Combined Remediation Effect Of Plant With Microorganisms In Pahs-Contaminated Soils

The environment problems are more and more severe along with high-speed economic development. Soil pollution remendiation has become an important issue in the environment field. Polycyclic aromatic hydrocarbons are kinds of aromatic compound. They are persistent due to their recalcitrance to microbial degradation, high hydrophobicity, and ability to be absorbed strongly to soil particles. The partial breakdown products of PAHs degradation have toxic, mutagenic, and carcinogenic properties, and thus remediation is of great importance. Bioremediation is a promising alternative approaches to soil remediation due to its convenience, cost effectiveness and environmental acceptability. In this dissertation, the uptake, accumulation and translocation behavior of PAHs in plants was investigated using pot experiments with PAHs-contaminated soils. Based on the above results, the combined-remediation effect of legumes inoculated with rhizobium was investigated. The main results are summarized below.Phytoremediation for soil PAHs with several legumes and grasses was investigated using a greenhouse study. The results indicated that eight plant species had different role in PAHs degradation and removal in soil after 90 days. The removal rates of alfalfa and perennial ryegrass were 48.4%,46.8%, respectively, and the biodegradation efficiency of 3-ring PAHs was high than that of 4-ring,5-ring and 6-ring PAHs. The plant species tested showed different capability in PAHs uptake, accumulation and translocation from soils. Bioconcentration factors (BCFs) of alfalfa and perennial ryegrass were 0.096 and 0.085, but their phytoextraction rates were only 0.017% and 0.013%. So alfalfa and perennial ryegrassthe have good rhizoremediation potential in PAH-contaminated soil.In order to further study combined bioremediation of plant with microorganisms for PAHs contaminated soil, we used four alfalfa genotypes inoculated with Rhizobium to remediate PAHs contaminated soil by a greenhouse pot experiment. The results showed that after 90 days the PAH degradation rate in the Rhizobium treatment was 35%; Planting alfalfa treatments caused 32%-53% of PAHs degradation rate in soil, and the degradation of PAHs for the combined-remediation treatment in soil was 54%-66%. Therefore, alfalfa inoculated with rhizobium treatment also had the highest BCFs and phytoextraction rates for PAHs from soils.In this paper, soil microbial ecological effect was evaluated after combined remediation by alfalfa inoculated with rhizobium in 90 days. Soil FDA hydrolysis activity, dehydrogenase activity, microbial biomass carbon and PAHs degration bacteria counts in soils were determined. The result showed that soil enzyme activities, microbial biomass carbon, PAHs degration bacteria counts in the alfalfa rhizobium combined-remediation treatment were significantly higher than those of other treatments after 90 days. The diversity of microbial communities in soils was analyzed by the Biolog method. The microbial communities in the treatments were different in richness and evenness. Genetic diversity of microbial communities in soils was analyzed by the PCR-DGGE method, it was found that the alfalfa inoculated with rhizobium combined-remediation treatment significantly affected soil microbial community diversity.