Dissolved methane recovery from anaerobic effluents using hollow fibre membrane contactors

Hollow fibre membrane contactor (HFMC) systems have been studied for the desorption of dissolved methane from both analogue and real anaerobic effluents to ascertain process boundary conditions for separation. When using analogue effluents to establish baseline conditions, up to 98.9% methane removal was demonstrated. Elevated organic concentrations have been previously shown to promote micropore wetting. Consequently, for anaerobic effluent from an upflow anaerobic sludge blanket reactor, which was characterised by a high organic concentration, a nonporous HFMC was selected. Interestingly, mass transfer data from real effluent exceeded that produced with the analogue effluent and was ostensibly due to methane supersaturation of the anaerobic effluent which increased the concentration gradient yielding enhanced mass transfer. However, at high liquid velocities a palpable decline in removal efficiency was noted for the nonporous HFMC which was ascribed to the low permeability of the nonporous polymer provoking membrane controlled mass transfer. For anaerobic effluent from an anaerobic membrane bioreactor (MBR), a microporous HFMC was used as the permeate comprised only a low organic solute concentration. Mass transfer data compared similarly to that of an analogue which suggests that the low organic concentration in anaerobic MBR permeate does not promote pore wetting in microporous HFMC. Importantly, scale-up modelling of the mass transfer data evidenced that whilst dissolved methane is in dilute form, the revenue generated from the recovered methane is sufficient to offset operational and investment costs of a single stage recovery process, however, the economic return is diminished if discharge is to a closed conduit as this requires a multi-stage array to achieve the required dissolved methane consent of 0.14 mg l−1.Yorkshire Water; Severn Trent Water; Anglian Water; Northumbrian Water; EPSR

Non-chemical treatments for preventing the postharvest fungal rotting of citrus caused by Penicillium digitatum (green mold) and Penicillium italicum (blue mold)

Background: Citrus is one of the most economically important horticultural crops in the world. Citrus are vulnerable to the postharvest decay caused by Penicillium digitatum and P. italicum, which are both wound pathogens. To date, several non-chemical postharvest treatments have been investigated for the control of both pathogens, trying to provide an alternative solution to the synthetic fungicides (imazalil, thiabendazole, pyrimethanil, and fludioxonil), which are mainly employed and may have harmful effects on human health and environment. Scope and approach: The current study emphasizes the non-chemical postharvest treatments, such as irradiations, biocontrol agents, natural compounds, hot water treatment (HWT), and salts, on the prevention of decay caused by P. digitatum and P. italicum, also known as green and blue molds, respectively. The mode of action of each technique is presented and comprehensively discussed. Key findings and conclusions: In vivo and in vitro experiments in a laboratory scale have shown that the control of green and blue molds can be accomplished by the application of non-chemical treatments. The mechanisms of action of the non-chemical techniques have not been clearly elucidated. Several studies have mentioned that the application of non-chemical treatments results in the synthesis of secondary metabolites with antifungal activities (i.e. polyphenols, phytoalexins) in fruit surface. Moreover, non-chemical treatments may exert direct effects on fungal growth, such as disruption of cell walls, inhibition of metabolic respiration, and disruption of energy production related enzymes.Centro de Investigación y Desarrollo en Criotecnología de Alimento

Non-chemical treatments for preventing the postharvest fungal rotting of citrus caused by Penicillium digitatum (green mold) and Penicillium italicum (blue mold)

