Removal Of Pyrene By Immobilized Microorganism Using Preadsorption On Corn Stalk-Embedding-crosslinking Immobilization Method

In this study, pyrene was chosen as a model compound for studies on the biodegradationof polycyclic aromatic hydrocarbons (PAHs). polyvinyl alcohol (PVA) and sodium alginate(SA) were used as the immobilized carrier whose best ratio was10%PVA+0.5%SA. GY2B+GP3B (73.6%) and GP3A+GP3B (76.8%) were selected as the immobilized object amongGY2B, GP3A, GP3B, GY2B+GP3A, GY2B+GP3B, GP3A+GP3B, three bacteria mixed.We used a complex immobilization method, involving pre-adsorption on corn stalk,cross-linking and entrapment, to immobilize the mixed culture. The mixture were at first drippedinto a solution of5%calcium nitrate to form the beads, then frozen at-20°C for12h and thawed at-4°C for12h then subsequently frozen again. The study had optimize the immobilizationparameters and operational conditions to obtain a high level of biodegradation in a relativelyshort time, and compare the degradation of pyrene of free and immobilized cells usingcomplex immobilization method in continuous cultures, investigate the process andmechanism of action, the physical and chemical properties, conducting a preliminaryassessment of the practical application of the immobilized mixed bacteria.The study found that the immobilized mixed bacteria are less sensitivity toenvironmental impact factors. Best operation temperature is30℃and pH is7. The range oftolerance of immobilized bacteria on the temperature, pH and contaminants had beenexpanded. Immobilization could protect bacterial from the environment impact factors, keepthe bacteria maintain a high degradation efficiency.Results showed the immobilized strain has higher pyrene removal efficiency than thefree strain in a relatively short time.97.3%pyrene has been removed by the immobilizedGY2B+GP3B in5days,97.0%pyrene has been removed by the immobilized GP3A+GP3Bin4days. From the data of the physical and chemical properties, the immobilized corn stalkbeads owns good mechanical strength coefficient. With the addition of the corn stalk, specificsurface area and particle diameter has been improved, the adsorption capacity was enhancedand the removal of pyrene was improved in a certain extent. Scanning electron micrographsimages showed that the outside and inside of the beads had a large number of pores and full ofskeleton structure. This kind of porous framework is beneficial to the diffusion of substrateand oxygen to the interior of the carrier. SEM images also indicated that cells weresuccessfully entrapped in the beads and grown well with no evidence of variation ordeformation. The immobilized microorganism bead was similar as a micro reactor consistingof adsorption and biodegradation. The results fully proved the feasibility and effectiveness to remove pyrene of the complex immobilized bacteria which was with a good prospect.From the GC-MS results, GP3A+GP3B’s metabolisms were1-hydroxypyrene,1-hydroxypyrene-sulfate,4,5-dihydropyrene and phenanthrene-4-carboxylate. Mixed bacteriaGP3A+GP3B should cooperate to degrade with independent metabolic process.GY2B+GP3B’s metabolisms were phenanthrene-4-carboxylat, dimethylated phthalic acid,1-hydroxy-2-naphthoic acid,1-naphthol and salicylic acid. It is likely that degradation ofpyrene was the cooperative result by mixed GY2B+GP3B bacteria. And the intermediatemetabolite products of GP3B were used as the ground substance by GY2B, which made thepyrene degradation a more complete one.