| Straw biomass is rich in cellulose,so use it as substrate for microbial fermentation is a research hotspot to obtain clean energy production.However,due to its low density and high water-holding capacity,especially corn stover,stratification and crusts appeared in the process of hydrogen production by photo fermentation.In this paper,magnetic stirring and shaking were used to enhance the homogeneity of the concentration in each phase.Based on hydrogen yield,the effects of different perturbance modes and perturbance intensities on photo-fermentation hydrogen production from corn stover were analyzed.The results showed that:Diverse stirring intensities had different effect on photo-fermentation hydrogen production from corn stover.Compared with static-culture,proper stirring intensity can shorten the hydrogen production delay period and prolong the peak period of hydrogen production,but too high intensity not only reduced the hydrogen production potential,but also prolonged the hydrogen production delay period.The highest hydrogen yield of 61.14±1.8 mL·g-1 VS was obtained at stirring intensity of 150 rpm,and the average hydrogen content achieved 50.06±1.43%,which were 26.22%and 8.76%higher than static-culture,respectively.Under this condition,the energy conversion efficiency achieved 3.98±0.12%.On the premise of optimum stirring intensity of 150 rpm,four intermittent stirring modes showed different influences on the hydrogen yield and hydrogen production rate.The highest hydrogen yield of 57.63±1.75 mL g-1 VS was obtained in intermittent stirring C2,with the ratio of standing time to stirring time was 2:1,and the maximum hydrogen production rate increased by 65.05%compared with continuous stirring.Hydrogen yield from corn stover hydrolysate under intermittent stirring C2 was 5.74%lower than continuous stirring,18.97%higher than static-culture,and the energy consumption minimized significantly.Oscillation could help to accelerate of gas release,shorten fermentation time and improve hydrogen production rate.Different shaking frequencies have significant effects on hydrogen production by photo-fermentation of corn stover with different substrate concentrations.When the substrate concentration was 2 and 4 g/180 mL,hydrogen production potential was reduced by adding shaking.The lowest hydrogen yield was obtained at high shaking velocities.The hydrogen yield at shaking frequency of 160 rpm was 27.68±1.02 and 41.93±0.40 mL·g-1 VS,respectively.With the increase of substrate concentration,the viscosity of hydrogen-producing hydrolysate increased,and the optimum shaking frequency also increased.When the substrate concentration was 6,8 and 10 g/180 mL,the maximum hydrogen yield was obtained at shaking velocities of 80,120 and 160 rpm,which were 57.08±0.83,57.62±1.37 and 62.28±0.84 mL·g-1 VS,respectively.The maximum energy conversion efficiencies of substrate concentration with 2,4,6,8 and 10 g/180 mL were obtained at shaking frequencies of 0,0,80,120 and 160 rpm,which were 3.02±0.08,3.83±0.07,3.72±0.05,3.75 ±0.09 and 4.05±0.05,respectively.Shaking significantly enhanced the energy conversion efficiency of high concentration com stover.Adding perturbance to the hydrogen production system of com stover photo－fermentation,the changes of pH value and reducing sugar in the fermentation broth were the same as those in the static culture.The pH value decreased significantly in the early stage of fermentation,and the higher the corn stover concentration,the greater the decline of pH value.With the proceed of fermentation,the accumulated small molecule acids were utilized by photosynthetic bacteria and the pH value increased slowly.The change of reducing sugar concentration is closely related to hydrogen production.The rapid decrease of sugar concentration in the early stage of fermentation was used for bacterial growth and hydrogen production,and then the change range becomes smaller,finally reached a dynamic equilibrium. |
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