The Immobilization Of Surfactant Producing Bacteria Bbai-1and Its Application In Oily Wastewater Treatment

Oil industry develops rapidly in recent years. But in the process of exploitationof oil resources, storage, using and transportation of petroleum products, a largeamount of oily wastewater was discharged. At present, there are three main methodsused in the sewage disposal process including physical method, chemical method andbiological method. Although the biological treatment is the safest technology withbetter economic benifits, bacterial loss and the unreusable feature limite itsapplication in the waste water treatment. Therefore, the immobilized microorganismtechnology appears as the times require. It can make microorganisms grow within aspecific region of space by some technical ways, such as carrier attachment. Theimmobilized microorganism technology can increase the bacteria concentration inlimited volume, enhance microbial tolerance to adverse environment, improve theefficiency of oily wastewater treatment and realize reuse of microorganisms. Atpresent, this technology has been widely used in the refractory organic wastewatertreatment, but its application in the wastewater treatment is still at a preliminary stage.In this study, the biological treatment process of oily wastewater was researched.In order to determine the optimal embedding material, the surfactant producing abilityand oil biodegradation efficiency of immobilized biosurfactant producing bacteriaBbai-1using sodium alginate immobilization method and PVA immobilizationmethod were compared. The compound bacteria of Bbai-1and hydrocarbon degradingbacteria were immobilized to treat oily wastewater. The main conclusions are listed asfollows:(1) The optimal conditions of surfactant production and oil degradation of Bbai-1were as follows:3%(v/v) of initial inoculum,2g/L of crude oil,25℃of temperature,1.5%of salinity,7of pH,7d of incubation time. Under these conditions, Surfacetension of medium was reduced to37mN/m, and oil degradation rate of Bbai-1was21%.(2) The comparison of the mass transfer experiments and scanning electronmicrograph (SEM) images of sodium alginate immobilized microorganisms beads(SA IMB) and sodium alginate-activated carbon immobilized microorganisms beads (SA-AC IMB), indicated that SA-AC IBM was more suitable for microbial growthand reproduction.(3) Four major immobilized factors of SA-AC IBM and PVA IBM wereinvestigated by orthogonal test. The optimal preparation conditions of SA-AC IBMwere as follows:3.5%(w/v) of alginate,0.5%(w/v) of activated carbon,4×10~7cell/mL of seed bacteria content and24h of cross-linking time. Surface tension ofalginate immobilized Bbai-1was reduced to32mN/m and oil degradation rate ofalginate immobilized Bbai-1reached37%, which were obviously better than freeBbai-1. The optimal preparation conditions of PVA IBM were as follows:7%(w/v) ofPVA,1%(w/v) of alginate,4%(w/v) of boric acid,6~7of boric acid pH,1%(w/v) ofCaCl2,4×10~7cell/mL of seed bacteria content,18h of crosslinking time,4℃ofcrosslinking temperature. Surface tension of PVA immobilized Bbai-1was reduced to34mN/m and oil degradation rate of PVA immobilized Bbai-1reached30%. Thecomparation of SEM and microsphere properties of SA-CA IBM and PVA IBM,indicated that SA–CA IBM was better for microorganisms growing.(4) The conditions of biosurfactant production and oil degradation for SA–CAIBM were optimized to be24h of activation time,20%(v/v) of the inoculum size,5dof incubation time,25℃~30℃of temperature,15g/L~25g/L of salinity,6~8of pH.Compared with free Bbai-1, the biosurfactant production and oil degradation ofimmobilized ones were significantly increased.(5) For the purpose of sweage treatment, biosurfactant producing bacteria Bbai-1and hydrocarbon degrading bacteria N-series were compounded with the ratio of1:1.The optimum conditions of oil degradation of compound bacteria were as follows:3g/L of crude oil,20℃~30℃of temperature,7~8of pH,25g/L~35g/L of salinity,15%of inoculum size. The comparison of oil degradation rate of free or immobilizedBbai-1、N-series and compound bacteria, indicated that Bbai-1could facilitate the oildegradation of N series. So it is feasible for biosurfactant producing bacteria in situsynthesis biosurfactants to facilitate crude oil biodegradation in oil degradationsystem.(6) In this paper, a low-cost semi-coke was used as the adsorbent material ofalginate IBM instead of activated carbon. Adsorption capacity of activated carbon andsemi-coke, the mass transfer of the microspheres and oil degradation rate werecompared. Results showed that the maximum adsorption capacity of activated carbon and semi-coke to bacteria was18.2×10~8cell/g and6.5×10~8cell/g respectively. Oildegradation rate of alginate-activated carbon IBM and alginate-semi-coke IBM canreach51.2%and43.4%respectively. SEM images showed that immobilized bacteriagrew well in the alginate-semi-coke IM.