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Research on hydrogen production by photofermentation has gained renewed interest in recent times because of its potential to generate hydrogen from renewable sources in a sustainable manner for use as an alternate energy carrier. Photofermentative bacteria use nitrogenase enzyme in the presence of adenosine triphosphate (ATP) and reducing power for hydrogen production in photobioreactors (PBRs). Depending on the pigments present in the bacteria, an optimal combination of photoparameters such as light source, intensity, duration, and wavelength have to be maintained in PBRs for efficient light-to-hydrogen conversion. In this article, over 130 literature reports on photoparameters are reviewed to aid in optimal design and operation of photobioreactors. This review includes a discussion of mathematical models reported in the literature to predict light attenuation and photochemical efficiencies of photobioreactors. As part of this study, models for predicting hydrogen evolution and predicting photochemical efficiency as a function of light wavelength and quantum requirement were developed and validated using a range of experimental data compiled from the literature. A case study is presented to illustrate how literature data could be used to size solar-based PBRs for hydrogen production. Based on this case study, it is concluded that major technological breakthroughs are required to reduce the current cost for biohydrogen production by solar-powered PBRs. [ABSTRACT FROM AUTHOR]

Abstract: Biohydrogen production by dark fermentation in batch reactors was modeled using the Gompertz equation and a model based on Anaerobic Digestion Model (ADM1). The ADM1 framework, which has been well accepted for modeling methane production by anaerobic digestion, was modified in this study for modeling hydrogen production. Experimental hydrogen production data from eight reactor configurations varying in pressure conditions, temperature, type and concentration of substrate, inocula source, and stirring conditions were used to evaluate the predictive abilities of the two modeling approaches. Although the quality of fit between the measured and fitted hydrogen evolution by the Gompertz equation was high in all the eight reactor configurations with r 2 ∼0.98, each configuration required a different set of model parameters, negating its utility as a general approach to predict hydrogen evolution. On the other hand, the ADM1-based model (ADM1BM) with predefined parameters was able to predict COD, cumulative hydrogen production, as well as volatile fatty acids production, albeit at a slightly lower quality of fit. Agreement between the experimental temporal hydrogen evolution data and the ADM1BM predictions was statistically significant with r 2 >0.91 and p-value <1E-04. Sensitivity analysis of the validated model revealed that hydrogen production was sensitive to only six parameters in the ADM1BM. [Copyright &y& Elsevier]

Abstract: Feasibility of biohydrogen production by dark fermentation at two temperatures (22°C and 37°C) in unbuffered batch reactors was evaluated using heat-treated compost as inocula and sucrose as substrate, without any initial pH adjustment or inorganic nutrient supplements. Gas production was quantified by two different pressure release methods – intermittent pressure release (IPR) and continuous pressure release (CPR). Hydrogen production (47.2mL/gCOD/L) and sucrose-to-hydrogen conversion efficiency (53%) were both found to be highest at the lower temperature and IPR conditions. Hydrogen production was higher at the lower temperature irrespective of the pressure release condition. The high yield of 4.3mol of hydrogen/mole of sucrose obtained in this study under IPR conditions at 22°C is equivalent to or better than the literature values reported for buffered reactors. Even though literature reports have implied potential inhibition of hydrogen production at high hydrogen partial pressures resulting from IPR conditions, our results did not show any negative effects at hydrogen partial pressures exceeding 5.0×104 Pa. While our findings are contrary to literature reports, they make a strong case for cost-effective hydrogen production by dark fermentation. [Copyright &y& Elsevier]

Abstract: Bacterial consortium capable of producing hydrogen in low pH (LpH) range of 3.3–4.3 is reported in this study. This operational pH is two full units below that of previously reported hydrogen producing organisms. Low pH inocula were derived from a batch biohydrogen reactor inoculated with heat treated compost (∼120°C, 2h), which was allowed to accumulate biogas to reach three atmospheres of equivalent headspace pressure and system pH of 3.0. Acclimation effect had positive influence on H2 production and LpH inocula were passed sequentially into more than 15 generations to achieve consistent conversion efficiency and hydrogen composition, further tested in 23 other culture cycles. With hydrogen composition in the headspace ranging from 50% to 60%, conversion efficiency of ∼43% achieved in LpH systems is comparable to that of other buffered systems. Feasibility of hydrogen production in LpH systems is demonstrated in unbuffered reactors under intermittent pressure release conditions and in absence of initial pH adjustment and stirring. Conversion efficiencies, however, decreased by ∼1-fold for each 3°C drop below the optimum temperature of 22°C. [Copyright &y& Elsevier]

Abstract: A kinetic model for photofermentative biohydrogen production is developed in this study to predict the dynamics of the process. The proposed model contains 17 parameters to describe cell growth, substrate consumption, and hydrogen evolution as well as inhibition of the process by biomass, light intensity, and substrate. Batch experimental results from the literature were used to calibrate and validate the model with malic acid as a model substrate, using Rhodobacter sphaeroides as a model biomass. Temporal hydrogen evolution and cell growth predicted by the proposed model agreed well with the experimentally measured data obtained from four literature reports, with statistically significant correlation coefficients exceeding 0.9. Based on sensitivity analysis performed with the validated model, only six of the 17 parameters were found to be significant. Model simulations indicated that the range of optimal light intensity for maximum hydrogen yield from malate by R. sphaeroides was 150–250W/m2. [Copyright &y& Elsevier]

Abstract: Most dark fermentation (DF) studies had resorted to above-ambient temperatures to maximize hydrogen yield, without due consideration of the net energy gain. In this study, literature data on fermentative hydrogen production from glucose, sucrose, and organic wastes were compiled to evaluate the benefit of higher fermentation temperatures in terms of net energy gain. This evaluation showed that the improvement in hydrogen yield at higher temperatures is not justified as the net energy gain not only declined with increase of temperature, but also was mostly negative when the fermentation temperature exceeded 25 °C. To maximize the net energy gain of DF, the following two options for recovering additional energy from the end products and to determine the optimal fermentation temperature were evaluated: methane production via anaerobic digestion (AD); and direct electricity production via microbial fuel cells (MFC). Based on net energy gain, it is concluded that DF has to be operated at near-ambient temperatures for the net energy gain to be positive; and DF + MFC can result in higher net energy gain at any temperature than DF or DF + AD. [Copyright &y& Elsevier]

• Graphene oxide supplement yield 73% pure biohydrogen with 85% conversion efficiency. • Graphene oxide (GO) supplement resulted in 297% higher biohydrogen yield. • Acetate fermentation pathway of H 2 production was retained by GO systems. • Optimal GO levels were identified for thermophilic biohydrogen systems. • Biodiversity and microbial community biodynamics were evaluated. Modern society envisions hydrogen (H 2) fuel to drive the transportation, industrial, and domestic sectors. Here, we explore use of graphene oxide nanoparticles (GO NPs) for greatly enhancing bio-H 2 production by a consortium based on Thermoanaerobacterium thermosaccharolyticum spp. Thermophilic batch bioreactors were set up at 60 OC and initial pH of 8.5 to assess the effects of GO NPs supplements on biohydrogen production. Under optimal GO NPs loading of 10 mg/L, the supplemented system yielded ∼ 300% higher H 2 yield (6.78 mol H 2 /mol sucrose) than control. Such an optimized system offered 73% H 2 purity and 85% conversion efficiency by promoted the desirable acetate fermentation pathway. Miseq Illumina sequencing tests revealed that the optimal levels of GO NPs did not alter the microbial composition of consortium. [ABSTRACT FROM AUTHOR]