Comparison of physicochemical characteristics and photofermentative hydrogen production potential of wastewaters produced from different olive oil mills in Western-Anatolia,Turkey

Olive oil extraction produces a dark-colored wastewater that contains nutrients that can be further processed using biotechnology, in parallel with treatment for disposal. For instance, olive mill wastewater (OMW) can be used as a substrate for photofermentative hydrogen production by purple bacteria. A comparative study was investigated with several OMW samples from different olive oil mills in Western-Anatolia, Turkey. The composition of OMW varies significantly for each mill; thus, a detailed physicochemical analysis of each sample has been carried out. Subsequently, samples were assessed for their functioning in anaerobic photofermentative hydrogen production by Rhodobacter sphaeroides O.U.001. The highest hydrogen production potential (19.9 m³ m^?3) was obtained by the OMW sample with the highest organic content (mainly acetic acid, 9.71 kg m^?3) and the highest carbon-to-nitrogen (C/N) molar ratio (73.8 M M^?1). The organic content was found to be composed of primarily acetic, aspartic, and glutamic acids. There was a linear relationship between C/N ratio and hydrogen production potential across the different OMW samples. This study is unique due to the wide range of analyses of OMW samples and the comparison of many parameters for hydrogen production from wastewater. The results obtained throughout this study can aid in the design of systems using wastewater for biohydrogen production. Particularly, the C/N ratio was found to be the best parameter for choosing a proper substrate.     

Effect of organic loading rate on fermentative hydrogen production from continuous stirred tank and membrane bioreactors

The influence of organic loading rates (OLRs) on the performance of fermentative hydrogen-producing bioreactors operating in continuous stirred tank reactor (CSTR) and membrane bioreactor (MBR) modes was examined. Five OLRs were examined, ranging from 4.0 to 30 g COD L^?1 d^?1, with influent glucose concentrations ranging from 1.3 to 10 g COD L^?1. At OLRs up to 13 g COD L^?1 d^?1, all influent glucose was utilized and the H₂ yield was not significantly influenced by OLR, although the yield in the CSTR mode was significantly higher than that in the MBR mode, 1.25 versus 0.97 mol H₂ (mol Gluc. Conv.)^?1, respectively. At an OLR of 30 g COD L^?1 d^?1, both reactor modes were overloaded with respect to glucose utilization and also had significantly higher H₂ yields of 1.77 and 1.49 mol H₂ (mol Gluc. Conv.)^?1 for the CSTR and MBR modes, respectively, versus the underloaded operation. At the intermediate OLR of 22 g COD L^?1 d^?1, the H₂ yield was maximized at 1.78 mol H₂ (mol Gluc. Conv.)^?1 for both the CSTR and MBR operation. Overall H₂ production was 50% higher in the MBR mode, 0.78 versus 0.51 moles d^?1, because the CSTR mode was overloaded with respect to glucose utilization at this OLR. These results suggest that an optimum OLR that maximizes H₂ yield and H₂ production may be near the OLR that causes overload with respect to substrate utilization. Additionally, while the CSTR mode is easier to operate and provides higher H₂ yields at underloaded and overloaded OLRs, the MBR mode may be preferable when operating near the optimum OLR.     

Enhanced biohydrogen production from cornstalk wastes with acidification pretreatment by mixed anaerobic cultures

Biohydrogen production from the cornstalk wastes with acidification pretreatment was reported in this paper. Batch tests were carried out to analyze influences of several environmental factors on biohydrogen production from cornstalk wastes. Two predominant bacterial morphologies, namely spore-forming rod shape bacteria and micrococcus were screened, purified, and identified after enriched from a hydrogen-producing fermentor with cow dung composts. The maximum cumulative H₂ yield of 149.69 ml H₂ g⁻¹ TVS was obtained at initial pH 7.0 and substrate concentration 15 g l⁻¹, the value is about 46-fold as compared with that of raw cornstalk wastes. The maximum hydrogen production rate was 7.6 ml H2 h⁻¹. The hydrogen concentration in biogas was 45–56% (v/v) and there was no significant methane observed in the biogas throughout this study. In addition, biodegradation characteristics of the substrate by microorganisms were also discussed. During the conversion of cornstalk wastes into hydrogen, the acetate, propionate, butyrate, and the ethanol were main by-products in the metabolism of hydrogen fermentation. The test results showed that the acidification pretreatment of the substrate plays a crucial role in conversion of the cornstalk wastes into biohydrogen gas by the cow dung composts generating hydrogen.     

