Effect Mechanism Of Vinasse On Removal Of Heavy Metals By Iron Plaque From Root Surface Of Constructed Wetland Plants

There are a certain amount of heavy metals such as Pb,Cd,Cu and Zn in domestic sewage.Efficient purification of heavy metals in sewage is a difficult problem to be tackled in the process of rural revitalization.Iron plaque(IP)has a significant influence on the absorption and accumulation of heavy metals in wetland plants,but the role of vinasse in regulating the related processes is not clear.This study hypothesized that the proper addition of vinasse could promote the formation of IP and the removal of Pb,Cd,Cu and Zn from the root surface of Iris pseudacorus in constructed wetlands.This study was to solve the problem of heavy metals in rural domestic sewage.We used the Iris pseudacorus,a kind of large aquatic plants,as the research object.By adding different amount of vinasse(mass ratio of 0,0.2%,0.4% respectively)test in constructed wetland experiment,dealing with low(L)and high(H)concentration of heavy metal pollution of sewage,with no added of heavy metals sewage as CK,we analyzed the the removal efficiency of heavy metals by constructed wetlands,the influence of the physiological and biochemical indexes of Iris pseudacorus,the formation of IP and its influence on absorption and transport of heavy metals,the microbial community structure of constructed wetlands substrates under different stress of heavy metals after adding different amount of vinasse.We also studied the effect of vinasse on heavy metal stress at transcriptome.It is expected to clarify the influence of vinasse on the formation of IP,the adsorption and transport of Pb,Cd,Cu and Zn,clarify the removal efficiency and removal mechanism of heavy metals in constructed wetlands by vinasse.The main conclusions as follows:(1)The vinasse contains C,O,Mg,P,K and other elements needed for plant growth,and functional groups related to the adsorption of heavy metals and ion exchange,such as carbonate group(C=O),-OH and C-H bonds,which are the reasons for the increase of root biomass and the good adsorption of Pb,Cd,Cu and Zn.(2)The study showed that the removal rate of heavy metals Pb,Cd,Cu and Zn in each Iris pseudacorus CWs treatment system with the addition of vinasse were good,and the water quality could be significantly improved.After a period of fluctuation,the removal rates of Pb,Cd,Cu and Zn reached95%,80%,100% and 60%.In the first 60 days of operation of CWs,the physical processes such as adsorption,complexation and precipitation of matrix are the main means to remove heavy metals such as Pb,Cd and Zn.(3)The addition of vinasse changed the cation exchange capacity and p H value of wetland substrate,directly affected the change of root oxidation power,and then affected the formation of IP.The results showed that the high concentrations of Pb,Cd,Cu and Zn can promote the formation of IP,while the low concentrations can inhibit the formation of IP.The heavy metals attached to the surface of vinasse interconverted with those in IP.IP facilitated the transfer of Cd and Zn to the ground portion,while Pb was mainly stored in IP and Cu was mainly stored in the root.(4)Under the stress of high concentration of heavy metals,after the addition of vinasse,Pb and Cd were mainly stored in cell wall and cytofluid,Cu was mainly distributed in cell wall and Zn was mainly distributed in cytofluid to alleviate toxicity.The addition of vinasse promoted the transfer of Cu and Zn to nucleus and chloroplast.(5)The addition of vinasse was the most favorable for CAT activity recovery,followed by POD activity.The ultrastructural changes of root tips showed that vinasse alleviated the toxic effects of heavy metals on nucleus,nucleoli,chromatin and cell membrane system to a certain extent.(6)Transcriptome analysis of leaves of Iris pseudacorus showed that phenylpropane-like biosynthesis pathway,starch and sucrose metabolism,and plant hormone signal transduction were related to the absorption,transport and detoxification of heavy metals by GO annotation and KEGG pathway enrichment.(7)Studies using high-throughput sequencing technology showed that the addition of vinasse significantly increased the number of bacterial community species and diversity of community structure in the substance,and increased the stability of wetland system.In conclusion,the addition of vinasse CWs treatment system has a good removal rate of heavy metals Pb,Cd,Cu and Zn,and can significantly improve the water quality.The vinasse promoted the binding of subcellular structure to heavy metals and the localization of heavy metals,which alleviated the toxic effect of heavy metals to a certain extent.The results provide a theoretical basis for regulating the absorption of heavy metals by wetland plants by vinasse,purifying water quality,regulating the microenvironment of wetland substrate,and realizing the construction of wetland to treat rural domestic sewage containing heavy metals.