| As the development of agriculture and industry, the tremendous use of fertilize,pesticide,industrial wastewater and solid wastes are dumped into environment incessantly,which leads a series of accident of contamination in groundwater and soil. According to the categories, pollutants can be classified into organic and inorganic pollutants. When organic pollutants run into the underground environment, they will contaminate soil and groundwater in the form of Non-aqueous phase liquid. NAPLs are difficult to dissolve in water, and are degraded very slowly, so they are pollution sources in soil and groundwater environment which can exist for many years. Therefore, remediation of organic pollution in soil and groundwater becomes one of the hot problems in the field of environment science and engineering. Traditional remediation method of organic pollution in soil and groundwater is pump-and-treat. It must pump abundant of groundwater to treat with organic pollutants for the low solubility of them, then recirculates the treated water into underground. The method has a low efficiency and rebounds easily, so it needs a long time to remediate. However, surfactants can enhance the solubility of the organic in water greatly. Based on the solublization, surfactant- enhanced remediation(SER) is developed and has became the major contents of study on soil and groundwater remediation.SER is based on the solublization and mobilization of surfactants to insoluble organic pollutants.so the NAPL in the acquifer and the pollutants in soil can be sweepouted by SER,then the remediation would finish through biodegradation and so on. It will take a short time to remediate,and SER is fit for the in-situ flushing in acquifer as well as vadose zone.As long as the development of SER,it has apply in in-situ flushing of soil and groundwater to organic pollutants successful.However, we should pay attention to the adsorption in soil except for the solublization of surfactants as using the SER.On the one hand,the efficiency of flushing is effected because of the large adsorption of surfactants in soil. On the other hands,the surfactants adsorbed in soil will bind a part of organic pollutants,and cause the adsorption of pollutants.At present,it is less reports about how to reduce the adsorption of surfactants during the flushing. In hence,it's necessary to find a approach that can reduce the adsorption of surfactants in in-situ flushing.Cationic surfactants usually would be adsorbed on the surface of soil grain strongly, therefore, anionic and nonionic surfactants are used more frequently in practical flushing. the adsorption loss of anionic surfactants is relatively small, but the CMC is big,the ability of solubility enhancement is small, therefore, the cost is high in practical remediation. As to nonionic surfactants, the ability of solubility enhancement is high, but the adsorption loss on soil grain surface is much more. At present, nonionic surfactants have been applied in soil flushing and bioremediation abroad.Researchers usually adopt single surfactant to flushing insoluble organic pollutants,but the efficiency is discontent. Recently,the efficiency can be enhanced through adding coexistence such as inorganic salt or organic polymer to flushing water.And the mixture of nonionic surfactant and anionic surfactant could contribute to the solublization to insoluble organic pollutants.But the change of adsorption for nonionic surfactant because of the addition of coexistence is not sure.Therefor,it is significant to study the effect of adsorption for nonionic surfactant because of the addition of coexistence. During the tertiary process, to reduce the quantity of surfactants,the normal approach is pre-absorbing cheap chemical agent to reduce the adsorption of surfactants in reservoir .The cost of oil washing can be greatly reduced if using lignosulfonate as the sacrifacial agent in the washing agent because of its low price.we could use lignosulfonate as the sacrifacial agent to reduce the adsorption of surfactants in the process of in-situ flushing.The solublization of nonionic surfactants is more powful than anionic surfactants.And Tween80 is one of the nonionic surfactants,the toxicity of Tween80 to microscopic organism is the lowest. Moreover, Tween80 is cheap and apply in the field of medicines and food widely. Adsorption of nonionic surfactants Tween80,Tween20 and anionic SDS on sand was investigated ,and the effect of adsorbing medium,temperature and PH on the adsorption of Tween80 on sand were evaluated.Then we tried to reduce the adsorption of Tween80 on sand through adding the coexistence (inorganic salts-CaCl2,organic polymer-PEG4,anionic surfactant-SDS and lignosulphonates-sodium lignosulphonate or ammonium lignosulphonate) to Tween80 solution.At last, simulated surfactants in-situ flushing vadose zone which was contaminated by nitrobenzene.And the results would illustrate the effect of coexistence to surfactants in-situ flushing.The results show:(1) Adsorption of anionic surfactant SDS is much less than of non-ionic surfactant Tween80,Tween20, and adsorption of Tween80 is more than of Tween20 on mid-sand. (2) In terms of adsorption of Tween80, the four mediums are in the sequence of silt clayï¹¥fine clayï¹¥ mid clay. The content of organic matter and temperature increase is benefit to adsorption of Tween80; And the adsorption is less in neutral or weak alkaline environment than acid environment. (3) Adsorption of Tween80 is enhanced when CaCl2 is added, while it has little change when PEG400 is added. (4) Adsorption of Tween80 will be increased when SDS is added in mixed flushing solution or firstly. (5) With the increase of molar fraction of lignosulphonates in mixing flushing solution, adsorption amount of Tween80 on sand decrease, especially when lignosulphonates is added firstly. (6) The infection of sodium lignosulphonate to water solubility enhancement of Tween80 and Tween80 +CaCl2 can be almost ignored, therefore, in simulated experiment,the change of flushing efficiency is due to adsorption of Tween80 with adding sodium lignosulphonate firstly. (7) The simulated experiment shows that flushing efficiency is evidently higher when adding sodium lignosulphonate firstly than flushing directly.
|
PDF Full Text Request