Migration And Transformation Mechanism Of Combined BDE-99 Pollution And Pollution-control During Infiltration Process

In order to repair the abandoned contaminated land in the village of Baiyangdian Village,combined pollutants of BDE-99 and heavy metal As was used as the main research contaminants.The soil along Fuhe River and Chaobai River in dry season was used as the percolation medium.The static adsorption and dynamic migration experiments were carried out to study the adsorption and migration characteristics of complex pollutants BDE-99 and As-BDE99 in soils.The adsorption commonality of pollutants in different soil types,migration and transformation of pollutants along soil depth and the main microbial communities with degradation function were analyzed.,Biochar and soil composite foundation columns were setup to strengthen the adsorption and degradation,capacity in order to reduce pollutants leaching into groundwater.The results show that the adsorption kinetics of BDE-99 is consistent with the two-chamber first-order kinetics model.The adsorption capacity is related to the surface area and pore volume.The contribution of fast adsorption to the total adsorption capacity is large.The adsorption of BDE-99 in soil is an exothermic process.With the temperature increasing,the adsorption equilibrium capacity decreases gradually,and the desorption process has hysteresis.When As and BDE-99 coexist,there is competitive adsorption phenomenon,which is mainly represented by competition between surface adsorption sites and competition of organic matter content.As reduced the adsorption capacity of BDE-99 and the contribution rate of fast adsorption.The higher the concentration of As,the greater the change of BDE-99 in soil adsorption capacity and fast adsorption contribution rate,the more easily BDE-99 desorbs.In the leaching column system,the effluent concentration of BDE-99 decreased with the increase of depth,and its metabolites were mainly BDE-28 and BDE-47,and a few high brominated products such as BDE-154 and BDE-153.The degradation of BDE-99 by microorganisms satisfies the first-order kinetics process.The half-life is about 3 d.The dominant genus of major degradation is Bacillus,Melhylophilus,Sphingomonas,Solirubrobacter and Terrimonas.The relative abundance of Methylophihls and Terrimonas increased by 32.5 and 18.3 times,respectively.The coexistence of inorganic anion-bicarbonate promotes the biodegradation of BDE-99.Because it can provide electron acceptors for degradation of BDE-99 and strengthen the biological metabolism function of the lower layer of soil column.The coexistence of heavy metal-As affects the adsorption of BDE-99 on the upper layer of the soil column,which makes the effluent concentration high,but has little effect on the final effluent concentration.The biochar composite soil layer strengthens the adsorption and biodegradation properties of the soil and has a certain impact on the soil microbial community structure.The three major genera with metabolic functions are Haliangium,Sphingomonas,and unidentified_Acdobacteria.The construction of biochar composite soil layer can effectively alleviate groundwater pollution and provide effective engineering measures for repairing the abandoned contaminated.