Study On The Advanced Treatment Of Source Water Based On Magnetic Strong-based Anion Exchange Resin Purification

Natural organic matter (NOM) in drinking water is a complex mixture containing humic substances and hydrophilic fractions. It can cause:colour, taste and odour problems; and increase the use of reagents in the subsequent treatment processes. And the most importantly, increase the formation of disinfection by-products (DBPs) during the chlorination process. Therefore, the efficient removal of NOM in drinking water treatment is of great importance. The conventional methods used in drinking water treatment including enhanced coagulation, O3-GAC, and membrane filtration. There are some disadvantages of these methods. Firstly, the removal of small hydrophilic organic molecules by coagulation was of low efficiency; Secondly, the ozonation process can generate byproducts like small hydrophilic organic molecules and bromate, which would increase the formation of DBPs and elevate the costs; Thirdly, membrane is easily contaminated by NOM that cutting down the life span. Recently, a new magnetic ion exchange resin MIEX(?) is developed by the ORICA Watercare(?) in Australian. The magnetic properties, fast sedimentation, high reaction rate, smaller size, easily desorption and regeneration as well as other advantages of MIEX(?) resin render it applicable in drinking water treatment. This study conducts systematic research into the comparation of a novel magnetic ion exchange resin named NDMP developed by our research group and MIEX(?) resins for the removal of NOM and inorganic ions. And this work also expounds the matching relationship between the physical structures of the resins and the physicochemical properties of NOM with regard to the absorption performance, in order to demonstrate the functional mechanisms. This work provides guidance to the integrated processes of NDMP with other treatment techniques. We also established a safety evaluation method for NDMP resin treatment and employed the magnetic resin technology in the water plant in Dafeng city in order to solve the seasonal high organic pollution problem in the raw water. The main contents and conclusions are as follows:(1) Four magnetic anion exchange resins (MAERs) were compared for the removal of NOM and mineral anions in drinking water treatment. The effect of water quality (pH, temperature, ionic strength, etc.) on the performance of MAER for the removal of NOM was also investigated. Among the four studied MAERs, the strong base resin named NDMP-1with high water content and enhanced exchange capacity exhibited the highest removal rate for dissolved organic carbon (DOC)(49%removal rate) and UV-absorbing substances (82%removal rate) with a resin dose of10mL/L after30min of contact time. Fluorine, Sulfate and nitrate concentrations were reduced by about63%,81%and92%with NDMP-1, respectively. Because of the higher specific UV absorbance (SUVA) value, the NOM in the raw water was removed more effectively than that in the clarified water by NDMP resin. Increase in temperature can improve the kinetics of the resin. Moreover, increasing the sulfate concentration in the raw water could decrease the removal rates of DOC and UV-absorbing substances.(2) By studying the functions mechanism of the resin and the physicochemical properties of NOM, we found that the resin has a high affinity for the medium-high molecular weight component with hydrophobic and aromatic characteristics. Meanwhile, the transitional hydrophilic component containing more carboxylic acid can be effectively removed by ion exchange. Coagulation process removed only part of the large molecular weight and hydrophobic organic compounds, showing no removal capabilities for small molecules components. The study of the coupling process of coagulation with resin treatment concluded that the pretreatment of resin could enhance the removal ability of subsequent coagulation process and reduce the coagulant dosage used in coagulation. On the other hand, the pretreatment of coagulation could reduce the blockage of resin and improve the resin performance for efficient removal of the hydrophobic components of NOM in the batch experiments.(3) NOM, ammonia nitrogen and hardness cations are common constituents of natural water which affect drinking water treatment. Combined ion exchange process is expected to be useful treatment for the removal of combined pollutants in raw water and benefit the following operation processes. Magnetic anion and cation exchange resins can be used in a single completely mixed reactor to remove NOM, ammonia nitrogen and hardness at the same time, also allowing for the most efficient use of the brine regeneration solution. Simultaneous removal of NOM (49%as dissolved organic carbon), ammonia nitrogen (46%) and total hardness (77%) were achieved by combined ion exchange treatment.(4) The NDMP resin could greatly reduce the formation of DBPs including trihalomethanes (THMs), haloacetic acids (HAAs) and haloacetonitriles (HANs) during the chlorination of raw water. Meanwhile, the cytotoxicity of the raw water after NDMP resin treatment during subsequent chlorination was greatly reduced. The effect of bromide ion and ammonia on the formation of DBPs during the chlorination of raw water was also investigated. The addition of bromide could enhance the cytotoxicity to cells in raw water due to the formation of more toxic brominated DBPs. And the addition of ammonia and nitrate contributes to the enhanced cytotoxicity to cells in this system, which might be explained by the formation of more toxic N-DBPs.(5) We established an advanced treatment project using magnetic ion exchange resin in the water plant in Dafeng city (daily capacity of5,000tons). Based on the monitoring results of continuous operation, we found that the magnetic resin could efficiently remove NOM in the raw water. After resin treatment, the CODMn of the effluent was lower than3mg/L which satisfies the new drinking water standards (GB5749-2006). The fixed investment costs of only100yuan/m3and the processing costs of0.08-0.10yuan/m3demonstrated that the magnetic ion exchange treatment can be applied as advanced drinking water treatment processes.