Research On Immobilization Of Polycyclic Aromatic Hydrocarbons Degrading Bacteria And The Degradation Characteristics Of Pahs By Immobilization Strains

Polycyclic Aromatic Hydrocarbons?PAHs?,a group of hardly degradable aromatic persistent organic pollutants,have“three-induced effects?carcinogenic,teratogenic and mutagenic?”,biomagnify as they move up through the food chain,and persistent in the environment for long period of time.These compounds are widely occurring in the environment via many ways,they are formed during combustion of fossil fuels and biomass fuels,incineration of waste,emission of“three wastes”,processing and production processes of steel?coking?and other petrochemical industry,transportation,petroleum spills and leakages as a result of anthropogenic sources.PAHs pose potential threats to human health and ecological environment,and they are one of the most important pollutants among the environmental research fields.In the paper,phenanthrene,fluoranthene and pyrene were selected as target PAHs compounds to acclimate PAHs-degrading bacteria,the physicochemical characteristics and molecular biology identification of the PAHs-degrading strain were carried out.Taking polyvinyl alcohol,sodium alginate and nano Alumina,as embedding carrier,were used to make embedded immobilized bacteria.Based on the apparent characteristics and physicochemical properties of the embedding beads,the degradation characteristics of target compound PAHs by bacterial suspension and embedding beads were compared,respectively.And the embedding beads was explored for the degradation of PAHs in contaminated soil washing effluent.The experimental results could give basic data and theoretical support for PAHs pollution restoration research about wastewater.The main contents and conclusions of the paper are listed as follows:Experimental study on the acclimation and identification of PAHs degrading strain.Taking phenanthrene,fluoranthene and pyrene as target pollutants,three target PAHs were used to acclimate the strain which was purified and isolated previously,and had good capability of degradation to phenanthrene and fluoranthene.For the purified strain?named S?,a series of experiments were conducted to analysize its morphological observation,growth curve determination,physiological and biochemical characteristics identification,16S rDNA preliminary identification and phylogenetic tree construction.Preparation,optimization and physicochemical properties analysis of embedding beads were studied.Polyvinyl alcohol?PVA?,sodium alginate?SA?and nano-alumina?ALNPs?were used as the embedding materials.Boron-CaCl₂ cross-linking method was used to immobilize the bacteria S to prepare embedded beads.The single factor experiments were conducted to compare the apparent characteristics,mass transfer properties and the effect of PAHs degradation of embedding beads which were added PVA,SA and ALNPs with different volume fraction,it was used to optimize the ratio of the embedding material.The results showed that the optimal material ratio of PVA,SA and ALNPs were:10%,0.8%,and 0.7%,respectively.The optimized prepared embedding beads were white with an average particle size of about 3 mm,they had good mechanical strength and mass transfer properties.The embedding beads provided a lot of effective contact and attached specific surface area for microorganisms,and the presence of voids and crevices in the beads were conducive to interception of microorganisms and the protection of microorganisms from the hydraulic disturbances and flushing.Experiments were conducted to study the degradation characteristics of bacterial suspension and embedding beads to PAHs.Comparative degradation experiments were conducted to explore the degradation of phenanthrene,fluoranthene and pyrene by strains suspension at the intersection between logarithmic phase and stationary phase and optimized embedding beads in mineral salt medium.The results showed that within15 days,the degradation efficiency of phenanthrene,fluoranthene and pyrene by embedding beads were 86.50%,83.65%and 80.90%,respectively.Compared with the bacterial suspension,the degradation efficiency of phenanthrene,fluoranthene and fluorene by embedding beads increased by 15.90%,21.75%and 22.80%,respectively.The effects of bacterial suspension and embedding beads on PAHs in soil washing effluent were preliminarily discussed.Non-ionic surfactant Tween 80 was choosed as the eluent,which was used to study the soil washing process of phenanthrene,fluoranthene and pyrene spiked soil,and the soil washing effluent was obtained.The bacterial suspension and embedding beads were transferred to the effluent,and the residual concentrations of phenanthrene,fluoranthene and pyrene in the effluent were determined by sampling.Three target PAHs degradation efficiency in soil washing effluent by bacterial suspension and embedding beads were compared under the experimental conditions.The degradation efficiency of phenanthrene,fluoranthene and pyrene by embedding beads were 89.14%,81.25%and 78.33%,respectively.Compared with the bacterial suspension,the degradation efficiency of phenanthrene,fluoranthene and fluorene by embedding beads increased by 15.91%,17.07%and 19.08%,respectively.The research work was financially supported by the National Natural Science Foundation of China?41101457?.In the study,the degradation characteristics of phenanthrene,fluoranthene and pyrene in mineral salt medium were discussed,and the bio-enhancement of PAHs in soil washing effluent by bacterial suspension and embedding beads were compared and analyzed.It was innovative in the optimization of the method for preparing embedding beads and the biodegradation of PAHs in soil washing effluent by embedding beads,which were not similar reports about the contents of this research within the same section.The results of this paper will provide theoretical support for the in-depth exploration of the immobilized microbial technology in the bioremediation process in PAHs compound pollution environment,and also broaden the research direction to removal of PAHs in soil washing effluent.