| Biohydrogen production is one of the most environmentally friendly ways of hydrogen production.Biohydrogen production mainly includes dark fermentation and light fermentation.Photo-fermentation form dark fermentation effluent will improve the hydrogen production yield of biohydrogen production.Currently studies mainly focus on the effects of various factors on biohydrogen production by dark-fermentation and photo-fermentation biohydrogen production,but the pilot-scale biohydrogen production technology needs further study.In the actual production process,the design,operation and automation control of the experimental platform of biohydrogen plant are very worthy of further study.In this paper,Computer Fluid Dynamics was used to simulate the velocity and concentration fields of biohydrogen production in dark-fermentation reactor and photo-fermentation reactor.From the point of view of hydrodynamics,the regulation calculation of the biohydrogen system was carried out.The experimental platform of the baffled continuous-flow dark-and photo-fermentation biohydrogen production was designed and built.The solar hot water was used to provide thermal insulation for the experimental platform of the device.The solar photoconductive fiber was used to provide light for the device,and the solar photovoltaic power generation was used to provide electrical support for the device.The automatic control and detection system of the device can automatically control the feeding,flow rate,stirring,switch of hot water,and sampling of reaction solution according to the experimental requirements.The effects of hydraulic retention time,substrate concentration and organic loading rate on biohydrogen production rate by dark-and photo-fermentation were studied.The results of this work provided a good theoretical and technical support for the development of pilot-scale biohydrogen production.The conclusions were summarized as follows:(1)Computer Fluid Dynamics was used to simulate fields of biohydrogen production in the reactor.It can be seen from the nephogram formation of velocity field that with the bacteria and hydrogen-producing mixture entering the dark-fermentation reactor and the photo-fermentation reactor,clear velocity field gradually formed in the reactor and finally tended to be stable.The baffled structure fully mixed the hydrogen-producing bacteria and the medium in the rector,which providing the hydrogen production performance of the device.Comparing the nephogram of velocity flow of the dark-fermentation reactor under different hydraulic retention time,it can be seen that the nephogram and the vortex in the reactor increased as the hydraulic retention time decreased from 48 h to 24 h.When hydraulic retention time was further decreased to 12 h,the nephogram in the reactor were weakend.The strengthening of vortex had a positive effect on enhancing the performance of hydrogen production.Similarly,comparing the velocity-field nephogram of the photo-fermentation reactor under hydraulic retention time,it can be seen that there was no significant difference in the velocity-field nephogram of the 4 chambers.However,with the decrease in hydraulic retention time from 72 h to 24 h,the velocity of the reaction liquid in the reactor becomes faster.(2)A baffled continuous flow dark-and photo-fermentation biohydrogen production platform was designed and built.The reactor consisted of a dark-fermentation reactor with a 3 m3 working volume and two photo-fermentation reactors,each with a 4 m3 working volume.Solar was used to provide thermal insulation,illumination,electric power in the biohydrogen production.The experimental platform was equipped with automatic control and detection system,which could realize the functions of feeding,stirring and data detection in the biohydrogen production.(3)The effects of hydraulic retention time(12-48 h)on the dark-fermentation biohydrogen production were studied with temperature of 35? initial pH of 7,and substrate concentration of 10 g L-1.It was found that hydrogen production rate increased first and then decreased with the decrease of hydraulic retention time from 48 to 12 h.a maximum hydrogen production rate of 40.45 mol m-3 d-1 was achieved at hydraulic retention time of 24 h.Reasonable control of hydraulic retention time can improve performance of pilot-scale continuous flow biohydrogen production.The effects of substrate concentration(10-40 g L-1)on dark-fermentation biohydrogen production were studied at the optimal hydraulic retention time of 24 h.It was found that hydrogen production rate increased with the increase in the substrate concentration(10-30 g L-1),whereas hydrogen production rate began to decrease when substrate concentration increased to 40 g L-1.The maximum hydrogen production rate of 100.16 mol m-3 d-1 was obtained at substrate concentration of 30 g L-1.The fermentative broth composition,pH value,oxidation-reduction potential,and hydrogen production rate of different chambers were significantly different.(4)The effects of hydraulic retention time(24-72 h)on the photo-fermentation biohydrogen production were studied with temperature of 30?,initial pH of 7,and substrate concentration of 10 g L-1.Hydrogen production rate increased from 64.29 mol m-3 d-1 to 83.48 mol m-3 d-1,when hydraulic retention time decreased from 72 h to 48 h.A maximum hydrogen production rate of 104.91 mol m-3 d-1 was achieved at hydraulic retention time of 24 h,with a corresponding hydrogen content of 43.44%-46.98%.Hydrogen production rate increased first and then decreased with the increase in substrate concentration at hydraulic retention time of 24 h.Hydrogen production rate increased first and then decreased with the increase in organic loading rate,while hydrogen production rate decreased gradually.A minimum hydrogen production rate of 64.13±4.58 mol m-3 d-1 was obtained at organic loading rate of 3.3 g L-1 d-1(hydraulic retention time 72 h,substrate concentration 10 g L-1),corresponding with a maximum hydrogen yield of 19.43±1.39 mmol g-1.A maximum hydrogen production of 148.65±4.19 mol m-3 d-1 was achieved at organic loading rate of 20 g L-1 d-1(hydraulic retention time 24 h,substrate concentration 20 g L-1).(5)The fermentative broth/gas characteristic of different chambers in the dark/light biohydrogen production was studied at hydraulic retention time of 24 h,substrate concentration of 10 g L-1,and initial pH of 7.Hydrogen production rate of 40.45 mol m-3 d-1,oxidation-reduction potential of-380 mV--439 mV,biomass concentration of 1.25 g L-1-1.52 g L-1,acetic concentration of 45.83 mM,butyric concentration of 15.00 mM were observed in the dark-fermentation hydrogen production.Hydrogen production rate of 23.34 mol m-3 d-1,oxidation-reduction potential of-420 mV--455 mV,biomass concentration of 1.26 g L-1.41 g L-1 were observed in the dark-fermentation hydrogen production.The removal rates of acetic and butyric reached 85.10%? 93.16%after hydrogen production,respectively. |
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