Citrus is one of the most economically important horticultural crops in the world. Citrus are vulnerable to the postharvest decay caused by Penicillium digitatum and P. italicum, which are both wound pathogens. To date, several non-chemical postharvest treatments have been investigated for the control of both pathogens, trying to provide an alternative solution to the synthetic fungicides (imazalil, thiabendazole, pyrimethanil, and fludioxonil), which are mainly employed and may have harmful effects on human health and environment.Scope and approachThe current study emphasizes the non-chemical postharvest treatments, such as irradiations, biocontrol agents, natural compounds, hot water treatment (HWT), and salts, on the prevention of decay caused by P. digitatum and P. italicum, also known as green and blue molds, respectively. The mode of action of each technique is presented and comprehensively discussed.Key findings and conclusionsIn vivo and in vitro experiments in a laboratory scale have shown that the control of green and blue molds can be accomplished by the application of non-chemical treatments. The mechanisms of action of the non-chemical techniques have not been clearly elucidated. Several studies have mentioned that the application of non-chemical treatments results in the synthesis of secondary metabolites with antifungal activities (i.e. polyphenols, phytoalexins) in fruit surface. Moreover, non-chemical treatments may exert direct effects on fungal growth, such as disruption of cell walls, inhibition of metabolic respiration, and disruption of energy production related enzymes.Fil: Papoutsis, Konstantinos. Universidad de Dublin; IrlandaFil: Mathioudakis, Matthaios M.. Institute of Olive Tree Subtropical Crops and Viticulture; GreciaFil: Hasperué, Héctor Joaquín. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; ArgentinaFil: Ziogas, Vasileios. Institute of Olive Tree Subtropical Crops and Viticulture; Greci

Parallel geometric multigrid schemes for hermite collocation finite element Method

Summarization: Numerical algorithms with multigrid techniques are among the fastest iterative schemes for solving large and sparse linear systems. In this work, we deal with the problem of efficiently organizing the computation involved in the iterative solution of this type of li- near systems combined with a multigrid technique, in order to compute on a Grid/Cluster computing environment. These linear systems arise from the discretization of elliptic BVPs by the Collo- cation method based on Hermite bi-cubic finite elements. Taking advantage of the Collocation matrix’s red-black ordered structure we organize efficiently the whole computation for the Gauss- Seidel and the preconditioned Bi-CGSTAB iterative methods as multigrid smoothers and map it on a pipeline architecture with master-slave communication. Implementations, through the Mes- sage Passing Interface (MPI) standard, are realized first on a 64-core of a 16-node SUN X2200M2 Grid computer, interconnected through a 1Gbps ethernet network, and then on a Hewlett-Packard Blade ProLiant BL465c Cluster computer. The performance of two parallel algorithms is pre- sented by speedup and time measurements.Παρουσιάστηκε στο: 9nd Hellenic-Europeαn Research on Computer Mαthemαtics and its Application

A parallel multigrid solver for incompressible flows on computing architectures with accelerators

Summarization: An efficient parallel multigrid pressure correction algorithm is proposed for the solution of the incompressible Navier–Stokes equations on computing architectures with acceleration devices. The pressure correction procedure is based on the numerical solution of a Poisson-type problem, which is discretized using a fourth-order finite difference compact scheme. Since this is the most time-consuming part of the solver, we propose a parallel pressure correction algorithm using an iterative method based on a block cyclic reduction solution method combined with a multigrid technique. The grid points are numbered with respect to the red–black ordering scheme for the parallel Gauss–Seidel smoother. These parallelization techniques allow the execution of the entire simulation computations on the acceleration device, minimizing memory communication costs. The realization is developed using the OpenACC API, and the numerical method is demonstrated for the solution of two classical incompressible flow test problems. The first is the two-dimensional lid-driven cavity problem over equal mesh sizes while the other is the Stokes boundary layer, which is a decent benchmark problem for unequal mesh spacing. The effect of several multigrid components on modern and legacy acceleration architectures is examined. Eventually the performance investigation demonstrates that the proposed parallel multigrid solver achieves an acceleration of more than 10× over the sequential solver and more than 4× over multi-core CPU only realizations for all tested accelerators.Presented on: Journal of Supercomputin

The water footprint of second-generation bioenergy: a comparison of biomass feedstocks and conversion techniques

