Inci Eroglu

Aspects of the metabolism of hydrogen production by Rhodobacter sphaeroides

Abstract Photosynthetic bacteria are favorable candidates for biological hydrogen production due to their high conversion efficiency and versatility in the substrates they can utilize. For large-scale hydrogen production, an integrated view of the overall metabolism is necessary in order to interpret results properly and facilitate experimental design. In this study, a summary of the hydrogen production metabolism of the photosynthetic purple non-sulfur (PNS) bacteria will be presented. Practically all hydrogen production by PNS bacteria occurs under a photoheterotrophic mode of metabolism. Yet results show that under certain conditions, alternative modes of metabolism—e.g. fermentation under light deficiency—are also possible and should be considered in experimental design. Two enzymes are especially critical for hydrogen production. Nitrogenase promotes hydrogen production and uptake hydrogenase consumes hydrogen. Though a wide variety of substrates can be used for growth, only a portion of these is suitable for hydrogen production. The efficiency of a certain substrate depends on factors such as the activity of the TCA cycle, the carbon-to-nitrogen ratio, the reduction-state of that material and the conversion potential of the substrate into alternative metabolites such as PHB. All these individual components of the hydrogen production interact and are subject to strict regulatory controls. An overall scheme for the hydrogen production metabolism is presented.

Substrate consumption rates for hydrogen production by Rhodobacter sphaeroides in a column photobioreactor

The effect of l-malic acid and sodium glutamate, which serve as the carbon and nitrogen source, respectively, on hydrogen production by Rhodobacter sphaeroides O.U.001 has been investigated in a batch water jacketed glass column photobioreactor (PBR), which has an inner volume of 400 ml. The PBR was operated at different carbon to nitrogen ratios at 32°C with a tungsten lamp at a light intensity of 200 W m−2. Carbon to nitrogen ratio was found to be an important parameter for bio-hydrogen production. Moreover, hydrogen gas production was dependent on certain threshold concentrations of sodium glutamate. l-malic acid consumption was found to be first order with respect to l-malic acid concentration, whereas sodium glutamate consumption was found to be second order with respect to glutamate concentration. It was concluded that there is a close relationship between the hydrogen production rate and substrate consumption rates. A kinetic model is developed, which relates hydrogen gas production per amount of biomass, l-malic acid, and sodium glutamate concentrations.

Photobiological hydrogen production by using olive mill wastewater as a sole substrate source

Abstract In the present work olive mill wastewater (OMW) collected from West Anatolia—Turkey during 2001, containing 36.02 g carbon, 5.26 g hydrogen, and 0.96 g nitrogen in 100 g suspended solid was used as a sole substrate for the production of hydrogen gas by Rhodobacter sphaeroides O.U.001 in 400 ml glass, column-photobioreactors. Hydrogen production studies on diluted-OMW were investigated in the range of 20% (v/v) and 1% (v/v) OMW containing media. Below 5% OMW containing media, bacterial growth rate fitted well to the logistic model where hydrogen production was observed for the ones below 4% OMW. A maximum hydrogen production potential (HPP) of 13.9 l H 2 / l OMW was obtained at 2% OMW. During the biological hydrogen production process, chemical oxygen demand (COD) of the diluted wastewater decreased from 1100 to 720 mg / l ; biochemical oxygen demand (BOD) decreased from 475 to 200 mg / l , and the total recoverable phenol content (ortho- and meta-substitutions) decreased from 2.32 to 0.93 mg / l . In addition, valuable by-products such as carotenoid (40 mg / l OMW ) and polyhydroxybutyrate (PHB) (60 mg / l OMW ) were obtained. According to these results, OMW was concluded to be a very promising substrate source for biohydrogen production process, with additional benefits of its utilization with regard to environmental and economical aspects.

Photoproduction of hydrogen from sugar refinery wastewater by Rhodobacter sphaeroides O.U. 001

Pretreated sugar refinery wastewater (SRWW) was used for the production of hydrogen by Rhodobacter sphaeroides O.U.001 in a 0.4 l column photobioreactor. Hydrogen was produced at a rate of 0.001 l hydrogen/h/l culture in 20% dilution of SRWW. To adjust the carbon concentration to 70 mM and nitrogen concentration to 2 mM, sucrose or L-malic acid was added as carbon source and sodium glutamate was added as nitrogen source to the 20% dilution of SRWW. By these adjustments, hydrogen production rate was increased to 0.005 l hydrogen/h/l culture. Continuous hydrogen production was achieved in the same medium for 100 days at three different dilution rates. The maximum hydrogen produced was 2.67 l (in 100 days) at a dilution rate of 0.0013 h−1.

Effect of clay pretreatment on photofermentative hydrogen production from olive mill wastewater

The aim of this paper was to gain further insight into the effect of the clay pretreatment process on photofermentative hydrogen production. This two-stage process involved a clay pretreatment step followed by photofermentation which was performed under anaerobic conditions with the illumination by Tungsten lamps. Rhodobacter sphaeroides O.U.001 was used for photofermentation. Higher amounts of color (65%), total phenol (81%) and chemical oxygen demand (31%) removal efficiencies were achieved after clay pretreatment process. During photofermentative hydrogen production with the effluent of clay pretreatment process, the main organic compounds resulting higher hydrogen production rates were found to be acetic, lactic, propionic, and butyric acids. Compared to photofermentation using raw olive mill wastewater ( 16LH2/LOMW), the amount of photofermentative hydrogen production was doubled by using the effluent of the clay pretreatment process (31.5LH2/LOMW). The reasons for the improvement of hydrogen production by clay treatment can be attributed to the high removal of the hardly biodegradable compounds such as phenols; minor removal of organic acids, sugars and amino acids that are known to enhance photofermentative hydrogen production; and the color depletion of raw OMW which might cause a shadowing effect on the photosynthetic bacteria.

