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With the use of biotechnology, hydrogen can be produced from wastewater rich in short-chain fatty acids. A previous study revealed the ability of Rhodobacter sphaeroides KKU-PS1 to produce biohydrogen from substrates mimicking succinate fermentation effluent. However, the process still requires optimization. Before illumination optimization, due to high concentration of the effluent, various effluent dilution factors ranging from 10 to 100 were compared, and the optimal dilution factor was determined to be 50. Light-emitting diode (LED) setups consisting of bands and tubes were compared, and various illuminated surface-to-volume ratios (S/V) were obtained. LED tubes were subsequently used for light intensity optimization in the range of 5–23 klux, revealing optimum light intensity at 15 klux, yielding 2202 mL H 2 /L and 13.8 mL H 2 /L/h as the cumulative hydrogen and maximum output rate, respectively. The lighting protocol at 15 klux and with a 6h–6h light-dark cycle improved the total light conversion efficiency by up to 3.1%. The study successfully optimized the process, with results rivalling those of a previous study using malate. [Display omitted] • Photofermentation can convert acidic fermentation effluents to hydrogen energy. • Dilution factor of 50 produced H 2 profile that was comparable to higher dilutions. • Cumulative H 2 peaked at 2202 mL H 2 /L at maximum rate of 13.8 mL H 2 /L/h with 15 klux. • Light saturation point was observed at 15–23 klux with similar H 2 productivity. • 6h–6h light-dark cycle achieved the highest light conversion efficiency of 3.1% at 240 h. [ABSTRACT FROM AUTHOR]

Abstract A common full-color method involves combining micro-light-emitting diodes (LEDs) chips with color conversion materials such as quantum dots (QDs) to achieve full color. However, during color conversion between micro-LEDs and QDs, QDs cannot completely absorb incident wavelengths cause the emission wavelengths that including incident wavelengths and converted wavelength through QDs, which compromises color purity. The present paper proposes the use of a recycling-reflection color-purity-enhancement film (RCPEF) to reflect the incident wavelength multiple times and, consequently, prevent wavelength mixing after QDs conversion. This RCPEF only allows the light of a specific wavelength to pass through it, exciting blue light is reflected back to the red and green QDs layer. The prototype experiment indicated that with an excitation light source wavelength of 445.5 nm, the use of green QDs and RCPEFs increased color purity from 77.2% to 97.49% and light conversion efficiency by 1.97 times and the use of red QDs and RCPEFs increased color purity to 94.68% and light conversion efficiency by 1.46 times. Thus, high efficiency and color purity were achieved for micro-LEDs displays. Graphical Abstract

[Display omitted] • A novel 70 L tubular photo-bioreactor for biohydrogen production was constructed. • The LCE of 4% can be achieved by the method of the built-in light source. • Maximum hydrogen yield of 7 mol H 2 /mol glucose was obtained in the batch stage. • The average hydrogen production rate can reach 22.8 mL H 2 /(L·h) at HRT of 5 d. A novel 70 L composite tubular photo-bioreactor was constructed, and its photo-fermentation hydrogen production characteristics of batch and continuous modes were investigated with glucose as the substrate in an outdoor environment. In the batch fermentation stage, the hydrogen production rate peaked at 37.6 mL H 2 /(L·h) accompanied by a high hydrogen yield of 7 mol H 2 /mol glucose. The daytime light conversion efficiency is 4 %, with 37 % of light energy from the sun. An optimal hydraulic retention time of 5 d was identified during continuous photo-fermentation. Under this condition, the stability of the cell concentration is maintained and more electrons can be driven to the hydrogen generation pathway while attaining a hydrogen production rate of 20.7 ± 0.9 mL H 2 /(L·h). The changes of biomass, volatile fatty acids concentration and ion concentration during fermentation were analyzed. Continuous hydrogen production by composite tubular photo-bioreactor offers new ideas for the large-scale deployment of photobiological hydrogen production. [ABSTRACT FROM AUTHOR]

A common full-color method involves combining micro-light-emitting diodes (LEDs) chips with color conversion materials such as quantum dots (QDs) to achieve full color. However, during color conversion between micro-LEDs and QDs, QDs cannot completely absorb incident wavelengths cause the emission wavelengths that including incident wavelengths and converted wavelength through QDs, which compromises color purity. The present paper proposes the use of a recycling-reflection color-purity-enhancement film (RCPEF) to reflect the incident wavelength multiple times and, consequently, prevent wavelength mixing after QDs conversion. This RCPEF only allows the light of a specific wavelength to pass through it, exciting blue light is reflected back to the red and green QDs layer. The prototype experiment indicated that with an excitation light source wavelength of 445.5 nm, the use of green QDs and RCPEFs increased color purity from 77.2% to 97.49% and light conversion efficiency by 1.97 times and the use of red QDs and RCPEFs increased color purity to 94.68% and light conversion efficiency by 1.46 times. Thus, high efficiency and color purity were achieved for micro-LEDs displays. [ABSTRACT FROM AUTHOR]