Biomass production and allocation in Jatropha curcas L. seedlings under different levels of drought stress

In a greenhouse experiment we applied three levels of drought stress and monitored growth variables and biomass production of Jatropha curcas seedlings propagated from three seed accessions. We determined biomass allocation, allometric relationships and plant traits. Well-watered J. curcas seedlings grew 0.81 ± 0.15 cm day^?1 in length and produced 1.49 ± 0.31 g dry biomass day^?1. Under medium stress (40% plant available water) the plants maintained a similar stem shape, although they grew at lower rate (stem length: 0.28 ± 0.11 cm day^?1; dry biomass production: 0.64 ± 0.18 g day^?1). Seedlings under extreme drought stress (no irrigation) stopped growing, started shedding leaves and showed shrinking stem diameter from the 12th day after the start of the drought treatment. The drought treatment did not influence the wood density (0.26 g cm^?3). The root/shoot ratio of the wet treatment was 0.27, which is low compared to other tropical trees. Both the biomass allocation and root/shoot were significantly influenced by drought. Plants of the different accessions were uniform in biomass production and plant traits. The allometric relationship predicting total aboveground biomass (B) with the stem diameter (D) (B = 0.029 × D^2.33; R² = 0.89) fits well in universal scaling models in which the exponent is expected to converge to ～2.67 at plant maturity. Based on a small validation data set from mature J. curcas individuals this hypothesis could be confirmed. A second regression model predicts the total leaf area (LA) as a function of stem diameter (LA = 2.03 × D^2.41; R² = 0.95). The estimated transpiration crop coefficient K_cb ranged from 0.51 to 0.60 for the well-watered plants.     

Optimization of molecular hydrogen production by Rhodobacter sphaeroides O.U.001 in the annular photobioreactor using response surface methodology

Photofermentative H₂ production at higher rate is desired to make H₂ viable as cheap energy carrier. The process is influenced by C/N composition, pH levels, temperature, light intensity etc. In this study, Rhodobacter sphaeroides strain O.U 001 was used in the annular photobioreactor with working volume 1 L, initial pH of 6.7 ± 0.2, inoculum age 36 h, inoculum volume 10% (v/v), 250 rpm stirring and light intensity of 15 ± 1.1 W m⁻². The effect of parameters, i.e. variation in concentration of DL malic acid, L glutamic acid and temperature on the H₂ production was noted using three factor three level full factorial designs. Surface and contour plots of the regression models revealed optimum H₂ production rate of 7.97 mL H₂ L⁻¹ h⁻¹ at 32 °C with 2.012 g L⁻¹ DL malic acid and 0.297 g L⁻¹ L glutamic acid, which showed an excellent correlation (99.36%) with experimental H₂ production rate of 7.92 mL H₂ L⁻¹ h⁻¹.     

Parthenium sp. as a plant biomass for the production of alkalitolerant xylanase from mutant Penicillium oxalicum SAUE-3.510 in submerged fermentation

The use of congress grass (Parthenium sp.) and water hyacinth (Eichhornia crassipes) as low cost raw materials for xylanase production from mutant Penicillium oxalicum SAU_E-3.510 in submerged fermentation was investigated. For development of mutant from wild type P. oxalicum SA-8 ITCC 6024, a strategy of mixed mutagenesis was followed using UV-irradiation and ethidium bromide, which had resulted into 1.87 fold increases in the activity of the enzyme. For enzyme production, the fungus was cultivated in mineral medium containing congress grass as carbon source. Considerably higher levels of production (475.2 ± 6.0 IU ml^?1) were achieved in media containing congress grass, although it was slightly less than that was obtained (488.5 ± 6.5 IU ml^?1) in presence of commercial oat spelt xylan. This fact confirms the feasibility of using this low cost non-food resource as an alternative carbon source to save costs of the enzyme production process. Maximum xylanase activity was reported at 55 °C with its stability at 80 °C for 2 h. The highest activity of xylanase at pH 9.0 and its stability at similar pH for 24 h denote the alkalitolerant nature of enzyme.     

