Viriato Semiao

Optimisation of MSW collection routes for minimum fuel consumption using 3D GIS modelling.

Collection of municipal solid waste (MSW) may account for more than 70% of the total waste management budget, most of which is for fuel costs. It is therefore crucial to optimise the routing network used for waste collection and transportation. This paper proposes the use of geographical information systems (GIS) 3D route modelling software for waste collection and transportation, which adds one more degree of freedom to the system and allows driving routes to be optimised for minimum fuel consumption. The model takes into account the effects of road inclination and vehicle weight. It is applied to two different cases: routing waste collection vehicles in the city of Praia, the capital of Cape Verde, and routing the transport of waste from different municipalities of Santiago Island to an incineration plant. For the Praia city region, the 3D model that minimised fuel consumption yielded cost savings of 8% as compared with an approach that simply calculated the shortest 3D route. Remarkably, this was true despite the fact that the GIS-recommended fuel reduction route was actually 1.8% longer than the shortest possible travel distance. For the Santiago Island case, the difference was even more significant: a 12% fuel reduction for a similar total travel distance. These figures indicate the importance of considering both the relief of the terrain and fuel consumption in selecting a suitable cost function to optimise vehicle routing.

Multi-criteria GIS-based siting of an incineration plant for municipal solid waste.

Siting a municipal solid waste (MSW) incineration plant requires a comprehensive evaluation to identify the best available location(s) that can simultaneously meet the requirements of regulations and minimise economic, environmental, health, and social costs. A spatial multi-criteria evaluation methodology is presented to assess land suitability for a plant siting and applied to Santiago Island of Cape Verde. It combines the analytical hierarchy process (AHP) to estimate the selected evaluation criteria weights with Geographic Information Systems (GIS) for spatial data analysis that avoids the subjectivity of the judgements of decision makers in establishing the influences between some criteria or clusters of criteria. An innovative feature of the method lies in incorporating the environmental impact assessment of the plant operation as a criterion in the decision-making process itself rather than as an a posteriori assessment. Moreover, a two-scale approach is considered. At a global scale an initial screening identifies inter-municipal zones satisfying the decisive requirements (socio-economic, technical and environmental issues, with weights respectively, of 48%, 41% and 11%). A detailed suitability ranking inside the previously identified zones is then performed at a local scale in two phases and includes environmental assessment of the plant operation. Those zones are ranked by combining the non-environmental feasibility of Phase 1 (with a weight of 75%) with the environmental assessment of the plant operation impact of Phase 2 (with a weight of 25%). The reliability and robustness of the presented methodology as a decision supporting tool is assessed through a sensitivity analysis. The results proved the system effectiveness in the ranking process.

A new iterative method to compute nonlinear equations

The aim of this paper is to construct a new efficient iterative method to solve nonlinear equations. The new method is based on the proposals of Abbasbandy on improving the order of accuracy of Newton-Raphson method [S. Abbasbandy, Improving Newton-Raphson method for nonlinear equations by modified Adomian decomposition method, Applied Mathematics and Computation 145 (2003) 887-893] and on the proposals of Babolian and Biazar on improving the order of accuracy of Adomians decomposition method [E. Babolian, J. Biazar, On the order of convergence of Adomian method, Applied Mathematics and Computation 130 (2002) 383-387]. The convergence of the new scheme is proved and at least the cubic order of convergence is established. Several examples are presented and compared to other methods, showing the accuracy and fast convergence of this new method. Also, it is shown in this paper, that the modified Adomians method developed by Babolian and Biazar to solve nonlinear equations [E. Babolian, J. Biazar, Solution of nonlinear equations by modified Adomian decomposition method, Applied Mathematics and Computation 132 (2002) 167-172] should be slightly modified, due to the fact that convergence of Adomians method does not ensure convergence of the modified method. An example illustrates this fact, which, unlike what is claimed by the authors, does not converge with their method, but with a simple different choice of the zero component becomes convergent.

