Biodegradation Of Di-n-butyl Phthalate In Wastewater By Immobilized Micrococcus Sp.

Phthalic acid esters (PAEs for short) are global toxic organic pollutants, belonging to atypical persistent organic pollutants (POPs), they are endocrine-disrupting chemicals. PAEshave been widely existed in the environment, and their pollutions are increasing annually inour country, which may cause serious environmental contamination and ecological risk.Microbial degradation is a key route for PAEs removal from the environment. In this paper,Di-n-butyl phthalate (DBP for short) was selected as a representative PAEs, firstly, ahigh-efficient microorganism capable of degrading DBP was isolated and identified, then thecharacteristics and mechanism of DBP biodegradation was investigated, the microbialimmobilization method using PVA as carrier was optimized, finally, the DBP removal fromwastewater by bioaugmentated systems was studied, and the dynamics of microbialcommunity structure was analyzed by Terminal Restriction Fragment Length Polymorphism(T-RFLP). The results have an important theoretic and practical significance for the removalof recalcitrant pollutants from wastewater.The main conclusions obtained from this study are as follows:(1) A high-efficient stain capable of degrading DBP was isolated and identified asMicrococcus sp., which can use DBP as sole carbon and energy source. DBP as high as500mg/L did not inhibit the growth of Micrococcus sp. The strain can use DBP and glucosesimultaneously. The degradation of DBP was not affected by the existence of glucose, DBP atlow concentration did not influence the degradation trend of glucose; however, DBP at highconcentration inhibited the glucose degradation at some degree. The addition of trace metallicelements could stimulate the bacterial growth and enhance DBP degradation. The results ofgas chromatography-mass spectrometry (GC/MS) analysis indicated the pathway of DBPdegradation was as follows: DBP was hydrolyzed to mono-butyl phthalate, then to phthalicacid, and finally to be completely degraded to carbon dioxide.（2）The microbial immobilization methods using polyvinyl alcohol (PVA) were studied,focusing on overcoming the swelling performance of immobilized cell beads. Based on thecomprehensive comparison of biologic activity, mechanical strength and chemical stability,PVA-SA was a suitable carrier for microbial immobilization. During immobilization processusing PVA as carrier, after cross-linking in saturated boric acid, the resulted immobilized cell beads were stored at4℃for24h, the swelling ratio of immobilized cell beads couldsignificantly decreased, and the biological activity of the beads did not obviously affected.The immobilization conditions using PVA as carrier were optimized, and the swelling ratioand relative biological activity of the immobilized cells prepared at this condition was15%and61%, respectively.（3）The microbial cells of Micrococcus sp. were entrapped by PVA carrier, the resultsindicated that after immobilization, the immobilized cells showed wider range of optimal pHand temperature in comparison with the free cells, suggesting the advantages of immobilizedmicrobial cells. The different methods for the storage of the immobilized cells was studied, itwas found that vacuum storage was a suitable storage method, the immobilized cells beadscould retain90%of its initial activity after12months in vacuum storage at4℃. The physicalcharacteristics and microbial activity of the beads changed with time, and stabilized finally.The swelling ratio and relative biological activity of the immobilized beads was less than20%and more than90%, respectively after30days application. The DBP degradation process byimmobilized Micrococcus sp. could be described by the Haldane inhibition kinetics equation.（4）The introduction of immobilized Micrococcus sp. into the activated sludge processcould speed up the start-up of the reactor. When the initial DBP concentration was50mg/L,the effect of the bioaumentation on the removal rate of DBP was not obvious; however, whenthe initial DBP concentration increased to the range of100-500mg/L, the introduction of theimmobilized cells could significantly enhanced the removal rate of DBP. The analyticalresults of T-RFLP indicated that the immobilized Micrococcus sp. could exist in the wholeoperational process. The introduction of the immobilized Micrococcus sp. had a significantimpact on microbial community structure of the activated sludge system.