Magnetic Anion Exchange Resin For Advanced Treatment Of Textile Wastewater:Fouling And Its Control

Advanced wastewater treatment is a necessary process for safeguarding the aquatic environment.However,designing a cost-effective treatment process is not easy,because the biological/secondary effluent always has a complex composition.As to the industrial wastewater,a large number of toxic chemicals,stimulating the activated sludge to produce various organic matters at high concentration,generally make the advanced treatment more difficult.Therefore,the practical application of the advanced treatment in industrial wastewater treatment plants is still not going well to date,especially in developing countries.NDMP of a magnetic anion exchange resin,as one renewable material at lower cost and with less energy consumption,is expected as a feasible technique to treat biological effluent efficiently,based on its good performance in treatment of drinking water and municipal biological effluent.In this study,textile biological effluent was chosen to evaluate the use feasibility of NDMP resin,considering its high treatment difficulty due to the large discharge volume with high concentration of both dissolved organic matter(DOM)and inorganic matter.The conclusions are as follows.First,the optimization of adsorption and desorption processes of NDMP for treatment of different textile biological effluents was carried out in the lab scale.After the treatment of 300 BV,NDMP removed 40%-80%DOC and over 92%color.At the same time,the inorganic anions were also removed near to the DOC removal,showing no obvious competitive adsorption with DOM.By balancing efficiency and cost,12%NaCl+0.5%NaOH of regeneration solution was used to regenerate the used NDMP.Under the above conditions,NDMP was fouled in different levels for treatment of different textile biological effluents.Note that the three of the five effluents,WJ,LN,and SX,had a serious fouling on the NDMP resin,which meant that a pretreatment process of NDMP for reducing its fouling was very necessary.Second,an analysis method on resin fouling behavior was established for the prevention against the fouling.The steps of this method are listed below.(1).Define a resin fouling index(RFI)to reflect the resin fouling level,according to the decrease of DOC removal after resin regeneration;(2).Fit the RFI with water indexes to identify the main resin foulant;(3).Investigate features of the resin foulant;(4).Analyze the fouling behavior.For the textile advanced treatment,the RFI of NDMP was related to the content of the high-MW protein-like substance with molecular weight(MW)over 7000 Da,rather than the values of DOC and UV254,and the concentration of any kind of inorganic anion.Based on the characterization results using EEM,HPSEC and FTIR,the resin foulant was considered to be the aggregate of protein and polysaccharide derived from the activated sludge stimulated by dyes.Because the pore-blocking was ruled out for explaining the hard desorption of the resin foulant,the hydrophobic repulsion of the foulant to the chloride ion in regeneration solution may be an important fouling mechanism.As to the fouled resin,there was a consistent removal of all the humic-like substances,but the removal of the low-MW protein-like DOM obviously decreased.Third,the ability of preventing the fouling of NDMP using four different kinds of techniques was investigated.Cation exchange resin could remove a small part of the resin foulant,without adverse impact on the DOM removal by NDMP,but it was unsuitable for NDMP as a pretreatment process because of its own rapid fouling.Two types of oxidation processes,ozonation and Fenton oxidation,hardly reduced the fouling level of NDMP,although they could oxidize the resin foulant into the matters with a smaller MW.Coagulation efficiently removed the resin foulant as the pretreatment process.How to optimize integration efficiency and maintain it for long-term running is a critical issue.A novel design method of targeting key DOM components(named TKDC design)for the integration was established in this study.The details of TKDC design are as follows.Among eight DOM components detected by HPSEC with a fluorescence detector(HPSEC-FLD),two protein-like compositions were identified as key components to optimize the integration process.On the one hand,the high-molecular-weight(high-MW)protein-like substance,fouling the AER without pre-coagulation,determined the integration sequence.On the other hand,the mid-low-MW protein-like substance,as the competitive component between AER and coagulation,was directly related to the integration efficiency.When coagulation was pre-posted,poly-ferric chloride(PFC)was demonstrated to be an efficient coagulant due to its preferential removal of the resin foulant and its slight removal of the mid-low-MW substance.In contrast,adding polyacrylamide into the PFC coagulation led to remove more resin-treated substances instead of resin foulants,which had an adverse impact on the integration.Therefore,both integration sequence and coagulant type should depend on the removal of the key components,rather than the removal of only a general DOC value.Fourth,the use conditions of NDMP in pilot plant scale were adjusted to improve the running stability according to the demand of treatment and operation.The size of the mixed reactor for NDMP treatment process was first designed by considering the limit of the influent velocity.Then,the resin fouling index was investigated after optimizing the regeneration condition.If NDMP had a serious fouling,poly-ferric chloride(PFC)should be used as the pretreatment process to reduce the fouling level.Taking SX as an example,the integration of PFC and NDMP after optimization using TKDC design method,had a very high DOC removal(86%),and showed a strong running stability based on little decline on DOC removal(only 3%)after 55 times regeneration.In addition,PFC+NDMP was better than PFC+MIEX,O3+Activiated carbon,and MF+RO on the running stability.In short,NDMP was suitable for the application of the particular engineering.