Study On Remediation Of Soil Contaminated By Phenylurea Herbicides With Different Types Of Biochar

Biochar is produced by cracking biomass materials(include wood,faeces,straw etc.)in anaerobic or anoxic condition as well as high temperature(under 700 ?).As a new type of environmental functional material,it has been a research hotspot and applied to different environments for its excellent adsorption efficiency to different pollutants,large porosity,large specific surface area,more functional groups and other characteristics.For example,biochar can be widely used in carbon sequestration,crop yield,water purification,heavy metal adsorption and soil improvement,especially for soil improvement,such as fixing soil CO2,delaying the leaching of fertilizer nutrients,degradating or inactivating soil harmful substances.Biochar particles can migrate in the soil with the migration of surface water,which affect the pollutants adsorbed on the surface.The wide use of herbicide especially the henylurea herbicides in the modern agriculture,not only lead to phenylurea herbicides residues in vegetables,fruits,grains,surface water and groundwater,but also degradate slowly.The main reason might be that phenylurea herbicides are not only water-soluble and chemically stable,but also long-term residual herbicides.Therefore,the three main kinds of phenylurea herbicides include monuron,diuron and linuron,were selected as the research object.Biochar was prepared by pyrolysis of wheat straw,rice straw,salix straw and maize stalk under 500 ? in anaerobic condition.The movement of biochar in the soil under different chemical conditions was discussed,such as ionic strength,salt ions and pH.Based on the results,the effects of biochar addition,pH and ionic strength on the migration of biochar in the combination of monuron,diuron and linuron were investigated.And the convection dispersion equation was used to fit the experimental data.The main conclusions as well as original points were listed as fellow:(1)The movement of biochar in the soil under different chemical conditions was discussed.With the increase of ionic strength and the decrease of pH,rice biochar will be more stranded in porous media.Under the same ionic strength and pH,retaining the total amount of rice biochar by Ca2+ was much stronger than that of Na+.The permeability curves of straw biochar under the experimental conditions were fitted by non-equilibrium convective diffusion equation.The correlation coefficient was above 0.99,which indicated that biochar was not only subjected to chemical force,but also physical force in the process of migration.(2)Orthogonal software is used to analyze the effect of wheat straw biochar(WSB),rice straw biochar(RSB-1),salix straw biochar(SSB)and maize straw biochar(MSB)on the adsorption process of monuron,diuron and linuron under different chemical conditions(pH,ions with different states,IS,biochar dosage).The surface functional groups and ash content of four kinds of biochar can be found to play an important role in the adsorption process of phenylurea herbicides.When the four kinds of biochar concentrations were more than 10 g/L,the adsorption effects of monuron,diuron and linuron were: MSB> RSB-1> WSB> SSB.The optimum pH,salt ion,IS and biochar additions of different types of biochar to remove certain phenylurea herbicide by orthogonal software were also confirmed.For example,the optimum removal level of monuron by rice straw biochar(RSB-1)was: p H=3,IS=0.1M(NaCl),RSB-1 concentration =10 g/L.(3)The effects of different chemical conditions(pH,different valence state salt ions,IS,biochar addition)on the migration of RSB-1 in the combination of monuron,diuron and linuron were further studied.The results were also analyzed by orthogonal software.For monuron,the best experimental conditions is p H=9,IS= 0.001M(NaCl)and Mbiochar / Mquartz sand =1% of RSB-1dosage,and the maximum removal rate reached 41.9%.For diuron,the best experimental conditions is pH=9,IS= 0.001M(NaCl)and Mbiochar / Mquartz sand =0.05% of RSB-1dosage,and the maximum removal rate reached 25%.For linuron,the best experimental conditions is pH=9,IS= 0.001M(NaCl)and Mbiochar / Mquartz sand =1% of RSB-1dosage,and the maximum removal rate reached 56.8%.The non-equilibrium convection dispersion equation was used to fit the penetration curve of RSB-1 in the combination of monuron,diuron and linuron,and further studied the effects of different chemical conditions on the activity of the herbicides.In summary,the restoration of henylurea herbicides in soil in four kinds of biochar were studied systematically,which can not only provide a good method for the efficient removal of phenanthrene herbicides,but also provide relevant theoretical basis and technical support for groundwater safety management and agricultural production.