Study On Selective Separation And Oxidation Removal Of Organics In Coal Chemical Industry Brine

The Coal Gasification Brine（CGB）is a typical reverse osmosis concentrated water within high salt and high organic compounds,and its effective treatment is still a huge challenge in nowadays.The currently technology,which is adopted in high-pressure reverse osmosis concentration and evaporation crystallization,would cause severe membrane contamination and evaporator corrosion int the process of dealing high concentrations of organic contaminants,which would significantly reduce the stability of the process.That process generates large amounts of mixed crystalline salts,which are expensive to dispose of and unaffordable for companies.Advanced Oxidation Processes（AOPs）are capable of efficiently removing organics from concentrated brine through the strong oxidizing properties of hydroxyl radicals（HO·）and are considered a promising technology for concentrated brine treatment,but the higher organic concentrations and the large amounts of radical quenchers and masking agents they contain inevitably lead to higher operating costs for AOPs.The development of selective separation technologies for specific organics in concentrated brine and more efficient complex oxidation technologies is expected to improve the removal efficiency and reduce the treatment cost of organics in concentrated brine.The paper starts from the selective separation of organic compounds in concentrated brine and advanced composite oxidation of multi-media,as well carries out the research and development of organic compounds resin adsorption,nanofiltration separation and electrically driven ultraviolet chlorine（E-UV/Cl₂）oxidation process and the organic compounds separation-oxidation synergistic removal mechanism.The paper firstly constructs a combined process of macroporous resin selective adsorption and E-UV/Cl₂ oxidation for the removal of organic compounds in CGB,and carries out research on the mechanism of organic compounds removal in the combined process and the regeneration method of adsorption-saturated resin and the biochemical degradability of desorbed liquid.The study showed that there was an obvious synergism between LS-109D macroporous resin adsorption and E-UV/Cl₂ oxidation combination,which could efficiently remove organic compounds from CGB,reduce the dissolved organic carbon（DOC）of wastewater from 163.41 mg/L to 26.58 mg/L,and transform the characteristics of organic compounds in CGB from higher fluorescence and higher molecular weight distribution to lower.The specific pore structure of LS-109D macroporous resin allows it to adsorb aromatic fluorescent components better with bursting Cl?and Cl₂^?-effects and low molecular weight organic acids that are insusceptible to HO·oxidation.E-UV/Cl₂ oxidation process fully utilizes Cl^-in CGB to produce highly reactive oxidants such as Free Chlorine（FC）,HO·,Cl·,O·and Cl₂^?-to strengthen the degradation of organic compounds.The FC arising from electrochemical oxidation on the anode surface allows rapid decolorization of the CGB,which results in an increase in the UV flux rate and an increase in the rate of radical production from UV photolysis of the FC,with a significant synergistic effect between electrochemistry,UV photolysis and chlorine oxidation.The adsorbed saturated LS-109D can be regenerated in an efficient way by elution with ultrasound assisted 363 K hot water,and the desorbed solution can be discharged up to the standard by the conventional activated sludge method after 60min pre-oxidation by ozone.For the interaction between organics and adsorbents in CGB,a mechanical module of atomic force microscopy（AFM）was used to set up a mechanism of force analysis and to measure the force between the adsorbent and the free radical quenched organics.The measurements showed that the interaction forces between the macroporous resin and these organics were four to seven times stronger in comparison to adsorbents such as alumina trioxide and activated carbon,and that the macroporous resin selectively adsorbed aromatic and ionic organics through the reaction of non-covalentπof the benzene ring,resulting in a more selective adsorption effect.In order to investigate the mechanism of DOC removal in the E-UV/Cl₂oxidation process in CGB,the study was conducted to investigate the pathways of reactive oxide generation such as free chlorine and free radicals.A quantitative relationship was established between the generation and conversion of reactive oxides based on the Volmer-Heyrovsky mechanism.The detection of the concentration of reactive oxides and the calculation of the quantitative relationship model showed that the concentration of FC in the E-UV/Cl₂ oxidation system was higher than that of free radicals,but the free radicals played a dominant role in the removal of dissolved organic matter（DOM）from CGB,with a contribution of 93.8%and a specific energy consumption of 2881 k Wh/kg DOC.Among various free radicals,Cl·,Cl₂^?-and O·contributed more to the oxidative removal of DOM than Cl O·,Cl OH·,HO·and CO₃^?-,etc.The concentrations of FC,Cl-and HCO₃^-have an effect on the conversion of free radicals,which leads to a decrease in the oxidation efficiency of organic matter.HO?was converted into Cl₂^?-by Cl^-,HO?and Cl?were converted into Cl O·by FC,HO?,Cl?and Cl₂^?-were converted into CO₃^?-by HCO₃^-.For the combined process of nanofiltration membrane filtration and E-UV/Cl₂oxidation,experimental studies on CGB treatment by nanofiltration membrane filtration and experimental studies on E-UV/Cl₂ oxidation treatment by membrane permeate were carried out using commercial TITAN nanofiltration membrane,home-made PES/Fe-TA and WS₂ two kinds of sparse nanofiltration membranes to explore the synergistic mechanism of organic compounds removal in the combined process.The study showed that the retention efficiency of commercial TITAN nanofiltration membranes for organic compounds in CGB was low,and WS₂ membranes would soon experience serious fouling during the treatment of CGB,leading to a continuous decrease in water flux and unstable operation of the membrane filtration process;when the adsorption and desorption of DOM within the nanopores of Fe-TA complexes reached equilibrium in the PES/Fe-TA membrane filtration treatment of CGB,the water flux was stable at When the adsorption and desorption of DOM in the Fe-TA complex nanopores reached equilibrium,the water flux was stable at 12.06 kg/m²?h,the DOC retention rate was 49.54%,and the DOC concentration was reduced from 163.41 mg/L to 84 mg/L,achieving stable operation and selective separation of organic compounds.After 90 min of E-UV/Cl₂ oxidation,the DOC concentration was reduced to 27.32 mg/L,and the fluorescent organics were completely removed,and the molecular weight of DOM was mainly distributed in the<1 k Da class.The effect of the adsorption was better than that of macroporous resins.This paper proposed a method for selective separation of organic compounds in CGB,explored the mechanism of E-UV/Cl₂ oxidation process to generate reactive groups for the high salt water quality of CGB,constructed a combined process of selective separation and E-UV/Cl₂ oxidation to treat CGB,advanced the application of organic removal technology in CGB in zero liquid discharge（ZLD）,and finally provided the reduction of hazardous waste in coal industry support,and promote the forward process of environmental protection and resource recovery in coal chemical industry.