Biohydrogen production by Rhodobacter capsulatus Hup mutant in pilot solar tubular photobioreactor

In this study, a pilot solar tubular photobioreactor was successfully implemented for fed batch operation in outdoor conditions for photofermentative hydrogen production with Rhodobacter capsulatus (Hup⁻) mutant. The bacteria had a rapid growth with a specific growth rate of 0.052 h⁻¹ in the batch exponential phase and cell dry weight remained in the range of 1–1.5 g/L throughout the fed batch operation. The feeding strategy was to keep acetic acid concentration in the photobioreactor at the range of 20 mM by adjusting feed acetate concentration. The maximum molar productivity obtained was 0.40 mol H₂/(m³ h) and the yield obtained was 0.35 mol H₂ per mole of acetic acid fed. Evolved gas contained 95–99% hydrogen and the rest was carbon dioxide by volume.     

Optical probing of anisotropic heat transport in the quantum spin ladder Ca9La5Cu24O41

A transient thermal imaging technique is used to monitor heat diffusion at the surface of the antiferromagnetic spin ladder material Ca₉La₅Cu₂₄O₄₁. This material shows highly anisotropic thermal conductivity due to a large uni-directional magnetic heat transport along the ladders. The thermal conductivity is measured using optical heating as well as electrical heating, yielding 37 ± 3 W m^?1 K^?1 for the fast (ladder) direction and 2.5 ± 0.5 W m^?1 K^?1 for the slow direction, respectively. The fast direction result is in agreement with the thermal conductivity measured using other dynamic methods, but about 60% lower than the thermal conductivity measured using steady state methods.     

Isolation and characterization of two soil derived yeasts for bioethanol production on Cassava starch

Two ethanol-producing yeast strains, CHY1011 and CHFY0901 were isolated from soil in South Korea using an enrichment technique in a yeast peptone dextrose medium supplemented with 5% (w v^?1) ethanol at 30 °C. The phenotypic and physiological characteristics, as well as molecular phylogenetic analysis based on the D1/D2 domains of the large subunit (26S) rRNA gene and the internally transcribed spacer (ITS) 1 + 2 regions suggested that they were novel strains of Saccharomyces cerevisiae. During shaking flask cultivation, the highest ethanol productivity and theoretical yield of S. cerevisiae CHY1011 in YPD media containing 9.5% total sugars was 1.06 ± 0.02 g l^?1 h^?1 and 95.5 ± 1.2%, respectively, while those for S. cerevisiae CHFY0901 were 0.97 ± 0.03 g l^?1 h^?1 and 91.81 ± 2.2%, respectively. Simultaneous saccharification and fermentation for ethanol production was carried out using liquefied cassava (Manihot esculenta) starch in a 5 l lab-scale jar fermenter at 32 °C for 66 h with an agitation speed of 2 Hz. Under these conditions, S. cerevisiae CHY1011 and CHFY0901 yielded a final ethanol concentration of 89.1 ± 0.87 g l^?1 and 83.8 ± 1.11 g l^?1, a maximum ethanol productivity of 2.10 ± 0.02 g l^?1 h^?1 and 1.88 ± 0.01 g l^?1 h^?1, and a theoretical yield of 93.5 ± 1.4% and 91.3 ± 1.1%, respectively. These results suggest that S. cerevisiae CHY1011 and CHFY0901 have potential use in industrial bioethanol fermentation processes.     

