Study Of The Transition Stage And Process Regulation Of Dark-Photo Bio-Hydrogen Production

Bio-hydrogen from agricultural straw,a green technology,realizes the integration of clean energy production and high value utilization of agricultural waste.Sequential dark-and photo fermentation hydrogen production method can enhance substrate conversion efficiency.The research of physical and chemical properties of transition state and regulation and mechanism are keys for high efficiency biohydrogen production in dark-and photo fermentation hydrogen production system.In the paper,the the characteristics of dark fermentation hydrogen production and photo fermentation hydrogen production were analyzed and the fermentation process were optimized.And then exploring the regulation mechanism of the transition state process of dark-and photo fermentation hydrogen production from the perspective of macroscopic hydrogen production performance and microscopic substrate electron transfer.Finally,the a gray prection model GM?1.6?was also established according to the experimental data.All the work can be summarized as follows.?1?During dark fermentation process,hydrogen yield from corn straw,rice straw,corncob and sorghum stalk by simultaneous saccharification and fermentation?SSF?were 20.54%,10.31%,13.99% and 5.92% higher than asynchronous saccharification and fermentation?ASF?,respectively,SSF offered a distinct advantage over ASF with respect to fermentation time decreasing from 108 h to 60 h.Results of Plackette Burman design showed that initial p H,temperature and enzyme loading had a statistically significant effect on SSF hydrogen production.Central composite design?CCD?was further carried out to evaluate interaction between the selected variables,the optimal conditions were determined to initial p H of 5.63,temperature of 45.41?,and enzyme loading of 200 mg/g,in which the maximum hydrogen yield was 83.67 m L/g TS.Hydrogen production pathways with SSF were main acetic acid and butyric acid fermentation.The concentrations of acetic acid and butyric acid in fermentation broth were 3652.23 ± 202mg/L and 945 ± 79mg/L.?2?Photosynthetic bacteria HAU-M1 can absorb 325 nm,382 nm,490 nm,592 nm,807 nm and 865 nm spectr,the results of spectral absorption showed that HAU-M1 capture photoelectron by chlorophyll a and carotenoids.Logistic equation was used to analyze the growth characteristics,themaximum concentration of the strain could reach 0.85 g / L,and the actual maximum value was 0.83 g / L.The optimum operating conditions of photosynthetic bacteria HAU-M1 were p H 7,temperature 30? and light intensity 3000 lx.HAU-M1 hydrogen production pathway was mixed fermentation pathway,and acetic acid fermentation pathway and butyric acid fermentation pathway were the main fermentation pathways.?3?The regulation mechanism of transition state of dark-and photo fermentation was proposed by analyzing the physicochemical properties of dark fermentation process and photo fermentation hydrogen production performance,the results showed that the highest hydrogen yield was obtained at the concentration of NH₄⁺ 2.12 ± 0.32 mm,and 5.31% of the substrate electronic energy was transferred to hydrogen;sodium chloride and ammonium chloride showed negative effect on substrate transfer,the largest proportion of the substrate electron transfered to hydrogen without the addition of sodium chloride and ammonium chloride,10.66%;the highest cumulative hydrogen production was 72.49 ± 2.5 m L at the dilution ratio of 1:0.5,and 27.24% of substrate electron transfered to hydrogen;using corn straw enzymolysis liquid to regulate the composition of organic matter in the transitional fermentation liquid,when the mixture ratio of enzymolysis liquid and dark fermentation effluents was 1:2,the conversion efficiency of organic carbon increases significantly,which is 1251.27 ± 54.78 H₂ m L/g TOC;high light intensity and inoculation amount lead to a large amount of energy in the substrate transferred towards bacteria and SMPs.The gray model GM?1,6?was established to predicted the hydrogen yield under different condition,and showed that the hydrogen production was positively correlated with dilution ratio,C/N and light intensity,but negatively correlated with ammonia concentration and inoculation amount,the average relative error of the model was 7.87%,which showed that the simulation effect was better.?4?The hydrogen production capacity of transition state could be enhanced by adding trace reagents and controlling fermentation mode.The optimal concentration of L-cysteine and Fe₃O₄ NPs was 300 and 100mg/L,respectively,under which the cumulative hydrogen production was 195.45 ± 8.6 and 190.81 ± 7.6m L,and the activity of nitrogenase was 1423 ± 44 and 1322 ± 32 nmol C₂H₂/m L/h.Excessive L-cysteineand Fe₃O₄ NPs resulted in much more substrate energy transfered to SMPs,the maximum substrate enectron transferred to hydrogen was 29.94% and 29.24% at 300 mg/L L-cysteine and 100mg/L Fe₃O₄ NPs.Controlling the adding time interval of L-cysteine and Fe₃O₄ NPs could improve the activity of nitrogenase without weakening flocculation and increase the H₂ production,the maximum H₂ yield of 234.55±7.5m L was obtained at 12 h interval time,35.94% substrate electrons diverted towards bio-H₂ generation,and the corresponding nitrogenase activity increased by 2.12 times as comparing to the control,at the interval of 24 h,24.22% of the substrate electrons were transferred to SMPS,resulting in a large amount of substrate electron waste.The modified Gompertz and Han-Levenspiel models were employed to model the effect of the L-cysteine and Fe₃O₄ NPs on hydrogen production,the fermentation system with L-cysteine and Fe₃O₄ NPs was non competitive inhibition,that is,the inhibition of hydrogen production increased with the increase of the concentration of reagents,and the predicted critical L-cysteine and Fe₃O₄ NPs concentrations were 4630.87 and 1969.18mg/L,respectively.Compared with batch and continuous mode,semi-continuous was a promising fermentation mode due to the continuous hydrogen production mode lead to the loss of hydrogen producing functional bacteria,50% decanting volume ratio and 24 h feeding interval time were found to be the best condition,under which the hydrogen production rate and hydrogen yield were 8.44 mL/h,1386.22 ± 44.23 mL H₂/g TOC,respectively,and 37.71% substrate electron transfered to hydrogen.