The photochemical and biological degradation of sulfamethoxazole (SMX) study
|School||Shanghai Normal University|
|Keywords||Sulfamethoxazole (SMX) photochemistry biodegradation biological inhibition kinetics|
With the development of industry and technology, various types of pollutantscontinue to be detected, and with the extensive application of antibiotics, a growingnumber of drug residues were detected in surface water, groundwater and the citywater plant. Sulfamethoxazole （SMX） has been widely used in clinical and farming asa kind of antibiotics because of its low prices, if it was discharged into a natural waterenvironment, it would difficult to be degraded by microorganism and easily generatedin vivo enrichment, so the harm can not be ignored. There are many researches on thedegradation of the SMX, but mineralization on SMX was rarely mentioned. Thissubject analyzed the SMX degradation rule, mineralization effect and its degradationpathway through researching SMX degradation under4protocols—UV, UV/H2O2,biological, UV/biological. I hope to this research can provide a reference for thedegradation and mineralization of sulfa drugs and even the other compoundscontaining N and S in the future.The research on degradation SMX under4protocols—UV, UV/H2O2, biological,UV/biological using ILPBR showed that:1) The rule of SMX degradation reactionsunder ultraviolet radiation accorded with one order reaction kinetics equation;Degradation rate was accelerated with the rise of UV intensity of the radiation and thepH decline; The higher the SMX initial concentration, the slower the degradation rate;The SMX removal rate was high when it was degradated by UV photolysis, whilst themineralization was low.2) H2O2could generate a strong oxidant· OH in ultravioletradiation, and it increased the rate of the SMX degradation significantly; Alkalineconditions was to the disadvantage of the SMX degradation due to consumptionof· OH by OH-and heavy metal ions; The higher the concentration of H2O2, thehigher the mineralization degree of organic matter, the COD removal rate reachedmore than80%in the solution which contained10mM H2O2after reacting8h.3) Thehigher the SMX concentration, the stronger the biological inhibition, UV/biologicalprotocol （UV/B） had shown its degradation advantage under different initial SMXconcentrations; Coupling reaction （UV/B） not only enabled SMX removal rate to 100%in the reaction time, but also the mineralization rate was increased significantly.4) The kinetic model of degradation SMX under biological protocol belonged to thetype of matrix suppression, while the degradation kinetics matched Monod equationunder UV/biological protocol.The research on culturing2types of microorganism （one was domesticated byglucose and another was domesticated by SMX） in the SMX solution and the SMXsolution after photolysis respectively showed that:1) For the microorganism whichhadn’t been domesticated by SMX: SMX had strong biological inhibition, and it washard to be used by SMX domesticated microorganisms, whilst the achievement ofremoving SMX could be reached through the co-metabolism of glucose; Themicroorganisms could use the products generated by treated SMX with photolysis,and SMX utilization rate was lower because that the intermediate products were easieruse for microorganisms, after the SMX solution was treated with UV utilization, onthe one hand the SMX concentration was lower, on the other hand the intermediateproducts were easier to be used for microorganism, so the biological inhibition ofSMX was alleviated.2) For the microorganism which had been domesticated by SMX:Can use single SMX as a carbon source for growth, SMX was rapidly degradedcompletely in the logarithmic growth phase of the microorganism, and the SMXsolution with high concentration didn’t have significant inhibition; The microbialstabilization period was significantly shorter in the SMX solution, the intermediateproducts were easier to be used by microorganism, and priority use of intermediateproducts for microorganism caused to the none degradation of SMX；Adding glucosedidn’t make the role of co-substrate to be reflected; The growth of SMX domesticatedbacteria in the SMX solution and the SMX solution treated with photolysis matchedwith Monod equation, saturation constant （Ks） of microbial growth decreasedsignificantly in the solution treated with photolysis, and it showed that the biologicalinhibition of intermediate products was smaller than SMX.The research on release rule of N and S elements which were contained in SMXunder protocol UV/H2O2showed that: after the reaction the N elements in SMXreleased in the form of NH4+, meanwhile the concentrations of NO2-and NO3-were very few. Following the addition of H2O2, the release rates of N and S weresignificantly increased. Without H2O2, N elements release reached only17.9%afterreacting480min and the corresponding figure was34.8%for S element, with theincrease in the concentration of H2O2, the release amount of N and S elementsincreased, when the dosage of H2O2was up to20mM, the N element release increasedto48.1%, and the S element released completely. Acidic conditions accelerated therelease rate of N and S elements, in pH=3and pH=7condition, N element release gotto40%after reacting180min and the S element released completely, at the same timein the condition of pH=10, the release of N element reached25.8%and the data was91.8%for S element after180min reaction.Through analyzing the literature and the data of N and S element release, Isurmised that after the fracture of nitrogen-sulfur bond (-NH-（S （O2）-）, only a smallamount of N element on the isoxazole ring and a small amount of S element on thesulfanilic acid were removed, and the mineralization effect was not very well. Afterthe addition of H2O2, with the nitrogen-sulfur bond (-NH-（S （O2）-） fractured, the Selement on the sulfanilic acid was released completely, while the N element wasdifficult to be released because of the steady of amino group on it, the N element onthe3-lsoxazolamine,5-methyl-was also released firstly, and the N element onisoxazole ring mostly.