• Energy Research

Abstract This paper presents the life cycle inventory (LCI) of hydrogen production by Clostridium butyricum fermentation of Scenedesmus obliquus hydrolysate. The main purpose of this work was to evaluate the potential of H 2 production from microalgal biomass and the respective energy consumption and CO 2 emissions in the bioconversion process considering the microalga production, acid hydrolysis of S. obliquus biomass, preparation of the inoculum and culture media, and fermentation. The scale-up to industrial production was not envisaged. The hydrogen yield obtained in this work was 2.9 ± 0.3 mol H 2 /mol sugars in S. obliquus hydrolysate. Results show that this process of biological production of hydrogen can achieve 7270 MJ / MJ H 2 of energy consumption and 670 kg CO 2 / MJ H 2 . The microalgal culture is the stage responsible for 98% of these total final values due to the use of artificial lighting. All stages and processes with the highest values of energy consumption and CO 2 emissions were identified for future energetic and environmental optimisation.

This paper presents a life cycle inventory of biohydrogen production by Clostridium butyricum through the fermentation of the whole Scenedesmus obliquus biomass. The main purpose of this work was to determine the energy consumption and CO2 emissions during the production of hydrogen. This was accomplished through the fermentation of the microalgal biomass cultivated in an outdoor raceway pond and the preparation of the inoculum and culture media. The scale-up scenarios are discussed aiming for a potential application to a fuel cell hybrid taxi fleet. The H2 yield obtained was 7.3 g H2/kg of S. obliquus dried biomass. The results show that the production of biohydrogen required 71-100 MJ/MJ(H2) and emitted about 5-6 kg CO2/MJ(H2). Other studies and production technologies were taken into account to discuss an eventual process scale-up. Increased production rates of microalgal biomass and biohydrogen are necessary for bioH2 to become competitive with conventional production pathways.

Abstract Hydrogen (H 2 ) gas is seen as an ideal future energy carrier because it is easily converted into electricity in fuel cells, liberates a large amount of energy per unit mass, and generates no air pollutants. In this work, biological hydrogen (bioH 2 ) was produced from the microalgal biomass of Scenedesmus obliquus which was used as a substrate for the fermentation by Enterobacter aerogenes ATCC 13048 and Clostridium butyricum DSM 10702. The bioH 2 produced by each strain was assessed for different S. obliquus biomass concentrations, using both dried (5% moisture) and “wet” (69% moisture) biomass. The highest bioH 2 production yields obtained were 57.6 mL H 2 /g VS alga from 2.5 g alga /L by E. aerogenes and 113.1 mL H 2 /g VS alga from 50.0 g alga /L by C. butyricum . The bioH 2 production rates, and biogas purity attained by using the wet biomass as a fermentation substrate were similar or higher than those obtained with the dried microalga. This means that the drying step is not needed and therefore saves considerable energy as this is one of the highest energy demanding stages when using this feedstock in fermentations for biofuels production.

This work targeted the energy recovery from food waste (FW), aiming at the implementation of a potentially participative process of FW conditioning before the non-sterile biological conversion to hydrogen (H2). Food waste conversion was initially performed under sterile conditions, achieving a maximum H2 productivity of 249.5 ± 24.6 mL H2 (L h)-1 and a total H2 production to 4.1 ± 0.2 L L-1. The non-sterile operation was implemented as a way of process simplification, but the total H2 production decreased by 59% due to the FW native microorganisms. To counteract this effect, FW was submitted to acid, microwave (MW), and combined acid and MW pretreatment. The application of 4 min MW, 550 W, efficiently controlled the FW microbial counts. The Clostridium butyricum bioaugmented conversion of MW-pretreated FW accelerated the H2 production to 406.2 ± 8.1 mL (L h)-1 and peaked the total H2 production and conversion yield to 4.6 ± 0.5 L L-1 and 234.6 ± 55.6 mL (g sugar)-1, respectively. These results exceeded in 63, 12 and 4%, respectively, the H2 productivity, total production and sugar conversion yield obtained under sterile conditions, and are encouraging for the future implementation of increasingly responsible waste valorisation practices.