This article describes the ability of the Chlorella vulgaris BEIJ strain G-120 to produce hydrogen (H 2) via both direct and indirect pathways without the use of nutrient starvation. Photobiological H 2 production reached a maximum rate of 12 mL H 2 L−1 h−1, corresponding to a light conversion efficiency (light to H 2) of 7.7% (average 3.2%, over the 8-day period) of PAR, (photosynthetically active irradiance). Cells presented a maximum in vivo hydrogenase activity of 25.5 ± 0.2 nmoles H 2 μgChl−1 h−1 and the calculated in vitro hydrogenase activity was 830 ± 61 nmoles H 2 μgChl−1 h−1. The strain is able to grow either heterotrophically or photo autotrophically. The total output of 896 mL of H 2 was attained for illuminated culture and 405 mL for dark cultures. The average H 2 production rate was 4.98 mL L−1 h−1 for the illuminated culture and 2.08 mL L−1 h−1 for the one maintained in the dark. • Chlorella produced H 2 by direct photosynthesis without applying sulfur-starvation. • Chlorella G-120 strain can release H 2 both in the light and in the dark. • Chlorella G-120 strain can be grown both autotrophically and heterotrophically. • Photobiological H 2 production by strain G-120 reached 7.7% efficiency (H 2 to light). • Photosynthetic rate of Chlorella G-120 surpassed that of C. reinhardtii CC-124. [ABSTRACT FROM AUTHOR]

[Display omitted] • Light spectra vary the biomass and bio-H 2 production via photo-fermentation process. • Red light spectrum is more beneficial for bacterial growth and biomass accumulation. • Green light spectrum has the largest effect on photo-fermentative bio-H 2 production. • LCE under green light illumination is 2-folds of that under control white light. • Bacteriochlorophyll and carotenoid absorb red and green light in photo-fermentation. Purple non-sulphur bacteria can only capture up to 10 % light spectra and only 1–5 % of light is converted efficiently for biohydrogen production. To enhance light capture and conversion efficiencies, it is necessary to understand the impact of various light spectra on light harvesting pigments. During photo-fermentation, Rhodobacter sphaeroides KKU-PS1 cultivated at 30 °C and 150 rpm under different light spectra has been investigated. Results revealed that red light is more beneficial for biomass accumulation, whereas green light showed the greatest impact on photo-fermentative biohydrogen production. Light conversion efficiency by green light is 2-folds of that under control white light, hence photo-hydrogen productivity is ranked as green > red > orange > violet > blue > yellow. These experimental data demonstrated that green and red lights are essential for photo-hydrogen and biomass productions of R. sphaeroides and a clearer understanding that possibly pave the way for further photosynthetic enhancement research. [ABSTRACT FROM AUTHOR]

It is well known that over the last 60 years the trend of long-lived greenhouse gas emissions have shown a strong acceleration. There is an increasing concern and a mounting opposition by public opinion to continue with the use of fossil energy. Western countries are presently involved in a so-called energy transition with the objective of abandoning fossil energy for renewable sources. In this connection, hydrogen can play a central role. One of the sustainable ways to produce hydrogen is the use of microalgae which possess two important natural catalysts: photosystem II and hydrogenase, used to split water and to combine protons and electrons to generate gaseous hydrogen, respectively. For about 20 years of study on photobiological hydrogen production, our scientific hopes were based on the application of the sulfur protocol, which indisputably represented a very important advancement in the field of hydrogen production biotechnology. However, as reported in this review, there is increasing evidence that this strategy is not economically viable. Therefore, a change of paradigm for the photobiological production of hydrogen based on microalgae seems mandatory. This review points out that an increasing number of microalgal strains other than Chlamydomonas reinhardtii are being tested and are able to produce sustainable amount of hydrogen without nutrient starvation and to fulfill this goal including the application of co-cultures.

