In-situ Oxidation Experiment On Groundwater Polluted By Aniline Compounds

In recent years,with the rapid development of industry and agriculture in China,the leakage of petrochemical raw materials and the overuse of pesticides and fertilizers have led to the indirect discharge of organic matter into groundwater through soil,resulting in the pollution of organic matter in groundwater.At present,the compound pollution of aniline in groundwater caused by pesticides and chemical raw materials is becoming more and more serious,which endangers the ecological environment and human health.At present,the research on the pollution of aniline substances in groundwater mainly focuses on the monitoring of water and soil environment,migration and transformation,degradation mechanism analysis and groundwater control and remediation technology in the presence of aniline,Chloroaniline and other single aniline substances.The research on oxidant and in-situ oxidation treatment technology of groundwater polluted by combined site,multi-aniline substances and so on is also carried out.Few reports have been reported.In this paper,aiming at the problem of aniline substances exceeding the standard in groundwater of a chemical site in Jilin City,the groundwater in the study area was investigated and monitored on the basis of the existing site data,and the environmental characteristics of groundwater in the study area?hydrochemical elements,hydrochemical types,aniline substances exceeding the standard components?were analyzed and studied.At the same time,based on the existing oxidizer research for treating organic substances,the decline was screened out.The optimum combination of oxidants for the removal of aniline and the content ratio of oxidants are optimized;the main factors affecting the oxidation and degradation of aniline are analyzed and the mechanism is studied;the migration and transformation of aniline in aquifer and the degradation of aniline in aquifer after adding oxidants are simulated indoors in a simulated tank,and the adsorption of volcanic slag in the simulated tank is carried out.The micro PRB technology is used to remove the over-standard separators in the middle of groundwater caused by the oxidation and degradation of aniline.The research results provide an important scientific basis for the research and application of the control and remediation technology of aniline compound contaminated groundwater.The main research results of this paper are as follows:1.The results of detection and analysis of groundwater samples show that the main iron,manganese and ammonia nitrogen in groundwater exceed the standard,with the highest concentration exceeding 1.73 mg/L,2.26 mg/L and 2.00 mg/L,respectively.The main aniline substances detected in groundwater are 2-ethoxyaniline and N-methylacetaniline,with the maximum detectable amounts being 4.22 mg/L and1.35 mg/L,respectively.2.In view of the current research status of oxidative degradation of organic compounds,the catalysts for hydrogen peroxide were screened from common metal ions and some transition metal ions,and the best activators for Na₂S₂O₈ were screened from Fe²⁺,H₂O₂ and NaOH,respectively.The results showed that Cu²⁺,Co²⁺,Fe²⁺catalyzed the degradation of aniline compounds by hydrogen peroxide with obvious effect.When n(Fe²⁺)/n?H₂O₂?=1:10 The removal rates of aniline were 85%,2-ethoxyaniline 90%,N-methylacetaniline 84%,m-nitroaniline 86%,o-nitroaniline88%,3.4-dichloroaniline 81%,respectively.The effect of activating Na₂S₂O₈ was as follows:H₂O₂>Fe²⁺>NaOH,and Fe²⁺composite H₂O₂ was used to activate Na₂S₂O₈ oxidation degradation system.After optimizing the content of Na₂S₂O₈,under the conditions of n(Fe²⁺):n?Na₂S₂O₈?:n?H₂O₂?=1:25:1000,there were six kinds of activated Na₂S₂O₈ oxidation degradation systems.The degradation rates of aniline were 89%,81%of N-methylacetaniline,99.6%of 2-ethoxyaniline,93%of m-nitroaniline,89%of o-nitroaniline and 79%of 3.4-dichloroaniline,respectively.Therefore,the oxidant Fe²⁺complex hydrogen peroxide was chosen to activate the oxidation degradation system of Na₂S₂O₈.3.To investigate the factors affecting the degradation rate of aniline in the process of oxidative degradation.The effects of initial pH value of sample solution,initial concentration of aniline substances,reaction temperature,oxidant dosage and inorganic ions in groundwater on the oxidation degradation of aniline substances were studied experimentally.The results showed that the degradation effect of aniline substances was the best when pH=7.The degradation rate of six aniline substances was above 90%,followed by alkaline condition and acid strip.Under this condition,the degradation efficiency of aniline is the worst;the degradation rate of aniline is higher in the initial concentration range of 0-20 mg/L,and decreases gradually with the increase of concentration;with the increase of temperature,the degradation rate of aniline shows a trend of first increasing and then decreasing.In the range of 30-40^C,the degradation rate of six aniline substances reached more than 90%;when oxidant was added in batches at the ratio of 40%:30%:30%,the degradation effect of aniline substances was the best,and the degradation rate of six aniline substances was increased by about 5%compared with that of one-time oxidant;the degradation effect of hardness on aniline substances was weaker;the oxidation degradation of aniline substances was effected by the presence of CO₃^2-and HCO ₃^-in batches.Under neutral conditions,HCO₃^-inhibited the oxidative degradation of aniline compounds more obviously;NH⁴⁺-N and NO₃-N had little effect on the oxidative degradation of aniline compounds,and NO₂-N had obvious inhibitory effect;SO₄^2-inhibited the oxidative degradation of aniline compounds more obviously when the concentration was more than 100 mg/L;Mn²⁺promoted the oxidative degradation of aniline compounds in the range of 0-10 mg/L.4.Running for 200 hours under the condition of fully simulating groundwater environment,with the addition of oxidant,the aniline substances in effluent are basically below the detection limit,the flow rate of groundwater in each aquifer medium is different,the degradation effect of aniline substances in each aquifer medium is also different,and the degradation effect of aniline substances in each aquifer medium is in turn from strong to weak as follows:Soil>fine sand>gravel.5.After repairing the oxidative degradation of aniline by PRB reaction wall,the excessive iron ions and SO₄^2-were detected at the outlet.The contents of total iron and SO₄^2-after repairing the wall were basically lower than the standard limits of drinking water.6.Scanning electron microscopy?SEM?and infrared spectroscopy?IR?were used to analyze the mechanism of action from the microscopic point of view.After the action,the pore on the surface of the medium was filled and bulged.During the oxidative degradation of aniline,chemical bonds such as C-H,C=C-O,C=C,C-O,N-H,C=O participated.