Enhancement Mechanisms Of Diesel Contaminated Soil Washing/Flushing With Surfactants And Additives And Prevention Of The Secondary Pollution

The diesel contaminated soil always causes serious heath to threaten in direct and indirect ways.The major drawbacks of traditional soil remediation technologies are a large amount of quantity,high energy costs,low effectiveness,secondary pollution production.The washing/flushing by means of surfactant solutions has been proven to be a promising technique for remediation of contaminated soil due to its economic,quick and low secondary pollution.Different kinds of surfactants were selected as washing/flushing agents in this thesis.The impact factors of diesel removal,the changes of interfacial force and surface tension were investigated.The mechanism for decontamination between soil grains and diesel was studied and compared.For further treatment of effluent simultaneously qualifiedly discharged,a natural carbon scavenger was synthesized.Meanwhile,the phytotoxicity of washing agents and the remediation method comprehensively were studied.It will provide more possibilities on scientific theory for high-quality diesel contaminated soil remediation.The main conclusion and innovation points of this thesis are as follows:(1)The detergency of anionic surfactants was higher than nonionic surfactants in the same concentration(CMC-fold).That was because the CMC of anionic surfactants was very high,more molecules were in the washing solution(with the same fold CMC fold concentration).And changing the p H of the washing liquid can significantly shift the diesel elution effect.It was found that the reduction of surface tension was the main mechanism.The oil content of contaminated soil had an extremely significant impact on the elution effect.For less than 9%of oil content contaminated soil,the oil removal can reach 95%with a single surfactant.When the oil content was higher than 9%,the efficiency increased slower by increasing surfactant concentration.The temperature significantly affected the diesel removal efficiency from 40?to 45?;the most level improvement could be achieved.With the increase of the aging time,the tightness of the combination of diesel pollutants and soil grains was shown to be very significant.With the action of sunlight and microorganism,the migration and transformation of diesel were weaker,.so the contaminated soil was more difficult to treat with very high efficiency.(2)Selecting nonionic surfactants as the contaminated soil washing/flushing agents,their CMCs were usually low.When the mechanism of surfactant“micelle solubilization”was used,the reagents'dosage can be greatly reduced,and the secondary pollution production.For the diesel-contaminated soil with 12%oil content,the cleaning effect of saponin was the best when the contaminated soil's volume ratio and the cleaning solution was 1:25.The contact angle of the contaminated soil was 30.46±0.8°,and the contact angle after cleaning was 8.80±0.2°;the hydrophilicity of the soil was restored after washing.(3)For the remediation of aging contaminated soil,the washing of a single surfactant could not play a good remediation effect.With sodium salt addition,the surface tension decreased,and the solubilization of diesel was enhanced.When washing 12%oil content and 30 d aged contaminated soil,saponin at 0.2 g L^-1,which was enhanced with 2%(saponin amount)humic acid sodium salt(HASS),the diesel removal was improved by over 10%.HASS could also prevent the inhibition of saponin on the arugula root systems growth.The root systems length of arugula,cucumber and lettuce increased by 5%,18%and 25%.Besides,the functionalized carbon nanoparticles were synthesized with over 80%growth promotion.(4)For in-situ washing remediation,the application of microbubble and mixture flushing agent(saponin and beta-cyclodextrin)with ratio(1:1)showed significant enhancement for surfactant flushing.The enhanced washing for diesel removal mechanisms includes the buoyancy effect,adhesion and quenching of microbubbles.For sand with 40%oil content,the best elution effect could be as high as 99.2%.(5)A two-shell structure nano-carbo scavenger(NCS)was synthesized to treat the effluent.The TOC of effluent with 0.2 g L^-1 mixture agent flushing was changed from 180.1 mg L^-1 to 2.6mg L^-1 with NCS treated and could be qualifiedly discharged.The NCS was evaluated with cell and embryo experiments and confirmed to be ecosystem friendly.(6)A study system of diesel contaminated montmorillonite(the most difficult part to wash in loam soil)washing remediation was built and combined with the removal rate and micelles'characterization to investigate the enhanced mechanism.Adding 2%HASS into 0.8 g L^-1 saponin solution,the hydrophobic volume space extended 239.8%,and the corresponding diesel removal rate was 45.3%.Sonicating the 0.8 g L^-1saponin solution for 25 min,the hydrodynamic diameter increased significantly,and the micelles volume increased 161.8%by 46.5%diesel removal rate.The enhanced diesel removal rate mechanisms for in-situ flushing include micelles solubilization,microbubbles flotation,and ultrasonic cavitation.