Abstract Background Fermentative production of lactic acid from algae-based carbohydrates devoid of lignin has attracted great attention for its potential as a suitable alternative substrate compared to lignocellulosic biomass. Results A Chlorella sp. GD mutant with enhanced thermo-tolerance was obtained by mutagenesis using N-methyl-N′-nitro-N-nitrosoguanidine to overcome outdoor high-temperature inhibition and it was used as a feedstock for fermentative lactic acid production. The indoor experiments showed that biomass, reducing sugar content, photosynthetic O2 evolution rate, photosystem II activity (F v/F m and F v′/F m′), and chlorophyll content increased as temperature, light intensity, and CO2 concentration increased. The mutant showed similar DIC affinity and initial slope of photosynthetic light response curve (α) as that of the wild type but had higher dissolved inorganic carbon (DIC) utilization capacity and maximum photosynthesis rate (P max). Moreover, the PSII activity (F v′/F m′) in the mutant remained normal without acclimation process after being transferred to photobioreactor. This suggests that efficient utilization of incident high light and enhanced carbon fixation with its subsequent flux to carbohydrates accumulation in the mutant contributes to higher sugar and biomass productivity under enriched CO2 condition. The mutant was cultured outdoors in a photobioreactor with 6% CO2 aeration in hot summer season in southern Taiwan. The harvested biomass was subjected to separate hydrolysis and fermentation (SHF) for lactic acid production with carbohydrate concentration equivalent to 20 g/L glucose using the lactic acid-producing bacterium Lactobacillus plantarum 23. The conversion rate and yield of lactic acid were 80% and 0.43 g/g Chlorella biomass, respectively. Conclusions These results demonstrated that the thermo-tolerant Chlorella mutant with high photosynthetic efficiency and biomass productivity under hot outdoor condition is an efficient fermentative feedstock for large-scale lactic acid production.

Highlights • Hybrid particles are synthesized by embedding quantum dots in wrinkled silica particles. • Wrinkled silica particles help dispersion of hybrid particles in QD/photoresist nanocomposites. • Wrinkled silica particles enhance quantum efficiency of nanocomposite by scattering effect. • A simple device is fabricated by placing QD/photoresist nanocomposite film on blue µ-LED chip. Abstract We have synthesized hybrid particles by embedding CdSe/ZnS quantum dots (QDs) into wrinkled silica nanoparticles. We found that increasing the QD loading decreased the quantum yield (QY) of the wrinkled silica-QD hybrid particles. Compared to the previously-reported silica-QD hybrid particles, the wrinkled silica-QD hybrid particles exhibited higher QY, because the QD surfaces were not chemically modified during the hybridization process. The hybrid particles and free QDs were then used to prepare QD/photoresist nanocomposites. Since photoresist resin contains non-solvent for QDs, nanocomposites containing free QDs showed noteworthy aggregation even at 1.5 wt%, which resulted in deteriorated efficiency and stability. However, we were able to fabricate QD/photoresist nanocomposites successfully using hybrid particles up to 30 wt%, as the wrinkled silica nanoparticles helped in the dispersion of the QDs. By varying the concentration of hybrid particles in the nanocomposites, we found that the hybrid particles at 20 wt% exhibited the highest quantum efficiency. Testing of wrinkled silica/photoresist nanocomposites (without QDs), fabricated with different concentrations of the wrinkled silica nanoparticles, revealed that the highest efficiency at 20 wt% hybrid particles was the result of enhanced scattering by the wrinkled silica nanoparticles. Finally, simple devices in which hybrid particles were placed on blue µ-LEDs were fabricated, and their luminescence properties were analyzed. [ABSTRACT FROM AUTHOR]

While the adoption of high-density apple orchards during the last decades has resulted in a significant improvement in yield and fruit quality, there is great disparity of opinion on the optimum density or the optimum tree shape. A 2-ha replicated field trial was planted in 1997 at the New York State Agricultural Experiment Station in Geneva, New York and continued through 2016, with 4 apple cultivars (‘Empire’, ‘Fuji’, ‘Gala’, and ‘McIntosh’), where we compared 8 tree planting densities (598, 840, 1026, 1283, 1655, 2243, 3262, and 5382 trees/ha), and two tree shapes (conic and V). At the lowest 2 densities, trees were planted on M.7 rootstock (598 trees/ha) and M.26 rootstock (840 trees/ha). At all of the higher tree densities, trees were planted on M.9. After 20 years, there was a strong negative correlation of tree planting density and trunk cross sectional area for all the cultivars and training systems, with the exception of ‘McIntosh’ in a V tree shape where no clear differences were observed. A different pattern for each cultivar was observed with respect to yield and planting density. High-density plantings were more appropriate for ‘Fuji’ and ‘Gala’, where conic tree shapes were better than V shapes. On the other hand, with ‘Empire’ and ‘McIntosh’ high planting density was not as beneficial. The highest yields from ‘McIntosh’ were realized at less than 3000 trees/ha with V tree shapes, or ∼3500 trees/ha with conic tree shapes. Planting density significantly affected firmness, soluble solids, fruit color, and fruit size. Light interception for each density and shape was measured only with ‘Empire’. Planting density had a strong positive effect on light interception. There were no significant differences in interception between tree shapes through the 4th leaf, however, after that more light was intercepted by the V shaped trees. Cumulative yield was a linear function of light energy intercepted by the canopy. While V tree shapes had more light interception, conic shapes seemed to have a better efficiency converting intercepted energy into yield. Planting density improved light interception, but decreased tree partitioning because of the need for more pruning leading to unbalanced trees. Tall Spindle at high planting density seemed to be the best option for cultivars with similar bearing habits such as ‘Fuji’ and ‘Gala’. [ABSTRACT FROM AUTHOR]

