Measurement and prediction of CO2 solubility in sodium phosphate monobasic solutions for food treatment with high pressure carbon dioxide

Two experimental systems were designed and tested to measure the CO₂ solubility in pure water and sodium phosphate monobasic solutions (0.240, 2.40 and 4.80 g/100 g water) at different pressures (7.5 and 15.0 MPa) and temperatures (35, 40 and 50 °C).The solubility experimental results were compared with the equilibrium conditions evaluated by applying three different thermodynamic models by means of the process simulation software Aspen Plus^®: (1) the Peng-Robinson equation of state (EOS), with the Wong and Sandler mixing rules (PRWS) and the excess Gibbs free energy calculated according to the UNIFAC method; (2) the Electrolytic Non-Random Two Liquids (ELECNRTL) with the Redlich-Kwong equation of state for aqueous and mixed solvent applications; (3) the completely predictive Soave-Redlich-Kwong (PSRK) equation of state.CO₂ solubility appeared to be a strong function of sodium phosphate monobasic concentrations. The predictions of the PRWS EOS agreed well with the experimental data in the pressure and temperature ranges tested. Larger differences between experimental and predicted results were observed for conditions close to the CO₂ critical point and for low sodium phosphate monobasic concentrations. Predictions of thermodynamic models 2 and 3 had much larger deviations from experimental data.     

Effects of heat treatment on microbial communities of granular sludge for biological hydrogen production

Dark fermentation shares many features with anaerobic digestion with the exception that to maximize hydrogen production, methanogens and hydrogen-consuming bacteria should be inhibited. Heat treatment is widely applied as an inoculum pre-treatment due to its effectiveness in inhibiting methanogenic microflora but it may not exclusively select for hydrogen-producing bacteria. This work evaluated the effects of heat treatment on microbial viability and structure of anaerobic granular sludge. Heat treatment was carried out on granular sludge at 100 °C with four residence times (0.5, 1, 2 and 4 h). Hydrogen production of treated sludges was studied from glucose by means of batch test at different pH values. Results indicated that each heat treatment strongly influenced the granular sludge resulting in microbial communities having different hydrogen productions. The highest hydrogen yields (2.14 moles of hydrogen per mole of glucose) were obtained at pH 5.5 using the sludge treated for 4 h characterized by the lowest CFU concentration (2.3 × 10(3)CFU/g sludge). This study demonstrated that heat treatment should be carefully defined according to the structure of the sludge microbial community, allowing the selection of highly efficient hydrogen-producing microbes.     

An integrated approach for optimal design of micro gas turbine combustors

The present work presents an approach for the optimized design of small gas turbine combustors, that integrates a 0-D code, CFD analyses and an advanced game theory multi-objective optimization algorithm. The output of the 0-D code is a baseline design of the combustor, given the required fuel characteristics, the basic geometry (tubular or annular) and the combustion concept (i.e. lean premixed primary zone or diffusive processes). For the optimization of the baseline design a simplified parametric CAD/mesher model is then defined and submitted to a CFD code. Free parameters of the optimization process are position and size of the liner hole arrays, their total area and the shape of the exit duct, while different objectives are the minimization of NO_x emissions, pressure losses and combustor exit Pattern Factor. A 3D simulation of the optimized geometry completes the design procedure. As a first demonstrative example, the integrated design process was applied to a tubular combustion chamber with a lean premixed primary zone for a recuperative methane-fuelled small gas turbine of the 100 kW class.     

Improved photocatalytic H2 production assisted by aqueous glucose biomass by oxidized g-C3N4

Chemically modified g-C₃N₄ for the photocatalytic H₂ evolution from water was explored. Bulk g-C₃N₄ was treated in hot HNO₃ aqueous solution to obtain the oxidized material (o-g-C₃N₄), tested in water containing glucose as model water-soluble sacrificial biomass, using Pt as co-catalyst, under simulated solar light. The behaviour of o-g-C₃N₄ was studied in relation with catalyst amount, Pt loading, glucose concentration. Results showed that H₂ production is favoured by increasing glucose concentration up to 0.1 M and Pt loading up to 3 wt%, and it resulted strongly enhanced using small amount of o-g-C₃N₄ (0.25 g L^?1). o-g-C₃N₄ possesses superior photocatalytic activity (～26-fold higher) compared to pristine g-C₃N₄, with H₂ evolution further improved by ultrasound-assisted exfoliation and evolution rates up to ca. 1370 μmol h^?1 per gram of catalyst, with excellent reproducibility (RSD < 6%, n = 3). Significant production was observed also in river water and seawater, with results far better (up to ca. 2500 μmol g^?1 h^?1) compared to commercial AEROXIDE^® P25 TiO₂ under natural solar light.     

Computing the solar vector

High-concentration solar thermal systems require the Sun to be tracked with great accuracy. The higher the system concentration, the greater this accuracy must be. The current trend in solar concentrator tracking systems is to use open-loop controllers that compute the direction of the solar vector based on location and time. To keep down the price of the tracking system, the controller is based on a low-cost microprocessor. These two facts impose important restrictions on the Sun position algorithm to be used in the controller, as it must be highly accurate and efficiently computable at the same time. In this paper, various algorithms currently available in the solar literature are reviewed and a new algorithm, developed at the Plataforma Solar de Almería, which combines these two characteristics of accuracy and simplicity, is presented. The algorithm allows of the true solar vector to be determined with an accuracy of 0.5 minutes of arc for the period 1999–2015.     

