Efficiency And Mechanism On Removing Typical PPCPs In Micro-polluted Source Water By Biological Aerated Filter

In recent years,people started to pay attention to impacts of trace contaminants pharmaceuticals and personal care products(PPCPs) on the environment,biological and human health,which was developed into global hot spots.Studies showed that some PPCPs had reproductive,neurological and toxicological effect on humans and other organisms or had carcinogenic potential.China,as the world's largest user of PPCPs of the countries,controlling water typical PPCPs in the water was particularly important to improve drinking water safety.However,on the one hand,PPCPs were derived mostly from everyday life,so urban sewage treatment plant was the main source.Traditional wastewater treatment processes for the purpose of removing organic matter and nutrients can not completely removed it,which resulted in polluting the receiving water body and receiving sludge,thereby affecting quality of urban source water and groundwater;the other hand,the removal effect of a considerable portion of PPCPs was not significant by conventional feed water treatment processes such as coagulation,sedimentation and filtration. Although ozone-based advanced oxidation technologies and membrane separation technology could effectively remove PPCPs in water,but due to many reasons,they did not actually applied to the water treatment.Thus,once PPCPs enter the water,which was bound to pose a serious threat to drinking water.Therefore,the most safe and effective strategy was to eliminate PPCPs in the water through the source water pretreatment process,so that it does not enter the follow-up water treatment systems.Study at home and abroad for PPCPs was concentrated on composition and the determination of PPCPs analysis.The question of how to effectively control PPCPs in the water, especially to control at source,so as not to enter the follow-up treatment systems and water treatment could actually be applied to the study of the process was relatively little.In the sight of the unique advantages of Biological Aerated Filter(BAF) and the reason for not effectively removing some of PPCPs,which was that insufficient reaction time and without acclimation,making use of adsorption and interception from filter material and biofilm made trace PPCPs in source water retained in BAF,and then degraded by oxidation of micro-organism.Though selecting a representative typical PPCPs,carbamazepine and bezafibrate,as the treatment objects,and choseing two different filter for comparison,removal characteristics of typical PPCPs at different operating conditions and macro-mechanism was studied.On this basis,carbamazepine and bezafibrate efficient degrading bacteria were screened out.Degradation mechanism and physiological biochemical characteristics of two kinds of highly efficient degradation bacteria also were studied,which further revealed degradation micro-mechanism of typical PPCPs.Through above researches,it was confirmed that BAF could not only effectively eliminate and reduce the potential hazards of PPCPs in drinking water and improve drinking water safety,but also provide reliable scientific basis for practical engineering applications,which has important practical significance.Due to difference of available biochemical between carbamazepine and bezafibrate,obtained results become more universal.Through researches,obtaining the following main conclusions and outcomes:1.Through analysis and comparison of typical PPCPs removal effect by BAF,reaching the following conclusions.(1)Under the condition of hydraulic loading 0.3 m3/m2.h(corresponding flow rate 2.4L / h,corresponding hydraulic retention time 2.7h),15.2-16.5℃,gas-water ratio 1.5:1 and the concentration of carbamazepine and bezafibrate in water being 78.5μg/L and 83.9μg/L,maximum removal rates of carbamazepine and bezafibrate was 7.8%and 10.8%by ceramic bed.Maximum removal rates of carbamazepine and bezafibrate was 6.1%and 7.5%by high-performance fiber Layer respectively.Two kinds of filter media in water have a certain adsorption to typical PPCPs, but adsorption was not significant,mainly due to smaller octanol-water partition coefficient and the similarity of surface functional groups with filter surface functional groups.