Effect And Mechanism Of NaNO₃ On Hydrogen Production By Enterobacter Sp. HDX08

High concentration organic wastewater could used as raw material to produce hydrogen by anaerobic dark fermentation,which has broad application prospects.However,the development of anaerobic biological hydrogen production is limited due to the influence of many factors,such as the salt content and type of wastewater.Nitrates are widely present in a variety of high-concentration organic wastewater such as food processing.Therefore,Enterobacter sp.HDX08(referred to as“bacterium HDX08”),a strain of high-efficiency anaerobic hydrogen producing bacteria screened by our research group,was used in this paper to study the effects of different NaNO₃ concentrations on its anaerobic hydrogen production performance.Through the analysis of ORP,coenzyme NADH,key enzyme activity,intermediate product and nitrogen balance calculation,the related influence mechanism was analyzed.The main conclusions are as follows:(1)The bacterium HDX08 is not only a strain of high-efficiency anaerobic hydrogen producing bacteria,but also has the ability of denitrification.When NaNO₃is present in the wastewater,denitrification will be carried out first by the bacteria.When the concentration of NaNO₃ was less than 1 g/L,the bacteria started denitrification first,followed by anaerobic hydrogen production.However,when the concentration of NaNO₃ was?2 g/L,denitrification was only performed.(2)When the concentration of NaNO₃ is 0.5 g/L,it can promote the anaerobic hydrogen production and ethanol production capacity of the bacteria;Compared with blank group without NaNO₃,the hydrogen and ethanol production of the strain were increased by 1.46 times and 3.25 times,respectively.When the concentration of NaNO₃was 1 g/L,the maximum hydrogen production of the bacteria lower than that of blank group,and the denitrifying denitrification system produced a large amount of N₂O,but not N₂.When the concentration of NaNO₃ was?8 g/L,the denitrification of this strain was significantly inhibited.(3)When NaNO₃ concentration was 0.5 g/L and 1 g/L,the starting time of hydrogen production by bacterium HDX08 bacteria was delayed by 4 h and 6 h compared with the condition without salt,which was used for NO₃^-denitrification to produce N₂O.The duration of hydrogen production was prolonged by 2 h and 10 h,respectively.(4)When the concentration of NaNO₃ in the wastewater is 0.5 g/L,the ORP value of the treatment system gradually decreases from-100 m V to about-350 m V,and at the same time,bacterium HDX08 can promote the production of more key enzymes such as coenzyme NADH,pyruvate dehydrogenase and ferredox reductase,thus improving the anaerobic hydrogen production capacity.(5)When the concentration of NaNO₃ in the wastewater is 2.0 g/L,the ORP value of the treatment system is maintained at 60 m V-90 m V,which is higher than the ORP(-400 m V--200 m V)required for anaerobic hydrogen production,and about 175.0 mg N/L(in terms of nitrogen)nitrite will be generated in the process.High ORP value and nitrite concentration inhibited the anaerobic hydrogen production of bacterium HDX08.