Transport Of EVO In Heterogeneous Aquifers And Its Influencing Factors Of Cr(Ⅵ) Contaminated Groundwater Remediation

Chromium compounds is an important chemical raw materials,non-complianced chromium-containing waste water and residue has caused serious groundwater pollution,and threatened the human health and environmental security.Study on the remediation of Cr(Ⅵ)contaminated groundwater is of great significance to environmental risk control and engineering remediation.Based on the previous studies,simulation experiments were conducted to study the migration characteristics of emulsified vegetable oil(EVO)in lens and layered heterogeneous aquifers,the effects of initial Cr(Ⅵ),carbon source,nitrate,sulfate and groundwater hardness on the remediation of Cr(Ⅵ)contaminated groundwater were also investigated.The results showed that:(1)The distribution of EVO in heterogeneous aquifers is excellent;retention of oil in aquifer media was high,which is favorable for the formation of microbial reation area;the permeability of aquifer was slightly decreased after EVO injection.(2)Cr(Ⅵ)concentration reach up to 110.0 mg/L can still be reduced by indigenous microbial community enhanced by EVO;however,as the increase of initial Cr(Ⅵ)concentration,the recovery efficiency decreased,which requires longer reaction zone.The hydrolysis and acidification is the rate-limiting step for remediation,which is important for competition of carbon source.Inhibitory effects of Cr(Ⅵ)on hydrolysis and acidification makes the utilization of EVO slowly,prolonging the life of reaction zone.(3)When the concentration of EVO is less than 5.0 g/L led to faster Cr(Ⅵ)reduction rate,and its concentration higher than 5.0 g/L may act some inhibitory on Cr(Ⅵ)reduction.(4)Nitrate can accelerate the reduction rate of Cr(Ⅵ);nitrate reduction can improve the p H of reaction system,promote the hydrolysis and acidification of EVO,raise the carbon source and electron donor concentration;concurrence of nitrate reduction and Cr(Ⅵ)reduction may make carbon competition.(5)Sulfate can reduce the reduction rate of Cr(Ⅵ)slightly;sulfate reduction occurs after nitrate reduction and Cr(Ⅵ)reduction,and no carbon source competition with them;sulfate reduction can make the reaction environment a strong reduction environment,which provides good conditions for the complete decomposition of EVO.(6)Groundwater hardness can slightly increase the reduction rate of Cr(Ⅵ);Ca,Mg can form precipitation with long-chain fatty acid,which improve the utilization effiencecy of carbon sources,and has a positive effect on long-term supply of carbon sources.