| Heavy metals and polycyclic aromatic hydrocarbons(PAHs) are the typical pollutants in contaminated wetland soils. Soils sampled from Longwan port and Longwan fort were analyzed and the results indicated that the concentrations of chromium and pyrene were relatively high and were 104.85 and 93.24 mg kg-1, respectively. Therefore, chromium and pyrene were used as model pollutants for bioremediation research.As an environmental friendly technology, microbial remediation has received more and more attention. In this study, two pyrene degrading bacteria W1 and W2 were isolated from the oil contaminated soils in Longwan port and these two strains were identified as Bacillus with respect to their 16 S rDNA. The proper growth conditions of these two strains were 30 °C, pH 7.0 and 0-1.0% salinity. The highest degradation efficiency of pyrene of strains W1 and W2 were at 30°C, pH 7.0 and pyrene initial concentration of 32 mg L-1. The degradation rates of pyrene by strains W1 and W2 were 70.7% and 65.7%, respectively. However, the degradation of pyrene by these two strains was significantly inhibited under the stress of Cr(VI). In order to improve the degradation rate of pyrene and remove Cr(VI) simultaneously, a consortium consisted with two pyrene degrading bacterial strains(Bacillus sp. W1 and Bacillus sp. W2) and one Cr(VI)-reducing bacterium Microbacterium sp. Y2 was constructed. Antagonism and tolerance assays indicated that the screened bacteria did not have any antagonistic effects and showed tolerance against the mixture of pyrene and Cr(VI). Therefore, these three strains could be mixed together as a consortium. The shake-flask test showed that the consortium W1-W2-Y2 was able to remove pyrene and Cr(VI) effectively and the removal rates of pyrene and Cr(VI) were 46.4% and 40.2%, respectively after 7 days of incubation.However, due to the competition of indigenous microbes, the toxicity of pollutants and the predation by protozoans, the exogenous microorganisms were difficult to survive in contaminated soils and thus the remediation effect was often not satisfied. The immobilization carriers offered a protective niche for inoculated microbes and hence improved exogenous microbes’ survivability. In this study, in order to evaluate the effects of various immobilization carriers and different immobilization strategies on removal of pyrene under the stress of Cr(VI), four types of biochars obtained from pineapple peels(PA), shaddock peels(SD), bagasses(BG) and reed straws(RD) were used for preparing immobilization carriers and a commercial activated carbon(AC) was included as a comparison. The microorganisms were immobilized by two different methods viz. physical adsorption on biochar supports and entrapment in alginate beads with biochar as carrier. The results showed that pyrene degrading strain entrapped in alginate bead with pineapple peels derived biochar as carrier showed the highest removal rate of pyrene and degraded 76% pyrene after 40 days of incubation. In order to further optimized the performance of immobilization carrier, biochars produced at different pyrolysis temperatures(350, 500 and 750°C) were utilized to adsorb pyrene and Cr(VI) in liquid systems. In addition, the influence of alginate concentration on the mechanical property and mass transfer performance of beads was also investigated. The results showed that biochar produced at 750°C had the highest adsorption capacity of pyrene and Cr(VI) and immobilized beads prepared by 5%(w/v) alginate showed excellent mechanical property and mass transfer performance.Finally, The consortium entrapped in alginate beads with pineapple peels derived biochar as carrier was utilized to repair pyrene and Cr(VI) co-contaminated soil. It turned out that addition of alginate embedded consortium with biochar as carrier to soils improved the removal of pyrene and Cr(VI) after 28 days of incubation and the removal rates were 82.32% and 55.64%, respectively. In addition, soil microbial activities and carbon source utilization ability were obviously enhanced when soil added with entrapped consortium. The diversity index and cluster analysis showed that the microbial community function diversity was relatively rich in soils added with entrapped consortium. |
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