J. M. S. Rocha

Photobiological hydrogen production: photochemical efficiency and bioreactor design

Abstract Biological production of hydrogen can be carried out by photoautotrophic or photoheterotrophic organisms. Here, the photosystems of both processes are described. The main drawback of the photoautotrophic hydrogen production process is oxygen inhibition. The few efficiencies reported on the conversion of light energy into hydrogen energy are low, less than 1.5% on a solar spectrum basis. However, these can be increased to 3–10%, by the immediate removal of produced oxygen. The photochemical efficiency of hydrogen production can be calculated theoretically, and is estimated to be 10% (on solar spectrum basis) for the photoheterotrophic process. With use of the theoretical photochemical efficiency, and the climatic data on sunlight irradiance at a certain location at a certain moment of the year, the theoretical maximum hydrogen production can be estimated. Data on H2 yields and photochemical efficiency from experiments reported in the literature are summarized. Photochemical efficiencies, essentially based on artificial light, can reach 10% or even more, but only at low light intensities, with associated low-H2 production rates. Some reflections on possible photobioreactors lead to two types of (modified) photobioreactors that might be successful for a large-scale biological hydrogen production.

Acetate as a carbon source for hydrogen production by photosynthetic bacteria

Hydrogen is a clean energy alternative to fossil fuels. Photosynthetic bacteria produce hydrogen from organic compounds by an anaerobic light-dependent electron transfer process. In the present study hydrogen production by three photosynthetic bacterial strains (Rhodopseudomonas sp., Rhodopseudomonas palustris and a non-identified strain), from four different short-chain organic acids (lactate, malate, acetate and butyrate) was investigated. The effect of light intensity on hydrogen production was also studied by supplying two different light intensities, using acetate as the electron donor. Hydrogen production rates and light efficiencies were compared. Rhodopseudomonas sp. produced the highest volume of H2. This strain reached a maximum H2 production rate of 25 ml H2 l(-1) h(-1), under a light intensity of 680 micromol photons m(-2) s(-1), and a maximum light efficiency of 6.2% under a light intensity of 43 micromol photons m(-2) s(-1). Furthermore, a decrease in acetate concentration from 22 to 11 mM resulted in a decrease in the hydrogen evolved from 214 to 27 ml H2 per vessel.

Growth aspects of the marine microalga Nannochloropsis gaditana

Nannochloropsis is well appreciated in aquaculture due to its nutritional value and the ability to produce valuable chemical compounds, such as pigments (zeaxanthin, astaxanthin...) and polyunsaturated fatty acids (EPA). Commercial exploitation needs high cell densities but the low growth rate and the small size of cells are practical difficulties. To increase biomass concentration the positive effect of several factors was evident: (i) pH approximately 8 control (with dilute Tris-HCl buffer); (ii) the continuous illumination (no evidence of photo-inhibition was observed); (iii) a quite large temperature range (25+/-5 degrees C); (iv) the presence of organic carbon source (with the danger of contamination); (v) the presence of urea as an additional nitrogen source (10 mM); (vi) a small air flow rate with large bubbles can be more efficient for CO(2) mass transfer (associated to reduced shearing).

Optimisation of the enzymatic synthesis of n-octyl oleate with immobilised lipase in the absence of solvents

The enzymatic synthesis of n-octyl oleate by direct esterification of the oleic acid and the octanol in a solvent-free medium was previously shown to be efficiently catalysed by a lipase from Rhizomucor miehei covalently linked to a graft copolymer, the partially hydrolysed poly(ethylene)-g co-hydroxyethyl methacrylate (PE-g co-HEMA). In this work we went further towards an optimisation of the production of n-octyl oleate taking into account several parameters that affect the catalytic activity of the preparation. The physical characteristics of the support, such as the particle size and the degree of hydrolysis of the copolymer, the amount of lipase used in the method of immobilisation, the water content of the reaction mixture and the operational conditions of reaction, in particular the temperature, were evaluated in order to achieve not only high activities but also a good stability of the preparation.

Effects of additives on the activity of a covalently immobilised lipase in organic media

Lipase from Mucor miehei was covalently immobilised onto the graft copolymer poly(ethylene)-g.co-hydroxyethyl methacrylate (PE-g.co-HEMA), partially hydrolysed, via a spacer arm of 1,6-diaminohexane activated with glutaraldehyde. To improve the lipolytic activity of the immobilised lipase (for the synthesis of isoamyl-caprylate, as a model), the effect of several additives was investigated. Polyethylene glycol (PEG), glutaraldehyde, organic solvents and buffers, were added during the immobilisation procedure and their effects are reported and compared with the behaviour of the lipolytic preparation without pre-treatment. An increase of 40-100% in the activity was obtained when small quantities of PEG 2000 and glutaraldehyde (used also as an activator of the spacer arm) were added. The activity had a maximum when the pH of the lipase attachment solution was 7.2 and buffered with phosphate. The effect of the aggregation level of biocatalyst particles on the amount of water retained, as well as the effect of the immobilisation on solid supports on the stability to organic solvents, is also reported.

