Construction Of PAHs-degrading Microecological Bacteria Flora And Its Biodegradation To Phenanthrene And Pyrene

Polycyclic aromatic hydrocarbons(PAHs),as a kind of typical persistent organic pollutants,are widely present in environmental media such as soil,sediments,and water bodies,with the characteristics of high toxicity,difficult biodegradation and high bioaccumulation.Microbial remediation has become the most promising PAHs pollution remediation technology due to its safety,eco-friendliness and economy.The environmental conditions of PAHs contaminated sites vary greatly over time and space,and PAHs often exist as a mixture,which hinders the continuous and efficient in situ bioremediation process.Therefore,the construction of highly efficient and compatible microecological bacteria flora and the study of PAHs biodegradation characteristics and mechanisms are of great significance for the in situ bioremediation of PAHs contaminated sites.In this paper,activated sludge from coking wastewater treatment plant was used as the initial source of bacteria,catechol,salicylic acid and phthalic acid were selected as the typical intermediate metabolites of PAHs,and phenanthrene and pyrene were selected as the target pollutants.The collaborative acclimation pattern of “intermediate metabolites – target pollutants” was used to acclimate the initial bacteria source to construct PAHs-degrading microecological bacterial flora(MBF)with high activity and compatibility,and then the flora was identified.On this basis,the effects of different initial pollutant concentrations and different environmental conditions(temperature,p H value and salinity)on the degradation of phenanthrene and pyrene by the microecological flora were investigated to explore the adaptability of the microecological bacteria flora to changes in environmental factors.Besides,the cometabolism substrates(benzene,xylene,catechol,salicylic acid,phthalic acid)were further added to study the effects of co-metabolism substrates on the growth of microecological bacteria flora,biodegradation of phenanthrene and pyrene,and communities during degradation.The results of the study were as follows:(1)16S rRNA sequencing was performed on the bacteria at different stages of acclimation.The analysis results showed that the acclimated bacterial flora with intermediate metabolites added was more evenly distributed.The dominant genera were Enterobacter sp.,Stenotrophomonas sp.,Delftia sp.,Burkholderia-CaballeroniaParaburkholderia sp.,Pseudomonas sp.and Achromobacter sp..After the target pollutants acclimation,the dominant genera was Pseudomonas sp.in MBF.The MBF was well tolerant to phenanthrene and pyrene with concentrations of 25 mg/L –200mg/L.When phenanthrene and pyrene existed alone,the degradation rates of phenanthrene after 5 days of cultivation time were from 56.0% to 99.3%,and the degradation rates of pyrene were from 33.9% to 73.1%.When phenanthrene and pyrene were used as a mixture,the concentrations of 50 mg/L and 100 mg/L of the mixture can promote the degradation of phenanthrene and pyrene by MBF,while the concentrations of 100 mg/L and 200 mg/L of the mixture inhibited the degradation of phenanthrene and pyrene by MBF.(2)The MBF had good adaptability to temperatures(25-35 ℃),p H values(5-8)and salinities((0-3 g/L Na Cl).When the concentration of the mixture of phenanthrene and pyrene was 100 mg/L,the degradation rates of phenanthrene and pyrene were from95.2% to 98.4% and from 60.5% to 76.1%,respectively,after culturing at 25-35 ℃for 5 days.When the p H value was 5-8,the degradation rates of phenanthrene and pyrene were from 96.1% to 97.8% and from 68.1% to 71.9%,respectively.At the salinity of 0-3 g/L Na Cl,the degradation rates of phenanthrene and pyrene were from90.7% to 96.3% and from 62.1% to 68.1%,respectively.There was no significant difference in the microbial community structure of MBF under different environmental factors,which indicated that microbial communities had good adaptability to the changes of temperature,p H value and salinity,and could adjust its own community structure to respond to changes in environmental conditions.(3)Under the conditions of 0.05%(w/v)catechol,salicylic acid,phthalic acid and100 mg/L of the mixture of phenanthrene and pyrene,the degradation rates of phenanthrene on day 5 were 64.6%,91.7%,89.6%,respectively,and the degradation rates of pyrene were 53.5%,68.1% and 71.8%,respectively.Under the coexistence of0.05%(v/v)benzene and xylene and 100 mg/L of the mixture of phenanthrene and pyrene,the degradation rates of phenanthrene on day 5 were 97.6%,96.9%,respectively,and the degradation rates of pyrene were 72.2% and 81.1%,respectively.When the mixture of phenanthrene and pyrene coexisted with catechol,salicylic acid,phthalic acid,benzene,and xylene,the preferred carbon source of MFC is the co-metabolism substrate.(4)16S rRNA sequencing showed that the addition of typical intermediate metabolites of PAHs(catechol,salicylic acid and phthalic acid)and monoaromatic hydrocarbons(benzene and xylene)significantly changed the microbial community structure.The cluster analysis showed that the control group without adding cometabolism substrates during biodegradation was clustered with the MBF.The group(catechol and salicylic acid as the co-metabolism substrates)owned similar microbial community structures and were clustered into one group,and the group with adding phthalic acid became a group.The group(benzene and xylene as the co-metabolism substrates)owned similar microbial community structures and were clustered into one group.There were 30 figures,6 tables,and 162 references in this paper.