| With the rapid development of urbanization and industrialization,groundwater pollution is becoming more and more serious in China.Nitrate(NO3-)and hexavalent chromium(Cr(Ⅵ))often occur in groundwater.Physicochemical method has some problems,such as high treatment cost,easy to produce concentrated solution and secondary pollution.Compared with physicochemical method,bioreduction is a more efficient and environment-friendly technology.Among them,membrane biofilm reactor(MBf R)is a new water treatment technology in which microorganisms use electron donors to degrade oxidized pollutants.A large number of studies have shown that in MBf R,the addition of electron donor can achieve the efficient removal of oxidized pollutants.At present,the commonly used electron donors include H2 and CH4.With the continuous application of methane in the field of removing oxidized pollutants,the oxidizability of other alkanes in natural gas has been concerned.Ethane is the most important component of natural gas except methane.In 2019,Nature reported the coupling process of ethane anaerobic oxidation and sulfate reduction,which provided a basis for ethane as an electron donor to degrade pollutants.Ethane is more oxidable than methane.Theoretically,it can be used as an electron donor to drive the reduction of nitrate and hexavalent chromium.But at present,there is no direct evidence.Therefore,if ethane can be used as an electron donor to drive the removal of nitrate and hexavalent chromium from groundwater,it will have important theoretical and practical significance for the development of new remediation technologies for nitrate and hexavalent chromium contaminated groundwater.In this paper,the reduction process of NO3-,Cr(VI)and the coexistence of NO3-and Cr(VI)driven by ethane as electron donor was studied in the ethane-based membrane biofilm reactor(C2H6-MBf R),and the microbial community structure and functional flora were analyzed.The main conclusions are as follows:(1)When the hydraulic retention time(HRT)is 3 d and the influent NO3--N concentration is 10 mg/L,the removal rate of NO3--N is about 97%.Mycobacterium and Proteobacteria are important functional bacteria.The microbial mechanism of nitrate reduction is the synergism between ethane oxidizing bacteria and nitrate reducing bacteria.The intermediate products produced by ethane oxidizing bacteria in the process of using oxygen to activate ethane will be used by nitrate reducing bacteria and act as electron donors to reduce nitrate.(2)When HRT=3d and Cr(VI)concentration in influent water is 0.8 mg/L,the Cr(VI)removal rate is about 95%.Deinococci and Mycobacterium are important functional bacteria.The microbial mechanism of hexavalent chromium reduction is the synergism between ethane oxidizing bacteria and chromate reducing bacteria.The intermediate products produced in the process of ethane activation by ethane oxidizing bacteria will be used by chromate reducing bacteria and used as electron donor to reduce hexavalent chromium.(3)When the influent contained 0.8 mg/L Cr(VI)and 4 mg/L NO3--N,the removal rate of Cr(VI)and NO3--N were 29% and 54%,respectively.Proteobacteria、Deinococci and Mycobacterium are important functional bacteria.In the process of NO3-and Cr(VI)reduction driven by ethane as electron donor,the intermediate products produced by ethane oxidizing bacteria in the process of activating ethane with oxygen are utilized by nitrate reducing bacteria and chromate reducing bacteria,and used as electron donor to reduce nitrate and Cr(VI).The decrease of NO3-and Cr(VI)removal efficiency is mainly due to the mutual inhibition of bacteria,especially the decrease of relative abundance of ethane oxidizing bacteria.This study provides a theoretical basis for the reduction process of nitrate and hexavalent chromium driven by ethane as an electron donor,which will contribute to the development of a new remediation technology for nitrate and hexavalent chromium contaminated groundwater using ethane. |
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