Biotechnological hydrogen production: research for efficient light energy conversion

The study of biological hydrogen production by using photosynthetic bacteria and cyanobacteria is described based on a national R&D project in Japan. We describe here the subjects examined in the research for photosynthetic bacteria: analysis of the relationship between the penetration of light to photobioreactor and hydrogen production, genetic engineering of photosynthetic bacteria to control the pigment content for making the light penetration easy. Examples of bench-scale reactors are shown. Genetic manipulation of hydrogenase to enhance the protein expression is also studied.     

Metabolic flux network and analysis of fermentative hydrogen production

Fermentative hydrogen production (FHP) has received a great R & D interest in recent decades, as it offers a potential means of producing H₂ from a variety of renewable resources, even wastewater via a low energy continuous process. Various extracellular metabolites including ethanol, acetate, butyrate and lactate can be produced during the fermentation, building a complex metabolic network of the FHP. Except for the recognition of its complexity, the metabolic flux network has not been well understood. Studies on biochemical reactions and metabolic flux network associated with the FHP in anaerobic fermentation system have only been drawn attention in recent years. This review summarizes the biochemical reactions taking place in the metabolic network of FHP. We discuss how the key operation factors influence metabolism in the FHP process. Recently developed and applied technologies for metabolic flux analysis have been described. Future studies on the metabolic network to enhance fermentative hydrogen production by strict anaerobes are recommended. It is expected that this review can provide useful information in terms of fundamental knowledge and update technology for scientists and research engineers in the field of biological hydrogen production.     

Integrated hydrogen production process from cellulose by combining dark fermentation, microbial fuel cells, and a microbial electrolysis cell

Hydrogen gas production from cellulose was investigated using an integrated hydrogen production process consisting of a dark fermentation reactor and microbial fuel cells (MFCs) as power sources for a microbial electrolysis cell (MEC). Two MFCs (each 25 mL) connected in series to an MEC (72 mL) produced a maximum of 0.43 V using fermentation effluent as a feed, achieving a hydrogen production rate from the MEC of 0.48 m³ H₂/m³/d (based on the MEC volume), and a yield of 33.2 mmol H₂/g COD removed in the MEC. The overall hydrogen production for the integrated system (fermentation, MFC and MEC) was increased by 41% compared with fermentation alone to 14.3 mmol H₂/g cellulose, with a total hydrogen production rate of 0.24 m³ H₂/m³/d and an overall energy recovery efficiency of 23% (based on cellulose removed) without the need for any external electrical energy input.     

Fermentative biohydrogen production: trends and perspectives

Biologically produced hydrogen (biohydrogen) is a valuable gas that is seen as a future energy carrier, since its utilization via combustion or fuel cells produces pure water. Heterotrophic fermentations for biohydrogen production are driven by a wide variety of microorganisms such as strict anaerobes, facultative anaerobes and aerobes kept under anoxic conditions. Substrates such as simple sugars, starch, cellulose, as well as diverse organic waste materials can be used for biohydrogen production. Various bioreactor types have been used and operated under batch and continuous conditions; substantial increases in hydrogen yields have been achieved through optimum design of the bioreactor and fermentation conditions. This review explores the research work carried out in fermentative hydrogen production using organic compounds as substrates. The review also presents the state of the art in novel molecular strategies to improve the hydrogen production.     

Agent-based modeling and simulation for the circular economy: Lessons learned and path forward

Circular economy aims at decoupling human activities from resource use and creating wealth. However, many have questioned the link between increased circularity and sustainability, resulting in several methodological approaches being developed to answer that question. This article analyzes and discusses the insights gained from applying agent-based modeling and simulation to study the techno-economic and social conditions promoting circularity and sustainability. This article analyzes the benefits and limitations of this technology and discusses future methodology developments within the circular economy context. Moreover, six limits of the circular economy concept are used to interpret insights from the literature: thermodynamic limits, system boundary limits, limits posed by the physical scale of the economy, limits posed by path dependencies and lock-in, limits of governance and management, and limits of social and cultural definitions. Promising research avenues are to use this methodology with machine learning, industrial ecology methods, and detailed geographic information.     