Production of bioethanol and associated by-products from potato starch residue stream by Saccharomyces cerevisiae

Potato starch residue stream produced during chips manufacturing was used as an economical source for biomass and bioethanol production by Saccharomyces cerevisiae. Results demonstrated that 1% H₂SO₄ at 100 °C for 1 h was enough to hydrolyze all starch contained in the residue stream. Two strains of S. cerevisiae (y-1646 and commercial one) were able to utilize and ferment the acid-treated residue stream under both aerobic and semi-anaerobic conditions. The maximum yield of ethanol (5.52 g L^?1) was achieved at 35 °C by S. cerevisiae y-1646 after 36 h when ZnCl₂ (0.4 g L^?1) was added. Addition of NH₄NO₃ as a source of nitrogen did not significantly affect either growth or ethanol production by S. cerevisiae y-1646. Some secondary by-products including alcohol derivatives and medical active compound were found to be associated with the ethanol production process.     

Biohydrogen using leachate from an industrial waste landfill as inoculum

Since hydrogen is a renewable energy source, biohydrogen has been researched in recent years. However, there is little data on hydrogen fermentation by a leachate from a waste landfill as inoculum. We investigated hydrogen production using a leachate from an industrial waste landfill in Kanagawa prefecture. The results showed no methane gas production and the leachate was a suitable inoculum for hydrogen fermentation. The maximum H₂ yield was 2.67 mol of H₂ per mol of carbohydrate added, obtained at 30 °C and initial pH 7. The acetate and butyrate production was significant when the H₂ yield was higher. The oxidation–reduction potential analysis of the culture suggested that hydrogen-producing bacteria in the leachate were facultatively anaerobic. Scanning electron microscope observations revealed hydrogen-producing bacteria comprised bacilli of about 2 μm in length.     

Improvement of photofermentative biohydrogen production using pre-treated brewery wastewater with banana peels waste

In this study, the impacts of banana peels pre-treatment stage on photofermentative hydrogen production of Rhodobacter sphaeroides 158 DSM using brewery wastewater (BWW) were investigated in a batch bioreactor. The experimental results indicate that banana peels pre-treatments can significantly enhance the cumulative hydrogen production. The maximum hydrogen production yield (408.33 mL H₂ L⁻¹_wastewater) was achieved from the substrate, which was composed of 50% BWW pretreated with 1 g L⁻¹ of banana peels for 2 h and 50% standard medium. This highest amount of hydrogen production was 2.7-folds higher than those that applied the same percentage of raw BWW as the substrate source.     

Assessment of nitrogen fertilization for the CO2 balance during the production of poplar and rye

This study was designed to consider all nitrogen fertilizer-related effects on crop production and emission of greenhouse gases on loamy sandy soils in Germany over a period of nine years (1999–2007). In order to set up a CO₂ balance for the production of energy crops, different nitrogen pathways were investigated, such as direct N₂O emissions from the soil and indirect emissions related to NO₃ leaching and fertilizer production. Fluxes of N₂O were measured in an experimental field using closed chambers. Poplar (Populus maximowiczii × P. nigra) and rye (Secale cereale L.) as one perennial and one annual crop were fertilized at rates of 0 kg N ha^?1 yr^?1, 75 kg N ha^?1 yr^?1 and 150 kg N ha^?1 yr^?1. The mean N₂O emissions from the soil ranged between 0.5 kg N ha^?1 yr^?1 and 2.5 kg N ha^?1 yr^?1 depending on fertilization rate, crop variety and year. The CO₂ fixed in the biomass of energy crops is reduced by up to 16% if direct N₂O emissions from soil and indirect N₂O emissions from NO₃ leaching and fertilizer production are included. Taking into account the main greenhouse gas emissions, which derive from the production and the use of N fertilizer, the growth of poplar and rye may replace the global warming potential of fossil fuels by up to 17.7 t CO₂ ha^?1 yr^?1 and 12.1 t CO₂ ha^?1 yr^?1, respectively.     

