more,while the content of HPOA(14.8%,10.4%,respectively)was less.The coagulation in the No.2 Water Plant showed low removal rate of the DOM,mainly removed HPOA(29.3%),HPON(16.2%).The ozone-biological activated carbon process has a good removal effect on HI(34.8%),but due to the production of biological metabolites,the content of TPIA increases and the removal rate of TPIN is only 2.4%.The biological contact oxidation pretreatment used in the Tongyu River Water Plant has a good removal effect on HI(35.0%),and the increased TPIA and TPIN in this process are removed in the subsequent coagulation process.The ion exchange resin further removed TPIA and HI,and the removal rates reached 45.5% and 38.1%,respectively,which improved the effluent quality.(3)Explore the potential of generation of disinfection by-products in the effluent of each process.The generation potential of haloacetic acid and trihalomethane is related to the content and composition of DOM.Haloacetic acid is mainly related to class II aromatic proteins,and the formation of trihalomethane is related to high molecular weight organic matter.The HI makes a major contribution to the formation of bromine-containing by-products.The new drinking water technology of biological contact oxidation pretreatment and ion exchange resin effectively reduces the content of DOM and disinfection by-products in the effluent.The removal rates of haloacetic acid and trihalomethane reached 82.4% and 72.9%,respectively,while the old process was only 51.7% and 32.6%.In general,coagulation sedimentation can remove HPOA to a certain extent.Biological method can remove HI which is difficult to be removed by coagulation,but biological metabolites will lead to the increase of TPIA and TPIN.The pre-biological law can remove the increased part through subsequent coagulation and sedimentation,effectively reducing the generation of DOC and disinfection by-products in the water body.