Remediation Of Atrazine Contaminated Soil By Co-pyrolysis Biochar Prepared By Corn Straw And Sludge Coupling Strain Arthrobacter Sp.DNS10

The excessive use of the herbicide atrazine has caused it to accumulate in the environment and pose a great threat to the ecological environment and biological health.Therefore,how to effectively reduce the residue of atrazine in the environment has attracted much attention.In recent years,biochar has been widely used in the field of environmental pollution control.With the continuous development of biochar preparation technology,people found that sludge and other biochar raw materials have the characteristics of low volatile content,high ash content,and low calorific value,which will lead to low pyrolysis process efficiency and high energy consumption;and some agricultural and forestry wastes such as rice husk,sawdust and other raw materials mainly composed of cellulose,hemicellulose and lignin have the characteristics of high carbon content and low ash content,resulting in problems such as low yield after pyrolysis.So how to solve the problem caused by the single raw material's own characteristics in the pyrolysis process has also attracted people's attention.This study used the method of co-pyrolysis of corn straw and sludge to investigate the adsorption and removal ability of different co-pyrolysis biochar to atrazine,the coupling characteristics with strain DNS10,and the remediation effect of atrazine contaminated soil.It can make the useful components inside the straw and sludge fully function by co-pyrolysis,and also provide a model for the resource utilization of corn straw and sludge.The main conclusions of this study are as follows:?1?By comparing the removal rates of atrazine for 15 kinds of biochar prepared under different pyrolysis temperatures?350 ^oC,550 ^oC,750 ^oC?and different mass ratios?corn straw:sludge=1:0,3:1,1:1,1:3,0:1?,it was found that under the same pyrolysis temperature conditions,the mass ratio of straw to sludge will affect the removal rate of atrazine by co-pyrolysis biochar.Among them,the co-pyrolysis biochar 750BC_?3:1?prepared under the conditions of the pyrolysis temperature of 750 ^oC and the mass ratio of corn straw to sludge is 3:1 has the highest removal rate of atrazine?29.66%?.?2?Characterize five kinds of biochar(750BC_?1:0?,750BC_?3:1?,750BC_?1:1?,750BC_?1:3?,750BC_?0:1?)by SEM-EDS,specific surface area analysis and FT-IR.The results show that 750BC_?3:1?has more pore structure and spherical structure,making it have a larger specific surface area?118.288 m²/g?and pore volume?0.078 cm³/g?.At the same time,with the increase of the mass ratio of sludge in the pyrolysis raw materials,the C element content decreased from 70.03%to14.58%,and the Si element content increased from 1.14%to 14.18%.At the same time,in addition to the main elements such as C,O,Si,Ca,750BC_?3:1?also contains higher levels of nutrient elements such as N,P,K,Mg,and heavy metals Pb,Cd,Cr,Cu.The contents of Pb,Cd,Cr,Cu are0.62%,0%,0.06%and 0.55%respectively,which are lower than the corresponding elements in the other four types of co-pyrolysis biochar.?3?Through the kinetics and isotherm studies on the adsorption of atrazine for five kinds of biochar(750BC_?1:0?,750BC_?3:1?,750BC_?1:1?,750BC_?1:3?,750BC_?0:1?),it was found that the q_eof atrazine for 750BC_?3:1?,750BC_?1:1?and 750BC_?1:3?are 5.73 mg/g,3.73 mg/g,and 2.83 mg/g respectively,indicating that as the mass ratio of sludge in the pyrolysis process increases,the q_eof atrazine by co-pyrolysis biochar gradually decreases.750BC_?3:1?has better adsorption capacity for atrazine,and its adsorption kinetics process and adsorption isotherm process are consistent with the pseudo-second-order kinetic model and Freundlich model,while the adsorption amount of atrazine by 750BC_?1:3?is only 2.83 mg/g,which is significantly lower than that of 750BC_?3:1?.At the same time,the adsorption characteristic fitting results show that the adsorption process of atrazine by 750BC_?1:3?is more in line with the pseudo-first-order kinetic model and Langmuir model.The above results indicate that the mass ratio of corn straw to sludge can affect the adsorption characteristics of co-pyrolysis biochar on atrazine.?4?The research on the process of exogenously regulating the growth of strains and the removal of target pollutants by co-pyrolysis of biochar with mud and stalks is rare,so this study examined the growth of strain DNS10 and the removal of atrazine under the presence of different concentrations of 750BC_?3:1?and 750BC_?1:3?.The results showed that under the conditions of the co-pyrolysis biochar dosage level set in this study?0-300 mg/L?,750BC_?3:1?had no negative effect on the growth of strain DNS10 and the removal rate of atrazine.Through SEM observation,it was found that when the concentration of 750BC_?3:1?was 300 mg/L,more strains DNS10 were attached to the surface.Through TEM analysis,it was found that there was obvious agglomeration of the strain during the treatment with biochar.When the concentration of 750BC_?3:1?was 300 mg/L,the phenomenon of strain agglomeration was more obvious,indicating that 750BC_?3:1?has a large specific surface area and a rough surface,which can help the strain to hang the film on the biochar material.At the same time,the removal rate of atrazine?97.55%?in the treatment group added with 300 mg/L 750BC_?3:1?was higher than that?89.38%?in the treatment group with the same concentration of 750BC_?1:3?added at 48 h,indicating that when the 300 mg/L biochar 750BC_?3:1?coexists with the strain DNS10,the strain has better ability to remove atrazine.At the same time,the fluorescence quantitative PCR results show that the expression level of the degradation gene trz N in the treatment group added with 300 mg/L 750BC_?3:1?was not significantly different from that in the CK treatment group without biochar.It is further confirmed that the presence of biochar750BC_?3:1?can guarantee the normal expression of the degradation gene trz N.?5?By coupling different amounts of 750BC_?3:1?and strain DNS10 into atrazine contaminated soil,combined with fluorescence spectroscopy analysis and high-throughput sequencing methods to investigate changes in basic properties such as p H and nutrition of atrazine contaminated soil,the response of soil bacterial community structure and the remediation effect.The results showed that when 750BC_?3:1?and strain DNS10 were applied to atrazine contaminated soil,as the amount of biochar added increases,the p H of the soil increased from 6.42 to 6.82,organic carbon,total nitrogen,effective Phosphorus,total phosphorus and available potassium content increased from1.55%,1.85 g/kg,45.39 mg/kg,0.68 g/kg,233.40 mg/kg to 2.22%,2.17 g/kg,66.30 mg/kg,1.29g/kg,405.09 mg/kg,indicating that the application of biochar is the main factor that causes changes in basic properties such as soil p H and organic carbon content.At the same time,the fluorescence spectrum analysis showed that the fluorescence intensity of DOM in the soil decreased significantly with the increase of the amount of biochar added in the coupling treatment group,indicating that the strain and biochar combined with DOM and changed the fluorophore material structure.At the same time,when the two were coupled and applied to contaminated soil,the abundance of the phylum of Verrucosa,Chlamydiae,Thaumarchaeota and others under the phylum level was higher than that of biochar and strains applied to the soil separately,while the abundance of the Nitrospira is significantly lower than the abundance in the J and B4 treatment groups,the Sphingomonas abundance at the genus level is lower than that in the J and B4 treatment groups,indicating that 750BC_?3:1?and strain DNS10 will be synergistic when they are applied together,which will affect the bacterial community structure in the soil.In addition,when the amount of 750BC_?3:1?added increased,the total content of atrazine in the coupling treatment group showed a decreasing trend,indicating that the addition of 750BC_?3:1?can enhance the removal effect of atrazine in the soil.