Identification of by-products in hydrogen producing bacteria; Rhodobacter sphaeroides O.U. 001 grown in the waste water of a sugar refinery

Rhodobacter sphaeroides O.U. 001 is able to produce hydrogen anaerobically upon illumination. The cells were screened for the presence of valuable by-products such as poly-β-hydroxy (PHB) butyric acid aiming to improve the feasibility of the system. Also waste water from a sugar refinery was used for bacterial growth to further increase the feasibility. Under aerobic conditions the standard growth media containing l-malic acid and sodium glutamate in 7.5/10 and 15/2 molar ratios and a medium containing 30% waste water from sugar refinery were used. In this case the maximum concentration of PHB produced were approximately 0.2 g l− 1 in both of the standard media whereas it was 0.3 g l− 1 in medium containing 30% waste water. By using the medium containing 30% waste water, PHB and hydrogen productions were determined under anaerobic conditions. The maximum concentration of PHB produced was around 0.5 g l− 1 and the amount of gas collected was 35 ml in 108 h. From these results it can be concluded that PHB can be collected during hydrogen production. The use of waste water from sugar refinery increased the yield.

Kinetics of gypsum formation and growth during the dissolution of colemanite in sulfuric acid

One of the most important boron minerals, colemanite, is dissolved in aqueous sulfuric acid to produce boric acid whereby gypsum is formed as byproduct. Filtration of gypsum has an important role in boric acid production because gypsum affects the efficiency, purity and crystallization of boric acid. The formation and growth kinetics of gypsum during the dissolution of colemanite in aqueous sulfuric acid were studied in a batch reactor by varying the temperature (60–901C), stirring rate (150–400 rpm), and initial concentrations of the reactants. The initial CaO/H2SO4 molar ratio was varied between 0.21–0.85 by keeping the initial concentration of sulfate ion at [SO4� ]o=0.623 mol/l, and 0.85–3.41 by keeping the initial concentration of colemanite at [B2O3]o=0.777 mol/l. The crystallization of gypsum from the solution was followed by monitoring the calcium ion concentration in the solution as it is decreased by the formation of calcium sulfate precipitate. The calcium ion concentration in the liquid phase first undergoes a rapid exponential decay and then slowly approaches an asymptotic value of the saturation concentration at the respective temperature. The saturation concentration decreases with the increasing temperature from 5.2 mmol/l at 601C to 3.1 mmol/l at 801C, however, further increase in the temperature up to 901C causes an increase in the saturation concentration to 5.1 mmol/l. The stirring rate was found to have no significant effect on dissolution in the range of 150–400 rpm. The minimum saturation concentration of the calcium ion was obtained at 801C when the initial CaO/H2SO4 molar ratio is 0.85. The boric acid concentration in the solution decreases with the decreasing initial concentration of sulfuric acid. After the fast dissolution reaction of colemanite in aqueous sulfuric acid, the nucleation of the gypsum crystals first occurs from the supersaturated solution and then the crystals grow on these nuclei. The needle like crystals become wider and taller on prolong crystallization. The rate of gypsum crystallization reaction was second order with respect to saturation level. The evaluation of the kinetic data in an Arhenius plot gives an activation energy of 3472 kJ/mol for the crystal growth of gypsum from the supersaturated solution obtained by dissolution of colemanite in aqueous sulfuric acid. r 2001 Elsevier Science B.V. All rights reserved.

Gelatin microspheres and sponges for delivery of macromolecules

Gelatin microspheres and gelatin sponges were prepared by coacervation and freeze drying techniques, respectively. Both systems were crosslinked with glutaraldehyde. The mean diameter of the microspheres were in the range of 40–80 mm and the mean pore size of the sponges was 130–220 mm depending on the preparation conditions. Bovine serum albumin (BSA) was added into the preparation solutions and entrapped in the microspheres and sponges. BSA addition to sponges was also achieved by addition of BSA-containing microspheres into the sponges. The release kinetics of BSA from the prepared systems were examined. Studies demonstrated that release is dependent on the amount of BSA present in the system and crosslinking densities of microspheres. It was concluded that gelatin microspheres and gelatin sponges are promising carrier matrices for macromolecules.

Continuous Hydrogen Production by Rhodobacter sphaeroides O.U.001

This paper describes hydrogen gas production by Rhodobacter sphaeroides O.U.001 using a column photobioreactor in batch and continuous operation. The effect of substrates on the hydrogen production rate was investigated in batch-type photobioreactor experiments. Substrate concentrations (L-malic acid and sodium glutamate) were measured by using high-pressure liquid chromatography. The gas produced was analyzed by gas chromatography.

Photobiological Hydrogen Production by Rhodobacter sphaeroides O.U.001 by Utilization of Waste Water from Milk Industry

Hydrogen production with photosynthetic microorganisms contributes to the protection of the environment, not only in producing a clean fuel but also in waste treatment processes. In this study, Rhodobacter sphaeroides, a photosynthetic bacteria, is used in photobiological hydrogen production by using waste water from the milk industry.