Study On The Method And Mechanism Of Electrokinetic Remediation Of Greenhouse Soil With High Accumulation Of Nitrogen And Phosphorus

Currently,nitrogen and phosphorus fertilisers are overused and misused in Chinese farmland,leading not only to an imbalance of soil nutrients and wasted resources,but also to a series of environmental problems.The problem of nitrogen and phosphorus enrichment in soil is particularly serious in greenhouse soils due to their closed nature.As a new technology for rapid in-situ remediation of contaminants,electro-remediation is efficient,reliable and economically competitive.The current electrokinetic remediation technology has limitations when applied to the removal of soil nitrogen and phosphorus,so there is an urgent need to develop a new electrokinetic remediation configuration to address the shortcomings of the existing technology,with a view to achieving in-situ removal of nitrogen and phosphorus without changing the ecological value of the remediated soil,forming a new,green and efficient in-situ treatment technology for surface contaminated soils,as well as studying the electrochemical behaviour of nitrate and the migration of phosphorus.The study also investigates the electrochemical behaviour of nitrate and the mechanism of phosphorus transport and transformation,which provides new ideas for the remediation of current surface contaminated soils.This study selected a typical vegetable greenhouse soil with high nitrogen and phosphorus accumulation in Shouguang City,Shandong Province as the research object,and conducted indepth research on the methods and mechanisms of soil electric remediation.Firstly,an optimized configuration for electric remediation was constructed,and the removal effects of different configurations and optimization parameters on nitrogen and phosphorus in soil were analyzed.Secondly,the electrochemical behavior of nitrates and the effects of hypochlorous acid and citric acid on nitrate reactions were studied through electrode processes.Finally,the mechanism of action between citric acid and soil phosphorus was studied using extraction experiments,particle size characterization,and other methods.The following studies have been obtained:(1)The optimal design of cation exchange membranes solves the problems of excessive acidification(pH<4)and excessive alkalization(pH>10)of soil caused by traditional electrokinetic remediation techniques.After remediation,the pH value of the soil remained at 8-9,slightly higher than the original soil(7);And the optimized configuration avoids reverse electroosmosis,which can save nearly 35%of energy consumption,forming a green,economic,and environmentally friendly optimized configuration for electrokinetic repair technology.(2)The electric remediation technique achieves efficient in-situ removal of soil nitrate.After 15 days of electric remediation,the average removal rate of nitrate nitrogen in soil can reach over 97%;The removal of over 50%of soil ammonium nitrogen has been achieved,with no significant impact on the organic nitrogen content in the soil.Electrokinetic remediation technology removes nitrogen from soil mainly through electrochemical reduction of nitrate.(3)The addition of citric acid stabilizes the pH of the entire system,increases the electrode potential,facilitates the electrochemical reaction of nitrate.The addition of sodium chloride effectively provides the system with movable charged ions and a sufficient amount of active chlorine,promoting the process of indirect oxidation of ammonia.The concentrations of inorganic nitrogen and total nitrogen in the electrolyte are in compliance with the Class A standard in the"Discharge Standard for Pollutants from Municipal Wastewater Treatment Plants"(GB 189182002),and no additional treatment is required,reducing repair costs,and forming a green and environmentally friendly nitrate removal technology.(4)The mechanism of electrokinetic remediation of soil phosphate is mainly the combined effect of electromigration of phosphate ions and electroosmotic flow.Using pure water as the optimal configuration of the circulating liquid,the removal efficiency of total phosphorus in the extreme soil can reach 16.5%,with an average removal efficiency of less than 6%.The reason for the low removal efficiency is that theactivation mechanism of citric acid on inorganic phosphorus ismainly based on proton-acid effect.As the extraction timeincreases,the phosphorus colloid particle size extracted bycitric acid from the soil increases and adheres to the large soilparticles,which affects the removal of phosphorus from the soil...