| As a conventional wastewater treatment technology,biochemical processes are widely used for industrial and domestic wastewater treatment.The secondary bio-treated sewage effluent is recognized as a good alternative water source due to its stable water quality and large quantity.However,the sewage effluent often contains various micro-pollutants,which pose problems for the reclamation of the effluent.Advanced treatment is considered an essential and effective way to meet the increasingly stringent discharge standard,as well as a tool for the reclamation and reuse of the effluent.The key of our study is the effective removal of effluent organic matter(EfOM)from bio-treated sewage with advanced wastewater treatment technology.In spite of extensive studies on the EfOM from domestic wastewater,there have been very few studies related to the EfOM from industrial wastewater.Compared to that in the domestic wastewater,EfOM in industrial wastewater is more complex in constituents,varying with industry category,production processes and wastewater treatment processes applied.Thus,it is an imperative but challenging task to scrutinize the constituents and characteristics of the EfOM as well as to explore effective treatment methods of the EfOM from industrial wastewater.In this thesis,we first selected EfOM from bio-treated coking wastewater as the research target.Coking wastewater is generated from coal coking,coal gas purification,and by-product recovery processes of coking,contains high level of refractory and inhibitory compounds recalcitrant to biodegradation,and the COD and chromaticity therein usually exceed the national standards.This will pose severe and long-term environmental and ecological threats to the receiving water bodies if it is discharged without further treatment.It is important to investigate the characteristics of the EfOM in detail in order to guide the design of advanced treatment methods for EfOM-loaded bio-treated coking wastewater.Four EfOM samples that are originated from different coking wastewater treatment plants in China were selected for characterization in terms of specific UV absorbance(SUVA),EfOM fractionation,size exclusion chromatography(SEC),and excitation-mission matrix(EEM)fluorescence spectroscopy.It was found that the predominant species in all EfOM samples were hydrophobic compounds.The measured SUVA values were between 4.37-4.95 L/mg·m and higher SUVA values were observed for hydrophobic fractions.Molecular weight(MW)distributions of the sampled EfOM revealed that most EfOM molecules fall in the range of 300-1500 Da.Stronger UV-absorbance was observed at the high MW(500-1500 Da)region than the one observed at the low MW region(<500 Da),indicating that relatively high MW compounds which include refractory and aromatic organic compounds were the main constituents in the sampled EfOM.EEM fluorescence characterization suggested the existence of aromatic proteins-and soluble microbial by-product-like substance as well as humic acid-and fulvic acid-like substance,and the former accounted for a larger proportion of the sampled EfOM based on the results from fluorescence regional integration(FRI).The above analysis revealed that the constitutes and characteristics of EfOM from different coking wastewater treatment plants were mostly similar.EfOM from coking wastewater mainly composed of high MW,hydrophobic,and aromatic organic compounds,significantly different from that in the domestic wastewater.Based on the understanding of the characteristics of EfOM,we synthesized a recyclable aminated hyper-cross-linked polymeric adsorbent(NDA-802),which featured with styrene-divinylbenzene skeleton,aminated functional groups,large specific surface area,and sufficient micropores.This adsorbent was specifically designed for the effective removal of EfOM from the bio-treated coking wastewater through the synergetic effect of ?-? interaction,micropore filling and acid-base interaction.Column adsorption experiments showed that NDA-802 exhibited much higher removal efficiency of EfOM than other polymeric adsorbents D-301(aminated low-cross-linking resin),XAD-4(moderate-cross-linking resin),and XAD-7(Polyacrylate resin).The removal efficiency of NDA-802 could be readily sustained according to continuous 28 cycles of adsorption-regeneration batch experiments.Moreover,the results of EfOM fractionation and EEM fluorescence spectroscopy indicated that NDA-802 possessed preferential adsorption affinity toward hydrophobic and aromatic compounds,resulting in efficient removal of these compounds which are known as precursors for disinfection byproducts.Based on the developed aminated hyper-cross-linked resin NDA-802,a combined process of "coagulation-sedimentation/sand filtration/resin adsorption" was developed for advanced treatment of the bio-treated coking wastewater from Liuzhou Iron and Steel Company.The resin adsorption was performed at a flow velocity of 6 bed volumes(BV)per hour,using 4%HCl and 6%NaOH as the regeneration reagent.The combined process could effectively reduce COD,SS,and chromaticity in the bio-treated sewage from 120-150 mg/L,30-50 mg/L and 100-150 degrees down to less than 80 mg/L,5 mg/L,and 20 degrees,respectively.The resultant effluent not only met the emission standard of pollutants for coking chemical industry in China(GB 16171-2012),but could also be partially used as recycled water in production.In addition to organic contaminants,phosphorus in the bio-treated sewage is another concern since phosphorus is regarded as the limiting nutrient responsible for the eutrophication of water bodies.In order to achieve simultaneous removal of organic and phosphorus pollutants from bio-treated sewage,we fabricated a novel,bifunctional nanocomposite adsorbent,HFO-802,by immobilizing hydrated ferric oxides(HFO)nanoparticles onto NDA-802.The coremoval of organic and inorganic pollutants was examined using p-nitrophenol(PNP)and phosphate as the model compounds.Three widely used adsorbents,including powdered activated carbon(PAC),macroporous polystyrene resin(XAD-4),and the host resin(NDA-802),were tested for comparison.HFO-802 exhibited superior properties during the simultaneous removal of PNP and phosphate as compared to the other adsorbents.The superior performances of HFO-802 were likely attributed to the unique hybrid structure of HFO-802,the encapsulated HFO nanoparticles exhibit preferable removal of phosphate through inner-sphere complexation,whereas the host NDA-802 captures PNP through micropore filling,?-? interactions,and acid-base interactions.More attractively,the exhausted HFO-802 was amenable to effective regeneration by using an alkaline solution,allowing for repeated use with constant coremoval efficiency over 10 continuous cycles of operation.The effect of solution pH,contact time,and ionic strength on the coremoval of PNP and phosphate using HFO-802 was further investigated to guide practical applications.This study provided some new insight for the understanding of EfOM from bio-treated coking wastewater.Based on the characterization of the EfOM and the understanding of the interactions between EfOM and the adsorbent,we developed a new technique employing resin adsorption for advanced treatment of bio-treated coking wastewater and further expanded the application scope of resin adsorption to the advanced treatment of various bio-treated sewages.The results reported herein could offer significant theoretical and practical guidance for the development of advanced treatment technique for the enhanced removal of EfOM from bio-treated sewage.Furthermore,this study shed some light on the development of bi-functional adsorbents for the coremoval of organic and inorganic pollutants from wastewater. |
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