| Environmental pollution due to the burning of fossil fuels makes it necessary to find alternative energy sources that are environmentally friendly. A great deal of attention is being paid to the usage of hydrogen (H2), a sustainable energy carrier which is clean, efficient and renewable; moreover it does not generate any toxic by-products. Through biological processing, hydrogen can be produced through dark fermentation from organic wastes. Additionally, there is also a need to dispose of human-derived wastes in an environmentally friendly manner, using wastes to produce hydrogen offers a possible alternative to current waste-disposal methods. Therefore, fermentative hydrogen production has attracted increasing attention in recent years. The suspended cell system and attached cell system have been frequently used for fermentative hydrogen production. Based on the above two systems for biohydrogen production, it was developed a novel continuous mixed immobilized sludge reactor (CMISR) for hydrogen production, so as to provide basic technical and theoretical foundation for industrial hydrogen production.A study of biohydrogen production was performed in a continous flow anaerobic fermentation reactor. Under the operational conditions of the inoculants, batch experiments were carried out to convert molasses wastewater pretreated by using anaerobic mixed bacteria at35℃, when the pH value, chemical oxygen demand (COD) and oxidation-reduction potential (ORP) of the efflunt ranged from3.7to4.57,1980to6407mg/L, and-230to-464mV, respectively. Soluble metabolites were predominated by acetate and ethanol, with smaller quantities of butyrate, valerate and propionate. The total amount of ethanol and acetate accounting for83.55%of the total terminal products after35days operation and stable ethanol-type fermentation was formed. The hydrogen volume content was estimated to be30-45%of the total biogas and the biogas was free of methane throughout the study. Furthermore, together with the corresponding degradation efficiencies and metabolites were compared. The rate of COD removal reached at a peak values of40.91%and stable at a value about20%. A mixed culture fermentation in a CSTR reactor system under the operational conditional was employed to convert this substrate into hydrogen with a yield of1.53m3/m3.d. Hydrogen generation using the fermentation process is possible with various type of wastewater using either mixed or pure cultures. This CSTR system showed that mixed microbial is an a promising high-efficient bioprocess for enhancing the hydrogen production from high-strength wasterwater. Moreover, hydrogen and ethanol are promising biofuels and have great potential to become alternatives to fossil fuels. The influence of organic loading rates (OLRs) on the production of fermentative hydrogen and ethanol were also investigated in a continuous stirred tank reactor (CSTR) from fermentation using molasses as substrate. Four OLRs were examined, ranging from8to32kg/m3d. The H2and ethanol production rate in CSTR initially increased with increasing OLR (from8-24kg/m3d). The highest H2production rate (12.4mmol/hl) and ethanol production rate (20.27mmol/hl) were obtained in CSTR both operated at OLR=24kg/m3d. However, the H2and ethanol production rate tended to decrease with an increase of OLR to32kg/m3d. The liquid fermentation products were dominated by ethanol, accounting for31%～59%of total soluble metabolities. Linear regression results show that ethanol production rate (y) and H2production rate (x) were proportionately correlated which can be expressed as y=0.5431x+1.6816(r2=0.7617). The total energy conversion rate based on the heat values of H2and ethanol was calculated to assess the overall efficiency of energy conversion rate. The best energy conversion rate was31.23kJ/hl, occurred at OLR=24kg/m3d.A continuous stirred-tank reactor (CSTR) process with granular activated carbon (GAC) was developed for fermentation hydrogen production from molasses-containing wastewater by mixed microbial cultures. Operation at35℃, an initial biomass of17.74g/L and hydraulic retention time (HRT) of6h, the CSTR reactor presented a continuous hydrogen production ability of5.9L/d and the biogas was free of methane throughout the experiment. Dissolved fermentation products were predominated by ethanol and acetate acid, with smaller quantities of propionic acid, butyric acid and valeric acid. It was found that GAC could make the immobilized system durable and stable in response to organic load impacting and low pH value. When the organic loading rate (OLR) ranged from8kgCOD/(m3d) to4kgCOD/(m3d), stable ethanol-type fermentation was formed, and the ethanol and acetate concentrations account for89%of the total liquid products. Moreover, the effects of organic loading rates (OLRs) on fermentative productions of hydrogen and ethanol were also investigated in a continuous stirred tank reactor (CSTR) with attached-sludge using molasses as substrate. The CSTR reactor with attached-sludge was operated under different OLRs, ranging from8to24kg/m3d. The H2and ethanol production rate essentially increased with increasing OLR. The highest H2production rate (10.74mmol/hl) and ethanol production rate (11.72mmol/hl) were obtained both operating at OLR=24kg/m3d. Linear regression results show that ethanol production rate (y) and H2production rate (x) was proportionately correlated and can be expressed as y=1.5365x-5.054(r2=0.9751). The best energy generation rate was19.08kJ/hl, occurred at OLR=24kg/m3d. In addition, the hydrogen yield was affected by the presence of ethanol and acetic acid in the liquid phase, and the maximum hydrogen production rate occurred while the ratio of ethanol to acetic acid was close to1.A novel continuous mixed immobilized sludge reactor (CMISR) containing activated carbon as support carrier was used for fermentative hydrogen production from molasses wastewater. When the CMISR system operated at the conditions of influent COD of2000-6000 mg/L, hydraulic retention time (HRT) of6h and temperature of35℃, stable ethanol type fermentation was formed after40days operation. The H2content in biogas and chemical oxygen demand (COD) removal were estimated to be46.6%and13%, respectively. The effects of organic loading rates (OLRs) on the CMISR hydrogen production system were also investigated. It was found that the maximum hydrogen production rate of12.51mmol/hL was obtained at OLR of32kg/m3d and the maximum hydrogen yield by substrate consumed of130.57mmol/mol happened at OLR of16kg/m3d. Therefore, the continuous mixed immobilized sludge reactor (CMISR) could be a promising immobilized system for fermentative hydrogen production. |
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