This work aimed to produce hydrogen (H2) simultaneously with pollutant removal from biodiesel wastewater by photocatalytic oxidation using a thermally-treated commercial titanium dioxide (TiO2) photocatalyst at room temperature (~30 °C) and ambient pressure. The effects of the operating conditions, including the catalyst loading level (1-6 g/L), UV light intensity (3.52-6.64 mW/cm2), initial pH of the wastewater (2.3-8.0) and reaction time (1-4 h), on the quantity of H2 production together with the reduction in the chemical oxygen demand (COD), biological oxygen demand (BOD) and oil and grease levels were explored. It was found that all the investigated parameters affected the level of H2 production and pollutant removal. The optimum operating condition for simultaneous H2 production and pollutant removal was found at an initial wastewater pH of 6.0, a catalyst dosage of 4.0 g/L, a UV light intensity of 4.79 mW/cm2 and a reaction time of 2 h. These conditions led to the production of 228 μmol H2 with a light conversion efficiency of 6.78% and reduced the COD, BOD and oil and grease levels by 13.2%, 89.6% and 67.7%, respectively. The rate of pollutant removal followed a pseudo-first order chemical reaction with a rate constant of 0.008, 0.085 and 0.044 min-1 for the COD, BOD and oil and grease removal, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nano-SnO 2 and cell immobilization technology were applied to PFHP process. • Immobilized cells produced more H 2 than free cells. • Nano-SnO 2 addition could promote PFHP performance. • The CHY increased by 18.54% with the addition of nano-SnO 2. • The light conversion efficiency increased by 12.41% with nano-SnO 2 addition. Bacterial immobilization is a common method in anaerobic fermentation, since of the maintenance of high bacterial activity, insurance of high density microbial during continuous fermentation, and quick adaptability to the environment. While, the bio-hydrogen production capacity of immobilized photosynthetic bacteria (I-PSB) is seriously affected by the low light transfer efficiency. Hence, in this study, photo-catalytic nano-particles (PNPs) was added into the photo-fermentative bio-hydrogen production (PFHP) system, and its enhancement effects of bio-hydrogen production performance were investigated. Results showed that the maximum cumulative hydrogen yield (CHY) of I-PSB with 100 mg/L nano-SnO 2 (154.33 ± 7.33 mL) addition was 18.54% and 33.06% higher than those of I-PSB without nano-SnO 2 addition and control group (free cells), and the lag time was the shortest indicating a shorter cell arrest time, more cells and faster response. Maximum energy recovery efficiency and light conversion efficiency were also found to be increased by 18.5% and 12.4%, respectively. [ABSTRACT FROM AUTHOR]

Due to its low-input requirements, high yield capacity in marginal soils, and high carbohydrate and vitamin A content, sweetpotato is an important food security crop. For effective breeding strategies, knowing and understanding the traits that drive diversity among varieties is required. In this study, a set representing the diversity of sweetpotato varieties was characterized through multivariate ordination based on growth parameters and physiological leaf traits. The dynamic of light interception, light use efficiency (LUE) parameters, and partition of assimilates to the storage roots of eight representative varieties were simulated through a crop growth model. Leaf mass per area (LMA), N and P content in leaves, light response curve parameters and carbon discrimination were assessed in potted plants at early-growing period (58 days after planting). Precocity proxies (inversely related to LMA and thermal time at maximum storage root growth) and conversion efficiency of intercepted radiation indicators (quantum yield and LUE) were important factors in the varieties ordination based on leaf traits and growth parameter scales, respectively. Leaf traits assessment at early stages could be used as a starting point for the screening of potential lines, which once identified can be further characterized using crop growth models. [ABSTRACT FROM AUTHOR]

