Isolation Of A Photosynthetic Bacteria And Its Biohydrogen Production Characteristics

Hydrogen is widely considered as one of the most applicationsof renewable energy sources in the21st century because it is a high calorificvalue and clean energy. Hydrogen production by biological processes is foundto be less energy intensive, consumption of mineral resources and sustainablecompared to thermochemical and electrochemical processes, it is more andmore concerned in the research and application, many countries had invested alot of resources to research it. On the study of biological hydrogen production,photosynthetic bacteria produce hydrogen had been researched a lot.Hydrogenproduction by photosynthetic bacteria is widely concerned because it has highhydrogen production efficiency, high substrate conversion rate andenvironmental friendly.A photosynthetic bacterium strain was isolated from the activate sludge ofa wastewater treatment plant through light enrichment and double flat lineation.The photosynthetic bacteria was identified as Rhodopseudomonas palustrisaccording to bacterial colony characteristics and16SrDNA gene sequence,named Rhodopseudomonas palustris.PB-Z.Hydrogen production by PB-Z was studied in this paper. The studyincluded the optimization of its growth conditions, the hydrogen productioncharacteristics at different nitrogen source, nitrogen source concentration,carbon source, carbon source concentration,initial pH, magnesium ion concentrations.The experiment results showed that(1) Anaerobic illuminationwas the optimal growth pattern of PB-Z, and sodium acetate was the bestcarbon source for PB-Z growth. When the light intensity was4500lux, theinitial pH was7, PB-Z had the highest growth activity.(2)PB-Z had the highesthydrogen production activity when using carbamide as nitrogen source, thehydrogen yield could reach91.2±4.5ml,the hydrogen yield of PB-Z was101.1±3.4ml when the carbamide concentration was10mmol/L,it was thehighest.(3) Glucose were the best carbon source for hydrogen production ofPB-Z. When the glucose concentration was70mmol/L,PB-Z has themaximum hydrogen yield and substrate conversion efficiency, they were123±3ml and69.7±1.9%. The maximum hydrogen production activity ofPB-Z was in the logarithmic phase of growth.(4)The best initial pH value toproduce hydrogen was7.0. As the fermentation proceeded, the pH of theculture medium significantly declined.It was because the photosyntheticbacteria could produce organic acid by decomposing glucose, theaccumulation of organic acids could cause the acidification of bacteriumsolution. Adjusting pH on time (every24h)could promote the hydrogenproduction of PB-Z. The total amount of hydrogen increased from124.7±2.7ml to221.7±8ml, the glucose conversion efficiency increased from68.1%to91.2%.(5) The best magnesium ion concentration for PB-Z to producehydrogen was5mmol/L. When the magnesium ion concentration increased,the synthesis of photosynthetic pigment was inhibited, the hydrogenproduction decreased significantly. The appropriate magnesium ionconcentration could effectively promote the synthesis of PB-Z photosyntheticpigment.On the basis of single factor experiment, Magnesium ionconcentrations, initial pH value, reaction time were selected as independentvariables, and the hydrogen yield as the response value, experimental resultswere simulated and analyzed by response surface methodology. A quadratic polynomial equation was established for describing the relationship betweenhydrogen yield and three independent variables. Response surface analysisresults demonstrated that the selected factors had significant correlation withthe hydrogen yield. The optimum conditions of hydrogen yield weredetermined to be magnesium ion concentration4.77mmol/L, initial pH value7.05, reaction time77.5h. Under these conditions, the hydrogen production ofPB-Z was137.8ml, the value agreed with the predicted value with4.8%deviation. The results showed that the experimental value was comparable tomodel prediction and the method was practical.