Research On Multi-soil-layering System Enhanced By Iron-Based Biochar

In recent years,the living and economic level of rural areas has been rapidly improved,human activities have intensified,and the rapid development of industry and agriculture has been further improved.The pollution of rural water environment has gradually become serious,especially the problem of nitrogen pollution in rural wastewater has gradually caused widespread focus on.Compared with traditional soil treatment technologies such as constructed wetlands,multi-media soil layer infiltration(MLS)system is a more costeffective and decentralized wastewater treatment technology with great potential.Conventional MSL systems often increase design and maintenance costs due to the addition of aeration and lead to the accumulation of nitrates in the system,which is not conducive to the survival of microorganisms.At the same time,the traditional MSL system has little research on the modification of materials.On the other hand,the microorganisms in the system are a key factor in the wastewater treatment process,but their role in the MSL denitrification treatment process is still understudied.In order to improve the performance of microorganisms in the MSL system and optimize the operating conditions of the MSL system,this study adopts the experimental method of factorial design to analyze and discuss the treatment effect of the MSL system under different operating conditions.The selected three operating parameters are factor A-the quality of the modified biological carbon.factor B-the concentration of ammonia nitrogen in the influent,and factor C-the intermittent influent time.The experiment ran for a total of 178 days.In terms of material modification,biological carbon was selected for research.Through a series of characterization methods and kinetic and adsorption isotherm model fitting,it was finally found that acid protonation could further improve the nitrate adsorption capacity of iron-based biological carbon.Nitrate adsorption on biological carbon is a monolayer adsorption with complex physicochemical properties.Through the analysis of the effluent performance of MSL,the three experimental factors have obvious effects on the treatment performance of the MSL system,and the multi-media soil system has good long-term operation stability.By comparison,it is known that the addition of modified biochar and intermittent reoxygenation can effectively improve the removal effect of MSL system for COD and ammonia nitrogen and other pollutants.A multivariate nonlinear regression model about the experimental factors was established by using the average value of the last cycle removal rate of COD.ammonia nitrogen,total nitrogen and total phosphorus as the response value,and through single factor analysis and factor interaction analysis,it was found that the concentration of ammonia nitrogen in the influent water There were negative effects on all four response values,while the addition of modified biochar had positive effects on all four response values.Intermittent reoxygenation had a positive effect on all except TN.In the study,we also used microbiome sequencing to reveal how the microbial community in the soil mixing module(SMB)changed before and after the operation of the MLS system.The role of microorganisms in the wastewater treatment process and the effects of each experimental factor condition on microorganisms with different functions are discussed.The OUT test and species distribution results showed that the addition of modified biochar(A1),lower ammonia nitrogen influent concentration(B-1)and intermittent reoxygenation(C1)all had a positive effect on the abundance of microorganisms.In order to deeply explore the mechanism in the denitrification process,we selected genes and enzymes closely related to the nitrification and denitrification processes to test the abundance and activity,and found that the addition of modified biological carbon can improve the efficiency of the MSL system.Abundance of genes related to the denitrification process.Compared with NXR enzyme,the activity of AMO enzyme has a greater impact on the effect of nitrification process.In the case of intermittent reoxygenation,it has an inhibitory effect on the abundance of narG gene,but it has a positive effect on the activity of NAR enzyme.,The results of this paper will help us to understand the complex process of sewage treatment in MSL system from the aspects of materials,operating conditions and microorganisms,especially the nitrogen treatment in MSL system has a deeper understanding.This provides data support for the optimization and further improvement of the MSL svstem in the future.