Background: Fermentative production of lactic acid from algae-based carbohydrates devoid of lignin has attracted great attention for its potential as a suitable alternative substrate compared to lignocellulosic biomass. Results: A Chlorella sp. GD mutant with enhanced thermo-tolerance was obtained by mutagenesis using N-methyl- N-nitro-N-nitrosoguanidine to overcome outdoor high-temperature inhibition and it was used as a feedstock for fermentative lactic acid production. The indoor experiments showed that biomass, reducing sugar content, photosynthetic O2 evolution rate, photosystem II activity (Fv/Fm and Fv'/Fm'), and chlorophyll content increased as temperature, light intensity, and CO2 concentration increased. The mutant showed similar DIC affinity and initial slope of photosynthetic light response curve (α) as that of the wild type but had higher dissolved inorganic carbon (DIC) utilization capacity and maximum photosynthesis rate (Pmax). Moreover, the PSII activity (Fv'/Fm') in the mutant remained normal without acclimation process after being transferred to photobioreactor. This suggests that efficient utilization of incident high light and enhanced carbon fixation with its subsequent flux to carbohydrates accumulation in the mutant contributes to higher sugar and biomass productivity under enriched CO2 condition. The mutant was cultured outdoors in a photobioreactor with 6% CO2 aeration in hot summer season in southern Taiwan. The harvested biomass was subjected to separate hydrolysis and fermentation (SHF) for lactic acid production with carbohydrate concentration equivalent to 20 g/L glucose using the lactic acid-producing bacterium Lactobacillus plantarum 23. The conversion rate and yield of lactic acid were 80% and 0.43 g/g Chlorella biomass, respectively. Conclusions: These results demonstrated that the thermo-tolerant Chlorella mutant with high photosynthetic efficiency and biomass productivity under hot outdoor condition is an efficient fermentative feedstock for large-scale lactic acid production. [ABSTRACT FROM AUTHOR]

The spectrum of light affects both the electrical energy consumption by plants and photosynthetic efficiency. In a plant factory, where light-emitting diodes (LEDs) serve as an alternative to solar light, the optimal spectrum of light should be carefully chosen to maximize the rate of photosynthesis and the electrical energy efficiency of the crop. The objectives of this study were to investigate the photosynthetic rate of different colored lettuces (reddish and green leaves), to quantify the spectral dependence of photosynthetic efficiency, and to optimize the LED spectrum for maximum canopy photosynthesis and electrical energy consumption in lettuce grown in a plant factory. Two lettuce cultivars ( Lactuca sativa L.), 'JeokChukMyeon' and 'CheongChukMyeon', were assessed for light absorption and photosynthetic efficiency at the single leaf and canopy levels, and the relative consumption of electrical energy from the LED lights was measured at 18 narrow wavelength bands of 10 nm from 400 to 700 nm. Anthocyanin and chlorophyll content (SPAD value) were measured and correlated with leaf color. Light interception by the canopy was estimated with light transmittance models. The light absorption was similar among the green and reddish lettuce cultivars at most wavelengths, but slightly higher in the reddish leaves around 550 nm (green region). In the reddish leaves, photosynthetic rates per incident photon of a single leaf had two peaks at 650-660 and 400-410 nm, while the photosynthetic rate per absorbed photon had three peaks at 650-660, 400-410, and 540-560 nm. In the green region of the light spectrum, both photosynthetic rates per incident photon and those per absorbed photon were lower in the reddish cultivars than in the green cultivars. The spectral dependence of light absorption at the canopy level was much weaker than that at the single leaf level. The quantum yield and absorption of green light at the canopy level were nearly same as those of blue and red lights, indicating that the photosynthetic efficiency of green light at the canopy level was higher than that at the single leaf level. The relative electrical energy consumption was lower in the green region than in the red and blue regions. Therefore, the photosynthetic efficiency based on electrical energy consumption at the canopy level was much lower with green LEDs than with blue or red LEDs. These results describe the plant response to the light spectrum at the canopy level and can be useful for optimizing artificial lighting sources for maximum plant productivity and energy-savings in a plant factory. [ABSTRACT FROM AUTHOR]

