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One of the major challenges in big cities is planning and implementation of an optimized, integrated solid waste management system. This optimization is crucial if environmental problems are to be prevented and the expenses to be reduced. A solid waste management system consists of many stages including collection, transfer and disposal. In this research, an integrated model was proposed and used to optimize two functional elements of municipal solid waste management (storage and collection systems) in the Ahmadabad neighbourhood located in the City of Mashhad - Iran. The integrated model was performed by modelling and solving the location allocation problem and capacitated vehicle routing problem (CVRP) through Geographic Information Systems (GIS). The results showed that the current collection system is not efficient owing to its incompatibility with the existing urban structure and population distribution. Application of the proposed model could significantly improve the storage and collection system. Based on the results of minimizing facilities analyses, scenarios with 100, 150 and 180 m walking distance were considered to find optimal bin locations for Alamdasht, C-metri and Koohsangi. The total number of daily collection tours was reduced to seven as compared to the eight tours carried out in the current system (12.50% reduction). In addition, the total number of required crews was minimized and reduced by 41.70% (24 crews in the current collection system vs 14 in the system provided by the model). The total collection vehicle routing was also optimized such that the total travelled distances during night and day working shifts was cut back by 53%.

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International audienceThrough a coupled experimental/modelling approach, this study investigates the functioning of a fixed bed bioreactor of Biolite beads, inoculated with Pseudomonas putida, in order to biotreat phenol contaminated waters at low Reynolds number. In particular the coupling between water flow and biomass growth is studied through the evaluation of the relationship between bed permeability reduction and biomass content as well as hydrodynamic effects on biological kinetics. In term of bioclogging, our results showed a very sharp decrease of the relative bed permeability well correlated with measured biofilm growth (for relative permeability greater than 0.8) as well as a saturation of the bed permeability at low relative porosity. However, most of the models available in the literature failed to describe our observed results. Our work permitted to show a strongly heterogeneous longitudinal biofilm development along the bed and thus a strongly heterogeneous longitudinal occupation of the porosity that decreased rapidly at the bed entry. Furthermore, the observed measured porosity saturation was shown to correspond to a biomass distribution involving the existence of channelling, through a growth/detachment equilibrium, rather than a complete clogging of the bed reactor. Biofilm microstructure built at the pore scale by bacteria (e.g. via the modulation of EPS production) probably explains the observed permeability/porosity results in the early stage of bed bioclogging. However, the present experiments do not allow measuring such a microstructuration effect. Through the analysis of a simple 1D model written at the mesoscale, we showed that the closure laws accounting for the different biological kinetics (growth, detachment, etc.) are flow dependent, as they represent effective properties and complex biological processes averaged at the mesoscale. Given the low Reynolds number investigated in the present paper, this dependency appears not only controlled by mass transfer evolution but may also involve more complex biological regulation (biological response to physical chemical stresses). As a consequence, formulations that are strictly valid at the cell scale (e.g. Monod formulation) should be used with care if no averaging or upscaling methods are used. The main conclusion of the present work is that the knowledge of macroscopic laws, such as the permeability-porosity relationship is not sufficient to account for the coupling between hydrodynamics and biomass growth in porous media. As bacterial biofilms are formed of populations able to adapt their metabolism to their evolving microenvironment, and in particular to hydrodynamic conditions, it appears that the predictive character of such models could be largely improved if these closure laws were not postulated a priori but deduced either from upscaling techniques, or, as in this paper, from ad hoc experiments performed at the global scale