Medium chain carboxylic acids production from waste biomass: Current advances and perspectives

Alternative chemicals to diverse fossil-fuel-based products is urgently needed to mitigate the adverse impacts of fossil fuel depletion on human development. To this end, researchers have focused on the production of biochemical from readily available and affordable waste biomass. This is consistent with current guidelines for sustainable development and provides great advantages related to economy and environment. The search for suitable biochemical products is in progress worldwide. Therefore, this review recommends a biochemical (i.e., medium chain carboxylic acids (MCCAs)) utilizing an emerging biotechnological production platform called the chain elongation (CE) process. This work covers comprehensive introduction of the CE mechanism, functional microbes, available feedstock types and corresponding utilization strategies, major methods to enhance the performance of MCCAs production, and the challenges that need to be addressed for practical application. This work is expected to provide a thorough understanding of the CE technology, to guide and inspire researchers to solve existing problems in depth, and motivate large-scale MCCAs production.     

The production of extracellular carbohydrates by estuarine benthic diatoms: the effects of growth phase and light and dark treatment

Epipelic diatoms are important constituents of estuarine microphytobenthic biofilms. Field‐based investigations have shown that the production of carbohydrates by such taxa is ecologically important. However, limited information exists on the dynamics of carbohydrate production by individual species of epipelic diatoms. The production of low and high molecular weight extracellular carbohydrates in axenic cultures of five species of benthic estuarine diatoms, Cylindrotheca closterium (Ehrenberg), Navicula perminuta (Grun.) in Van Heurck, Nitzschia frustulum (Kütz.) Grunow, Nitzschia sigma (Kütz.) Grunow, and Surirella ovata (Kütz.) Grunow, were investigated. All species produced colloidal (water‐soluble) carbohydrates during growth, with maximal production occurring during stationary phase. During logarithmic growth, approximately 20% of extracellular carbohydrates consisted of polymeric material (extracellular polymeric substances [EPS]), but during stationary phase, EPS content increased to 34%–50%. Pyrolysis–mass spectrophotometry analysis showed differences in the composition of EPS produced during logarithmic and stationary phase. All species synthesized glucan as a storage carbohydrate, with maximum glucan accumulation during the transition from log to stationary phase. Short‐term labeling with ¹⁴C‐bicarbonate found that between 30 and 60% of photoassimilates were released as colloidal carbohydrate, with EPS consisting of approximately 16% of this colloidal fraction. When cells were placed in darkness, EPS production increased, and between 85 and 99% of extracellular carbohydrate produced was polymeric. Glucan reserves were utilized in dark conditions, with significant negative correlations between EPS and glucan for N. perminuta and S. ovata. Under dark conditions, cells continued to produce EPS for up to 3 days, although release of low molecular weight carbohydrates rapidly ceased when cells were dark treated. Three aspects of EPS production have been identified during this investigation: (1) production during rapid growth, which differs in composition from (2) EPS directly produced as a result of photosynthetic overflow during growth limiting conditions and (3) EPS produced for up to 3 days in the dark using intracellular storage reserves (glucans). The ecological implications of these patterns of production and utilization are discussed.     

Toward a low-carbon and circular building sector: Building strategies and urbanization pathways for the Netherlands

Buildings are an important part of society's environmental impacts, both in the construction and in the use phase. As the energy performance of buildings improve, construction materials become more important as a cause of environmental impact. Less attention has been given to those materials. We explore, as an alternative for conventional buildings, the use of biobased materials and circular building practices. In addition to building design, we analyze the effect of urbanization. We assess the potential to close material cycles together with the material related impact, between 2018 and 2050 in the Netherlands. Our results show a limited potential to close material cycles until 2050, as a result of slow stock turnover and growth of the building stock. At present, end-of-life recycling rates are low, further limiting circularity. Primary material demand can be lowered when shifting toward biobased or circular construction. This shift also reduces material related carbon emissions. Large-scale implementation of biobased construction, however, drastically increases land area required for wood production. Material demand differs strongly spatially and depends on the degree of urbanization. Urbanization results in higher building replacement rates, but constructed dwellings are generally small compared to scenarios with more rural developments. The approach presented in this work can be used to analyze strategies aimed at closing material cycles in the building sector and lowering buildings' embodied environmental impact, at different spatial scales.     

