Bioremediation Of Marine Oil Spill By Embedded Immobilized Bacterial-microalgae Consortia

After marine oil spills, residual petroleum hydrocarbon can last long-term in the marine environment, which not only cause huge persistent damage to marine ecosystems,and also threaten human health seriously. The restoration of marine oil spill environment is extremely urgent to be done. The bioremediation technique processing marine oil spill has become a hot research spot both in domestic and abroad. But these problems, to avoid the microorganism erosion in the marine environment, improve the efficiency of microbial degradation and tolerability, are still bottlenecks need to be overcame. The application of immobilized microorganism technology can solve these problems. The immobilized bacterial-microalgae consortia were used to degrade the crude oil in this thesis, in order to provide theoretical basis and technical support for the field application and promotion of marine oil spill bioremediation.In this thesis, petroleum hydrocarbon degradation bacteria strains were isolated from seawater polluted by crude oil, and a high efficient petroleum hydrocarbon degradation bacteria consortium was built. Then the bacterial-microalgae consortia were constructed with the bacterial consortium and petroleum-degrading microalgae. After that bacteria consortium, microalgae and bacterial-microalgae consortia were embedded immobilized,respectively. The environmental conditions(crude oil concentration, salinity, pH,temperature, and the degradation time) for the hydrocarbon degradation were optimized. At optimal degradation conditions, 6 microbial groups' degradation characteristics of petroleum hydrocarbons were evaluated. In the last part of the paper, degradation properties of crude oil by embedded immobilized bacterial-microalgae consortia were observed in the simulated marine environment. The main conclusions obtained as follows.(1) Five bacteria strains and one microalgae were isolated, and identified as Exiguobacterium sp.(Exiguobacterium sp.ASW-1), Pseudomonas aeruginosa(Pseudomonas aeruginosa ASW-2), Alcaligenes sp.(Alcaligenes sp. ASW-3,Alcaligenes sp. ASS-1), Bacillus sp.(Bacillus sp.ASS-2) and Chlorejla vulgaris(Chlorejla vulgaris LH-1), respectively. The best mixing ratio of bacteria consortium is ASW-1:ASW-2: ASW-3: ASS-1: ASS-2=1:1:1:1:1. The best mixing ratio of bacterial-microalgae consortia is bacteria consortium: LH-1=1:2. Under the optimum conditions, the crude oil degradation rate of the bacteria consortium, LH-1 and bacterial-microalgae consortia reached 60.39%, 30.72% and 68.94%. The crude oil degradation products were detected by GC/MS. The results showed that the n-anlkanes(C12-C32) degradation rates of free bacteria consortium and bacterial-microalgae consortia were 53.50% and 78.73%, and the 16 typical PAHs degradation rates of them were 40.62% and 48.70%. And there was no diffirence for free microalgae degrade n-anlkanes and 16 typical PAHs, the degration rates were both about 33%.(2) Sodium alginate-activated carbon-CaCl2 was used as embedded immobilization support material. The optimal preparation conditions of sodium alginate, activated carbon and CaCl2 were as follows: 2.5%(w/v) of alginate, 0.5%(w/v) of activated carbon, 3%(w/v) of CaCl2 and 24 h of cross-linking time. Under the optimum conditions, the crude oil degradation rates of the embedded immobilized bacteria consortium, LH-1 and bacterial-microalgae consortia reached 67.03%, 37.34% and 73.96%, were higher than free microorganism'. The results of crude oil degradation products showed that embedded immobilized microorganism could degrade n-anlkanes(C12-C32) better than free microorganism. And there was a bit improvement of degrading 16 typical PAHs.(3) The effects of concentration of crude oil, salinity, pH, temperature and degradation days on crude oil degradation by petroleum hydrocarbon degradation microorganism were observed. The results indicated that whether bacterial-microalgae consortia were embedded immobilized or not, they can withstand a wider range of environment conditions than bacteria consortium and LH-1 do. And environmental factors on the embedded immobilized bacteria consortium, LH-1 and bacterial-microalgae consortia have less effect than the situation without embedded immobilized.(4) The results of the indoor simulation experiment indicated that immobilized bacterial-microalgae consortia have a significant increase in degradation efficiency of crude oil, in the indoor simulation experiment conditions. The degradation efficiency of crude oil by immobilized bacterial-microalgae consortia increases with time goes on. In particular, the degradation rate dramatically increased in the first seven days of the experimental stage, and reached about 50%.