Summarization: Bioenergy is the most widely used type of renewable energy. A drawback of crops applied for bioenergy is that they compete with food and use the same natural resources like water. From a natural resources perspective, it would be more efficient to apply the large potential of available crop residues. In this paper, we calculate the water footprint (WF) of ten crop residue types and a few other second-generation bioenergy feedstocks (miscanthus, eucalyptus and pine). Further we estimate the WF of energy carriers produced through different conversion techniques (heat or electricity from combustion and gasification, bioethanol from fermentation and oil from pyrolysis), using the global WF standard. The WFs of crop residues, miscanthus and wood show a large variation. Crop residues have a smaller WF than miscanthus and wood. Given a certain feedstock, the WF of pyrolysis oil is smaller than the WF of bioethanol from fermentation. The WFs of heat from combustion or gasification are similar. The WF of electricity by combustion ranges from 33 to 324 m3/GJ and the WF of electricity by gasification from 21 to 104 m3/GJ. This research concludes that it is relatively water-efficient to apply crop residues, and that the production of miscanthus and wood for bioenergy is less favourable. Crop residues can best be converted to oil rather than to ethanol. Electricity from gasification has a smaller WF than electricity form combustion; heat from combustion has a smaller WF than heat from gasification. By showing the water efficiency of different feedstocks and techniques to produce second-generation bioenergy, the study provides a useful basis to wisely choose amongst different alternative forms of second-generation bioenergy.Presented on: Journal of Cleaner Productio

High-order accurate numerical pressure correction based on geometric multiGrid schemes for the incompressible navier-stokes equations

Summarization: ForthenumericalsolutionofincompressibleNavier-Stokesequations using a high order accurate discretization method a global pressure correction method can applied. This is equivalently with the solution of a Poisson-type boundary value problem at each time step which is the most computationally intense procedure of the numerical method. In this work, several Multi-Grid schemes are developed for the numerical solution of the large and sparse linear system arising from the discretization of the Poisson-type pressure correction on staggered grids. Multigrid techniques are not straightforward in this case, because the coarse grid does not constitute part of the fine grid. Appropriate restriction and extension operators are designed for the efficient application of multigrid proce- dure. The performance investigation using the V-cycle, W-cycle and Full Multi- Grid algorithms, resulted that multigrid schemes can accelerate significantly the numerical solution process.Παρουσιάστηκε στο: Conference in Numerical Analysi

The sustainable siting of small hydroelectric plants

Summarization: This paper aims to present the procedure under which a sustainable plant, like a small hydroelectric plant (SHP), can be installed and deployed, especially in countries with complicated administrative and legislative systems. Those must be defined by the rules that characterize sustainable spatial planning, which aims at the environmental protection, the insurance of better living conditions and finally at the economic development within the frame of the principle of sustainability and its three basic dimensions: social, economical and environmental. The main principles of spatial planning are accepted from the jurisprudence of the Hellenic Council of State, either as an appropriate condition for the protection of important ecosystems or as specific expression of the principle of prevention of environmental damage. In this framework it is accepted that the development is experienced, initially to a total and general planning, whose essential part is the assessment and modification of distributed land uses. Besides, the main characteristics of the siting of SHPs and the criteria demanded for their smooth integration and operation are presented.Παρουσιάστηκε στο: Energy Polic

Multigrid cell-centered techniques for high-order incompressible flow numerical solutions

Summarization: A multigrid pressure correction scheme suitable for high order discretizations of the incompressible Navier–Stokes equations is developed and demonstrated. The pressure correction equation is discretized with fourth-order compact finite-difference approximations. Iterative methods based on multigrid techniques accelerate the most demanding part of the overall solution algorithm, which is the numerical solution of the arised large and sparse linear system. Geometrical multigrid methods, using partial semicoarsenig strategy and zebra line Gauss–Seidel relaxation, are employed to efficiently approximate the solution of the resulting algebraic linear system. Effects of various multigrid components on the pressure correction procedure are evaluated and new high-order transfer operators are developed for the case of cell-centered grids. Their convergence rates are also compared with commonly used intergrid transfer operators. Furthermore, numerically comparisons between different multigrid cycle approaches, such as V-, W- and F-cycle, are presented. The performance tests demonstrate that the new pressure correction approach significantly reduces the computational effort compared to single-grid algorithms. Furthermore, it is shown that the overall high order accuracy of the numerical method is retained in space and time with increasing Reynolds number.Presented on: Aerospace Science and Technolog