Experimental Study On Chemical Oxidation Remediation Of High Ammonia Nitrogen Contaminated Soil In A Chemical Fertilizer Contaminated Site

China is a big country of fertilizer production,consumption and export.In recent years,with the relocation of chemical fertilizer plants,a large number of chemical fertilizer contaminated plots have been left behind in cities.Most of these plots contain high concentrations of ammonia nitrogen,which will pose a certain risk to the surrounding environment.Therefore,it is urgent to repair them.Chemical oxidation remediation technology has been widely used in the field of soil remediation with the advantages of fast remediation speed,good effect and low cost.In this paper,Fenton,activated persulfate and sodium hypochlorite were selected to repair the soil polluted by high ammonia nitrogen.The effects of dosage,initial pH,reaction time and temperature on the repair effect were investigated by response surface methodology.According to the changes of soil pH,organic matter and microbial activity before and after chemical oxidation,the optimum oxidant was determined.The paper has the following results:（1）The results of single factor experiment showed that the optimum reaction conditions of Fenton method were as follows:H₂O₂ dosage was 8.00 mmol/g,Fe²⁺dosage was 0.80 mmol/g,pH value was 3.00,reaction time was 150 min,temperature was 40°C.The optimum reaction conditions were as follows:sodium persulfate dosage was 8.00 mmol/g,Fe²⁺dosage was 1.00 mmol/g,pH value was 7.00,reaction time was 180 min,temperature was 40°C;The optimum reaction conditions of sodium hypochlorite method were as follows:sodium hypochlorite dosage was 1.25m L/g,pH value was 7.00,reaction time was 60 min,and temperature was 20°C.（2）Response surface methodology optimization results showed that the optimal reaction conditions of Fenton oxidation were as follows:H₂O₂dosage 10.00 mmol/g,Fe²⁺dosage 1.00 mmol/g,reaction time 180 min,pH 3.30,and temperature 50°C.Under these conditions,the removal rate of ammonia nitrogen was 69.58%.The optimal reaction conditions for activated persulfate were as follows:sodium persulfate dosage 8.00 mmol/g,Fe²⁺dosage 1.00 mmol/g,citric acid dosage 0.20mmol/g,reaction time 180 min,pH 7.50,and temperature 40°C.Under these conditions,the removal rate of ammonia nitrogen was 84.55%.The optimum reaction conditions of sodium hypochlorite oxidation were as follows:sodium hypochlorite dosage 1.26 m L/g,reaction time 69 min,pH 6.50 and temperature23°C.Under these conditions,the ammonia nitrogen removal rate was 93.83%.（3）The effects of three oxidants on soil physical and chemical properties and ecological environment were analyzed by comparing the changes of soil pH,organic matter and microbial activity before and after the reaction.The experimental results show that:After Fenton treatment,soil pH decreased from 3.30 to 2.20,organic matter content decreased by 51.86%,and catalase activity decreased by 24.64%.After activated persulfate treatment,soil pH decreased from 7.70 to 5.40,organic matter content decreased by 32.51%,catalase activity decreased by 13.45%;After sodium hypochlorite treatment,pH increased from 6.20 to 9.20,soil organic matter content decreased by 41.21%,and catalase activity decreased by 37.25%.By comprehensive comparison,among the three oxidants,the activated persulfate had the smallest ecological environmental risk to the soil,which was the best oxidant.