The Mechanisms Of Bisphenol A Degradation By Catalytic Oxidation Via Peroxymonosulfate Activation And Biological Treatment With Immobilized Laccase

This thesis systematically investigates the performance of a novel chemical and enzymatic treatment for effective degradation of Bisphenol A.The healthy,environmentally friendly,and cost-effective removal of organic pollutants to nontoxic end-products is one of the key concerns of researchers.One of the most efficient,modern,and beneficial water treatment techniques is reactive oxygen species'oxidative remediation of organic pollutants such as hydroxylic(HO^·)and sulphate SO₄^·–radicals.Because of its unusual physico-chemical properties,such as high stability against decomposition and high potential for release of SO₄^·–and HO^·peroxymonosulphate(PMS)has been increasingly considered for advanced oxidation(AOPs)in the degradation of organic pollutants in recent years.The use of biocatalysts to replace chemical catalysts encourages the production and development of green industrial processes because of their outstanding features such as catalytic performance,poor toxicity,biodegradability,high specificity and mild reaction conditions.Laccases are multi-copper oxidases that can oxidize a broad variety of compounds,including aromatic amines,mono di,and polyphenols,methoxy phenols,and ascorbates,with the aid of molecular oxygen as a co-substratum.Laccases are currently being studied for a variety of biotechnological applications,including delignification of plant biomass for biofuel production,biopulping,biobleaching,bioremediation,and detoxification of textile dyes/effluents,oxidation of organic pollutants,stabilization of fruit juices,biosensors,beverage,textile,animal feed,paper and pulp,and degradation of organic pollutants.This study was hypothesized to achieve following objectives(I)to evaluate the efficiency of biochemical methods for the degradation of BPA in water;(II)to investigate the effects of operating parameters on BPA degradation by biochemical methods;(?)determination of the degradation/intermediate products and degradation pathway was also proposed.The main content of the study are as follows:(1)This study demonstrated that Fe(?)/peroximonosulphate(PMS)could be an efficient advanced oxidation process(AOP)for wastewater treatment.Bisphenol A(BPA)was chosen as a model pollutant in the present study.Fe(?)-activated PMS system proved very effective to eliminate 92.18%of BPA(20 mg/L)for 30-min reaction time at 0.50mmol/L PMS,1.5 g/L Fe(?),pH 7.0.The maximum degradation of BPA occurred at neutral pH,while it was suppressed at both strongly acidic and alkaline conditions.Organic and inorganic ions can interfere with system efficiency either positively or negatively,so their interaction was thoroughly investigated.Furthermore,the presence of organic acids also affected BPA degradation rate,especially the addition of 10 mmol/L citric acid decreased the degradation rate from 92.18%to 66.08%.Radical scavenging experiments showed that SO₄^·–was the dominant reactive species in Fe(?)/PMS system.A total of 5BPA intermediates were found by using LC-MS.A possible degradation pathway was proposed which underwent through bridge cleavage and hydroxylation processes.Acute toxicity of the BPA degradation products was assessed using Escherichia coli growth inhibition test.These findings proved to be promising and economical to deal with wastewater using iron mineral for the elimination of organic pollutants.(2)In this study,a transition-metal-free approach i.e.,CO₃^2-activated PMS method was tested to degrade BPA.The CO₃^2-/PMS system showed excellent catalytic activity by degrading 100%BPA within 40 min reaction time.BPA degradation showed pseudo-first-order kinetics with rate constant(k)value of 0.0918 min^-1.The effects of initial concentration of CO₃^2-,PMS,BPA,pH,and inorganic anions,including nitrate(NO₃^-),sulfate(SO₄^2-),chloride(Cl^-),phosphate(PO₄^-),and humic acid(HA)were studied.The addition of NO₃^-,SO₄^2-,and PO₄^-in the CO₃^2-/PMS system decreased BPA degradation%,whereas a high concentration of Cl^-and HA addition promoted BPA degradation%.Electron paramagnetic resonance and radical scavenging experiments verified that both the SO₄^·–and HO^·were generated in the CO₃^2-/PMS system.According to liquid chromatography-mass spectrometry results,the possible degradation pathways for BPA were suggested.Toxicity experiments revealed that BPA metabolites were not toxic.It could be concluded that the CO₃^2-/PMS system is a promising process for removing BPA in different types of water(ultrapure,lake,and wastewater)(3)In the current study,instead of chemical strategy,enzymatic treatment strategy was selected.We hypothesized that two remediation approaches would produce different sets of products,and would pass through different pathways.For this,laccase(Trametes versicolor)was immobilized on Cu-alginate beads to degrade BPA.Using immobilized laccase,96.12%degradation of BPA(10 mg/L)was achieved(0.5g immobilized laccase,pH 5.0,30?,and 150 rpm)at 1 h of reaction.The immobilized laccase exhibited higher storage stability as compared to free enzyme.Results revealed that the BPA products were non-toxic.Response surface methodology(RSM)was applied to find out the effect of immobilization parameters(sodium alginate concentration,CuSO₄ molarity,and hardening time)on the activity of immobilized laccase.Based on RSM,maximum activity(4.77U/m L)could be achieved at 3%sodium alginate concentration(W/V),0.141mmol/L CuSO₄ molarity and 90 min hardening time.LC-MS analysis of BPA products showed that only one product(hydroxylation products)was common in chemical and enzymatic treatment.Immobilized laccase could also degrade BPA in real water,hence could be considered as an efficient candidate for removing BPA in water.(4)In this study,a different immobilization material(Ba-alginate)other than previous study,was tested and the response surface methodology was adopted to optimize the conditions for BPA degradation.Further,bio-transformation was studied by employing FTIR analysis.The immobilized laccase showed higher storage stability and kinetics(K_mand V_max)as compared to free enzyme.Furthermore,reusability and tolerance against the metals was studied for immobilized laccase,and the results revealed that immobilized laccase has significant reusability and tolerance against metals.The application of immobilized laccase was tested for BPA removal using RSM.Experimental results showed that maximum BPA removal(84.34%)was achieved when temperature was 40?,BPA 2mg/L and time 50 minutes.GC-MS has detected the oxidative degradation product from bisphenol A.The findings disclosed a new support for the immobilization of laccases,and the immobilized laccase had great potential to degrade BPA in aqueous solution.