The effect of the ladder-type spacers configuration in NF spiral-wound modules on the concentration boundary layers disruption☆

Abstract The laminar flow structure and concentration distribution in a narrow rectangular channel simulating the feed channel of nanofiltration (NF) spiral-wound modules are investigated. The continuity, Navier—Stokes equations and the solute continuity equation are solved by the control volume formulation. To validate the numerical predictions, NF permeation experiments with an aqueous solution of sodium chloride (2 g/l) at 25°C were performed in a laboratory cell with a rectangular feed channel (2 mm height × 30 mm width × 20 cm length) filled with a ladder-type spacer with a transverse inter-filament distance of 3.8 mm. The numerical results show that the average concentration polarization for the membrane wall with adjacent transverse filaments is independent of the distance to the channel inlet, while for the membrane wall without adjacent filaments the average concentration polarization increases with the channel length. This is due to the fact that in the first case the concentration boundary layer is periodically disrupted by the transverse filaments while in the second case the concentration boundary layer grows continuously along the channel length. The experimental results of the NaCl apparent rejection coefficients are compared to the model predictions, the agreement being good. These results clearly establish how crucial the spacers configuration is in the optimization of the spiral wound module efficiency.

Hydrodynamics and concentration polarization in NF/RO spiral-wound modules with ladder-type spacers

Abstract The hydrodynamics and concentration polarization in the feed-channel of a NFIRO spiral-wound module with ladder-type spacers were investigated by computational fluid dynamics. The momentum and mass transport equations together with the appropriate boundary conditions were solved numerically by the control volume formulation for stable two-dimensional laminar flow. Permeation experiments with aqueous solutions of sodium chloride at feed concentration of 2 gll and 25°C were performed in a laboratory NF cell with a spacer-filled channel (2 mm height × 30 min width × 20 cm length) in order to validate the numerical model. The tested spacer had a set of transverse filaments with a diameter of 1.0 mm, equally spaced and connected by two longitudinal filaments, with a distance between the axis oftwo consecutive filaments of 3.8 mm, forming a ladder-type structure. A thin-film composite nanofiltration membrane from Separem (Italy) was used. The numerical results show that the concentration polarization index exhibits strong local variations, and its profile is correlated with the flow pattern. It was also found that the increase of the Reynolds number is not by itself a sufficient condition to enhance the hydrodynamic conditions over the whole membrane: an adequate control of the flow structure through the careful selection of the cross section of the filaments is also indispensable. Good agreement was observed between the predicted and experimental values of the apparent rejection coefficient for all the range of operating conditions tested.

Spray characterization: numerical prediction of Sauter mean diameter and droplet size distribution

A simplified equation of the Nukiyama-Tanasawa type for droplet size distribution in sprays is obtained from the synergetic concept of entropy information, assuming spherical droplets and zero and infinity as their limit sizes. The introduction of Sauter mean diameter (SMD) definition in that equation yields a new distribution function dependent solely on SMD, which is calculated from available correlations for pressure-jet and pre-filming airblast atomizers. For plain-jet airblast atomizers a new and dimensionally consistent correlation is determined. Several droplet size distributions are then predicted. Experimental data are compared with predictions of SMD; the agreement is satisfactory.

The effect on mass transfer of momentum and concentration boundary layers at the entrance region of a slit with a nanofiltration membrane wall

Abstract An integrated model based on the finite volume formulation to numerically simulate the fluid flow of the feed phase in nanofiltration systems is presented. This model accounts for the transport phenomena occurring inside the membrane through the use of appropriate boundary conditions. It allows for predictions of developing laminar flows hydrodynamics and mass transfer of aqueous solutions in slits with permeable walls. The experimental cell (200 mm ×30 mm ×2 mm ) simulates the two-dimensional conditions of flows in spiral-wound modules channels. Experimental data validate predictions of apparent rejection coefficients and permeate fluxes. Correlations for the concentration/hydrodynamic boundary layers thickness ratio, δ ω / δ u =2.92 Sc −0.37 Re p −0.17 [( x / h ) Re −1 +0.013 Sc 0.45 Re p 0.75 ] 0.5 , and for the permeation Stanton number, St =1.3( l / h ) −0.2 Re 0.05 Re p −0.4 Sc −0.1 (1− f ′)/ f ′, are proposed, in the range 250 0.02 p and 570 sC

