| Hydrogen energy is regarded as the cleanest renewable energy to achieve carbon neutrality and replace fossil energy.The zero-negative carbon emission feature of photofermentation biological hydrogen production technology has attracted wide attention from all sectors of society.At the same time,magnetic biological effect has been proved to be closely related to microbial molecular structure,microbial activity and microbial metabolism,and affect the hydrogen production process of photo-fermentation.In this paper,using giant reed as substrate,the effects of static magnetic field and its co-addition with magnetic nanoparticles on photo-fermentation biological hydrogen production were studied.The characteristics of hydrogen production,fermentation fluid characteristics,soluble new metabolites and nitrogenase activity during hydrogen production were analyzed.The results of hydrogen production were fitted and analyzed using the modified Gompertz equation.The process of photo-fermentation hydrogen production in static magnetic field was optimized to improve the activity of hydrogen producing microorganisms and strengthen the process of hydrogen production via photo-fermentation.The experimental results showed that:(1)The static magnetic field had a positive effect on the hydrogen production process of photosynthetic bacteria.The maximum cumulative hydrogen production(112.7 m L/g TS)and maximum hydrogen production rate(3.87 m L/g TS/h)were obtained at 20 m T magnetic field intensity,which were significantly increased by 26.1% and 20% compared with that of without external magnetic field,respectively(p<0.05).In addition,at the magnetic field intensity of 20,30 and 40 m T,the delay period of hydrogen production was shortened by 56.7%,46.9% and 66.8% compared with the control group(9.43 h),respectively.At the peak of hydrogen production of 36 h,the reducing sugar yield(0.8 g/L)was 2.52,2.33 and 2.55 times that of the control group(0.03 g/L),respectively.The addition of static magnetic field also ensured the low oxidation-reduction potential(-450~-420 m V)and promoted the conversion of substrate to volatile fatty acids.The energy conversion efficiency of 10,20,30 and 40 m T magnetic fields increased by 6%,27.27%,21.2% and 25.8%,respectively,compared with the control group(6.6%).(2)The optimal magnetic field intensity of 20 m T and the co-addition of magnetic nanoparticles could further improve the cumulative hydrogen production in the process of photosynthetic biological hydrogen production.Under the influence of 20 m T magnetic field and 100 mg/L magnetic Fe3O4 NPs,the cumulative hydrogen production increased by 24.2% compared with 85.66 m L/g TS,while the addition of magnetic Fe NPs and Ni NPs increased by 8.8% and 20.5% compared with the equal intensity of magnetic field.Kinetic analysis showed that the addition of magnetic nanoparticles could obtain the highest hydrogen production potential.Moreover,the further addition of magnetic nanoparticles also enlarged the content of reducing sugar yield to varying degrees.In addition,the further addition of magnetic nanoparticles reduced the concentration of ethanol,enhanced the metabolism of volatile fatty acids of photosynthetic bacteria,and promoted the conversion of substrates to acetic acid and butyric acid.(3)The static magnetic field and its co-addition with magnetic nanoparticles were beneficial to the improvement of nitrogenase activity.During the experiment,the nitrogenase activity remained between 80.6 IU/L and 84.3 IU/L.With the stimulation of 20 m T static magnetic field intensity,the nitrogenase activity achieved the highest level(121.13 IU/L)at 18 h.After further addition of 100 mg/L magnetic Fe3O4 NPs,the nitrogenase activity reached 157.7 IU/L at 12 h,which was 1.87 times that of the control group.The results revealed that the nitrogenase activity was obviously enhanced under the co-addition of static magnetic field and magnetic nanoparticles,which indicated that the static magnetic field and its combination effect with magnetic nanoparticles had positive effects on the activity of key enzymes in photosynthetic bacteria and hydrogen production.(4)Based on the optimal 20 m T static magnetic field intensity and 100 mg/L Fe3O4 NPs concentration,the optimum fermentation process was obtained: The illumination condition was 4000 Lux,p H was 7 and the inoculated volume ratio of bacteria was 20%.Under different single factor conditions,the hydrogen production delay period of photosynthetic bacteria was shortened to different degrees under the optimal fermentation conditions,which indicated that appropriate fermentation conditions played a crucial role in shortening fermentation time and enhancing the hydrogen production performance of photosynthetic bacteria. |
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