Study On Reduction Of Organic Matters And Bio-Toxicity From Wastewater Treatment Plant Effluent By Oxidation-Ultrafiltration

Wastewater landscape reuse is the main form of reclaimed water,and also the main measure to solve the urban water crisis and improve the urban water environment.However,there are many risks of reclaimed water,such as organic pollution of effluent organic matters?EfOMs?,eutrophication by nitrogen and phosphorus,health risk by pathogenic microorganism.Direct reuse without treatment can easily lead to eutrophication of urban slow-flow water and increase the bio-toxicity,which brings serious ecological and health risks.Therefore,it is necessary to carry out advanced wastewater treatment for wastewater treatment plants?WWTPs?effluent to improve the landscape water quality.In this paper,transformation mechanism of effluent organic matter?EfOMs?,bio-toxicity reduction and membrane fouling mechanism were investigated during oxidation-ultrafiltraion.comprehensive evaluation of three sets of advanced wastewater treatment trains?such as coagulation-sand filter,coagulation-biological aeration filter?BAF?,and ozonation-biological activated carbon?BAC??was conducted,and the degradation of nutrients,bulk organic matters,organic micropollutants?OMPs?and bio-toxicity were investigated.Results showed that coagulation by PACl was effective in removing phosphorus.Ammonia increased after ozonation,but decreases in subsequent BAC effluent.Humics with molecular weight?MW?of 1-20 kDa decreased in ozonation.Coagulation was ineffective for OMPs removal,but the subsequent BAF could promote the bio-degradation of some OMPs?such as oxytetracycline,caffeine and sulfadiazine?.Ozonation was much effective in removing OMPs more than 90%,in which phenolic group,deprotonated aniline and methoxy group in benzene ring are the main sites attacked by ozone,and C=C bond and amino are also reactive with ozone.BAF was effective for estrogenic activity removal but ineffective for genotoxicity removal.Ozonation showed high performance for the both bio-toxicity reduction.UV₂₅₄ and fluorescence indicator removals showed high relationship with OMPs and genotoxicity reduction,and OMPs removal was related well with estrogenic activity removal.Degradation behavior of EfOMs and bio-toxicity reduction during ozonation,UV/H₂O₂ and UV/PS was studied.Results showed that much lower mineralization of EfOMs was observed in ozonation compared with UV based advanced oxidation processes?UV-AOPs?.UV-AOPs could produce a continuous decline of DOC,while ozonation showed limited DOC removal after a certain extent.With equimolar oxidants addition,UV/PS was more effective in removing EfOM than UV/H₂O₂.Four fluorescence components were analyzed,including three humic components?component 1,2 and 4?and one protein component?component 3?.The degradation of fluorescence components in the oxidation processes conformed to the pseudo first-order kinetics.Humics components are preferentially degraded in UV/PS and ozonation,while protein organics are more easily removed in UV/H₂O₂ process.Low MW organics increased during ozonation,but the MW of organics showed a constant decreased in the UV-AOPs.Ozonation had a poor removal on the some ozone-refractory OMPs,while UV-AOPs were effective in removing all the OMPs.The genotoxicity of secondary effluent was effectively removed by oxidation.Oxidation?including ozonation,UV/H₂O₂ and UV/PS?-ultrafiltraion were comprehensively evaluated for degradation and reduction of EfOMs,OMPs and bio-toxicity.Meanwhile,membrane fouling characteristics were also investigated.Results showed that UF removed EfOMs ineffectively.OMPs removal in ultrafiltraion was below 40%,and genotoxicity removal was only 15%.The removals of high MW of humics and protein components?component 3?were obvious in oxidation.The degradation order for EfOMs was UV/PS>ozonation>UV/H₂O₂.Ozonation-UF partially removed OMPs,while UV-AOPs showed high performance in degrading OMPs.Genotoxicity of secondary effluent after oxidation pretreatments was not detected.Ozonation and UV/H₂O₂ showed approximately the same degree of mitigation to membrane fouling,while UV/PS showed the best mitigation to membrane fouling.Based on the characterization of fouled membrane,particle distribution of the EfOMs had little effect on membrane fouling,and reversible membrane pollution was mainly caused by protein components and soluble microbial by-products.According to the results of infrared spectrum analysis,the total fouling of UF membrane was caused by the synergistic effect of EfOMs.The roughness of membranes proved that UV/PS is the most effective process to alleviate membrane fouling.