Study On Advanced Treatment Of Bio-treated Textile Wastewater Based On The Novel Magnetic Ion Exchange Resins

In this study, the composition, properties and potential environmental hazards of the soluble organic matter (DOM) in several types of typical bio-treated dyeing wastewater were analyzed. The removal efficiency and adsorption mechanism of novel magnetic resin (NDMP), in contrast with other adsorbents, for DOM were investigated. The desorption solution of NDMP resin was separated by nano-filtration (NF) membrane, and the filtrate’s performance in NDMP regeneration was evaluated. Concentrated filtrate was processed and its physical and chemical properties and biological toxicity were then studied. Novel combination treatment process and reactors for NDMP adsorption were set up, and the quality of advanced treated water was considered to satisfy both the discharge standard in China’s key drainage basins and the requirement of dyeing and finishing industry for production.Firstly, the composition, structure and chemical groups of DOM from different sources of bio-treatment dyeing wastewater were varied, but the DOM in all effluents were consisted of dye stuffs, additives, metabolites of dyes and additives, microbial metabolites and humic-like substances. The molecular weight (MW) of DOM was mostly in1k-3k Da, while organics with similar chemical groups were in the wide MW region. The main components of DOM were hydrophilic organic (HPI), which were mainly composed of metabolites of microorganism. The concentration of humic-like substances in the DOM was in a low level. HPI and organic acids had more carboxyl and phenolic hydroxyl groups and were featured by aromatic structures, while neutral organics had less acidic groups and were featured by significant linear organic carbon structure. HPI and organics with MW<3k Da had higher bio-toxicities. Disinfection byproducts formation potentials (DBP-FPs) of bio-treated textile wastewater were higher than municipal wastewater, and HPI in effluent had the highest DBP-FPs.Secondly, the adsorption performance of macroporous styrene resins on DOM was better than acrylic resins, but styrene resins had lower desorption ability. The adsorption efficiency of NDMP resin for DOM was higher than MIEX. Small-particle resin exhibited faster adsorption rate for removing DOM, and the pseudo-second-order kinetic model was able to describe its adsorption process. Average MW of DOM had no significant effect on the resin adsorption rate, but more acidic groups in DOM accelerated the adsorption rate of resins. Adsorption efficiencies of resins for HPI and neutral DOM were lowest. Acrylic resins had higher removal rate for hydrophobic acid (HPOA) than styrene resins, however, the adsorption performance of styrene resins on HPI were better than acrylic resins. Anion resins had dramatic effect on removal of bio-toxicities and DBP-FPs of bio-treated textile wastewater, but they also increased nitrogen-generated DBP-FPs. The pH of effluents had no obvious effects in helping styrene resins absorb DOM, but higher pH was able to increase the performance of acrylic resin in absorbing DOM. High concentration of sodium sulfate in effluents reduced the performance of acrylic resin in removing DOM. The composition of weak acid/strong base resins increased the DOM adsorption rate of anion exchange resin by about20%.Thirdly, NF processes were able to filtrate and concentrate desorption solution of NDMP conveniently. Chromophoric, aromatic and large organic molecules were concentrated in NF concentrate. NF filtrate had less aromatic organics and NF had a brilliant performance on concentrating chloride ions. Moreover, the filtrated chloride ions could be reused for regenerating NDMP. NF concentrate oxidized by H2O2had no obvious bio-toxicity. The optimal parameters of oxidization were H2O22%(v/v), Fe2+2.5g/L, pH4and reaction time is2h. Fenton oxidation pretreatment could increase the performance of NF concentration on NDMP desorption solution.The optimized resin particle size of NDMP in real application is0.15-0.18mm, and higher resin concentration and smaller resin size could both increase the reaction rate of resin adsorption. However, the over-dosing resin in reactors was not able to increase the adsorption efficiency of NDMP significantly. The DOM adsorption ability of NDMP in reactors was only depended on concentration of DOM in reactors and the reactor kinetics were in accordance with the first-kinetic model. The average removal efficiencies of NDMP for COD, TN and TP in real effluents were50%,48%and68%respectively. Bio-treatment process units were stable after oxidized NF concentrate was discharged into it.