| Straw biomass which is rich in cellulose and hemicellulose can be converted into clean hydrogen energy by microbial metabolic pathways.Bio-hydrogen production by co-fermentation from two or more kind of hydrogen producing bacteria as an effective way of biological hydrogen production,which can combine the characteristics of different hydrogen producing bacteria and exert their advantages,thus,it can improve the hydrogen production efficiency.Based on the synergy between different hydrogen producing bacteria,with corn straw as raw materials,the main factors affecting bio-hydrogen production by co-fermentation from Enterobacter aerogenes AS1.489 and photosynthetic bacteria HAU-M1 were studied and optimized in this paper.This paper was completed under the support of the national natural science foundation project "Study on the regulation mechanism and coupling characteristics of energy cascade of biological hydrogen production in two steps of dark-photo fermentation"(Project No.: 51676065).Firstly,components and enzymatic hydrolysis rate of corn straw were measured and analyzed,so as to discuss the feasibility of bio-hydrogen production by co-fermentation with corn straw as raw materials.Then,the growth of Enterobacter aerogenes AS1.489 and photosynthetic bacteria HAU-M1 was determined and their growth rule was explored.Then,single factor experiments and Box-behnken Design(BBD)of response surface were used to optimize the main factors affecting bio-hydrogen production by co-fermentation from Enterobacter aerogenes AS1.489 and photosynthetic bacteria HAU-M1.Finally,the p H and reducing sugar content in the process of bio-hydrogen production by co-fermentation from Enterobacter aerogenes AS1.489 and photosynthetic bacteria HAU-M1 at the optimal conditions were measured and analyzed,and the changes of surface morphology,composition and structure of corn straw before and after fermentation were analyzed by scanning electron microscope(SEM),Fourier infrared spectra(FTIR)and X-ray diffraction(XRD).The purpose of this study is to provide references and basis for further research on bio-hydrogen production by co-fermentation from different hydrogen producing bacteria based on straw biomass.The results showed that:(1)Corn straw was mainly composed of element C(63.54%)and O(30.78%),and the contents of cellulose and hemicellulose of it were 38.53% and 22.79%,respectively.Under the condition of enzyme load of 250 mg/g,the reducing sugar concentration was 1.36 mg/m L when corn straw after mechanical crushing has been digested for 72 h,at this time,the enzymatic hydrolysis rate was as high as 54.50%.Therefore,to produce hydrogen by co-fermentation with agricultural waste corn straw is an effective way for energy output.(2)Cell dry weight was regarded as a parameter to measure the bacterial growth situation,Enterobacter aerogenes AS1.489 and photosynthetic bacteria HAU-M1 reached the late stage of logarithmic growth period and the early stage of stable growth period after being training about 48 h,at this time,the cell dry weight of Enterobacter aerogenes AS1.489 and photosynthetic bacteria HAU-M1 were 1.16 g/L and 1.20 g/L,respectively,and bacterial activity and concentration were relatively high at this time.(3)Through the single factor experiments,the optimal conditions of substrate concentration of 35 g/L,initial p H value of 6.5,light intensity of 3500 lux,fermentation temperature of 30 ? and inoculation concentration of 40% for bio-hydrogen production by co-fermentation from Enterobacter aerogenes AS1.489 and photosynthetic bacteria HAU-M1 were obtained.At the same time,it was also got that primary and secondary order of the influence of the above various factors on bio-hydrogen production by co-fermentation from Enterobacter aerogenes AS1.489 and photosynthetic bacteria HAU-M1 was initial p H value > fermentation temperature > substrate concentration >light intensity > inoculation concentration.(4)Through the BBD experiments,the optimal conditions for bio-hydrogen production by co-fermentation from Enterobacter aerogenes AS1.489 and photosynthetic bacteria HAU-M1 were finally determined as substrate concentration of 41.6 g/L,initial p H value of 6.6 and fermentation temperature of 30.3?,and the maximum cumulative hydrogen yield of 362.4 m L was obtained under this conditions.Validation experiments were performed under this conditions,the actual cumulative hydrogen yield of 353.7 m L was got,the relative error between actual values and predicted values was 2.4%,the results showed that this model had a good fitness.Variance analysis results of BBD experiments showed,interaction between substrate concentration and initial p H value had the most significant effect on bio-hydrogen production by co-fermentation from Enterobacter aerogenes AS1.489 and photosynthetic bacteria HAU-M1,and interaction between initial p H value and fermentation temperature influence on it the second,and interaction between substrate concentration and fermentation temperature had minimal influence on it.(5)Pictures of SEM showed that corn straw after bio-hydrogen production by co-fermentation were fragmented and messy,and structure of them became loose and frivolous,and some holes irregularly distributed on their surface,and fiber structures had basically been destroyed.Through the analysis of the change of the position and intensity of characteristic peaks in FTIR,the absorption peaks near 1425 cm-1,1510 cm-1 and 1730 cm-1of corn straw after bio-hydrogen production by co-fermentation disappeared,and the intensities of the absorption peaks near 2900 and 895 cm-1 reduced,which suggested that the structures of cellulose and hemicellulose of corn straw were effectively destroyed in the process of hydrogen production.According to the results of XRD,diffraction intensity of corn straw after bio-hydrogen production by co-fermentation was lower than that of corn straw before hydrogen production,and crystallinity of corn straw after bio-hydrogen production by co-fermentation increased,which also showed fiber structures of corn straw were effectively destroyed and utilized during the process of hydrogen production. |
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