Hydrogen photosynthesis by Rhodobacter capsulatus and its coupling to a PEM fuel cell

Four different mutant strains of Rhodobacter capsulatus (IR1, IR3, IR4 and JP91), a photosynthetic purple non-sulfur bacterium, were tested for their ability to produce hydrogen in a 3 L volume photobioreactor coupled to a small PEM fuel cell. The four mutants, together with the wild-type strain, B10, were grown at 30 °C under illumination with 30 mmol L⁻¹ dl-lactate and 5 mmol L⁻¹ l-glutamate as carbon and nitrogen source, respectively. Bacterial growth was measured by monitoring the increase in absorbance at 660 nm, and hydrogen yield, and substrate conversion efficiency were measured under the same conditions. The hydrogen production capability of the five strains was then compared and shown to be in the order: IR3 > JP91 > IR4 > B10 > IR1. The most preferment strain, IR3, showed a substrate conversion efficiency of 84.8% and a hydrogen yield of 3.9 L L⁻¹ of culture. The biogas produced by these photobioreactor cultures was successfully used as feed for a small PEM fuel cell system, with the mutant IR3 showing the most sustained hydrogen and current production. The maximum current was similar to that obtained using pure hydrogen produced by a small electrolysis cell (High-Tec Inc.).     

Protonic battery based on a plasticized chitosan-NH4NO3 solid polymer electrolyte

Plasticized chitosan-proton conductor polymer electrolyte films were prepared by dissolving chitosan powder, ammonium nitrate (NH₄NO₃) salt and ethylene carbonate (EC) plasticizer in acetic acid solution. The highest conductivity of the chitosan-salt with 40 wt.% NH₄NO₃ in the film at room temperature was 8.38 ± 4.11 × 10⁻⁵ S cm⁻¹ and this increased to 9.93 ± 1.90 × 10⁻³ S cm⁻¹ with 70 wt.% EC. Batteries with a configuration of: Zn + ZnSO₄·7H₂O/18 wt.% CA-12 wt.% NH₄NO₃-70 wt.% EC/MnO₂ provided an open-circuit voltage of 1.56 ± 0.06 V. The discharge characteristics using a 1 mA constant current demonstrated a capacity of 17.0 ± 2.6 mAh. The internal resistance was 29.8 ± 5.1 Ω. While the highest power density was 8.70 ± 1.91 mW cm⁻².     

Thermophilic biohydrogen production from energy plants by Caldicellulosiruptor saccharolyticus and comparison with related studies

Air-dried samples of sweet sorghum, sugarcane bagasse, wheat straw, maize leaves and silphium were utilized without chemical pretreatment as sole energy and carbon sources for H₂ production by the extreme thermophilic bacterium Caldicellulosiruptor saccharolyticus. The specific H₂ production rates and yields were determined in the batch fermentation process. The best substrate was wheat straw, with H₂ production capacity of 44.7 L H₂ (kg dry biomass)^?1 and H₂ yield of 3.8 mol H₂ (mol glucose)^?1. Enzymatically pretreated maize leaves exhibited H₂ production of 38 L H₂ (kg dry biomass)^?1. Slightly less H₂ was obtained from homogenized whole plants of sweet sorghum. Sweet sorghum juice was an excellent H₂ source. Silphium trifoliatum was also fermented though with a moderate production. The results showed that drying is a good storage method and raw plant biomass can be utilized efficiently for thermophilic H₂ production. The data were critically compared with recently published observations.     

Nutrients' removal from aquaculture wastewater using the macroalgae Gracilaria birdiae

Intensive aquaculture releases large amount of nutrients into aquatic ecosystems and can lead to eutrophication of coastal waters. Studies conducted in aquaculture systems have demonstrated that the seaweeds are efficient in reducing nutrients and at the same time provides extra income, when species of economic importance are used. This study was conducted to evaluate whether Gracilaria birdiae could be cultivated efficiently for the production of useful algal biomass and removal of nutrients from shrimp pond effluents. The results obtained showed a gradual increase in biomass and relative growth rate (RGR) over the experimental period. Mean RGR between the weeks varied significantly (p < 0.01), reaching a maximum of 3.6 ± 0.35% d^?1 and a minimum of 1.6 ± 0.52% d^?1. The mean for the whole period was 2.6% d^?1. The biofiltration capacity of G. birdiae was confirmed by the significantly reduced concentration of the three nutrients analyzed (PO₄^3?, NH₄⁺ and NO₃^?) over the study period. The concentration of PO₄^3? decreased by 93.5%, NH₄⁺ by 34% and NO₃^? by 100% after the 4-week experimental period. The results obtained in this study indicated that G. birdiae can be used in aquaculture systems as a biofilter. In addition, the macroalgae biomass produced offers alternative source of raw material for the extraction of the phycocolloid agar, human food and animal feed.     

