Research On The Phytoremediation Mechanism Of PAHs In Coal Gangue Soil Enhanced By Humic Acid From Kitchen Compost

Coal mining usually brought polycyclic aromatic hydrocarbons(PAHs)contamination.However,since the weak fertility of the contaminated soil,this makes its bioremediation less efficient.The kitchen compost products,which faced the problem of waste resourcing,contained a large amount of nutrients such as humic acid(HA),which had potential nutritional value for remediation of PAHs-contaminated soil.Therefore,the investigated 7 typical coal gangue sites located in the coal mining gathering area in Huainan City,Anhui Province.Based on the survey results,a study on the effect of indoor kitchen compost products on the adsorption and transformation of chrysene(Chr)in soil was carried out.In addition,a study on the effect and mechanism of HA-enhanced phytoremediation of Chr-contaminated soil was conducted.The results of the soil survey in the coal mining area showed that a total of 11 PAHs were present at the 7 sites.The PAHs were all enriched only in the surface layer of the soil,probably due to the strong binding of soil organic matter(SOM)and PAHs.Based on the differences in PAHs concentrations,we screened 4 sites from the 7 coal sites.And the correlations between PAHs concentration,DOM(dissolved organic matter)and microorganisms were systematically analyzed in this work.The abundance of Sphingomonas and Nocardioides decreased and Mycobacterium increased with the increasing concentration of PAHs.However,PAHs contamination reduced the diversity of soil microorganisms.DOM was mainly produced by microorganisms in the coal mine area.However,the biological activity remained low,which was influenced by the high proportion of HMW-PAHs in the mine area.The increased content of LWM-PAHs and DOM favored the activity of soil microorganisms,which might be due to the increased aromaticity of DOM that facilitated the bioavailability of PAHs.The results of the study on the effect of HA on the adsorption and transformation of Chr in soil showed that the Chr dissipation rate in the unfertilized Chr-contaminated soil(Chr1 to Chr3)was between 42.01% and 48.59%.The Chr removal rates in Chr-contaminated soil with the application of F(solid compost)and its DOM and HA ranged from 40.96% to 85.46%,55.44%to 77.74%,and 47.12% to 71.79%,respectively.The magnitude of PAHs removal in different compost fractions was F≈DOM>HA>W.This indicated that the addition of F and DOM and HA can promote the removal of the soil Chr,and F or DOM was more effective.The application of food compost products(F,DOM,HA)can improve the removal of minerals from the soil because the compost products provide SOM,AK,TN and P elements to the soil,and F > DOM >HA.Composting also increased species abundance and enhanced microbial activities in contaminated soils.The top 5 dominant phyla of compost products(F,DOM,HA)were Proteobacteria,Actinobacteriota,Firmicutes,Chloroflexi and Acidobacteriota,which were the same as the top 5 dominant phyla of the Chr-contaminated soil.In addition,the application of F caused a significant increase in the abundance of Actinobacteriota and Firmicutes.And the application of DOM and HA caused a significant increase in the abundance of Proteobacteria and Actinobacteriota,respectively.Studies on the effects and mechanisms of HA-enhanced phytoremediation of Chrcontaminated soils showed that phytoremediation increased Chr removal in unfertilized Chrcontaminated soils(Chr1 to Chr3)to 45.21% to 53.02%.The application of F,DOM,and HA increased th removal rates of Chr in phytoremediated soils with Chr1 to Chr3 concentrations to51.79% to 86.34%,48.52% to 79.52%,and 47.20% to 71.10%.The magnitude of the removal rate of Chr in phytoremediated soils with different compost components was: F > DOM > HA >W.This indicated that the application of F and its DOM and HA can promote the phytoremediation of the Chr-contaminated soil,and the application of F was more effective.Alfalfa increased the abundance of inter-root Proteobacteria,Actinobacteriota,and Firmicutes.Fertilization provided SOM,K,N,and P elements for plant growth and inter-rhizosphere bacteria,and significantly increased the abundance of Bacillus in plant-growing soil,and F >DOM > HA.The obtained results provide a basis for better understanding the contamination characteristics and microbial communities of coal gangue PAH-contaminated sites.It provide a scientific way of resource utilization for kitchen waste composting products.It provides ideas and theoretical support to effectively improve the remediation efficiency of soil PAHs.