Interplay between light intensity,chlorophyll concentration and culture mixing on the hydrogen production in sulfur‐deprived Chlamydomonas reinhardtii cultures grown in laboratory photobioreactors

Relationships between light intensity and chlorophyll concentration on hydrogen production were investigated in a sulfur‐deprived Chlamydomonas reinhardtii culture in a laboratory scale photobioreactor (PBR) equipped with two different stirring devices. In the first case, the culture was mixed using a conventional magnetic stir bar, while in the second it was mixed using an impeller equipped with five turbines. Experiments were carried out at 70 and 140 µmol photons m^?2 s^?1 in combination with chlorophyll concentrations of 12 and 24 mg L^?1. A high light intensity (140 µmol photons m^?2 s^?1, supplied on both sides of the PBR) in combination with a low chlorophyll concentration (12 mg L^?1) inhibited the production of hydrogen, in particular in the culture mixed with the stir bar. An optimal combination for hydrogen production was found when the cultures were exposed to 140 µmol photons m^?2 s^?1 (on both sides) and 24 mg L^?1 of chlorophyll. Under these conditions, the hydrogen production output rate reached about 120 mL L^?1 in the culture mixed with the stir bar, and rose to about 170 mL L^?1 in the one mixed with the impeller. These outputs corresponded to a mean light conversion efficiency of 0.56% and 0.81%, respectively. However, the efficiency increased to 1.08% and 1.64%, respectively, when maximum hydrogen rates were considered. The better performance of the dense cultures mixed with an impeller was mainly attributed to an intermittent illumination pattern to which the cells were subjected (time cycles within 50–100 ms) which influenced the hydrogen production (1) directly, by providing the PSII with a higher production of electrons for the hydrogenase and (2) indirectly, through a higher synthesis of carbohydrates. The fluid dynamics in the PBR equipped with the impeller was characterized. The better mixing state achieved in the PBR of the new configuration makes it a useful tool for studying the hydrogen production process involving photosynthetic microorganisms, and provides a better insight into the physiology of the process. Biotechnol. Bioeng. 2009; 104: 76–90 © 2009 Wiley Periodicals, Inc.     

Temperature responses are a window to the physiology of dark respiration: differences between CO2 release and O2 reduction shed light on energy conservation

We showed that temperature responses of dark respiration for foliage of Pinus radiata could be approximated by Arrhenius kinetics, whereby E ₀ determines shape of the exponential response and denotes overall activation energy of respiratory metabolism. Reproducible and predictable deviation from strict Arrhenius kinetics depended on foliage age, and differed between R _CO2 and R _O2. Inhibition of oxygen reduction ( R _O2) by cyanide (inhibiting COX) or SHAM (inhibiting AOX) resulted in reproducible changes of the temperature sensitivity for R _O2, but did not affect R _CO2. Enthalpic growth – preservation of electrons in anabolic products – could be approximated with knowledge of four variables: activation energies ( E ₀) for both R _CO2 and R _O2, and basal rates of respiration at a low reference temperature ( R _REF). Rates of enthalpic growth by P. radiata needles were large in spring due to differences between R _REF of oxidative decarboxylation and that of oxygen reduction, while overall activation energies for the two processes were similar. Later during needle development, enthalpic growth was dependent on differences between E ₀ for R _CO2 as compared with R _O2, and increased E ₀( R _O2) indicated greater contributions of cytochrome oxidase to accompany the switch from carbohydrate sink to source. Temperature-dependent increments in stored energy can be calculated as the difference between R _CO2▵ H _CO2 and R _O2▵ H _O2.     

