| Polycyclic aromatic hydrocarbons (PAHs), mainly formed from the incombustion of fossil fuels and biomass, are a typical persistent organic pollutants (POPs) in the environment. A large number of PAHs were emitted into environments as the development of modern industry and agriculture, and eventually accumulated in the soil, which cause serious soil PAHs pollution, and hence impose a great threat on agricultural production, human health, and terrestrial ecosystems safety. The control and remediation of PAHs-contaminanted soil have become one of the hot field in the fields of environmental science and soil chemistry. Microbial degradation is the fundamental way for PAHs dissipation in contaminated soil, and immobilized technology is an important technique for bioaugmentation, which displayed a great potential for soil remediation. Based on a brief summary of soil PAHs pollution status and main remediation technology, the dissertation give a detailed review on the mechanisms, developmental status, future trend and key problem of immobilized-microorganism technology in soil remediation. In the dissertation, fresh plant residues and biochar were selected as two type of immobilized carrier, and B1 (Pseudomonas putida purcased from china general microbiological culture collection center) and B2 (bacteria isolated from PAHs-contaminated soil used in the study) were selected as model of microorganism. The enhanced remediation of actual PAHs-contaminated soil by immbobilized B1 and B2 with plant residues and biochar as carrier were studied. The sorption of PAHs to plant residues and their structure-effect relationships were investigated, and the effects of using plant residues and their extracts as carbon sources for stimulating PAHs dissipation by microorganism were evaluated. Impacts of biochar produced under a series of temperature on PAHs sorption to soil were investigated. B1 and B2 were immobilized with plant residues and biochar, the sorption-degradation of PAHs by these immbolized bacteria were studied at solution system, and the remediation of 16 PAHs in sewage irrigated soil in Shengyang, China by these immbolized bacteria were studied. The observations in this work will offer a theoretical gist for developing an economic, high efficiency, and environmentally-friendly technology for remediation of soil contaminated with organic pollutants. The main original conclusions of this work are drawn as follows.(1) The sorption of PAHs to plant residues and their structure-effect relationships were studied, and the effects of plant residues and their extract on PAHs dissipation were investigated, the sorption-degradation of PAHs by immobilized B1 and B2 with plant residues as carrier were illustrated. Partition effects is the dominant mechanism for PAHs sorption by plant residues, and the magnitude of phenanthrene partition coefficients (Kp, mL/g) followed in the order of wood chip (2484±24.24)< ryegrass root (2777±58.62)< orange peel (2970±39.80)< bamboo leave (3746±96.54)< pine needle (5306±92.49). Except wood chip sample, the Kp value of phenanthrene sorption by other four plant residues were positively correlated with aromaticity (H/C), while negatively correlated with polarity [(O+N)/C] and sugar content of the biosorbents. The carbon-normalized partition coefficients (Koc) for PAHs sorption to bamboo leave were linearly correlated with octanol-water partition coefficients (Kow) of PAHs. Plant extract could stimulate the sorption-degradation of PAHs by bacteria, in which orange peel extract exhibited the highest effeciency for stimulating PAHs degradation by bacteria B1 at solution system, while bamboo leave extract was the best one to enhance PAHs degradation by bacteria B2. Fresh plant residus displayed positive effects on PAHs dissipation in the contaminated soil. Amended with 1% plant residues, PAHs removal were increased by 15-20% of 2-ring, 20-39% of 3-ring,14-24% of 4-ring,12-23% of 5-ring, and 17-26% of 6-ring PAHs. Bamboo leaves exhibited the most effective one, which is mainly attributed to its flavonoids and phenolics rich property. Sorption is an important process for PAHs removal from water by immobilized-bacteria. The sorbed-PAHs were available to immobilized-bacteria, and the degradation of sorbed-PAHs by immobilized-bacteria with wood chip and orange peel as carrier immobilized were stronger than those with bamboo leaves and pine needle.(2) Impacts of biochar on PAHs sorption by soil were studied, the sorption-degradation of PAHs by immobilized-bacteria with biochar as carrier were evaluated. Biochar produced under higher pyrolytic temperature exhibited higher sorption affinity with PAHs. The sorption isotherms of PAHs to P100 were linear, and the nonlinearity and sorption capacity were increased with the increase of pyrolytic temperatures for biochar. P100 added to soil increased the linearity of sorption isotherm due to the linear-type isotherm of P100. While the nonlinearity of sorption isotherm for P300, P400, P700 amended soil were increased with the increase of biochar content in soil. Biochar produced under high pyrolytic temperature demonstrated high efficiency in improving the sorption affinity of biochar-amended soil, and the total sorption were largely controlled by biochar when P300 content was larger than 0.5%, and P400 and P700 content above 0.1%. The predicted sorption of soil amended with P100 and P300 was consistent with their experimental values. However, for P400 and P700 amended soil, the actual sorption were lower than the predicted at low PAHs concentration. Sorption is an important process for PAHs removal from water by the immobilized-bacteria. The sorbed-PAHs were available to the immobilized-bacteria, and the degradation of sorbed-PAHs by P400 immobilized bacteria showed higher effeciency than immobilized-bacteria with P100, P300, P700 as carrier. The extractable phenanthrene and pyrene on P400 immobilized-B2 were decreased by 23%,15% as compared to phenanthrene, pyrene on P400 immobilized particle without bacteria.(3) Immobilized-bacteria were amended into sewage irrigated soil in Shenyang, China for PAHs remediation. Immobilized-carrier could stimulate PAHs degradation by indigenous microorganism as well as immobilized bacteria, and the biochar is a more excellent immobilized carrier than plant residues. P700 immobilized-bacteria were the most effctive one. At 90 days of inoculation, the recovery of 3,4,5,6 ring PAHs in soil amended with P700 immobilized-bacteria were decreased by 24%,22%,24%,38% as compared to no immobilized-bacteria amended soil. The high efficiency of P700 immobilized-bacteria for soil remediaotion may be attribute to its high PAHs sorption affinity. |
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