Anaerobic rumen SBR for degradation of cellulosic material.

Hydrolysis of organic particulates under anaerobic conditions is generally regarded as the rate limiting step in solid digestion processes. Rumen-based ecosystems appear to achieve very high hydrolysis rates for cellulosic organic material. This study aimed at the development and demonstration of an anaerobic sequencing batch reactor (SBR) process operating with a rumen-based microbial inoculum. Fibrous alpha cellulose was used as sole carbon substrate and the use of an SBR operating cycle allowed the utilisation of a high liquid flow rate (hydraulic retention time of 0.67 d) while maintaining a much longer solids retention time of 7 d. Complete mass balances for carbon and nitrogen, as well as COD balancing allowed the full characterisation of the process stoichiometry and kinetics. Elemental analysis of the biomass revealed a composition of C5H4.8O2.4N0.7, which is quite different from other generic biomass compositions used in the literature. The anaerobic rumen SBR was compared with another rumen-based reactor system in the literature which used a continuous filtration process for solid/liquid separation. This comparison showed that the volatile fatty acid production rate from cellulose in the anaerobic SBR was comparable with the performance achieved in the continuous system, although loading, substrate type and media composition were quite different between these two studies. Further evaluation of the anaerobic rumen SBR is required to determine its practical application for other substrates and to demonstrate the scale-up potential of this concept.     

Gasification inhibition in chemical-looping combustion with solid fuels

Chemical-looping combustion (CLC) is a novel technology that can be used to meet growing demands on energy production without CO₂ emissions. The CLC process includes two reactors, an air and a fuel reactor. Between these two reactors oxygen is transported by an oxygen carrier, which most often is a metal oxide. This arrangement prevents mixing of N₂ from the air with CO₂ from the combustion giving combustion gases that consist almost entirely of CO₂ and H₂O. The technique reduces the energy penalty that normally arises from the separation of CO₂ from other flue gases, hence, CLC could make capture of CO₂ cheaper. For the application of CLC to solid fuels, the char remaining after devolatilization will react indirectly with the oxygen carrier via steam gasification. It has been suggested that H₂, and possibly CO, has an inhibiting effect on steam gasification in CLC. In this work experiments were conducted to investigate this effect. The experiments were conducted in a laboratory fluidized-bed reactor that was operating cyclically with alternating oxidation and reduction periods. Two different oxygen carriers were used as well as an inert sand bed. During the reducing period varying concentrations of CO or H₂ were used together with steam while the oxidation was conducted with 10% O₂ in N₂. The temperature was constant at 970 °C for all experiments. The results show that CO does not directly inhibit the gasification whereas the partial pressure of H₂ had a significant influence on fuel conversion. The results also suggest that dissociative hydrogen adsorption is the predominant hydrogen inhibition mechanism under the laboratory conditions, thus explaining why char conversion is much faster in a bed of oxygen carrying material, compared to an inert sand bed.     

Impact of three different TiO2 morphologies on hydrogen evolution by methanol assisted water splitting: Nanoparticles, nanotubes and aerogels

Increasing the activity of a photocatalyst goes through the improvement of both its absorption (light) and adsorption (reactant) properties. For a given semiconducting material, the charge carrier separation is also a very important step. Properly combining chosen phases is one option to improve this separation (example of the commercial P25) and depositing platinum on the surface of the catalyst, another one. In some cases, coupling both may nevertheless lead to a decrease of photoactivity or at least limit the potentiality of the catalyst. A third option, consisting in modifying the morphology of the photoactive phase, has shown very promising results.In this study, we have elaborated, characterized and evaluated the hydrogen evolution potentiality (through methanol assisted water splitting) of different TiO₂ morphologies: nanoparticles, nanotubes and aerogels. These materials have shown different behaviours depending on both their composition and morphology. Different types of separation processes have been claimed to account for the observed different photoactivities, with more or less pronounced synergetic effects, due to: the use of Pt as a co-catalyst, the mixture of different TiO₂ phases (anatase and TiO₂(B) or rutile) and the specific morphology of the samples (nanotubes or aerogels). Among all the tested samples, the TiO₂ aerogel supported Pt one exhibited very promising performances, three times as active as P25 supported Pt, which is already much more active than pure P25 in our testing conditions.     

Sources and variations of mercury in tuna

While the bulk of human exposure to mercury is through the consumption of marine fish, most of what we know about mercury methylation and bioaccumulation is from studies of freshwaters. We know little of where and how mercury is methylated in the open oceans, and there is currently a debate whether methylmercury concentrations in marine fish have increased along with global anthropogenic mercury emissions. Measurements of mercury concentrations in Yellowfin tuna caught off Hawaii in 1998 show no increase compared to measurements of the same species caught in the same area in 1971. On the basis of the known increase in the global emissions of mercury over the past century and of a simple model of mercury biogeochemistry in the Equatorial and Subtropical Pacific ocean, we calculate that the methylmercury concentration in these surface waters should have increased between 9 and 26% over this 27 years span if methylation occurred in the mixed layer or in the thermocline. Such an increase is statistically inconsistent with the constant mercury concentrations measured in tuna. We conclude tentatively that mercury methylation in the oceans occurs in deep waters or in sediments.     

Poly(3-hexylthiophene)/C60 heterojunction solar cells: Implication of morphology on performance and ambipolar charge collection

The performance of heterojunction organic solar cells is critically dependent on the morphology of the donor and acceptor components in the active film. We report results of photovoltaic devices consisting of bilayers and bulk heterojunctions using poly(3-hexylthiophene) (P3HT) and Buckminsterfullerene C₆₀. White light power efficiencies of η2.2% (bulk heterojunction) and 2.6% (bilayer) were measured after a thermal annealing step on completed devices. Optical and structural investigations on non-annealed bilayer thin films indicated a distinct porosity of the spin-coated polymer, which allows C₆₀ to penetrate the P3HT layer and to touch the anode. This resulted for these bilayer solar cells in the experimental observation that electrons were collected predominantly at the cathode after photo-excitation of P3HT, but predominantly at the anode after C₆₀ excitation. A morphological model to explain the ambipolar charge collection phenomenon is proposed.     

Modeling of mechanical response of FRP composites in fire

A thermomechanical model is presented for predicting the time-dependent deflections of cellular FRP slab elements subjected to mechanical loading and fire from one side. The model comprises temperature-dependent mechanical property sub-models for the Young’s modulus, viscosity and coefficient of thermal expansion. Two different thermal boundary conditions were investigated: with and without liquid-cooling of the slab elements in the cells. A finite difference method was used to calculate the deflection at each time step. Deflections resulting from stiffness degradation due to glass transition and decomposition of the resin dominated over those resulting from viscosity and thermal expansion. The predicted total deflections compared well with the measured results over a test period of up to 2 h. The failure mode of the non-cooled specimen could be explained.