Evolution Of Emulsified Oil Reaction Zone And Its Remediation Mechanism For Cr(?)contaminated Groundwater

Hexavalent chromium is a common groundwater contamination,and it mainly comes from chrome ore exploitation,chromium slag stockpile and a variety of industries,including metallurgy,tanning,textile,and so on.As a human carcinogen listed in Group “A”,Cr(?)contaminant effects human health and its remediation has great importance and significance.Emulsified oil has the advantage of good mobility,slow-release,high-efficiencyand cheapness.Emulsified oil reaction zone has a good application prospect for remediation of contaminated groundwater by injecting emulsified oil to aquifer.In this thesis,influence of various additive substances onemulsified oil performance had been studied;an optimal enhanced emulsified oil named P-ESO had been selected and prepared.By injection of P-ESO in three dimensional simulator,evolution of emulsified oil reaction zone building procedure and remediation for Cr(?)contaminated groundwater had been studied.Microbial community structure and diversity was also researched to better understand degradation mechanism of Cr(?).This research laid a theoretical foundation for the application of emulsified oil reaction zone in Cr(?)contaminated groundwater.Adding additive substance P to traditional emulsified oil could stimulate more rapid start-up of emulsified oil reaction zone,anaerobic and reducing environment was formed faster.After being injected in simulator,emulsified oil could migrate well along to groundwater flow path,it could migrate 100 cm in four days.Emulsified oil reaction zone was developed in eighteen days,and its dimension was 100 cm wide,30 cm deep and 50 cm high.Above 90% emulsified oil was retained by soil,this port of emulsified oil could provide electron for growth and metabolize of microorganism long-termly.During this process,emulsified oil was decomposed to ultimate product acetate,pH and ORP of system declined.Oxygen reduction,nitrate reduction,iron reduction and sulfate reduction occurred respectively on the first,first,seventh,seventh day after emulsified oil injection.On the thirty-second day,DO,nitrate,sulfate in reaction zone had been exhausted,and concentration of ferrous was above 40mg/L.Emulsified oil reaction zone could remediate Cr(?)contaminated groundwater with remediation efficiency above 97.53% over 480 days.Cr(?)contaminating fluid of 20mg/L concentration was flowed into the simulator,and it was remediated rapidly in leading edge of reaction zone,this region was also injection area.On the 150 th day,Cr(?)penetrated simulator from the substratum of reaction zone which region had fewer emulsified oil.After the 300 th day,pollution scope of Cr(?)continuously extended,in the meantime,region of reaction zone continuously narrowed.During the process,various of biogeochemical reaction experience following stage: hit by Cr(?),recover,stabilize and gradually weak.Emulsified oil could promote the morphology of iron in medium to transform to be more bioavailable.Portion of iron bound to carbonate,Fe-Mn oxides and organic matter increased.Degraded Cr(?)bounded to organic matter and deposited in medium.Emulsified oil could domesticate microorganisms in reaction zone for the first time,the number of species eliminated and communities diversity decreased.Microorganisms which could utilize emulsified oil or its degradation products increased and reproduced massively.Among them,Geobacter,Pseudomonas could reduce iron and nitrate,respectively.Clostridium sensu stricto could degrade emulsified oil,reduce nitrate,iron and sulfate,and it was the most important microbe during development process of emulsified oil reaction zone.Cr(?)contaminated groundwatercould domesticate microorganisms in simulator for the second time.The number of species eliminated and communities diversity decreased.75 days after Cr(?)contaminated groundwater flowing into simulator,remediation for Cr(?)in reaction zone depended heavily on reduction of various biogeochemical reaction product including NO2-?S2-?Fe2+,and a small proportion of remediation relied on bio-reduction of Pseudomonas,contamination was completely degraded in leading edge of reaction zone.After 240 days,remediation for Cr(?)in reaction zone depended mostly on bio-reduction and bio-sorption of Exiguobacterium,Citrobacter,Acinetobacter and Pseudomonas.