This work aimed to produce hydrogen (H2) simultaneously with pollutant removal from biodiesel wastewater by photocatalytic oxidation using a thermally-treated commercial titanium dioxide (TiO2) photocatalyst at room temperature (~30 °C) and ambient pressure. The effects of the operating conditions, including the catalyst loading level (1–6 g/L), UV light intensity (3.52–6.64 mW/cm2), initial pH of the wastewater (2.3–8.0) and reaction time (1–4 h), on the quantity of H2 production together with the reduction in the chemical oxygen demand (COD), biological oxygen demand (BOD) and oil and grease levels were explored. It was found that all the investigated parameters affected the level of H2 production and pollutant removal. The optimum operating condition for simultaneous H2 production and pollutant removal was found at an initial wastewater pH of 6.0, a catalyst dosage of 4.0 g/L, a UV light intensity of 4.79 mW/cm2 and a reaction time of 2 h. These conditions led to the production of 228 μmol H2 with a light conversion efficiency of 6.78% and reduced the COD, BOD and oil and grease levels by 13.2%, 89.6% and 67.7%, respectively. The rate of pollutant removal followed a pseudo-first order chemical reaction with a rate constant of 0.008, 0.085 and 0.044 min−1 for the COD, BOD and oil and grease removal, respectively.

In the present work, a Chlorella vulgaris mutant, named as SDEC-3M, was screened out through the combination of the isolation using 96-well microplates and traditional UV mutagenesis. Compared with its parent (wild type), the growth of SDEC-3M preferred higher CO 2 (15% v/v) environment to ambient air (0.038% CO 2 (v/v)), indicating that the mutant qualified with good tolerance and growth potential under high level CO 2 (high CO 2 tolerance) but was defective in directly utilizing the low level CO 2 (high CO 2 requiring). The genetic stability under ambient air and high level CO 2 was confirmed by a continuous cultivation for five generations. Higher light conversion efficiency (14.52%) and richer total carbohydrate content (42.48%) demonstrated that both solar energy and CO 2 were more effectively productively fixed into carbohydrates for bioethanol production than the parent strain. The mutant would benefit CO 2 biofixation from industrial exhaust gas to mitigate of global warming and promote biofuel production to relieve energy shortage. [ABSTRACT FROM AUTHOR]

To promote continuous phototrphic H2 production with photosynthetic bacteria, an innovative annular optical fiber illuminating bioreactor for both biofilm formation and light transmission was developed. Steady biofilm of indigenous photosynthetic bacteria Rhodopseudomonas palustris was successfully obtained on the surface of side-glowing optical fiber. With the sufficient light supply and uniform light distribution, strategies on improvement of continuous hydrogen production and light energy conversion were then investigated. Hydrogen production rate of 0.85 mmol g−1h−1 and Light conversion efficiency of 47.1% were attained under operating conditions of monochromatic light illumination at 530 nm with light intensity of 19.5 μmol photos m−2s−1, hydraulic retention time of 5 h and initial pH of 7.0. © 2015 American Institute of Chemical Engineers Environ Prog, 35: 455-460, 2016 [ABSTRACT FROM AUTHOR]

Microalgae represent promising organisms for the sustainable production of commodities, chemicals or fuels. Future use of such systems, however, requires increased productivity of microalgal mass cultures in order to reach an economic viability for microalgae-based production schemes. The efficiency of sunlight-to-biomass conversion that can be observed in bulk cultures is generally far lower (35–80%) than the theoretical maximum, because energy losses occur at multiple steps during the light-driven conversion of carbon dioxide to organic carbon. The light-harvesting system is a major source of energy losses and thus a prime target for strain engineering. Truncation of the light-harvesting antenna in the algal model organism Chlamydomonas reinhardtii was shown to be an effective way of increasing culture productivity at least under saturating light conditions. Furthermore engineering of the Calvin–Benson cycle or the creation of photorespiratory bypasses in A. thaliana proved to be successful in terms of achieving higher biomass productivities. An efficient generation of novel microalgal strains with improved sunlight conversion efficiencies by targeted engineering in the future will require an expanded molecular toolkit. In the meantime random mutagenesis coupled to high-throughput screening for desired phenotypes can be used to provide engineered microalgae. [ABSTRACT FROM AUTHOR]

Abstract: H2 is a clean, renewable and energy-efficient fuel. However, in order for it to be a fuel effectively utilizable at an industrial level, key issues about its economically and environmentally sustainable production have still to be solved. Microbial hydrogen production is a process with a low environmental impact and, among microbial processes, photofermentation is considered a promising and sustainable solution. However, the energy input for the biological processes is still higher than the energy output in the form of H2 gas. One possibility for improving this ratio is to increase the efficiency of the process while at the same time reducing electricity consumption, both of which relate to the issue of an optimal photobioreactor design. This review focuses on recent advances made in photobioreactor design towards higher light conversion efficiency, a greater hydrogen production rate and substrate conversion in hydrogen production processes carried out with purple non sulfur bacteria, giving particular attention to the light source and to illumination protocols. Recent achievements in outdoor hydrogen production in large scale photobioreactors are also reviewed. [Copyright &y& Elsevier]

