| With the rapid increase in offshore oil transportation and oil exploitation, marineoil spill accidents have continued to increase. Oil spill poses great threats and it hasbecome one of the most serious marine ecological disasters. Boremediation, whichhas many advantages such as less secondary pollution and low-cost, has become aimportant method to remove petroleum hydrocarbon pollution in oil-spilled shorelineand intertial zone. What’s more, adding hydrocarbon degrading bacteria, nutrient andsurfactant have become important technical means to strengthen the remediation. Butin the process of oil spill remediation, these bioremediation agents are more likely tobe washed out by the wave action. Therefore, these bioremediation agents not onlycan not promote the degradation of oil pollutants, more seriously, it may cause localseawater eutrophication and lead to secondary pollution.In order to solve the limitation of bioremediation agents in the application of oilspill, especially in the rapid loss of nutrient and sufactant in the marine environment.In this research, the aim is focused on preparing a comprehensive bioremediationagent. It is obtained by appropriate match of three kinds of substances, i.e., microbe,nutrient and biosurfactant. The product’s density is less than the seawater and it is amicrocapsule with lipophilic surface. The comprehensive bioremediation agent cannot only float in the seawater surface and adsorpt in the oil spill, but also releaseslowly nutrients and biosurfactants, which making oil emulsification and dispersion.What’s more, it can provide a long adequate nutrition agent for petroleumhydrocarbon degrading bacteria. In this research, we started form the compatibility ofhydrocarbon degrading bacteria, nutrients and biosurfactants. The role ofbiosurfactant and nutrient in promoting the degradation of crude oil were explored,that providing a theoretical basis for the three mixed-embedded. After that, we developed the “three-in-one” microcapsule comprehensive bioremediation agent. Bythe outdoor oil spill simulation test, the effect of the comprehensive bioremediationagent in the oil spill was investigated. The simulation test provides technical supportfor field application of bioremediation of marine oil spill.This study mainly includes three parts, which are briefly introduced as follows:1. The choice of oil-degrading bacteria, biosurfactants and nutrients in oill spillbioremediation agent and research on the compatibility with each otherWith octadecane and QHD32-6FPSO crude oil as sole carbon source,respectively, rescreening and identification of oil degrading bacteria. The antibacterialactivity of rhamnolipid was studied by disk diffusion method. We also researched theeffect of water-soluble organic nutrients on the growth of bacteria. The results showedthat three consortiums, named as PS-1, TJ-2and O-1-1were enriched through acontinuous enrichment screening. The strains were identified as Pseudomonasaeruginosa, Acinetobacter venetianus and Bacillus cereus. The rhamnolipid did notproduce inhibitory effect on these three bacteria in the range of500mg/L.Water-soluble organic nitrogen sources and phosphorus sources were able toeffectively promote the growth of three bacteria. So we choosed the threehydrocarbon degrading bacteria, rhamnolipid, yeast and glycerophosphate as theingredients of “three-in-one” microcapsules comprehensive bioremediation agent,they played the role of providing bacteria, emulsifier and nutritional agents,respectively.Further studies showed that the effect of rhamnolipid on degradation ofoctadecane by P. aeruginosa PS-1, A. venetianus TJ-2, B. cereus O-1-1was found tobe dependent on rhamnolipid concentration and bacteria species. When rhamnolipidconcentration below the critical micelle concentration(CMC), rhamnolipid increasedthe rate of hydrocarbon biodegradation in two ways: increasing solubilization anddispersion of the hydrocarbon and increasing in cell surface hydrophobicity. Whenrhamnolipid concentration above the critical micelle concentration(CMC),rhamnolipid increased the rate of hydrocarbon biodegradation in two ways: increasingthe aqueous dispersion of octadecane by micellar solubilization, being utilization as a co-metabolic substrates by A. venetianus TJ-2, B. cereus O-1-1. But higherrhamnolipid concentration i.e.,80mg/L caused an initial inhibition onbiodegration of octadecane because of utilization of rhamnolipids prior tooctadecane by P. aeruginosa PS-1.2. Preparation of “three-in-one”comprehensive oil spill bioremediation agentbased on the microencapsulation technologyIn this paper, solium alginate was used as microcapsule wall material, differentcharacteristics such as diameter, embedding rate, loading capability and releaseprofiles were evaluated to compare the applicability of microcapsule bioremediationagent. Differet methods including piercing-solidifying method and water-in-oil weretried to prepare the comprehensive bioremediation agent. The results showed that,the method of water-in-oil method had a lower embedding rate of nitrogen andphosphorus, only1.6%and13%, respectively. But the prepared microcapsule usingmethod of piercing-solidifying method with300μm aperture had the betterperformance, the mean diameter of alginate microspheres was3mm, with a goodspherality. The nitrogen and phosphorus embedding rate were98%and38%(w/w),respectively. The nitrogen and phosphorus loading capability were8.5%and3.6%(w/w), respectively. Sustained release of nutrients can be maintained24h. All of thatmeet the initial requirements of the oil spill bioremediation agent.3. Effect of comprehensive bioremediation agent on biodegradation water-sufaceoil spillThe the effect of comprehensive bioremediation agent on enhancing oil-spillseawater biodegradation was evaluated through outdoor oil spill simulationexperiments, and the untreated experimental plot is treated as control system. Theresult showed that, in14d repair time, compared with the control system, nutrientscontent in bioremediation agents system were much higher than control system.C/N/P (w/w) content was200:10:1and that can meet the needs of the oil degradingbacteria on nutrients. The total number of heterotrophic bacteria and oil-degradingbacteria in comprehensive bioremediation agent system is twice as many as controlsystems’. In comprehensive bioremediation agent system, the total petroleum hydrocarbon degradation rate was31%, increasing by11%compared with the contorl.The total alkane degradation rate was80.6%, total aromatics degradation rate reachedto60.4%, increasing by19%and9.8%, respectively, compared with the contorlsystem. |
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