The thesis presents and evaluates the application of the paradigm of agents to the management of the urban wastewater system. The system is conceptualised as a multi-agent system from the development of the models of agents and communication paths. In the development, it has become obvious that coordination (of volumes and pollutant loads) between all the wastewater treatment inputs and the available capacity of the treatment is a key point in the system’s performance. To consider this factor, a coordinating agent is defined. This agent executes the coordination of inputs and the prioritisation of industrial wastewaters when the treatment does not have sufficient available capacity. The prioritisation is solved by a meta-heuristic of ant colony optimisation, which has been instantiated by four algorithmic versions. Finally, the system has been implemented and consecutive cycles of simulation have been executed with the conclusion that the paradigm of agents is a feasible proposal. / La tesi presenta i avalua l’aplicació del paradigma d’agents en la gestió d’un sistema d’aigües residuals urbanes. El sistema es conceptualitza com a sistema multiagent a partir del desenvolupament dels models d’agents i d’enllaços de comunicació. En el desenvolupament s’evidencia que la coordinació (de volums i càrregues contaminants) entre totes les aportacions d’aigües residuals al tractament i la capacitat disponible d’aquest, constitueix un punt clau del funcionament del sistema. Per tal de considerar-ho, es defineix un agent Coordinador que executa la coordinació de les aportacions al tractament i a més, la priorització dels efluents industrials quan el tractament no disposa de capacitat suficient per admetre totes les propostes d’aportacions. La priorització es resol emprant una metaheurística d’optimització de colònia de formigues, la qual s’instancia mitjançant quatre versions algorísmiques diferents. Per últim, s’implementa el sistema i s’executen cicles consecutius de simulació mostrant com el paradigma constitueix una proposta factible.

The overall goal of this research is to develop an integrated system dynamics framework for sustainable management of municipal water and wastewater systems. Canadian municipalities have traditionally relied on grants received from senior levels of government to finance construction of water supply and wastewater collection infrastructure. User fees for water and wastewater services were determined so as to recover only the operating expenditures with no allowance to recoup the capital costs of infrastructure. As the infrastructure assets started approaching the end of their service life, investments needed to rehabilitate these assets were deferred in the expectation of receiving further grants for this purpose. Hence, a significant backlog of deteriorated infrastructure has accumulated over the years. Recently enacted regulations require that all expenditures incurred on provision of water and wastewater services should ultimately be financed from user fee based revenues. Another piece of legislation provides for establishment of service performance standards. Urban water and wastewater systems involve interconnections among physical infrastructure, financial, and socio-political factors. Several interacting feedback loops are formed due to these interconnections and render the management of water and wastewater infrastructure as a complex, dynamic problem. Existing asset management tools in the literature are found inadequate to capture the influence of feedback loops. A novel system dynamics approach is used to develop a demonstration model for water and wastewater network management. Model results for a case study show significance of feedback loops for financial sustainability of the system. For example, user fees have to be substantially increased to achieve financial sustainability, especially when price elasticity of water demand is considered. A detailed causal loop diagram for management of wastewater collection networks is presented. The causal loop diagram lays out qualitative causal relationships among system components and identifies multiple interacting feedback loops. Based on this causal loop diagram, a system dynamics model comprised of a wastewater pipes sector, a finance sector, and a consumers sector, is developed. Policy levers are included in the model to facilitate formulation of different financing and rehabilitation strategies for the wastewater collection network. Financial and service performance indicators included in the model allow comparison of different financing and rehabilitation strategies. Data requirements for implementation of the model are discussed. The wastewater collection network model is implemented for a case study of a medium-sized Canadian municipality with a substantial backlog of deteriorated pipes. A methodology for parameterization of the model using existing data sources is presented. Simulation results indicate that different financing strategies ranging from no borrowing to full utilization of debt capacity can achieve similar total life-cycle costs but with significantly varying impacts for consumers in terms of service performance and financial burden. A detailed causal loop diagram for management of a watermain distribution network is employed to identify feedback loops. The causal loop diagram is then developed into a system dynamics model comprised of watermain pipes, financial, and consumer sectors. Data requirements for implementation of the model are discussed.

The main objective pursued in this thesis targets the development and systematization of a methodology that allows addressing management problems in the dynamic operation of Urban Wastewater Systems. The proposed methodology will suggest operational strategies that can improve the overall performance of the system under certain problematic situations through a model-based approach. The proposed methodology has three main steps: The first step includes the characterization and modeling of the case-study, the definition of scenarios, the evaluation criteria and the operational settings that can be manipulated to improve the system’s performance. In the second step, Monte Carlo simulations are launched to evaluate how the system performs for a wide range of operational settings combinations, and a global sensitivity analysis is conducted to rank the most influential operational settings. Finally, the third step consists on a screening methodology applying a multi-criteria analysis to select the best combinations of operational settings. / El principal objectiu d’aquesta tesi és desenvolupar una metodologia que permeti abordar els problemes de gestió del cicle industrial de l’aigua. La metodologia proposada suggereix estratègies de gestió que poden millorar el rendiment general del sistema en determinades situacions problemàtiques. La metodologia proposada es basa en un model matemàtic de simulació d’aquestes infraestructures i consta de tres passos. El primer pas inclou la caracterització i modelització del cas d’estudi, la definició d’escenaris, criteris d’avaluació i paràmetres d’operació del sistema. En el segon pas, es llancen simulacions Monte Carlo (MC) amb l’objectiu d’avaluar com es comporta el sistema segons diferents estratègies d’operació. Per tal d’identificar els paràmetres d’operació més influents es du a terme una anàlisi global de sensibilitat. Finalment, el tercer pas consisteix en una metodologia d’avaluació basada en solucions Pareto i un anàlisi multicriteri per tal de seleccionar les millors estratègies d’operació.

In the last decades and due to the Water Framework Directive implementation, the urban wastewater cycle management has become more complex. The concept of integrated urban wastewater system management is introduced, and it becomes necessary to consider some new data as the sewer system characteristics or the receiving body. In this sense, environmental decision support systems (EDSS) are very useful and powerful tools to support during the decision making process. A new EDSS for the integrated urban wastewater system management has been developed integrating data from several sources (bibliographic, theoretical or historical) and a real case-based virtual system able to perform simulations. Results demonstrate the benefits of using this kind of systems in comparison with a standard approach, which do not use the expert knowledge and encourages continuing with this research in order to improve the quality and efficiency of this type of EDSSs / En les darreres dècades, i degut a la implementació de la Directiva Marc de l’Aigua, la gestió del cicle urbà de l’aigua ha esdevingut més complexa. S’introdueix el concepte de gestió integrada de conca, i és necessari considerar certa informació, com les característiques de la xarxa de clavegueram o del medi receptor. D’aquesta manera, els sistemes de suport a la decisió ambiental (EDSS) són eines potentíssimes que faciliten la presa de decisions en aquest camp. S’ha desenvolupat un nou EDSS per a la gestió integrada de conca que utilitza una base sòlida de coneixement expert, integrant informació de diverses fonts (bibliogràfiques, teòriques o històriques) i dos sistemes virtuals basats en dades reals sobre els quals és possible realitzar simulacions. Els resultats demostren que aquest sistema presenta beneficis importants respecte a una gestió estàndard sense sistema expert, i esperona a prosseguir amb la recerca i el desenvolupament per a millorar-lo