Study On The Degradation Performance Of Nitrobenzene In Groundwater By Surfactant Solubilization With Synergistic Persulfate

As an important component of the earth’s water supply,groundwater is closely related to human development.With the rapid development of agriculture and industry,a large number of non-aqueous phase liquids（NAPLs）have entered groundwater causing serious hazards.Nitrobenzene（NB）as a dense non-aqueous phase liquids（DNAPLs）has extremely low water solubility,poor biodegradability,carcinogenic,teratogenic and mutagenic properties,and causes serious impact on human health and ecological environment in groundwater.Surfactant-enhanced aquifer remediation technology（SEAR）uses the amphiphilic nature of surfactants to improve the flow and solubility of NAPLs,enhance the migration ability of contaminants,and increase their solubility in the aqueous phase;the subsequent flushing solution can degrade the contaminants in the aqueous phase through further physicochemical treatment to achieve the removal effect.Based on the above principles,Tween 80,sodium dodecylbenzene sulfonate（SDBS）and combination systems were selected for solubilization of nitrobenzene in this thesis.The effects of surfactant concentration,temperature,p H,ionic strength and coexisting organic matter on the solubilization of nitrobenzene by surfactants were investigated.The desorption experiments of different types of surfactant solutions on contaminated media were carried out to investigate the desorption effect of surfactant solutions under different particle size and water-to-soil ratio conditions.One-dimensional simulated column experiments were also conducted to evaluate the actual flushing effect of surfactants on contaminated media.Finally,the degradation performance of the persulfate system on solubilized nitrobenzene was investigated,and the effects of various environmental factors on the persulfate advanced oxidation process were considered.The main results and conclusions are as follows:（1）The solubilization of nitrobenzene by Tween 80 increased with the increase of concentration and temperature,and decreased with the increase of p H.When anionic-nonionic surfactants were mixed,the greater the proportion of nonionic surfactants,the better the solubilization effect.The high concentration of inorganic electrolytes promoted the solubilization effect of nitrobenzene.Under the condition of the same mass concentration of Cl^-,the size of cationic effect was Ca²⁺>Mg²⁺>K⁺>Na⁺;under the condition of the same mass concentration of Na⁺,the size of anionic effect was SO₄^2->Cl^->HCO₃^-.The configuration of six different types of groundwater ionic systems all promoted the surfactant solubilization of nitrobenzene.The presence of naphthalene or aniline inhibited the solubilization of nitrobenzene by Tween 80,where the inhibition of naphthalene was greater than that of aniline.（2）The desorption effect of contaminated sand with different particle sizes increased with the increase of Tween 80 concentration,and changed little with the increase of SDBS concentration.The desorption efficiency of 50 g/L Tween 80 solution could reach more than90%.The anionic-nonionic surfactant solution was compounded,and the desorption effect of the contaminated medium was enhanced with the increase of the proportion of Tween 80.The addition of inorganic electrolytes and short-chain alcohols was beneficial to enhance the desorption effect of surfactants,but there was an optimal compounding ratio between short-chain alcohols and surfactants,and too many short-chain alcohols will occupy the solubilization sites of surfactants and reduce the desorption effect of pollutants.The desorption efficiency of the surfactant was slightly improved by increasing the water-to-soil ratio.In the one-dimensional simulated column rinsing experiments,increasing the surfactant concentration or compounding with inorganic electrolytes and short-chain alcohols were beneficial to the rapid removal of organic pollutants.The cumulative removal rates（12 PV）of nitrobenzene by 5 g/L Tween 80+10 g/L CaCl₂,5 g/L Tween 80+20%C₂H₅OH and 50 g/L Tween 80 were 60.72%,61.23%and 63.11%,respectively.（3）The effect of sodium persulfate in degrading nitrobenzene after solubilization was stronger than that of sodium percarbonate,and the reaction speed was fast and the degradation efficiency was high.When the amount of sodium persulfate was 60 m M,the degradation efficiency of nitrobenzene was 82.03%in 10 min;the degradation efficiency was more than 98%in 120 min.The optimal molar ratio of the three substances in the citric acid chelated divalent iron activated sodium persulfate system was 6:1:1.The degradation efficiency of nitrobenzene by the persulfate system decreased with the increase of the initial solution p H;the reaction rate was accelerated and the reaction time was shortened with the increase of the temperature.The three different types of surfactant solubilization systems（5 g/L Tween 80,5 g/L Tween 80+10g/L CaCl₂,5 g/L Tween 80+20%C₂H₅OH）all showed good degradation effect of persulfate,and the reaction reached the equilibrium state in 20 min;the degradation efficiency of nitrobenzene could reach more than 96%in 120 min.