Hydrogen production by phososynthetic bacteria: Culture media, yields and efficiencies

Publisher Summary Hydrogen is recognized nowadays as the fuel of the future. For its large scale use, the production of large quantities of economic hydrogen is essential. However, biological hydrogen production, as an environmental-friendly resource of energy, must be developed in order to be an alternative technology, so that it can be used when other goals become more important than price. Hydrogen can be produced by photo-fermentation with photosynthetic bacteria, carried out with suitable nutrients, under anaerobic conditions, in the absence of nitrogen gas, with illumination and with stressful concentrations of nitrogen sources. The main enzymes involved are nitrogenase and hydrogenase. Valuable by-products can also be formed. These advantages put together with waste treatment give this system potential at a short term. The design of photobioreactors with efficient light transfer is still lacking. The optimal production of hydrogen by photosynthetic bacteria, to be economically attractive, has to take into account several parameters, such as the productivity, the light efficiency, and the yield on carbon source.

Lipase immobilisation on to polymeric membranes

Lipase (EC 3.1.1.3) from Candida rugosa was covalently immobilised on to cellulose, cellulose derivatives (cellulose acetate and cellulose phthalate) and cellulose composite membranes using activating agents such as sodium periodate or carbodiimide. Other non-cellulosic polymeric membranes (nylon, polyurethane, chitosan and hydroxyethyl methacrylate-co-methyl methacrylate) were also prepared and used for lipase immobilisation. The results obtained showed that the expressed activities are of the same order of magnitude for similar enzyme loadings when compared with those obtained from literature.

Preparation and characterization of polyethylene based graft copolymers. Applications in the immobilization of enzymes

Abstract In the last few years new copolymeric supports for the immobilization of biological compounds have been developed. The graft copolymer polyethylene-g.co-hydroxyethyl methacrylate, partially hydrolyzed, has shown to be a very promising support for this purpose. The more recent work in the preparation and characterization of this copolymer, as well as the immobilization of a lipase, is reported in this paper. Branches of poly(hydroxyethyl methacrylate) were grafted onto low density polyethylene by using gamma radiation. The influence of the presence and absence of air, as well as the monomer concentration on the yield of grafting were evaluated. The obtained copolymers were characterized by DSC and FTIR. The influence of the support properties on the synthesis biocatalytic activity was detected.

Prehydrolysis of Eucalyptus globulus Labill. hemicelluloses prior to pulping and fermentation of the hydrolysates with the yeast Pichia stipitis 10th EWLP, Stockholm, Sweden, August 25–28, 2008

Abstract The aim of this work was to evaluate the potential of Eucalyptus globulus hemicelluloses, mainly xylan, for bioethanol production. Hemicelluloses have been removed prior to pulping by auto-hydrolysis and an acid-catalysed hydrolysis. As the hydrolysates obtained were rich in xylose, the yeast Pichia stipitis was selected for fermentation. It was confirmed that the yeast performance is strongly dependent on pH and the presence of inhibitors, such as lignin. The addition of Ca(OH)2 was successful for lowering the concentration of inhibitors and adjusting the pH. The strain was grown in culture media with increasing volumetric percentages of treated hydrolysates up to 100% (v/v), supplemented with nutrients other than the carbon and energy source. This methodology shortened the lag phase of fermentation and improved the performance of yeast. Maximum ethanol concentration (12 geth l-1), productivity (0.22 geth l-1 h-1), and yield (0.48 geth gxyl eqs -1) were achieved with treated acid-hydrolysates. These results are similar to those obtained by a synthetic medium with an equivalent xylose concentration.

Mechanical Properties of Particle Reinforced Resin Composites

The objective of the present work is the evaluation of the contents of inorganic particles in the mechanical and tribological behavior of polymeric matrix composites. In order to control easily the production of the specimens, a polyester resin was used as matrix and silica particles were added as inorganic filler. The volumetric particle content was ranged from 0 to 46%. In order to understand the influence of the inorganic load was evaluated the mechanical and tribological behaviors for several percentage of particle content was evaluated. There are several applications of inorganic fillers where their volume percentage is important, namely in dentistry. In posterior restorative resin materials, the particles percentage in volume goes up to 50 or more. In most cases spherical and irregular shaped fillers are dispersed randomly. In the studied composites the filler has irregular shape therefore the connection between the matrix and the particles is more effective. Function of the shape, concentration degree and particle size of the filler the composite mechanical properties vary greatly. All of these factors influence the mechanical properties of the particlereinforced composite, namely: wear resistance, hardness, flexural modulus, flexure strength and toughness The morphology of the failure surfaces was observed by scanning electron microscopy and the results were widely discussed.