Selection of the activated sludge configuration during the conceptual design of activated sludge plants using multicriteria analysis

This paper presents an extension of an existing systematic conceptual design methodology for urban wastewater treatment plants (WWTP) that combines a hierarchical decision process with mathematical modeling (Vidal et al. Ind. Eng. Chem. Res. 2002, 41, 4992-5005). The main contributions of this new approach are (i) to refine criteria selection and quantification used to compare the competing options with different sources of information (dynamic simulation, model-based cost estimations, literature and expert knowledge); (ii) to propose different value functions to normalize the effect of the criteria used; and (iii) to include a visual representation (gray-scale approach) that eases the visualization of the objectives that were not accomplished and of the main handicaps of the evaluated options. Finally a case study, where an activated sludge configuration for carbon and nitrogen removal is selected, and a sensitivity analysis, to show the influence of the context in the final decision, are also presented.