Research On Biodegradation And Persulfate Oxidation Process For Removing Typical Phenolic Organic Pollutants

Phenolic organic pollutants are difficult to be biodegraded and have biological toxicity.Environment problems caused by human emissions of these pollutants become increasingly serious and have threatened human health.Therefore,it is important to develop technologies for removal of these organic pollutants.In this dissertation,three typical phenolic organic pollutants,bisphenol A(BPA),tribromophenol(TBP)and tetrabromobisphenol A(TBBPA),are chosen as model pollutants to study their degradation by biological technologies and advanced oxidation processes based on the new oxidant Na2S2O8(PS).The major results of this study are summarized as follows:(1)The removal of typical phenolic compounds in activated sludge system was analyzed and compared.The biodegradation process utilizing activated sludge domesticated in poor nutrition environment was found to be consistent with zero-order kinetic model when the initial level of BPA and TBP was in the range of 10～100 mg/L and 10～50 mg/L,respectively.Fed-batch reactor(FBR)coupling batch degradation experiments showed that the specific adsorption rate qbd decreased with the increase of initial pH value.Under the same reaction conditions,the specific adsorption rate qbd of BPA was larger than that of TBP and the specific biodegradation rate qbio showed the same trend.This indicated that the difficulty of biodegradation of three typical phenolic organic contaminants followed:TBBPA>TBP>BPA.Glucose as additional carbon source could promote the degradation of BPA and the intermediates of TBP by co-metabolism.Both Cu2+ and Ni2+ could inhibit biodegradation.The citric acid as a complexing agent could reduce or even eliminate the inhibitory effect of Cu2+,which provides an effective process of detoxifying poisoning caused by heavy metals.(2)The effects of complexing agents such as tartaric acid,citric acid and EDTA and reducing agents such as hydroxylamine,sodium thiosulfate and ascorbic acid were studied on oxidation of TBP and BPA in Fe2+/PS system.The results showed that the complexing agents and the reducing agents could strongly enhance the degradation of TBP and BPA and tartaric acid as complexing agent and hydroxylamine as reducing agent performed best.The choice of reducing agent depended on its redox potential as well as its reaction rates with oxidants and radicals,which should not be too low and to fast to prevent the reductant from rapid consumption.The complexing agents and reducing agents co-fortified Fe2+/PS/TA/HA system could enhance the degradation of organic pollutants under neutral condition.The inhibitory effect of HCO3-was greater than that of Cl-.The probe experiments showed that ·OH and SO4·-dominated oxidation species in the Fe2+/PS/TA/HA system.(3)Photodegradation process of the three phenolic organic compounds under UV light was investigated.When the initial concentration of three organic compounds was 50 mg/L,photodegradation of TBP and TBBPA was found to be consistent with pseudo-first-order kinetic model,while that of BPA was found to be consistent with zero-order kinetic model.The photolysis rate constants of TBP and TBBPA decreased with increase of initial organic concentration and increased with rise of temperature.Photolysis rate constants of TBP and TBBPA decreased with increase of phenol concentration due to competitive absorption.Through comparing UV photolysis of three phenolic organic compounds,it can be known that brominated compounds are prone to be photodegraded under UV photolysis and the more the number of brominated atoms was,the faster the photolysis rate was and the better the photochemical activity was,which followed the order as TBBPA>TBP>BPA.Debromination mainly occurred during photodegradation of TBP,that is,C-Br bond broke under ultraviolet light excitation and generated dibromophenol,monochlorophenol and phenol.TBBPA underwent β-bond cleavage(chemical bond cleavage between the isopropyl group and the benzene ring)as well as C-Br bond cleavage under ultraviolet light and finally generated 2,6-dibromophenol and 2,4-dibromophenol-4-isopropyl-phenol.(4)The oxidation of TBP in UV/PS,UV/Fe2+/PS and UV/H2O2 systems was compared,and the mineralizaion of TBP in these processes was consistent with preudo-first-order kinetic model.For the UV/H2O2 system,the mineralization rate reached 67.0%and the reaction rate constant was 0.0073 min-1 when pH was 9.0.For UV/PS system,TBP had the highest mineralization efficiency when pH was 3.0,reaching 79.0%within 150 minutes and mineralization rate constant was 0.0107 min-1.When pH was 3.0,UV/Fe2+/PS system showed the greatest synergistic effect.Inorganic anions Cl-,NO3-and HCO3-could inhibit the mineralizaion of TBP in UV/PS and UV/H2O2 with the following sequence:NO3->HCO3->Cl-.In UV/PS system,the yield of SO4·-in 60 min was 6.08 times of that of ’OH when the initial pH value was 7.0 and the dosage of PS was 1.5 mM.The yield of SO4·-in UV/Fe2+/PS was significantly higher than that in UV/PS,which was 135.2 μM and 107.1 μM,respectively.Both UV/PS and UV/H2O2 processes could improve the biodegradability of wastewater and effect of UV/PS(B/C =0.11)was better than that of UV/H2O2(B/C =0.07).The amount of BrO3-generated after 150 min reaction in UV/H2O2,UV/PS and UV/Fe2+/PS was 0 mg/L,5.88 mg/L and 7.50 mg/L,respectively.The degradation pathways of TBP in both UV/H2O2 and UV/PS systems were proposed through the analysis of degradation intermediates.(5)In order to combine with the photolysis characteristics of TBBPA and the synergistic effect of UV/Fe2+/PS system,UV-UV/Fe2+/PS was set up to treat TBBPA.The oxidation of TBBPA in UV/PS and UV-UV/Fe2/PS systems was compared under alkaline conditions and the yield of SO4·-in UV-UV/Fe2+/PS was significantly higher than that in UV/PS.The biodegradability of TBBPA was improved after being treated by UV/PS and TBP acclimated water as inoculation solution performed better than the youth river water.The concentration of Br-increased firstly and then decreased in UV-UV/Fe2/PS system,and the final concentration of BrO3-was 1.06 mg/L,which was higher than 0.03 mg/L in UV/PS.Compared with the formation of BrO3-during the oxidation of TBP,it could be inferred that the more complex the compound’s structure was,the less BrO3-it generated.The degradation pathway of TBBPA in UV/PS system was proposed through the analysis of degradation intermediates.(6)The oxidation of BPA in UV/PS and UV/Fe2+/PS systems was studied and compared.UV/Fe2+/PS performed better than UV/PS due to synergistic effect.Meanwhile,When the dosage of Fe2+ and PS dosage was 0.158 mM and 0.792 mM,the amount of SO4·-generated in 60 min was 48.1 μM and 71.1μM,respectively.The mineralizaion rate constant in UV/PS system increased with the decrease of BPA concentration.Insoluble phenolic oligomers were generated in process.