Biophotolysis Of Water Research Articles

Balancing photosynthesis, O2 consumption, and H2 recycling for sustained H2 photoproduction in pulse-illuminated algal cultures

Sustained H2 photoproduction by green alga Chlamydomonas reinhardtii is achieved under pulse-illumination superimposed on continuous low background light. Pulse-illuminated algae act as biocatalysts producing H2via direct water biophotolysis.

Natural Hydrogen: A New Source of Carbon-Free and Renewable Energy That Can Compete With Hydrocarbons

Natural Hydrogen: A New Source of Carbon-Free and Renewable Energy That Can Compete With Hydrocarbons

Photosynthetic hydrogen production: Novel protocols, promising engineering approaches and application of semi-synthetic hydrogenases.

Photosynthetic production of molecular hydrogen (H2 ) by cyanobacteria and green algae is a potential source of renewable energy. These organisms are capable of water biophotolysis by taking advantage of photosynthetic apparatus that links water oxidation at Photosystem II and reduction of protons to H2 downstream of Photosystem I. Although the process has a theoretical potential to displace fossil fuels, photosynthetic H2 production in its current state is not yet efficient enough for industrial applications due to a number of physiological, biochemical, and engineering barriers. This article presents a short overview of the metabolic pathways and enzymes involved in H2 photoproduction in cyanobacteria and green algae and our present understanding of the mechanisms of this process. We also summarize recent advances in engineering photosynthetic cell factories capable of overcoming the major barriers to efficient and sustainable H2 production.

Water oxidation by photosystem II is the primary source of electrons for sustained H2 photoproduction in nutrient-replete green algae

The unicellular green alga Chlamydomonas reinhardtii is capable of photosynthetic H2 production. H2 evolution occurs under anaerobic conditions and is difficult to sustain due to 1) competition between [FeFe]-hydrogenase (H2ase), the key enzyme responsible for H2 metabolism in algae, and the Calvin-Benson-Bassham (CBB) cycle for photosynthetic reductants and 2) inactivation of H2ase by O2 coevolved in photosynthesis. Recently, we achieved sustainable H2 photoproduction by shifting algae from continuous illumination to a train of short (1 s) light pulses, interrupted by longer (9 s) dark periods. This illumination regime prevents activation of the CBB cycle and redirects photosynthetic electrons to H2ase. Employing membrane-inlet mass spectrometry and [Formula: see text], we now present clear evidence that efficient H2 photoproduction in pulse-illuminated algae depends primarily on direct water biophotolysis, where water oxidation at the donor side of photosystem II (PSII) provides electrons for the reduction of protons by H2ase downstream of photosystem I. This occurs exclusively in the absence of CO2 fixation, while with the activation of the CBB cycle by longer (8 s) light pulses the H2 photoproduction ceases and instead a slow overall H2 uptake is observed. We also demonstrate that the loss of PSII activity in DCMU-treated algae or in PSII-deficient mutant cells can be partly compensated for by the indirect (PSII-independent) H2 photoproduction pathway, but only for a short (<1 h) period. Thus, PSII activity is indispensable for a sustained process, where it is responsible for more than 92% of the final H2 yield.

Molecular biohydrogen production by dark and photo fermentation from wastes containing starch: recent advancement and future perspective.

Changing lifestyle is increasing the energy demand. Fossil fuel is unable to deliver such huge energy. Clean energy from renewable source can solve this problem. Hydrogen is a clean and energy-efficient fuel and used for electricity generation by fuel cells or can be used in combustion engine. Easy availability of starch wastes from different industrial food processing wastes makes it a potential source for hydrogen (H2) generation. Among various processes such as steam reforming, electrolysis, biophotolysis of water and anaerobic fermentation, anaerobic fermentation technique is environmentally friendly and requires less external energy, making it a preferred process for H2 generation. Dark fermentation process can use wide range of substrates including agricultural and industrial starchy waste with low level of undesirable compounds. Application of both anaerobic dark and photofermentation can improve H2 yield and production rate. H2 production from wastes containing starch serves dual benefit of waste reduction and energy generation. As starch is a polymer and all hydrogen-producing bacteria cannot produce amylase to hydrolyze it, a pretreatment step is required to convert starch into glucose and maltose. In this present review paper, we have summarized: (i) potential of various types of starch-containing wastes as feedstock, (ii) various fermentation techniques, (iii) optimization of external process parameter, (iv) application of bioreactor and simulation in fermentation technique and (v) advancement in H2 production from starchy wastes.