In this study, we described an efficient electrical power generating system containing cyanobacterial photo-H2 production and custom-built proton exchange membrane fuel cell (PEMFC). The filamentous N2-fixing cyanobacterium Anabaena cylindrica was used as the photo-H2 producer. A photosynthesis inhibitor-diuron (DCMU) was used for the enhancement of photo-H2 production in the culture under argon gas. For the first time, a total of 1.0 μM DCMU was found to be the most effective treatment, as this produced 3.6 fold higher levels of H2 in microalgae. By measuring polarization curve, the gas mixture collected from the culture was proven to be an effective fuel for electrical generation through a custom-built PEMFC. When the PEMFC was directly combined with the culture tube, the cells generated as much as 843 mV during a 5-day incubation due to the efficient conversion of solar energy to H2 by A. cylindrica. Light energy conversion efficiency (LCE) for both solar energy to H2 and solar energy to electricity were also determined. The LCE for the cyanobacterial conversion of solar energy to H2 reached a peak at four days with a maximal value of 2.05% and an average value of 1.70% ± 0.17. The corresponding LCE for the conversion of solar energy to electricity in this system was 1.13% at peak and 0.94% ± 0.09 on average. [ABSTRACT FROM AUTHOR]

Abstract: Platymonas subcordiformis, a marine green alga, was demonstrated to photo-biologically produce hydrogen when regulated by a kind of proton uncoupler CCCP (Carbonyl Cyanide m-Chlorophenylhydrazone). In this paper, hydrogen production experiments by P. subcordiformis were carried out in a torus photobioreactor equipped with a mass spectrometer and other necessary sensors so that instantaneous gas components could be measured and other successive physiological states could be well recorded. Hydrogen production performances at different cell densities were compared. We demonstrated that with six folds biomass increasing, hydrogen yield increased almost thirty times. Along with the increase of total hydrogen production yield, rate and duration of mass hydrogen production yield were also much higher. This meant that each alga cell was more efficient in hydrogen production experiments at high cell density. The energy utilization efficiency of hydrogen production from P. subcordiformis was further calculated, average energetic yield of light conversion to hydrogen energy was about 0.3%. Here, characteristics of hydrogen metabolism were also studied. By comparing hydrogen production kinetics, photosystem II activity and change trends of endogenous substrates, we gained the knowledge that photosystem II activity and substrates consumption played an important role in P. subcordiformis hydrogen production at different phases. [Copyright &y& Elsevier]

Abstract: Photofermentative hydrogen production from olive mill wastewater by Rhodobacter sphaeroides O.U.001 was investigated under different regimes of illumination. The analysis included measurements of biomass accumulation, H2-production, high-value bio-product accumulation (polyhydroxybutyrate and carotenoid) and measurements of the medium pH as a function of growth and productivity. Batch cultures were grown under continuous light (CL) or 12 h light/12 h dark (12L/12D) diurnal cycles. Growth under CL or 12L/12D cycles yielded about the same amount of biomass (0.5 g dry cell weight per L culture) and volume of H2 gas (50 ml H2 per L culture). On the other hand, 12L/12D cultures showed a pronounced lag in biomass and H2 accumulation. Advances described in the work would find application in lowering operational costs for hydrogen production by better management of the energy source and cheap feedstock utilization. Compare to CL, equivalent amount of hydrogen gas accumulation within shorter time interval denoted to have two times higher hydrogen production rate and light conversion efficiencies via diurnal cycles, which can yield 50% savings on consumed energy source. [Copyright &y& Elsevier]

Abstract: The application of a cell immobilization technique to a biofilm-based photobioreactor was developed to enhance its photo-hydrogen production rate and light conversion efficiency. Rhodopseudomonas palustris CQK 01 was initially attached to the surface of packed glass beads to form a biofilm in this experiment. Then, the biofilm photobioreactor (BPBR) was illuminated by light-emitting diodes with light wavelengths of 470, 590 and 630nm and hydrogen was evolved with glucose being the sole carbon source. Under the illumination condition of 5000lux illumination intensity and 590nm wavelength, the BPBR showed good hydrogen production performance: the hydrogen production rate was 38.9ml/l/h and light conversion efficiency was 56%, while the hydrogen yield was 0.2molH2/molglucose. Furthermore, results show that the highest hydrogen production rate and glucose removal rate were obtained when the glucose concentration is 0.12M, the optimal pH 7 and optimal temperature of influent liquid 25°C. [Copyright &y& Elsevier]