(2) In the case of sufficient DO,with the hydraulic loading increases,removal rate of PPCPs presented downtrend.Typical PPCPs removal rate by ceramic BAF is higher than the high-performance fiber ball BAF.When the hydraulic load is larger,the main function of BAF for the removal of carbamazepine is the retention adsorption role of filter material and biofilm and biological flocculation,bio-oxidation is not obvious.But bezafibrate removal was mainly microbial bio-oxidation.The difference was caused by difference of carbamazepine and bezafibrate in available biochemical.(3) Gas-water ratio affects the processing performance of BAF.With the increase of gas-water ratio,removal rate of PPCPs have typically higher.When the gas-water ratio was 1:1 and above,the removal rate changed little.But when the gas-water ratio dropped to 0.5:1,the typical removal rate of PPCPs sharply decline.Gas-water ratio should be chosen to meet effluent DO in the 3mg/L or over.When the gas-water relatively high,typical PPCPs removal rate by ceramic BAF is higher than high-performance fiber ball BAF,and when the gas-water is relatively low,the high-performance fiber ball BAF on PPCPs removal rate is higher than the typical ceramic BAF.This is because when the gas-water ratio was too low,DO in the water become the limiting factor.Highly-efficient fiber ball BAF has better mass transfer effects,so it had relatively high remove rate.(4) Under the optimum operating conditions,namely,the hydraulic loading of 0.2 m3/m2.h,gas-water ratio 1.5:1,water temperature 20℃,pH of water being alkaline,the ceramic BAF for carbamazepine and bezafibrate,the average degradation rate was 47%and 63.8%respectively and the average degradation rate of carbamazepine and bezafibrate was 43.98%and 59.34%by high-performance fiber ball BAF respectively.For the purpose of removing refractory organic matter in the water,light filter tended not to be chosen.(5) When carbamazepine and bezafibrate co-exist in the source water,bezafibrate was preferentially degraded.The presence of bezafibrate had effects on degradation rate of carbamazepine.The above-mentioned phenomenon is due to difference in available biochemical between bezafibrate and carbamazepine.From the view of the degradation rate of carbamazepine, its main removal depended on adsorption on filter and biofilm and biological flocculation.(6) The removal of carbamazepine and bezafibrate mainly occurred in the location of 40cm in BAF.During the location,the average removal rate accounted for 70%of total removal rate.2.Following the above basis of the study,the highly efficient degradation bacteria was screened out of for typical PPCPs from BAF.(1) Optimal degradation conditions of(Pseudomonas putida.) X-6 strain for carbamazepine: initial pH is 7.3 or so,the temperature is 30℃,oscillation rate was 160r/min,250mL bottle of liquid cone-shaped volume of 100mL,the strain inoculation was 0.6%(w/v) and initial concentration of carbamazepine was 10mg/L.Under these conditions,after 3 days,the degradation rate of carbamazepine is 45.52%.X-6 strains of carbamazepine degradation mainly through the biological oxidation so that the dissolution of carbamazepine occurred,the possible degradation pathway of carbamazepine:For the first,through the biological oxidation,CBZ was oxidized into CBZ-EP(10,11-dihydro-10,11-epoxy-Carbama-zepine),and through the hydrolysis CBZ-EP was converted to CBZ-DiOH(10,11-dihydro-1011-dihydroxy ca-rbamazepine).In the role of oxidative decarboxylation by pyruvate and NADH2,CBZ-DiOH was decomposed into a single benzene ring material,and then by the citric acid cycle eventually was mineralized.Degradation products which contain CBZ-EP and CBZ-DiOH,which had been detected in municipal sewage treatment process.(2) Optimal degradation conditions of(Pseudomonas plecoglossicida.) B-3 strain for bezafibrate:initial pH is 6.8-7.6,the temperature is 30-35℃,oscillation rate was 160r/min, 250mL bottle of liquid cone-shaped volume of 100mL,the strain inoculation was 0.5%(w/v) and initial concentration of bezafibrate was 15mg/L.Under these conditions and initial concentration of bezafibrate was 10mg/L,after 2.5 days,the degradation rate of bezafibrate was 59.81%.Bezafibrate degradation by B-3 strain first occurred chain scission by hydrolysis and was degraded into acetic acid,ethyl acetate and other small organic molecules,which then further was oxidized until the final mineralization.