Efficient Degradation Of Chromium-trichloroethylene By Biological Precipitation Sulfidated Nanoscale Zero-valent Iron

Groundwater pollution has been concerned by researchers because of its concealment,persistence and complexity.Among them,the mixed pollution between Cr(Ⅵ)and trichloroethylene(TCE)is representative in groundwater.These pollutants exist in the form of dense non-aqueous phase liquid(TCE)and dissolved heavy metal(Cr(Ⅵ)),which is difficult to degrade in the environment.Nanoscale zero-valent iron(nZVI)has the potential to remove mixed pollutants in wastewater at the same time,and is considered to be a promising material for in-situ remediation of soil and groundwater.However,due to its high reactivity,nZVI is prone to hydrogen evolution reaction in aqueous medium,which has great defects in practical application.In recent years,sulfidated nanoscale zero-valent iron(S-nZVI)has been proposed to overcome the problem that nZVI is easy to be oxidized by water.The sulfurized iron shell formed on its surface can effectively inhibit the hydrogen evolution reaction and has stronger adsorption capacity and dechlorination efficiency.However,when S-nZVI degrades the compound pollution of Cr(Ⅵ)and TCE,Cr(Ⅵ)is very easy to passivate with the surface of s-nzvi,which seriously inhibits the degradation of TCE.In order to solve the above problems,the biological precipitation sulfidated nanoscale zero-valent iron(BP-S-nZVI)was prepared by the biological sulfurization method based on sulfate reducing bacteria(SRB),which degraded the compound pollution of Cr(Ⅵ)and trichloroethylene.Compared with chemical precipitation sulfidated nanoscale zero-valent iron(CH-S-nZVI)prepared by chemical method,the negative charge on the surface of BP-S-nZVI can reduce the adsorption of Cr(Ⅵ)on the surface of S-nZVI particles.More importantly,the SRB extracellular polymer adhered to the surface of BP-S-nZVI also provides an additional way for Cr(Ⅵ)removal,which can effectively remove Cr(Ⅵ)and make more Fe~0 used for TCE removal.In this experiment,the dechlorination efficiency of TCE by BP-S-nZVI with different sulfur iron ratio under the coexistence of Cr(Ⅵ)was investigated,and the amount of SRB extracellular polymer adhered to the surface of the material was controlled by adjusting the exposure time of the material in the bacterial solution,so as to explore its influence.At the same time,the removal path of Cr(Ⅵ)in the reaction system was explored.The experimental results show that in the compound pollution,BP-S-nZVI effectively overcomes the inhibition of Cr(Ⅵ),and BP-S-nZVI with the best S/Fe molar ratio of 1.0 has achieved the best degradation effect.The removal rate of Cr(Ⅵ)is 94.8%,and the removal efficiency of TCE is 83.1%,which is 1.52 times that of CH-S-nZVI.BP-S-nZVI improves the electronic selectivity of TCE in Cr(Ⅵ)-TCE co-pollution.The SRB extracellular polymer adhered to the surface of the material also provides an additional way for the removal of Cr(Ⅵ),effectively avoids the passivation problem between Cr(Ⅵ)and S-nZVI,and can degrade the composite pollution of Cr(Ⅵ)-TCE more efficiently.