Study On The Microbiology Of Rhizosphere Soil Of Landfill Vegetation And The Control Characteristics Of Chlorinated Alkane Pollution

Domestic waste landfill is an important source of greenhouse gas emissions.Volatile chlorinated hydrocarbons(CAHs)are the main pollutants in landfill gas,and their warming potential is hundreds of times that of carbon dioxide.Therefore,researchs on CAHs emission reduction need to be carried out urgently.Vegetation is a good in situ bioremediation medium,which can provide a good growth environment for microorganisms,at the same time,the compounds secreted by vegetation roots can cooperate with microorganisms to degrade toxic and harmful gases such as methane and chlorinated alkanes by biological oxidation.At present,the vegetation types involved in the overburden are diverse,but little research has been reported on soil microhabitat information and bio-oxidation characteristics of the root systems of different vegetation.Carrying out relevant researchs is of great significance to improve the micro ecological information of landfill vegetation,optimize suitable vegetation,strengthen the degradation of landfill pollutants,reduce landfill carbon emissions,and realize China's"double carbon"strategy.Based on these,the paper conducted a study on the microbiology of rhizosphere soil of landfill vegetation and the control of typical chlorinated alkane pollution.The main conclusions are as follows:(1)The characteristics of plant community structure in the overburden of a landfill in Chongqing were investigated,and the species of indigenous vegetation and the composition of rhizosphere microbial community in the landfill were clarified.(1)Herbaceous plants are the dominant vegetation in the overburden,and the microbial diversity of the vegetation cover area was significantly higher than that of the bare soil.(2)Under vegetation cover,the microbial growth environments(e.g.,water content,p H,and CAHs content)in the inter-root zone are altered.Compared to that under no vegetation cover,the activities and diversities of functional microorganisms are significantly enhanced.(3)In total,more than 18 phyla of microorganisms were detected in soil samples from all different vegetation root systems,and the dominant phyla were Proteobacteria,Acidobacteriota,Chloroflexi,Actinobacteria,Gemmatimonadota and Bacteroidota.(2)Microbial diversity sequencing analysis and metabolomics technology analysis were conducted to explore the microbial community structure and metabolite characteristics at different root depths.(1)The relative abundance of three functional microorganisms in the inter-root soil of different vegetation basically showed the pattern of Proteobacteria>Acidobacteria>Firmicutes,among which the relative abundance of Proteobacteria and Acidobacteria did not differ significantly at different vegetation depths,while the relative abundance of Firmicutes was highest only at 15 cm and 20 cm of mugwort and 20 cm of acid mold.It can be inferred that mugwort and acid mold could effectively enhance the activity of Firmicutes and facilitate their survival in the anoxic layer.(2)A comparative analysis of the metabolites of the four vegetation root soils revealed that the abundance of cinnamic acid was significantly higher in the root soils of the structural tree than in the other three vegetation root soil samples.Cinnamic acid belongs to the aromatic organic acids and can be consumed by inter-root bacteria easily,thus promoting the growth of root microorganisms,and the structural tree root environment can significantly influence the inter-root environment for biological activity.(3)A static batch experiment was used to investigate the sorption transformation characteristics of chlorinated alkanes in vegetated rhizosphere soil.(1)In this study,the equilibrium concentration and equilibrium sorption of three chlorinated alkanes were found to be non-linear in 11 vegetation rhizosphere soils,including bare soil,Amaranthus spinosus L.and Cassia tora Linn,by isothermal sorption kinetic fitting,and the sorption isotherms were in accordance with the Freundlich model(R²=0.6753?0.9999).The isothermal sorption lines in rhizospheric soils of Eleusine indica,Capsicum annuum L.,Cyperus glomeratus L.,Oryza sativa L.and Phragmites australis were in accordance with the Langmuir model(R²=0.4236?0.9704).(2)Compared with bare soil,vegetated rhizospheric soil had higher pollution sorption capacity,and the sorption rates of chlorinated alkanes in vegetated root soil varied from 0.01?1.92?g·kg^-1_soil·h^-1 and 0.15?0.43?g·kg^-1_soil·h^-1 in bare soil,which was much greater than the degradation of chlorinated alkanes by mulched soil reported in the literature rate.(4)The biooxidation efficiency of chlorinated alkanes and methane in different vegetation rhizosphere soils were examined to explore the soil bioactivity in different vegetation inter-root reinforcement zones.(1)The maximum methane oxidation capacity of soil with different vegetation roots was 24 h.The worst methane oxidation capacity was found in bare soil,and the maximum methane oxidation capacity of Amaranthus spinosus was 8.45 mg·m L^-1·d^-1.(2)Based on the structural characteristics of soil functional microbial communities in different vegetation root systems,combined with the strong and weak methane oxidation capacity,it was hypothesized that Methylomicrobium and Methylobacter might play an important role in methane biooxidation.(3)The degradation of Trichloromethane(CF)by different vegetated rooted soils ranged from 0.12?0.29 mg _CF·g^-_soil¹,and the degradation rates ranged from 1.71?2.82 mg _CF·g^-1_soil·d^-1.Therefore,enhancing the biological oxidation activity of mulch vegetation can effectively reduce the adverse environmental impact of Trichloromethane CF.