Abstract The biological hydrogen production from Spirogyra sp. biomass was studied in a SBR (sequential batch reactor) equipped with a biogas collecting and storage system. Two acid hydrolysis pre-treatments (1N and 2N H 2 SO 4 ) were applied to the Spirogyra biomass and the subsequent fermentation by Clostridium butyricum DSM 10702 was compared. The 1N and 2N hydrolyzates contained 37.2 and 40.8 g/L of total sugars, respectively, and small amounts of furfural and HMF (hydroxymethylfurfural). These compounds did not inhibit the hydrogen production from crude Spirogyra hydrolyzates. The fermentation was scaled up to a batch operated bioreactor coupled with a collecting system that enabled the subsequent characterization and storage of the biogas produced. The cumulative hydrogen production was similar for both 1N and 2N hydrolyzate, but the hydrogen production rates were 438 and 288 mL/L.h, respectively, suggesting that the 1N hydrolyzate was more suitable for sequential batch fermentation. The SBR with 1N hydrolyzate was operated continuously for 13.5 h in three consecutive batches and the overall hydrogen production rate and yield reached 324 mL/L.h and 2.59 mol/mol, respectively. This corresponds to a potential daily production of 10.4 L H 2 /L Spirogyra hydrolyzate, demonstrating the excellent capability of C. butyricum to produce hydrogen from microalgal biomass.

This work evaluated the effects of condensable syngas impurities on the cell viability and product distribution of Butyribacterium methylotrophicum in syngas fermentation. The condensates were collected during the gasification of two technical lignins derived from wheat straw (WST) and softwood (SW) at different temperatures and in the presence or absence of catalysts. The cleanest syngas with 169 and 3020 ppmv of H2S and NH3, respectively, was obtained at 800 °C using dolomite as catalyst. Pyridines were the prevalent compounds in most condensates and the highest variety of aromatics with cyanide substituents were originated during WST lignin gasification at 800 °C without catalyst. In contrast with SW lignin-based condensates, the fermentation media supplemented with WST lignin-derived condensates at 1:100 vol. only supported residual growth of B. methylotrophicum. By decreasing the condensate concentration in the medium, growth inhibition ceased and a trend toward butyrate production over acetate was observed. The highest butyrate-to-acetate ratio of 1.3 was obtained by supplementing the fermentation media at 1:1000 vol. with the condensate derived from the WST lignin, which was gasified at 800 °C in the presence of olivine. B. methylotrophicum was able to adapt and resist the impurities of the crude syngas and altered its metabolism to produce additional butyrate.

In this work, hydrogen (H2) was produced through the fermentation of Spirogyra sp. biomass by Clostridium butyricum DSM 10702. Macronutrient stress was applied to increase the carbohydrate content in Spirogyra, and a 36% (w/w) accumulation of carbohydrates was reached by nitrogen depletion. The use of wet microalga as fermentable substrate was compared with physically and chemically treated biomass for increased carbohydrate solubilisation. The combination of drying, bead beating and mild acid hydrolysis produced a saccharification yield of 90.3% (w/w). The H2 production from Spirogyra hydrolysate was 3.9 L H2 L-1, equivalent to 146.3 mL H2 g-1 microalga dry weight. The presence of protein (23.2 ± 0.3% w/w) and valuable pigments, such as astaxanthin (38.8% of the total pigment content), makes this microalga suitable to be used simultaneously in both food and feed applications. In a Spirogyra based biorefinery, the potential energy production and food-grade protein and pigments revenue per cubic meter of microalga culture per year was estimated on 7.4 MJ, US $412 and US $15, respectively, thereby contributing to the cost efficiency and sustainability of the whole bioconversion process.

Abstract Scenedesmus obliquus biomass was used as a feedstock for comparing the biological production of hydrogen by two different types of anaerobic cultures: a heat-treated mixed culture from a wastewater treatment plant and Clostridium butyricum DSM 10702. The influence of the incubation temperature and the carbon source composition were evaluated in order to select the best production profile according to the characteristics of the microalgal biomass. C. butyricum showed a clear preference for monomeric sugars and starch, the latter being the major storage compound in microalgae. The highest H 2 production reached by this strain from starch was 468 mL/g, whereas the mixed culture incubated at 37 °C (LE37) produced 241 mL/g. When the mixed culture was incubated at 58 °C (LE58), a significant increase in the H 2 production occurred when xylose and xylan were used as carbon and energy source. The highest H 2 yield reached by the LE37 culture or in co-culture with C. butyricum was 1.52 and 2.01 mol/mol of glucose equivalents, respectively. However, the ratio H 2 /CO 2 (v/v) of the biogas produced in both cases was always lower than the one produced by the pure strain. In kinetic assays, C. butyricum attained 153.9 mL H 2 /L h from S. obliquus biomass within the first 24 h of incubation, with a H 2 yield of 2.74 mol/mol of glucose equivalents. H 2 production was accompanied mainly by acetate and butyrate as co-products. In summary, C. butyricum demonstrated a clear supremacy for third generation bioH 2 production from S. obliquus biomass.