Degradation Of Polycyclic Aromatic Hydrocarbons In Soil During Composting By Inoculating Bacteria In Different Period

Polycyclic aromatic hydrocarbons(PAHs)are a kind of hydrophobic aromatic pollutants that persist in the environment.They are listed as the main object of environmental pollution control because of their refractory,carcinogenic,teratogenic,and mutagenic characteristics.Organic solid waste composting is an environment-friendly bioremediation method.In this paper,leaves,cow manure combined with phenanthrene(Phe),fluoranthene(Fla),and benzopyrene(Ba P)were used as compost materials for composting,and Comamonas testosteroni(C.t)was used as an exogenous bacterial agent to establish a laboratory simulated composting system.The content of PAHs,relevant physicochemical indexes,and enzyme activities in the composting process was measured.The changes in microbial diversity and community structure were analyzed by highthroughput sequencing technology,and the functional genes were quantified by fluorescence quantitative PCR.The effects of types of organic solid wastes and bacterial inoculation methods on the degradation of PAHs were studied,and the remediation effect of rotten fertilizers obtained from different composting treatments on PAHs contaminated soil was explored.0.8 % C.t was inoculated to the simulated composting system in the heating stage(0d),cooling stage(25 d),or in two stages(0 d and 25 d),respectively.CM and LW composting were divided into four treatments: without inoculation(K),inoculation in the heating period(R),inoculation in the cooling period(C),and inoculation in both the heating and cooling period(RC).The p H value,organic matter(OM),soluble amino acid(AA),and soluble sugar(SS)were significantly changed during composting.The change of physicochemical indexes in the CM group after the addition of bacteria C.t was generally 14?15 days after inoculation,while in the LW group was 25?30 days after inoculation.Overall,the R treatment and C treatment have a better transformation effect on the organic component.R treatment can accelerate the decomposition and utilization of AA,SS,and OM by microorganisms in the early stage,while the C treatment can promote the decomposition and utilization of refractory substances in the later stage.The content of PAHs in different treatment groups was detected by gas chromatography-mass spectrometry(GC-MS).At the end of composting,the degradation rates of Phe,Fla,and Ba P in all treatment groups were more than 70 %,46 %,and 36 %respectively,and the highest were 90.13 %,68.55 %,and 52.46 %.The degradation rates of PAHs in each inoculation treatment group(R,RC,and C)were higher than those in K.The activities of dehydrogenase(DHA),urease(Ur),laccase(Lac),catechol dioxygenase(C12O,C23O)and polyphenol oxidase(PPO)in the composting process were detected.It was found that most of the enzyme activities were inhibited when the initial PAHs content was high,while inoculation would increase some enzyme activities which was adapted to the pollution degree of PAHs.Lac activity played an important role in the CM group for PAHs degradation,while DHA activity was related to PAHs degradation in the LW group.The R treatment group of CM and the C treatment group of LW had the best degradation effect on total PAHs.High throughput sequencing technology was used to detect the microbial community structure of each treatment group at 0 d,14 d,25 d,40 d,and 55 d of composting.It was found that the bacteria in CM and LW groups came from 23 phyla.The inoculation of C.t and the promotion of composting changed the microbial community structure in the composting system promoted the succession of microorganisms and improved the richness and diversity of species.Through quantitative analysis of 16 S r RNA,3?-hydroxy steroid dehydrogenase coding gene(3?-HSD),catechol dioxygenase coding gene(C12O,C23O),and phenol hydroxylase coding gene(Phe1)by q PCR,it is found that inoculation will increase the abundance of 3?-HSD and Phe1.In the CM group,the gene abundance of 3?-HSD and Phe1 in the CR and CC treatment group was higher than that in CRC,while in LW,LRC played a stronger role.In addition,LR significantly increased the relative abundance of C23 O.The inoculation of exogenous bacterial changes the correlation between bacteria and various indexes in the system.Finally,CR treatment in the CM group had the best degradation effect on Fla and Ba P,while the CRC treatment group had the best degradation effect on Phe.In the LW group,the bacteria with synergistic degradation of Phe and Fla are formed,which makes LC have the highest degradation efficiency of Phe and Fla,while Ba P is similar in each inoculated group.Eight kinds of rotten fertilizers obtained from bacterial-inoculated composting of different materials in different periods were applied to PAHs contaminated soil respectively.They were divided into cattle manure(M)group and leaf waste(W)group according to the source of compost group.The treatment used K,R,RC,and C of compost,and set up natural attenuation(NA)treatment group.After being cultured at 28 ? for 30 days,the content of PAHs was measured.In general,the addition of rotten fertilizer changes the p H of PAHs in contaminated soil,improves the activity of a variety of soil enzymes,and promotes the degradation of PAHs,especially Ba P.After 30 days of culture,the degradation rates of Phe,Fla,and Ba P were the highest in WRC,MC,and MR treatment groups,arrive 78.19 %,71.24 %,and 73.04 % respectively.In summary,this study established the remediation system of PAHs contaminated soil by inoculated composting of two materials in different periods,provided a C.t inoculation mode with a better effect on PAHs degradation by composting of different materials,analyzed the changes of relevant physicochemical properties in different composting systems and the response of soil enzyme activities and genes to PAHs,and explored the potential mechanism of PAHs degradation by C.t in composting.This study also simulated the return of rotten fertilizer to the field in the laboratory to explore the remediation effect of rotten fertilizer obtained in different ways on PAHs contaminated soil,to provide a more practical composting scheme for the remediation of PAHs contaminated soil.The C.t in this study widely exists in nature.Three kinds of representative PAHs were selected to simulate the soil PAHs pollution in Northeast China.This study is expected to provide some ideas and a theoretical basis for the remediation of PAHs contaminated soil in Northeast China.