Abstract: The relationship between hydrogen generation and the age of culture was investigated under fed-batch growth conditions. The specific growth rate (μ e) was determined during the log phase of the growth curve and the μ eMax was 0.02643h−1. Boltzmann''s sigmoidal regression model was used to determine the specific rate of hydrogen evolution (μH): the maximum was 0.04440h−1. At low irradiance (36–75Wm−2), an inverse relationship was found between μH and I; after increasing the irradiance further, μH reached a plateau (0.00916h−1). The maximum reactor yield of cumulative hydrogen (4.5l) was obtained at an irradiance of 320Wm−2, but the highest hydrogen evolution rate (17.217mlh−1) was achieved at 500Wm−2. The light conversion efficiency reached its maximum (6.91%) at the lowest irradiance investigated (36Wm−2); when the irradiance increased further, it decreased progressively down to 0.36%. [Copyright &y& Elsevier]

• 24 h dark + 24 h light duration alternation improved the HY by 6.7 %. • LCE was enhanced by 114.7 % via 24 h dark + 24 h light duration alternation. • Light period after inoculation had the closest relation with average HPR. • Decreased dark period after inoculation would increase the HY. Suitable illumination project would help in achieving high light conversion efficiency (LCE) for photo-fermentation. This study proposed an improvement strategy for LCE of photo-fermentative hydrogen production (PFHP) with a photosynthetic consortium by adopting light–dark duration alternation. For this purpose, 6 projects (continues light, 24 h light + 24 h dark, 24 h dark + 24 h light, 48 h light + 48 h light, 48 h dark + 48 h light, and continues dark) light disturbances were carried out to estimate the strategy. The fluctuation of cell growth (OD660) was corresponded to the light–dark alternation. 24 h dark + 24 h light alternation achieved the maximum hydrogen yield (HY) of 390.9 mL/g TS cell (6.7 % higher than continuous light) and maximum improvement of LCE of 114.7%. Moreover, heat map analysis revealed that the light period after inoculation had the closest relation (Pearson's r = 1) with the average hydrogen production rate (HPR) of photo-fermentation. Besides, decreased dark period after inoculation would increase the hydrogen yield of photo-fermentation. [ABSTRACT FROM AUTHOR]

Abstract: Cyanobacteria provide an efficient system for producing from water using solar energy. The energy conversion efficiency can be defined by the ratio of produced to the light energy absorbed. An IR and opalescent plate method was used to measure the light energy absorbed. Since cyanobacteria absorb light in the visible range but not in the infrared range, the net amount of light energy absorbed by the cells can be estimated by measuring the IR and visible light intensities transmitted through the biochamber. A rectangular biochamber was used for measuring the conversion efficiency from light energy to energy. A quantum meter and radiometer were used to measure the light intensity transmitted through the chamber. Anabaena variabilis was cultured in a BG11 medium with 3.6mM NaNO and the light intensity was 40–50 in the growth phase and 120–140 in the production phase. The maximum production was 50ml for 40h and cell density was 1.2g/l. The production rate was 4.1ml dry cell weight/h. Based on the light absorbed in the production phase, the energy conversion efficiency from light to was 1.5% on average and 3.9% at the maximum. Based on the light energy absorbed in the cell growth and production phases, the energy conversion efficiency was 1.1% on average. [Copyright &y& Elsevier]

It is well known that over the last 60 years the trend of long-lived greenhouse gas emissions have shown a strong acceleration. There is an increasing concern and a mounting opposition by public opinion to continue with the use of fossil energy. Western countries are presently involved in a so-called energy transition with the objective of abandoning fossil energy for renewable sources. In this connection, hydrogen can play a central role. One of the sustainable ways to produce hydrogen is the use of microalgae which possess two important natural catalysts: photosystem II and hydrogenase, used to split water and to combine protons and electrons to generate gaseous hydrogen, respectively. For about 20 years of study on photobiological hydrogen production, our scientific hopes were based on the application of the sulfur protocol, which indisputably represented a very important advancement in the field of hydrogen production biotechnology. However, as reported in this review, there is increasing evidence that this strategy is not economically viable. Therefore, a change of paradigm for the photobiological production of hydrogen based on microalgae seems mandatory. This review points out that an increasing number of microalgal strains other than Chlamydomonas reinhardtii are being tested and are able to produce sustainable amount of hydrogen without nutrient starvation and to fulfill this goal including the application of co-cultures. [ABSTRACT FROM AUTHOR]