This paper describes a simulation-optimization model aimed at helping water utilities determine the best way to operate large-scale multisource water-supply systems. The operation of water systems is optimized taking into account the principal planning objectives defined for interventions that include reducing operating costs, satisfying demand, delivering water of appropriate quality, and not prompting the use of emergency sources. The model allows that these planning objectives may not be completely fulfilled in critical circumstances (e.g., droughts) when goals have to be prioritized by the water utilities. The model is a highly nonlinear programming problem and is solved with the general algebraic modeling system (GAMS), using the MINOS algorithm (GAMS/MINOS). The application of the model to the multimunicipal urban water-supply system of the Algarve shows its capabilities for optimizing the operation considering economic and noneconomic goals included in the objective function and to cope with future shortages in critical circumstances by improving the conjunctive use of the different water sources with interannual planning time horizons.

This paper reports on the qualitative and quantitative screening of groundwater sources for integration into the public water supply system of the Algarve, Portugal. The results are employed in a decision support system currently under development for an integrated water resources management scheme in the region. Such a scheme is crucial for several reasons, including the extreme seasonal and annual variations in rainfall, the effect of climate change on more frequent and long-lasting droughts, the continuously increasing water demand and the high risk of a single-source water supply policy. The latter was revealed during the severe drought of 2004 and 2005, when surface reservoirs were depleted and the regional water demand could not be met, despite the drilling of emergency wells. For screening and selection, quantitative criteria are based on aquifer properties and well yields, whereas qualitative criteria are defined by water quality indices. These reflect the well's degree of violation of drinking water standards for different sets of variables, including toxicity parameters, nitrate and chloride, iron and manganese and microbiological parameters. Results indicate the current availability of at least 1100 l s⁻¹ of high quality groundwater (55% of the regional demand), requiring only disinfection (900 l s⁻¹) or basic treatment, prior to human consumption. These groundwater withdrawals are sustainable when compared to mean annual recharge, considering that at least 40% is preserved for ecological demands. A more accurate and comprehensive analysis of sustainability is performed with the help of steady-state and transient groundwater flow simulations, which account for aquifer geometry, boundary conditions, recharge and discharge rates, pumping activity and seasonality. They permit an advanced analysis of present and future scenarios and show that increasing water demands and decreasing rainfall will make the water supply system extremely vulnerable, with a high risk of groundwater salinization and ecosystem degradation.

A mathematical model to simulate the biological processes occurring in a membrane bioreactor (MBR) is presented. The model accounts for different MBR technical features by introducing specific permeability parameters for the applied membrane system. The model accounts for the heterotrophic storage process and the formation of soluble microbial products. The introduction of an inhibition coefficient influencing the anoxic kinetics enables the model to simulate the particular operating conditions of the plant, such as a high or low dissolved oxygen concentration in the denitrification tank. The model was applied at the MBR wastewater treatment plant of Vila Nova do Ceira (Portugal) which uses a classic pre-denitrification cycle. Data for calibration and validation were sampled at the same wastewater treatment plant. Calibration was achieved by varying the kinetic parameters of the model to match the simulation results to the experimental data. The values of the kinetic parameters were similar to those found in the literature. The validation was performed by two different methodologies to analyse the model response to diverse operating conditions, and to evaluate the resilience of the MBR. Calibration and validation results were evaluated with mean average error, root mean square error and fractional mean bias as performance indexes. In most cases, these indexes confirmed the high accuracy of the model. Overall, the results of the calibration and validation steps enriched the proposed model by providing an effective biological description of the processes characterizing the MBR. Thus, the model is a reliable tool for the management, and designing of MBR.

Increased demand, reduced supply, or the imposition of new regulations might evince the physical limitations of the current infrastructure of a water-supply system and force structural intervention. The problem consists of determining capacity expansion solutions for multisource water-supply systems from a long-term perspective, with some representation of the uncertainty that can be involved and the risk-averse behavior of the decision makers. The systemic approach proposed includes a detailed simulation of physical processes, such as the water storage in surface reservoirs, the groundwater flow in aquifers, and the water transport, with explicit representation of water quality. Water quality is a crucial element in multisource systems because the quality of the source water often varies. Different capacity expansion solutions can be obtained that explicitly balance the trade­offs between the gains in system performance and the cost of the solution. The application of the systemic approach develo...