Explaining diversity of livestock-farming management strategies of multiple-job holders: importance of level of production objectives and role of farming in the household

We characterised the livestock-farming management strategies of multiple-job holders and identified which variables contributed most to the differentiation of these strategies. We hypothesised that they would mainly be differentiated by the contribution of the farming income to the total household income and the availability of the household members for farming. The multiple-job holding livestock-farmer's motivations, decisions and actions about both multiple-job holding and livestock farming were obtained in semi-directed interviews of 35 sheep farmers who held multiple jobs, on farm and off farm. They were synthesised into six variables characterising the diversity of the livestock-farming objectives and management guidelines. Thanks to a multiple factorial analysis, we showed that the diversity of the sheep-farming management strategies of multiple-job holders was better explained by two factors 'level of motivation of the farmer to get high technical results' and 'more personal fulfilling v. the family business conception of farming', than the factors we hypothesised. Within our sample, the performances ranged from 0.7 to 1.4 weaned lambs per ewe per year. Six sheep-farming management strategies were identified. They illustrated the importance of the level of production objectives and of farming income expectation, which were found to be independent, in explaining diversity. No direct relationship between farm work organisation and sheep-farming management strategy was identified. Explaining the diversity of the livestock-farming management strategies of multiple-job holders appears to require that all the benefits expected from farming and their hierarchy be identified before analysing how they are translated into production objectives and management guidelines.     

Reconstitution of the water-oxidizing complex in manganese-depleted photosystem II preparations using synthetic binuclear Mn(II) and Mn(IV) complexes: production of hydrogen peroxide

Reconstitution of Mn-depleted PSII particles with synthetic binuclear Mn complexes (one Mn(II)₂ complex and one Mn(IV)₂ complex) was examined. In both cases the electron-transfer rates in the reconstituted systems were found to be up to 75–82% of that measured in native PSII but the oxygen evolution activity remained lower (<5–40%). However, hydrogen peroxide was also produced by the reconstituted samples. These samples therefore represent a new type of reconstituted PSII that generates hydrogen peroxide as the final product in reconstituted PSII centers.     

Multiple and reversible hydrogenases for hydrogen production by Escherichia coli: dependence on fermentation substrate,pH and the F0F1-ATPase

Molecular hydrogen (H₂) can be produced via hydrogenases during mixed-acid fermentation by bacteria. Escherichia coli possesses multiple (four) hydrogenases. Hydrogenase 3 (Hyd-3) and probably 4 (Hyd-4) with formate dehydrogenase H (Fdh-H) form two different H₂-evolving formate hydrogen lyase (FHL) pathways during glucose fermentation. For both FHL forms, the hycB gene coding small subunit of Hyd-3 is required. Formation and activity of FHL also depends on the external pH ([pH]_out) and the presence of formate. FHL is related with the F₀F₁-ATPase by supplying reducing equivalents and depending on proton-motive force. Two other hydrogenases, 1 (Hyd-1) and 2 (Hyd-2), are H₂-oxidizing enzymes during glucose fermentation at neutral and low [pH]_out. They operate in a reverse, H₂-producing mode during glycerol fermentation at neutral [pH]_out. Hyd-1 and Hyd-2 activity depends on F₀F₁. Moreover, Hyd-3 can also work in a reverse mode. Therefore, the operation direction and activity of all Hyd enzymes might determine H₂ production; some metabolic cross-talk between Hyd enzymes is proposed. Manipulating of different Hyd enzymes activity is an effective way to enhance H₂ production by bacteria in biotechnology. Moreover, a novel approach would be the use of glycerol as feedstock in fermentation processes leading to H₂ production, reduced fuels and other chemicals with higher yields than those obtained by common sugars.     

