João A. Zeferino

Robust optimization approach to regional wastewater system planning

Wastewater systems are subject to several sources of uncertainty. Different scenarios can occur in the future, depending on the behavior of a variety of demographic, economic, environmental, and technological variables. Robust optimization approaches are aimed at finding solutions that will perform well under any likely scenario. The planning decisions to be made about wastewater system planning involve two main issues: the setup and operation costs of sewer networks, treatment plants, and possible pump stations; and the water quality parameters to be met in the water body where the (treated) wastewater is discharged. The source of uncertainty considered in this article is the flow of the river that receives the wastewater generated in a given region. Three robust optimization models for regional wastewater system planning are proposed. The models are solved using a simulated annealing algorithm enhanced with a local improvement procedure. Their application is illustrated through a case study representing a real-world situation, with the results being compared and commented upon.

Optimal location and sizing of storage units in a drainage system

Adapting urban stormwater drainage systems is essential to handling increased urbanization and climate change. Within an urban area, storage units are an efficient solution to reduce peak runoff, but their implementation involves complex decisions. This paper presents a novel optimization model for defining, in existing sewer drainage systems, the number of storage units, their location, size and the orifice dimensions. The orifice is used to reduce storage unit outflow regulating downstream flows. These components allow an integrated flow control and flooding reduction throughout the network. The desired solution should offer the lowest cost and try to avoid any major flooding impact. The model includes hydraulic, flood and capacity constraints and it is solved through a simulated annealing algorithm that calls upon a dynamic rainfall-runoff simulator for complete evaluation of each solution. The performance of the optimization model is assessed through a case study inspired by a real urban sewer network. A novel optimization model for location and sizing of storage units is proposed.Orifices are optimized to regulate the outflow from the storage units.The model aims to avoid flood throughout the entire network at a minimum expense.A simulated annealing algorithm is designed to solve the model.SWMM is used to evaluate the effects of each rainfall event on the drainage system.

Multi-objective model for regional wastewater systems planning

The planning problems posed by regional wastewater systems consist of determining an efficient solution for the layout of the sewer networks, and for the location, type, and size of the pump stations and treatment plants to be included in the systems. These problems have typically been addressed through optimisation models with a cost-minimisation objective. However, in a world increasingly more concerned with sustainable development, factors other than economic must be considered. In this paper, we describe a multi-objective model for regional wastewater systems planning. Through a model of this type, it is possible to identify solutions that are a good compromise with regard to conflicting objectives. For presentation purposes, we chose to focus on three objectives: minimisation of capital costs; minimisation of operating and maintenance costs; and maximisation of dissolved oxygen. The multi-objective model is handled through the weighting method and solved through a simulated annealing algorithm. Its application is illustrated for three test instances designed to replicate real-world problems.

Regional Wastewater System Planning under Population Dynamics Uncertainty

AbstractRegional wastewater systems are used for the collection and treatment of the wastewater generated in a region and aimed at guaranteeing surface water quality. The volumes of wastewater to process depend on future population and thus are affected by the uncertainty inherent to population dynamics. In this article, we present a robust approach to the planning of regional wastewater systems under population dynamics uncertainty. The approach searches for the optimal configuration of the sewer networks and for the best location, type, and size of the possible pump stations and treatment plants to include in the system. It assumes uncertainty to be described by a given number of discrete scenarios of known probabilities and relies on discrete nonlinear optimization models whose objective is to minimize the expected regret of solutions with respect to total costs. As demonstrated through a case study developed for the North Baixo Mondego area in central Portugal, the results obtained through the propose...

Siting and sizing the components of a regional wastewater system: a multiobjective approach.

This paper describes a multiobjective approach for the siting and sizing of the components of a regional wastewater system. This approach can be particularly helpful for the coherent and harmonious implementation of the Water Framework Directive. Three criteria are considered for finding efficient solutions. A simulated annealing algorithm improved by a local search algorithm is used and the results of three case studies are presented and compared.

Adapted optimization model for planning regional wastewater systems: case study

Wastewater systems are of crucial importance to the promotion of sustainable development. Through an integrated planning approach, the costs can be minimized and the resulting benefits maximized. A planning approach at regional level exploits the economies of scale, while achieving a better environmental performance. In this paper we set out a decision support approach for the planning of regional wastewater systems. Optimization models are used, aimed at finding optimal configurations for the location, type and size of the systems infrastructure: sewers, pump stations, and wastewater treatment plants. Solutions are evaluated in terms of the cost of installing, operating and maintaining the infrastructure, and the water quality in the river that receives the treated wastewater. The river water quality varies in accordance with the effluent discharges, and is assessed using environmental parameters. The models are solved with a simulated annealing algorithm complemented by a local improvement procedure. Its application is illustrated through a case study in the Una river basin region, in Brazil.

A DECISION SUPPORT MODEL FOR THE OPTIMAL SITING AND SIZING OF STORAGE UNITS IN STORMWATER DRAINAGE SYSTEMS

Climate change and urbanization are the main factors involved in increasing cities’ susceptibility to flood events. Extreme rainfall events are occurring more often due to climate change and this, together with the effect of impermeable surfaces, means that the runoff increases. Consequently, the existing stormwater drainage systems need to be adapted. One solution to adapt these systems would be to include infrastructure elements, such as storage units, in the hydraulic network to control flow and reduce peak flows. This paper presents a decision support model for the optimal siting and sizing of storage units with flow control in existing urban stormwater systems where flood events are frequent. Direct flood damage will be taken into account in the decision process, and thus the cost of construction and maintenance of storage units will be considered along with the cost of flood damage, in the determination of the solution to be implemented. This damage relates to losses in the affected areas and depend on the land use type (e.g. uses of buildings) and on the flood depth affecting it. A computer program, OptSU, was developed to implement the model. It includes a resolution method based on a simulated annealing algorithm that calls upon a hydraulic simulator whenever necessary. The optimization model is then tested on a case study inspired by a real urban stormwater system in Portugal.

Robust design of wastewater systems at regional level.

Wastewater systems are of crucial importance in the promotion of sustainable development. Their implementation is very complex because there are many different issues to be considered simultaneously (environmental, economical, social, and technical). The Water Framework Directive (WFD) brought new challenges to the definition of appropriate designs for such systems. In particular, they should be determined so that they are capable of performing well even during extreme events. Therefore, the uncertainty inherent to the water environments where the wastewater systems are included must be considered since the beginning of the decision processes where these systems are dealt with. In this paper is presented a robust optimization model for helping to define the configuration of sewer networks and the location and size of the treatment plants where the effluent carried by the sewers will be processed before being discharged into some water body. Its application to a case study illustrates how the model can be used to analyze the implications of increasing the reliability of wastewater systems upon the costs of these systems.