Effect Of Spent Filter Backwash Water Reuse On The Formation Potential Of Disinfection By-Products

To save water,many water plants have included a certain percentage of spent filter backwash water?SFBW?for reuse.SFBW reuse can strenthen coagulation characteristics of the low turbidity water,effectively remove hydrophobic pesticides,metal aluminum,iron and manganese in water,etc.Generally considering,its will not adversely affect the effluent water quality.Chemical pre-oxidation can improve the removal efficiency of pathogenic microorganisms such as turbidity,SUVA,Cryptosporidium and Giardia,but the process will change the hydrophilicity and hydrophobic organic component ratio of organic matter in water.The reuse of SFBW will lead to a significant increase in the concentration of particulate matter in the raw water,and the input of the pre-oxidant may oxidize some of the particulate organic matter to dissolved organic matter,thereby affecting the concentration and composition of dissolved organic matter in the filtered water,thereby affecting the formation potential of disinfection by-products?DBPFP?.In order to explore the effect of pre-oxidation on DBPFP in conventional drinking water treatment?coagulation-filtration-precipitation,CSF?process under SFBW reuse conditions,this study selected the raw water from a water treatment plant in Xi'an as the experimental object,with three types of the SFBW reuse ratio and four common pre-oxidants?sodium hypochlorite,potassium permanganate,chlorine dioxide and ozone?were used in the laboratory to simulate the water treatment process in the beaker,and the characteristics of organic matter in the water and DBPFP were studied.The correlation between the conversion of disinfection by-products?DBPs?precursors and DBPFP was studied by establishing the relationship between organic matter characterization parameters and DBPFP;The bromine insertion factor?BIF?value was introduced to assist the analysis of the formation potential of brominated disinfection by-product?DBP-Br?and its influencing factors.Mainly got the following conclusions:?1?The reuse of SFBW can promote the efficiency of coagulation sedimentation.With the increase of the recycling ratio,the turbidity removal rate in the CSF process increased,and the influent UV254 and dissolved organic carbon?DOC?decreased,and the effluent turbidity after the pre-oxidation treatment was less than 1 NTU.After reuse,the proportion of hydrophilic organic matter in water is significantly increased.Compared with hydrophilic organic matter,the removal rate of hydrophobic organic matter by CSF is higher,and pre-oxidation is not conducive to the removal of the overall level of organic matter.?2?In the CSF treatment process,with the increase of the SFBW recycling ratio,the amount of trihalomethanes?THMs?is slightly reduced,while the haloacetic acid formation potential?HAAFP?,haloacetonitrile formation potential?HANFP?,halogenated nitromethane?HNMFP?and halogenated ketone formation potential?HKFP?increased,but the total amount of five types of DBPFP remained basically unchanged.After the introduction of pre-oxidation treatment,the increase of the reuse ratio will cause the increase of the magnitude of the formation potential,and the influence of the four pre-oxidants on DBPFP is as follows:NaClO>KMnO₄>ClO₂>O₃.?3?In the CSF and Pre-CSF water treatment processes,the increase of bromide ion concentration will inhibit the formation of chlorination disinfection by-product?DBP-Cl?and promote the formation of DBP-Br,while promoting the increase of total DBPs and the degree of halogenation.Higher organic formation.An increase in Br-concentration may change the distribution ratio of bromine,increase the ratio of HAA-Br and THM-Br,and inhibit the formation of HAN-Br.Preoxidation promotes the formation of HAA-Br and HAN-Br and reduces the THM-Br ratio.In addition,reuse can reduce the BIF value of DBPs,which is not conducive to the generation of DBP-Br.?4?Under the conditions of SFBW,the DBPFP decreased significantly after disinfection with NaClO,and the production of THMs,HAAs,HANs,HNMs and HKs decreased respectively.94.0%,84.0%,97.9%,20.2%and 94.5%achieved control of DBPFP with better chlorine disinfection.