Greenhouse gas emissions of the production chain behind consumption of products in Austria: Development and application of a product‐ and technology‐specific approach

Globalization has been one main driver affecting our whole economy. Thus, greenhouse gas emissions (GHGs) associated with imports and exports should get addressed in addition to the national emission inventory according to the United Nations Framework Convention on Climate Change (UNFCCC), which is focused on territorial emissions only. To enable a correct calculation for imports and exports and to find the most emission‐intensive products and their origin, a product‐ and technology‐specific approach would be favorable which has not been applied up to now. This article addresses this research gap in developing and applying such an approach to calculate the GHGs behind consumption of products in Austria. It is based on physical flows combined with life‐cycle‐based emission factors and emission intensities derived from sector‐ and country‐specific energy mix, for calculating all emissions behind the production chain (resources to final products) of products consumed in Austria. The results have shown that consumption of products in Austria leads to about 60% more emissions than those of the national inventory and that the main part of these emissions comes from the provision of products. The most emission‐intensive products are coming from the chemical and the metal industry. In particular, imports are the main driver of these emissions and are more emission intensive than those produced in Austria. As a result, it is necessary to look at practical measures to reduce emissions along the production chain not only in Austria, but especially abroad as well.     

Kinetic modeling of light limitation and sulfur deprivation effects in the induction of hydrogen production with Chlamydomonas reinhardtii: Part I. Model development and parameter identification

Chlamydomonas reinhardtii is a green microalga capable of turning its metabolism towards H2 production under specific conditions. However this H2 production, narrowly linked to the photosynthetic process, results from complex metabolic reactions highly dependent on the environmental conditions of the cells. A kinetic model has been developed to relate culture evolution from standard photosynthetic growth to H2 producing cells. It represents transition in sulfur-deprived conditions, known to lead to H2 production in Chlamydomonas reinhardtii, and the two main processes then induced which are an over-accumulation of intracellular starch and a progressive reduction of PSII activity for anoxia achievement. Because these phenomena are directly linked to the photosynthetic growth, two kinetic models were associated, the first (one) introducing light dependency (Haldane type model associated to a radiative light transfer model), the second (one) making growth a function of available sulfur amount under extracellular and intracellular forms (Droop formulation). The model parameters identification was realized from experimental data obtained with especially designed experiments and a sensitivity analysis of the model to its parameters was also conducted. Model behavior was finally studied showing interdependency between light transfer conditions, photosynthetic growth, sulfate uptake, photosynthetic activity and O2 release, during transition from oxygenic growth to anoxic H2 production conditions.     

Kinetic modeling of light limitation and sulfur deprivation effects in the induction of hydrogen production with Chlamydomonas reinhardtii. Part II: Definition of model‐based protocols and experimental validation

Photosynthetic hydrogen production under light by the green microalga Chlamydomonas reinhardtii was investigated in a torus‐shaped PBR in sulfur‐deprived conditions. Culture conditions, represented by the dry biomass concentration of the inoculum, sulfate concentration, and incident photon flux density (PFD), were optimized based on a previously published model (Fouchard et al., 2009. Biotechnol Bioeng 102:232–245). This allowed a strictly autotrophic production, whereas the sulfur‐deprived protocol is usually applied in photoheterotrophic conditions. Experimental results combined with additional information from kinetic simulations emphasize effects of sulfur deprivation and light attenuation in the PBR in inducing anoxia and hydrogen production. A broad range of PFD was tested (up to 500 µmol photons m⁻² s⁻¹). Maximum hydrogen productivities were 1.0 ± 0.2 mL H₂/h/L (or 25 ± 5 mL H₂/m² h) and 3.1 mL ± 0.4 H₂/h L (or 77.5 ± 10 mL H₂/m² h), at 110 and 500 µmol photons m⁻² s⁻¹, respectively. These values approached a maximum specific productivity of approximately 1.9 mL ± 0.4 H₂/h/g of biomass dry weight, clearly indicative of a limitation in cell capacity to produce hydrogen. The efficiency of the process and further optimizations are discussed. Biotechnol. Bioeng. 2011;108: 2288–2299. © 2011 Wiley Periodicals, Inc.