Technical feasibility of reforming anaerobic digestion and landfill biogas streams into bio-hydrogen

Hydrogen can be produced through different pathways, i.e., natural gas reforming, gasification of coal, and electrolysis of water. A more sustainable pathway is through bio-H2, which can be produced by bio-photolysis of water and photo-fermentation and dark fermentation of organic matters (OM). However, these routes are still limited by their specific energy requirement, process slowness, and microorganism sensitivity. These limitations can be mitigated by producing bio-H2 via steam reforming of biogas sources such as landfill or anaerobic digester. In this study, the influence of the methane concentration in the biogas stream on reforming metrics was investigated. Two levels of modeling were pursued here: equilibrium and high fidelity numerical simulations. The former considers several reaction constants, elemental mass conservation, and energy balance. The latter model is based on the reactive Navier-Stokes of non-isothermal and multiple species flow in a cylindrical reactor. Process metrics such as species concentrations and conversion percentages as well as thermal process efficiencies were delineated and evaluated. Results showed that methane concentration has a pronounced influence on the resulting hydrogen concentration and the overall reforming efficiency. The anaerobic CH4 source resulted in a mole fraction of near 0.3 for H2 and a reforming efficiency of 36%. These values are much lower than those evaluated for natural gas (mole fraction of 0.5 for H2 and reforming efficiency of 75%). Although this work illustrates the technical feasibility of biogas reforming, it highlights the low attained process efficiency that can be improved to achieve sustainable bio-H2 production.

Bio-hydrogen production from waste materials: A review

When hydrogen burns in air, it produces nothing but water vapour. It is therefore the cleanest possible, totally non-polluting fuel. This fact has led some people to propose an energy economy based entirely on hydrogen, in which hydrogen would replace gasoline, oil, natural gas, coal, and nuclear power. Hydrogen is a clean energy source. Therefore, in recent years, demand on hydrogen production has increased considerably. Electrolysis of water, steam reforming of hydrocarbons and auto-thermal processes are well-known methods for hydrogen gas production, but not cost-effective due to high energy requirements. As compare to chemical methods, biological production of hydrogen gas has significant advantages such as bio-photolysis of water by algae, dark and photo-fermentation of organic materials, usually carbohydrates by bacteria. New approach for bio-hydrogen production is dark and photo-fermentation process but with some major problems like dark and photo-fermentative hydrogen production is the raw material cost. By using suitable bio-process technologies hydrogen can be produced through carbohydrate rich, nitrogen deficient solid wastes such as cellulose and starch containing agricultural and food industry wastes and some food industry wastewaters such as cheese whey, olive mill and baker's yeast industry wastewaters. Utilization of aforementioned wastes for hydrogen production provides inexpensive energy generation with simultaneous waste treatment. This review article summarizes bio-hydrogen production from some waste materials with recent developments and relative advantages.

Process and reactor design for biophotolytic hydrogen production

The green alga Chlamydomonas reinhardtii has the ability to produce molecular hydrogen (H2), a clean and renewable fuel, through the biophotolysis of water under sulphur-deprived anaerobic conditions. The aim of this study was to advance the development of a practical and scalable biophotolytic H2 production process. Experiments were carried out using a purpose-built flat-plate photobioreactor, designed to facilitate green algal H2 production at the laboratory scale and equipped with a membrane-inlet mass spectrometry system to accurately measure H2 production rates in real time. The nutrient control method of sulphur deprivation was used to achieve spontaneous H2 production following algal growth. Sulphur dilution and sulphur feed techniques were used to extend algal lifetime in order to increase the duration of H2 production. The sulphur dilution technique proved effective at encouraging cyclic H2 production, resulting in alternating Chlamydomonas reinhardtii recovery and H2 production stages. The sulphur feed technique enabled photobioreactor operation in chemostat mode, resulting in a small improvement in H2 production duration. A conceptual design for a large-scale photobioreactor was proposed based on these experimental results. This photobioreactor has the capacity to enable continuous and economical H2 and biomass production using green algae. The success of these complementary approaches demonstrate that engineering advances can lead to improvements in the scalability and affordability of biophotolytic H2 production, giving increased confidence that H2 can fulfil its potential as a sustainable fuel of the future.