Numerical modelling of mass transfer in slits with semi‐permeable membrane walls

A mathematical model to predict the concentration polarisation in nanofiltration/reverse osmosis is described. It incorporates physical modelling for mass transfer, laminar hydrodynamics and the membrane rejection coefficient. The SIMPLE algorithm solves the discretised equations derived from the governing differential equations. The convection and diffusive terms of those equations are discretised by the upwind, the hybrid and the exponential schemes for comparison purposes. The hybrid scheme appears as the most suitable one for the type of flows studied herein. The model is first applied to predict the concentration polarisation in a slit, for which mathematical solutions for velocities and concentrations exist. Different grids are used within the hybrid scheme to evaluate the model sensitivity to the grid refinement. The 55×25 grid results agree excellently for engineering purposes with the known solutions. The model, incorporating a variation law for the membrane intrinsic rejection coefficient, was also applied to the predictions of a laboratory slit where experiments are performed and reported, yielding excellent results when compared with the experiments.

A case study of fuel savings through optimisation of MSW transportation routes

Purpose – The high costs of collection and transportation of municipal solid waste (MSW) on the overall waste management budget (sometimes more than 75 per cent) makes it an issue to be urgently addressed for improvement. The paper aims to focus on the optimisation of routing networks for waste collection/transportation.Design/methodology/approach – The paper proposes herein the application of geographic information system (GIS) 3D route modelling for waste collection/transportation to optimise the route according to the minimum fuel consumption criterion to different municipalities of the island of Santo Antao of Cape Verde.Findings – The optimisation for the lowest fuel consumption yields 52 per cent savings in fuel, when compared to that for the shortest distance, even travelling a 34 percent longer distance, which shows the importance of considering simultaneously the relief of the territory and the lowest fuel consumption criterion when optimising vehicle routes.Practical implications – With such a s...

Operation costs and pollutant emissions reduction by definition of new collection scheduling and optimization of MSW collection routes using GIS. The case study of Barreiro, Portugal

This work proposes an innovative methodology for the reduction of the operation costs and pollutant emissions involved in the waste collection and transportation. Its innovative feature lies in combining vehicle route optimization with that of waste collection scheduling. The latter uses historical data of the filling rate of each container individually to establish the daily circuits of collection points to be visited, which is more realistic than the usual assumption of a single average fill-up rate common to all the system containers. Moreover, this allows for the ahead planning of the collection scheduling, which permits a better system management. The optimization process of the routes to be travelled makes recourse to Geographical Information Systems (GISs) and uses interchangeably two optimization criteria: total spent time and travelled distance. Furthermore, rather than using average values, the relevant parameters influencing fuel consumption and pollutant emissions, such as vehicle speed in different roads and loading weight, are taken into consideration. The established methodology is applied to the glass-waste collection and transportation system of Amarsul S.A., in Barreiro. Moreover, to isolate the influence of the dynamic load on fuel consumption and pollutant emissions a sensitivity analysis of the vehicle loading process is performed. For that, two hypothetical scenarios are tested: one with the collected volume increasing exponentially along the collection path; the other assuming that the collected volume decreases exponentially along the same path. The results evidence unquestionable beneficial impacts of the optimization on both the operation costs (labor and vehicles maintenance and fuel consumption) and pollutant emissions, regardless the optimization criterion used. Nonetheless, such impact is particularly relevant when optimizing for time yielding substantial improvements to the existing system: potential reductions of 62% for the total spent time, 43% for the fuel consumption and 40% for the emitted pollutants. This results in total cost savings of 57%, labor being the greatest contributor, representing over €11,000 per year for the two vehicles collecting glass-waste. Moreover, it is shown herein that the dynamic loading process of the collection vehicle impacts on both the fuel consumption and on pollutant emissions.