Wastewater Systems Management at the Regional Level

Wastewater Problems in the Context of an Integrated Water Resources Management

There is a world-wide concern about ‘good water status’, a concept that should be analyzed within the framework of an Integrated Water Resources Management (IWRM). A systemic view should be considered in order to develop methodological tools capable of handling simultaneously all the facets (environmental, economical, social and technological) involved in the IWRM approach. Wastewater systems are very sensitive water systems that should be properly planned and managed so that they can contribute to a better environment. These issues have to be tackled at regional level, because past experience suggests that in many cases it is impossible to find efficient planning and management solutions to wastewater problems unless these solutions are sought for relatively large geographical areas. Local solutions often lead to the misspending of natural and capital resources and to the generation of pollution foci. The solutions that can be envisaged lie between two extremes: one where each community deals with its own wastewater and the other where wastewater from all communities is treated in a single plant (Figure 1).

Figure 1.

Extreme solutions for wastewater problems at regional level

The Role of the Decision Models

Decision models are crucial to obtaining good solutions that will enhance IWRM. They can be tailored to incorporate the various interdependencies and interactions between the technical, economic, environmental and social aspects appropriate to achieving consistent and harmonious solutions. Decision models for wastewater systems involve a component for wastewater collection and another for wastewater treatment plants. How to design the sewer network to convey wastewater to the treatment plants? What location and size should be defined? These issues have to be considered simultaneously. The decision models should represent real world systems realistically and should include appropriate simulation models to carefully assess the effects of the decisions to be taken. The search for the optimum solution somewhere between the two extremes mentioned above is a very complex task, given the extraordinarily high number of possible combinations for collecting wastewater and transporting it to the various available locations of wastewater treatment plants (examples in Figure 2).

Figure 2.

Different solutions for wastewater problems at regional level

An important criterion for defining the solution is cost, with all the other issues involved in such problems it is usually represented as a constraint. We should keep in mind that decision models have to be considered within a wider decision process. Various solutions close to the optimum solution should be provided to decision makers, solutions that take into account specific economic and physical characteristics of real world problems. The decision procedure should be interactive, where decision makers can ask engineers at any time for a sensitivity analysis to assess the consequences of including new aspects or slightly changing some parameters.