Study On Degradation Performance Of Nitrobenzene In Groundwater By Tween-80 Synergized Sulfide Nano Zero-Valent Iron/Persulfate

Groundwater is an important part of fresh water resources.In recent years,organic pollution of groundwater has seriously threatened human living environment.Therefore,it is an urgent task to study efficient remediation technology of organic pollution of groundwater.In this paper,nitrobenzene,a typical DNAPL（Dense nonaqueous phase liquid）pollutant,was selected as the target pollutant.In order to overcome the shortcomings such as the easy agglomeration and oxidation of nano zero-valent iron（n ZVI）,sulfide nano zero-valent iron（S-n ZVI）was modified by post-sulfurization method.S-n ZVI was combined with persulfate（PS）to form a reduction oxidation system,and Tween-80 solubilization synergied to form Tween-80/S-n ZVI/PS remediation system,while combining persulfate oxidant with slow release technology.The Fe²⁺produced by S-n ZVI reduction of nitrobenzene was used to activate PS to degrade aniline.The degradation performance and mechanism of the Tween-80/S-n ZVI/PS system on nitrobenzene and the feasibility of its application in the actual contaminated site were explored through the analysis of influencing factors,characterization means and soil column simulation experiment.The main research results of this paper are as follows:（1）The experimental results of S-n ZVI/PS degradation of nitrobenzene showed that S-n ZVI could effectively reduce nitrobenzene to aniline,and the Fe²⁺produced by S-n ZVI reduction of nitrobenzene could quickly activate PS in a short time,and the oxidative degradation rate of aniline reached 91.53%within 5 min.The degradation rates of nitrobenzene and aniline under the optimal dosage of S-n ZVI=70 mg and PS=1.2 m M for 100 mg/L nitrobenzene reached 97.45%and 86.25%,respectively.The initial p H of solution had no significant effect on the degradation of nitrobenzene and aniline in S-n ZVI/PS system.The degradation of nitrobenzene by S-n ZVI system was the best under acidic condition（p H=3）,while the degradation of aniline by S-n ZVI/PS system was the best under alkaline condition（p H=9）.（2）The surfactant Tween-80 had a strong solubilization effect on nitrobenzene when the concentration was above the critical micellar concentration（CMC）.The Tween-80/S-n ZVI/PS degradation of nitrobenzene experimental results showed that the degradation rates of nitrobenzene and aniline at the optimal dosage of S-n ZVI=70 mg and PS=1.2 m M for solubilized nitrobenzene by Tween-80 were 96.74%and 100%,respectively.When the concentration of Tween-80 was 0.2-0.6 g/L,it had a negative effect on the degradation rate of nitrobenzene by S-n ZVI,and a positive effect on the degradation performance of aniline by S-n ZVI/PS.However,as the concentration of Tween-80 increased,it had no significant effect on the degradation of nitrobenzene and aniline.The initial p H of solution had no significant effect on the degradation rate of nitrobenzene in Tween-80/S-n ZVI system,but the degradation efficiency of aniline in Tween-80/S-n ZVI/PS system was poor in acidic conditions.The sulfoferride on the surface of S-n ZVI had efficient electron transfer,which could improve the degradation rate of nitrobenzene and aniline in the system to a certain,and Fe（0）and Fe（II）-S would be gradually consumed along with the reaction,and the oxidation product after the reaction of S-n ZVI was mainly Fe₃O₄.During the degradation of aniline in the Tween-80/S-n ZVI/PS system,a series of intermediates were generated.（3）PS slow-release gel material was prepared by nano-silica sol.The experimental results of gel release performance showed that the solidification time of PS slow-release gel was the shortest under the condition of p H=5.5 and Si O₂=40wt%.The increase of Si O₂ mass fraction would reduce the rate of gel release PS,and the increase of PS content would shorten the gel solidification time to a certain extent.In the experiment of degradation of nitrobenzene by Tween-80/S-n ZVI/PS slow-release gel,the degradation rate of 70 mg S-n ZVI/PS gel（40wt%Si O₂,3.46wt%PS）on 100 mg/L solubilized nitrobenzene by Tween-80 for 3 h reached 99.68%,and the residue of aniline was 3.21 mg/L.In the one-dimensional sand column simulation experiment,compared with Tween-80 and Tween-80/S-n ZVI systems,Tween-80/S-n ZVI/PS slow-release gel system had significantly better degradation of nitrobenzene and aniline,and the cumulative degradation rates of 1m L pure nitrobenzene by 14 PV（700 m L）in 5 g/L Tween-80/1.3 g S-n ZVI/6.5 g PS slow-release gel（40wt%Si O₂,3.46wt%PS）was 87.49%,and the effluent concentrations of aniline was 28.74 mg/L,indicating that the existence of PS slow-release gel could not only degrade aniline but also improve the degradation rate of nitrobenzene.