Hydrogen Production Of Dark-fermentation Of Enterobacter Aerogenes And Its Combined Process With Photosynthetic Bacteria

Hydrogen production by bio-fermentation technology has broadprospects for development, but at this stage, both dark and photo-fermentativebio-hydrogen technology have their shortcomings and limitations, respectively. Thelow efficiency of energy transforming and high-cost of hydrogen production, whichgreatly restricted the development of bio-hydrogen production, especially limiteddevelopment of bio-hydrogen production by bio-energy such as crop stalks. Thereare vast straws in our country and biomass is rich in resources, but it couldn’t bedirectly used for bio-fermentation hydrogen production. They produce hydrogenonly after passing through the high cost of enzyme solution or combining with otherphysical and chemical pretreatment methods. It becomes an important elementlimiting the hydrogen production economy of straws and other cellulosic biomass.However, by selecting the high-efficient strains of hydrogen production andcombining the advantages of dark and photo-fermentative bio-hydrogen technology,it could get a range of optimum process parameters. It will be able to break thelimitations of hydrogen production of cellulosic biomass, improve gas productionrate and hydrogen conversion rate of bio-hydrogen production technique, getcombination of microorganisms with high economic efficiency of hydrogenproduction, and achieve the corresponding process conditions, which provided theimpetus for bio-hydrogen production technology from academic research to practicalapplication.This paper is financially supported by the National Natural Science Foundation(No.51376056)“Study on the regulation mechanism of biomass multiphase flowphotosynthetic hydrogen production process and its photo-thermal transfercharacteristic”. We choose strains (Enterobacter aerogenes) with high effective darkfermentation and photosynthetic bacteria (HAU-M1) that our lab preserved asstrains of hydrogen production, to study on hydrogen production by dark andphoto-fermentation combined. Through enriching culture of Enterobacter aerogenes,we have its basic rules and optimum fermentation conditions to produce hydrogen.With total hydrogen production and hydrogen production rate as the main evaluationindex, parameters of Enterobacter aerogenes which uses glucose to producehydrogen have been optimized. At the same time, the compositions of volatile fattyacids in fermentation reaction liquid are analyzed by liquid phase method. Twodifferent treatment ways through sterilization and non-sterilization are adopted forfermentation reaction liquid and after a series of pre-treatment; it continues to beused for hydrogen production by photo-fermentation. Effects of reaction liquid ofdark-fermentation and Enterobacter aerogenes on hydrogen production byphotosynthetic bacteria have been analyzed. Biological strengthening effect between Enterobacter aerogenes and photosynthetic bacteria is further studied. Meanwhile,we study the hydrogen production capacity of Enterobacter aerogenes based on cornstraw as substrate. Results show that:(1) Under the conditions of the volume ratio of reserved air and medium is1:5,the temperature is37℃, the pH is neutral and organic nitrogen is existed,Enterobacter aerogenes is most suitable for growth and reproduction. They canreach the logarithmic period at28hours. Enterobacter aerogenes has a goodacid-resisting in the pH range of7to4.5, which is beneficial for continuoushydrogen production process. Moreover, fermentative hydrogen production cycles ofEnterobacter aerogenes is very variable (between68h to156h).The optimumconditions of the shortest fermentative hydrogen production cycle of68h are asfollows: the temperature is35℃,the pH is6.5,meanwhile, the carbon-nitrogen ratiois3. Based on these conditions, hydrogen production rate and hydrogen conversionrate could reach to the value of261.5ml/g glucose and2.1mol H2/mol glucoserespectively.(2) The main components of volatile fatty acids include formic acid, ethanol,acetic acid and a small amount of butyric acid, which are beneficial to takeadvantages of photosynthetic bacteria. Acetic acid significantly reduces after the endof photosynthetic hydrogen production and it indicates that acetic acid is firstly usedby photosynthetic bacteria.The result of experiments shows that it is beneficial onimproving the yield of hydrogen production when sterilized fermentation broth isadded to the process of photosynthetic hydrogen production. Total gas productionand hydrogen production would pick up as fermentation broth is increased. Impacton photosynthetic hydrogen production when unsterilized fermentation broth isadded: total gas production and hydrogen production would pick up as fermentationbroth is increased when the amount of addition ranges from12.5to25percent. Thisis because acetic acid, butyric acid, and other small molecules of fermentation brothto join, increasing the amount of carbon. But it is up to50percent, gas productionwould be decrease, which is caused by excessive consumption of glucose whenmuch Enterobacter aerogenes are added. The sterilized fermentation broth has acertain impact on the dynamics pH value of hydrogen production system, generallyreduced by about0.7. The pH value of experimental group that is fermentation brothcontaining live Enterobacter aerogenes added, reduce by about2.2percent. This isbecause the metabolism of Enterobacter aerogenes and the increasing of smallmolecular acid. With the subsequent reaction of hydrogen production, acetic acid isgradually decomposed and pH value will rise, up to about6.0.(3) It indicates that Enterobacter aerogenes has the capacity of biologicalenhancement. Hydrogen production delay of strengthen group A is shortened and gasstarts to produce after12h; the fermentation cycle is shortened to5.5d; hydrogenproduction rate would be faster; the percentage of hydrogen increases, up to51percent; as carbon sources and acid-base environment changed, and cell would age,the process is terminated. Compared to the photosynthetic group, gas production improves by20.3percent and hydrogen production increases by49.6percent. Thefermentation cycle of strengthen group B is shortened to4.0d. This is mainly due todepletion of the carbon source, hydrogen production is terminated. Compared withthe strengthen group A, the total gas production does not cut by half in proportion,but improves by30.5percent, and hydrogen production increased by28.0percent. Itmeans that the low concentration of carbon source is beneficial for bio-enhancingbetween Enterobacter aerogenes and photosynthetic bacteria.(4) Enterobacter aerogenes has certain ability of directly using of corn stalk,but their efficiency is not high, capacity is very limited. Relatively speaking, cornstalk through premixed treatment and enzyme treatment has a better effect ofhydrogen production. Its total gas production and hydrogen production are higherthan untreated group and the effect of enzyme treatment is the best. Nevertheless, thetotal hydrogen production of Enterobacter aerogenes which uses of straw throughenzymatic hydrolysis is less than using of equivalent glucose. The proportion ofhydrogen among the gas which uses of straw through enzymatic hydrolysis is muchlower than the glucose group.