Effects of dark/light bacteria ratio on bio-hydrogen production by combined fed-batch fermentation of ground wheat starch

Bio-hydrogen production by combined dark and light fermentation of ground wheat starch was investigated using fed-batch operation. Serum bottles containing heat-treated anaerobic sludge and a mixture of Rhodobacter sp. was fed with a medium containing 20 g dm^?3 wheat powder (WP) at a constant flow rate. The system was operated at different initial dark/light biomass ratios (D/L). The optimum D/L ratio was 1/2 yielding the highest cumulative hydrogen (1548 cm³), yield (65.2 cm³ g^?1 starch), and specific hydrogen production rate (5.18 cm³ g^?1 h^?1). Light fermentation alone yielded higher hydrogen production than dark fermentation due to fermentation of volatile fatty acids (VFAs) to H₂ and CO₂. The lowest hydrogen formation was obtained with D/L ratio of 1/1 due to accumulation of VFAs in the medium.     

Novel heat transfer fluids for direct immersion phase change cooling of electronic systems

We describe the use of computer-aided molecular design (CAMD) and figure of merit (FOM) analysis to identify new heat transfer fluids for direct immersion cooling of electronic systems. Thirty-five new fluids, with thermophysical properties in the range 320 K < T_b < 370 K, k > 0.09 W m^?1 K^?1 and H_vap > 35 kJ mol^?1, were identified via a CAMD approach. Further analysis of these 35 fluids led to the selection of 1,1,1-trifluoro-3-methylpentane (C₆H₁₁F₃) for experimental evaluation. C₆H₁₁F₃ was synthesized from commercially available precursors, and its thermophysical properties were measured to verify its FOM. Next, the pool boiling performance of a mixture of 7 wt.% C₆H₁₁F₃ + 93 wt.% HFE 7200 was determined using a 10 mm × 10 mm grooved Si thermal test chip coated with copper. An improvement of 7% in the critical heat flux (CHF) was obtained, suggesting that C₆H₁₁F₃ is worth further examination as a candidate for direct immersion phase change cooling applications.     

A novel Al and Y codoped ZnO/n-Si heterojunction solar cells fabricated by pulsed laser deposition

Al and Y codoped ZnO (AZOY) transparent conducting oxide (TCO) thin films were first deposited on n-Si substrates by pulsed laser deposition (PLD) to form AZOY/n-Si heterojunction solar cells. However, the properties of the AZOY emitter layers are critical to the performance of AZOY/n-Si heterojunction solar cells. To estimate the properties of AZOY thin films, films deposited on glass substrates with various substrate temperatures (T_s) were analyzed. Based on the experimental results, optimal electrical properties (resistivity of 2.8 ± 0.14 × 10^?4 Ω cm, carrier mobility of 27.5 ± 0.55 cm²/Vs, and carrier concentration of 8.0 ± 0.24 × 10²⁰ cm^?3) of the AZOY thin films can be achieved at a T_s of 400 °C, and a high optical transmittance of AZOY is estimated to be >80% (with glass substrate) in the visible region under the same T_s. For the AZOY/n-Si heterojunction solar cells, the AZOY thin films acted not only as an emitter layer material, but also as an anti-reflected coating thin film. Thus, a notably high short-circuit current density (J_sc) of 31.51 ± 0.186 mA/cm² was achieved for the AZOY/n-Si heterojunction solar cells. Under an AM1.5 illumination condition, the conversion efficiency of the cells is estimated at only approximately 4% (a very low open-circuit voltage (V_oc) of 0.24 ± 0.001 V and a fill factor (FF) of 0.51 ± 0.011) without any optimization of the device structure.