Plant-microorganism Remediation And Surfactant Enhanced Remediation Technology For Organic Contamination In Soil Of Iron And Steel Plant

Iron and steel plant production process will produce persistent organic pollutants(POPs).POPs stay in the soil,can migrate over long distances,and are highly toxic,easy to be absorbed and accumulated by organisms,posing threat to human health.Semi-volatile organic compounds including PAHs,PCBs and petroleum hydrocarbons are paid close attention to in steel sites.It is very important to adopt appropriate methods to remove pollutants in steel sites.Bioremediation is generally considered an attractive technique for removing organic contaminants from soil.In this study,a plant-microbial joint remediation of organic compound pollution in the contaminated soil of iron and steel plant was carried out,and rhamnolipid was added as a strengthening measure,so as to establish a set of standard treatment mechanism and provide a scientific basis for the remediation and reuse of the contaminated site.The main research contents and conclusions are as follows:(1)Five kinds of plants,including ryegrass(Lolium perenne L.),alfalfa(Medicago sativa L.),soybean(Glycine max(Linn.)Merr),Sudan grass(Sorghumsudanense(Piper)Stapf.)and purple jasmine(Mirabilis jalapa L.),were selected for pot experiment to study the remediation effect of plants on soil organic matter in iron and steel site,and to analyze the effect of organic pollutants on plant physiological indexes,so as to screen the dominant plants that can be used for remediation of organic pollutants.The results showed that the contaminated soil inhibited the growth of plants,but not the growth of ryegrass.The stem and leaf growth of alfalfa was significantly inhibited,and the root extension of soybean and purple jasmine was also significantly inhibited.Soil pollution caused the decrease of chlorophyll content and membrane lipid peroxidation of five species of plants,and also stimulated the tolerance of plants to organic pollutants.The content of SOD and POD in ryegrass increased with the increase of pollution degree,its antioxidant mechanism was stronger.The removal effect of ryegrass on PAHs was the best,which was 33.97%and 26.81%in light and heavy contaminated soil,respectively.Purple jasmine had the best removal effect on TPH,which was 38.41%and 37.65%in light and heavy contaminated soil,respectively.The removal rate of dl-PCBs by ryegrass was also the highest,which was 43.42%and 46.45%in light and heavy contaminated soil,respectively.Ryegrass and purple jasmine were the dominant plants for remediation of compound pollution of organic matter.(2)The remediation effect of two exogenous bacteria,namely OBT and solid agent of Bacillus subtilise-Sphingosperms,on soil organic pollutants was studied,and the remediation effect of ryegrass,microbial agent,ryegrass-microbial agent on remediation and soil microenvironment were compared.The results showed that the removal efficiency of PAHs,TPH and dl-PCBs were 70.76%,69.02%and 78.56%,respectively,by adding two kinds of exogenous bacteria and planting ryegrass.Bioremediation improved the activities of dehydrogenase,urease and Fluorescein diacetate(FDA)in soil,which were closely related to soil microbial activity and soil quality.At the same time,bioremediation could also improve the physical and chemical properties of soil.Soil microbial richness and biodiversity were the highest under ryegrass-solid bacteria treatment,followed by the treatment of ryegrass-mixed microbial agent.Proteobacteria,Actinobacteria,Bacteroidetes,Chloroflexi and Gemmatimonadetes were the dominant bacteria in the soil under different treatments.Devosia,Azotobacter,Luteimonas and Pseudomonas were relatively abundant in the soil.All the bioremediation groups improved the relative abundance of Proteobacteria,and the addition of solid agent and planting ryegrass also increased the abundance of Bacteroidetes.All the bioremediation groups also increased the relative abundance of Pseudomonas,and planting ryegrass and adding OBT promoted the abundance of Azotobacter.(3)The effects of adding different concentrations of rhamnolipid on the removal of organic pollutants by plant-mixed bacteria agent were analyzed,and the technical model of surfactant enhanced bioremediation of organic compound pollution was preliminarily established.The results showed that the addition of rhamnolipe significantly increased the removal rates of PAHs,TPH and dl-PCBs(p<0.05),especially the addition of 50 mg/kg rhamnolipe,and also increased the abundance of microbial community,but the effect on microbial community diversity was not different from that of 0 mg/kg and 100 mg/kg rhamnolipe.Adding rhamnolipid could increase the relative abundance of Proteobacteria and Bacteroidetes,and also increase the abundance of Luteimonas.In the treatment of planting ryegrass,rhamnolipid increased the relative abundance of Actinobacteria,Bacteroidetes and Devosia,while in the treatment of planting purple jasmine increased the relative abundance of Proteobacteria,Bacteroidetes and Pseudomonas.