A novel nutrient control method to deprive green algae of sulphur and initiate spontaneous hydrogen production

The green alga Chlamydomonas reinhardtii has the ability to produce clean and renewable molecular hydrogen through the biophotolysis of water. Hydrogen production takes place under anaerobic conditions, which may be imposed metabolically by depriving the algae of sulphur. Sulphur-deprivation typically requires the spatial and temporal separation of the algal growth and hydrogen production stages. This would typically require separate photobioreactors for each stage as well as a costly and energy intensive medium exchange technique such as centrifugation, making the process difficult to scale up.The aim of this paper is to show how these two stages are able to take place in a single reactor and hence eliminate the need for a separation step and for an additional reactor. To achieve this we have investigated the sulphate and acetate consumption and uptake rates during algal growth under different illumination conditions. The experiment has been repeated in various photobioreactor geometries in order to determine a reactor-independent relationship between the algal growth and nutrient consumption kinetics. Using this relationship, the initial sulphur and acetate concentrations of the algal medium have been optimised so that these nutrients run out at the exact moment when the maximum algal cell density is reached. This nutrient control method allows a fully-grown algal culture to enter spontaneous hydrogen production mode, eliminating the need for a medium separation technique and for an additional photobioreactor.Hydrogen production rates and yields were measured by membrane-inlet mass spectrometry (MIMS) in a novel photobioreactor designed specifically to facilitate the green algal hydrogen production process. The nutrient control method of sulphur-deprivation has proven to be superior to the traditional methods of centrifugation and dilution. Hydrogen production by nutrient control reached a maximum rate of 1.30 ml/l/h and a yield of 112.7 ml/l, compared to maximum rates of 0.18 ml/l/h and 1.11 ml/l/h, and yields of 28.0 ml/l and 102.7 ml/l for the dilution and centrifugation methods, respectively. Nutrient control has been identified as the method of choice for green algal hydrogen production.

Aerobic Hydrogen Accumulation by a Nitrogen-Fixing Cyanobacterium, Anabaena sp

Hydrogen evolution by a nitrogen-fixing cyanobacterium, Anabaena sp. strain N-7363, was tested in order to develop a water biophotolysis system under aerobic conditions. A culture of the strain supplemented with carbon dioxide under an air atmosphere evolved hydrogen and oxygen gas, which reached final concentrations of 9.7 and 69.8%, respectively, after 12 days of incubation. Hydrogen uptake activity was not observed during incubation, and nitrogenase was thought to be the sole enzyme responsible for the hydrogen evolution.

Biophotolysis of water: the light saturation curves

Biophotolysis of water: the light saturation curves

Co-immobilization effect on H2 production by a chloroplast membranes-hydrogenase system

Chloroplast membranes immobilized within a BSA-GA matrix or within an alginate gel have been associated with native or immobilized hydrogenase in order to produce hydrogen gas through biophotolysis of water. Due to the reaction geometry, co-immobilization of chloroplast membranes with the enzyme inside the same matrix considerably improved the amount of H2 produced and the initial activity. The use of entrapment methods such as alginate gel allowed diffusion of proteins through the matrix. Electron microscopic observations illustrated these results.

Hydrogen formation by the biophotolysis of water via glycolate and formate.

I am substituting for Professor H. G. Wood who was scheduled to chair this session but because of last minute commitments was unable to attend this meeting. Knowing his interests in the theme of this symposium I am sure he would have opened the session with a few remarks about some of the interesting research he is doing in the field of microbial metabolism. With your permission I will utilize some of his time to report some results we have obtained on the biophotolysis of water with the formation of hydrogen.KeywordsHydrogen FormationGlycolic OxidaseMain CompartmentFormic HydrogenlyaseGlycolate FormationThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

“Living electrode” as a long-lived photoconverter for biophotolysis of water

Living blue-green algae (Mastigocladus laminosus), immobilized on an SnO(2) optically transparent electrode with calcium alginate, functioned as an anodic photoelectrode on continuous illumination for periods of time adequate for use in a conventional electrochemical cell. This "living electrode" shows promise of use as a long-lived photoconverter of solar radiant energy to electric energy and as a suitable replacement for unstable chloroplast systems.

Enzymes as catalysts of electrochemical reactions

The paper describes a theory for constructing electrocatalysts based on immobilized enzymes. High-rate enzymatic electron-transfer reactions in solutions and heterogeneous systems are analyzed. Macrokinetics of electrocatalysis with enzymes anchored to equiaccessible surface electrodes is discussed, and a number of expressions interrelating electrode potential and current output on the one hand, and kinetic and microkinetic characteristics of the system on the other, are derived. Electron transfer from the enzyme active center to the conducting matrix is discussed. Two mechanisms are considered: the direct electron transfer mechanism and the mechanism involving intermediate carriers (mediators). The technological potential of immobilized enzyme electrocatalysis is surveyed (bioelectrochemical converters, biophotolysis of water, specific electrosynthesis, biochemical sensors).