Study of complexing reactions causing the depletion of gadolinium ions from the moderator of CANDU-PHW nuclear reactors

The addition of gadolinium nitrate solution in the moderator of Hydro-Québec's Gentilly 2 reactor led to an unexpected depletion of gadolinium (Gd) by precipitation. Analysis of moderator samples revealed that bicarbonate (HCO₃^?) was the main anionic impurity. A study of the complexing reactions of Gd in concentrated solutions (0.0509M) of Gd(NO₃)₃ showed that in the absence of HCO₃^? and at pH < 6, the species in equilibrium are distributed as follows: predominant: Gd³⁺, NO₃^? and [GdNO₃]²⁺; and traces: [GdOH]²⁺ and [Gd(NO₃)₂]⁺. An increase in pH over 6.4 led to the formation of the solid phase: Gd₂(OH)_5.1(NO₃)_0.9. In the presence of bicarbonate, the solid phase Gd₂(OH)_5.0(NO₃)_1.0 is visually detected at a pH as low as 5.8. In other respects, analysis of dilute solutions (0.00065M) of Gd(NO₃)₃ containing bicarbonate allows the solid phase precipitating between pH 5.5 and 6.6 to be ascribed to the formula Gd₂(OH)₄CO₃·3H₂O. In the absence of HCO₃^?, no precipitation occurred up to pH 6.8. Finally, the loss of Gd from the moderator was established as being due to the formation of a hydroxide carbonate salt.     

Aeration of large-scale municipal wastewater treatment plants: state of the art.

Aeration is the most energy-intensive operation in wastewater treatment, amounting to 45-75% of plant energy costs. Fine-pore diffusers are today almost ubiquitous in municipal wastewater aeration, due to their advantageous aeration efficiency (mass of oxygen transferred per unit energy required). Nevertheless, older municipal treatment facilities and many industrial treatment plants are still equipped with coarse-bubble or surface aerators. Fine-pore diffusers are subject to two major disadvantages: a) fouling, if not cleaned periodically; b) decrease in oxygen transfer efficiency caused by dissolved surfactants. Coarse-bubble and surface aerators are typically not subject to the traditional problems affecting fine-pore diffusers. Nonetheless, they achieve oxygen transfer at the expense of increased energy intensity. The increased biomass concentration associated with high mean cell retention time (MCRT) operations has a beneficial effect on aeration. Nutrient-removing selectors are able to further increase aeration efficiency, as they sorb and utilize the readily available substrate which otherwise would accumulate at bubble surfaces and dramatically decrease aeration efficiency. We summarise here our 30-year long experience in aeration research, and results obtained with clean- and process-water tests are used to show the beneficial effects of high MCRT operations, the beneficial effect of selectors, and the decline of aeration efficiency due to dissolved surfactants.     

New Physical Optics Approach for an Efficient Treatment of Multiple Bounces in Curved Bodies Defined by an Impedance Boundary Condition

A new physical optics (PO) formulation is presented to treat radiation and scattering problems of curved bodies, including multiple reflections between the body parts. The approach uses electric and magnetic PO currents that are expanded as exponential terms. These terms are defined by spatially slow-varying amplitude and exponent functions. All the reflections of a multiple bounce contribution are computed by using PO, considering a very efficient recursive scheme to evaluate the PO integrals using quasi-analytical expressions. The complex problem of obtaining the shadowed areas in curved bodies for multiple reflections is avoided, thanks to the electric and magnetic PO currents chosen. These currents extend over the complete area of the body, including lit or shadowed parts. In the lit parts, the currents provide the reflected field, while in the shadow parts, they give a scattered field that, together with the incident field, causes a total null field in the shadows. The currents do not radiate on their back directions. This approach is useful for the analysis of bodies that can be characterized electrically by an impedance boundary condition (IBC). A combination of these currents with the angular Z-buffer (AZB) ray tracing technique makes it possible to analyze simple or complex cases efficiently.     

Conservative Wetting and Drying Methodology for Quadrilateral Grid Finite-Volume Models

Algebraic equations relating fluid volume and the free surface elevation in partially wetted quadrilateral computational cells are derived and incorporated into a Godunov-type, finite-volume, shallow-water model. These equations make it straightforward to reconstruct the free surface elevation based on the volume of fluid in a computational cell, the dependent variable tracked by finite volume models for conservation purposes, regardless of whether the cell is fully or partially wetted. Improvements to the variable reconstruction process streamline the computation of mass and momentum fluxes with approximate Riemann solvers, yielding a model that simulates sub-, super-, and transcritical flows over irregular topography with wetting and drying fronts. Furthermore, the model is free from fluid and scalar mass conservation errors and it eliminates nonphysical distributions of scalars by avoiding artificial concentration and/or dilution at wet/dry interfaces. Use of this wetting and drying methodology adds roughly 10% to the execution time of flow simulations.