Effect Of Trace Elements On Biological Hydrogen Production By Anaerobic Fermentation Of Organic Wastewater

The world is turning to a search for clean energy sources to mitigate coming climate change and the impending shortage of readily available fuel to provide the energy necessary for present and projected human activities.A variety of possible fuel sources are being examined at present.Among these,many have proposed using hydrogen as an energy carrier in a future hydrogen economy.However,a sustainable,renewable supply of hydrogen to power this economy is required.Biohydrogen production by degradation of organic substances is considered as the promising and sustainable option in production of new energy,for its outstanding characteristics of clean,environmentally friendly and without consumption of fossil energy.In this work we focused on microbial hydrogen production with fermentative bacteria to use organic wastewater or other wastes as raw materials,which produce an energy product and simultaneously reduce the pollution strength of the wastes.We studied the influences of various environmental conditions,such as the concentration of substrates and the concentration of nitrogen sources for the systems associated with anaerobic mixed cultures.The effect and biocompatibility of several nanoparticles on hydrogen-producing bacteria were investigated.The results obtained in these studies provide a theoretical and experimental basis for large-scale biohydrogen productions in the practical processes of organic wastewater treatments.The basic conclusions are as follows:(1)Glucose was used as substrate to produce hydrogen with mixed fermentative bacteria in batch tests.The inoculum used in this study were mixed anaerobic hydrogen-producing bacteria derived from activated sludge,cow dung and pig manure,which can convert glucose,sucrose,starch,etc.to hydrogen with high efficiency.The efficiencies of hydrogen production were high at the concentration of 18-30 g·L-1 substrate,for the system inoculumed with activated sludge.The degradation of glucose for all the tests reached 95%.(2)Yeast powder and NH4Cl were used as nitrogen sources to produce hydrogen with mixed fermentative bacteria in batch tests.When the concentrations of nitrogen source increased,the hydrogen production yield kept steadily for yeast powder systems,however,the hydrogen yield decreased obviously for NH4Cl systems.The experimental results manifested that NH4Cl could be used as nitrogen source in practical wastewater treatments.(3)FeSO4 and mesoporous Fe3O4 nanoparticles were used to study the effect of iron on anaerobic hydrogen production with mixed fermentative bacteria in batch tests.When the concentrations of mesoporous Fe3O4 nanoparticles were 400 mg·L-1,the efficiencies of hydrogen production and the bacterial growths were higher than the blank test and the metabolic pathway was butyrate fermentation.The maximum amount of hydrogen production(1.53 mol·mol-1 glucose)was obtained at the Fe3O4 nanoparticles concentration of 400 mg·L-1,and the maximum percent of hydrogen was 43.8%.(4)Anaerobic biohydrogen fermentation using platinum nanoparticles as catalysts was investigated.Both the percentages and yields of hydrogen produced in all of the tests with platinum nanoparticles were lower than the blank test.The addition of platinum nanoparticles contributed to a longer lag phase on the fermentation of biohydrogen.The above results indicated that platinum nanoparticles was not suitable for the bioactivity improvement of hydrogen-producing microbes.(5)Anaerobic biohydrogen fermentation using gold nanoparticles as catalysts was investigated in two cultures(including the pure culture and the mixed culture).Both the percentages and yields of hydrogen produced in the tests using with 5-nm-gold nanoparticles were higher than the corresponding blank test.The addition of gold nanoparticles changed the metabolic way of hydrogen-producing bacteria,and decreased the production of ethanol,lactic acid and propionic acid.The maximum cumulative yield of hydrogen obtained at the test of the pure culture with 5-nm-gold particles was 2.21 mol per mol glucose,and the maximum percent of hydrogen was 55.0%.The results indicated that gold nanoparticles could remarkably improve the bioactivity of hydrogen-producing microbes.(6)A biohydrogen production system coupling the glucose degradation by two cultures(included alkaline pretreated mixed culture and non-pretreated mixed culture)and hydrogen production using silver nanoparticles as catalysts was investigated.The addition of silver nanoparticles changed the metabolic way of hydrogen-producing bacteria,and decreased the production of ethanol,propionic acid and valeric acid.Both the percentages and yields of hydrogen produced in the tests using silver nanoparticles were higher than the corresponding blank test.The tests with 20 nmol·L-1 silver nanoparticles behaved better than others.The maximum cumulative yield of hydrogen was 2.48 mol per mol glucose,and the maximum percent of hydrogen was 61.5%.The results indicated that silver nanoparticles could remarkably improve the bioactivity of hydrogen-producing microbes.That is,silver nanoparticles could not only improve the kinetics of biohydrogen production,but increase the total volumetric production from glucose.In the meanwhile,the addition of silver nanoparticles has another significant effect on the activation of hydrogen-producing bacteria.The results obtained in these studies are expected to provide basic and engineering data for the practical processes aimed to producing stable and prolonged hydrogen from wastewater.