The aim of this paper is to provide a methodology for a better understanding of the cost structure of
wastewater treatment processes. This methodology may be useful in the planning of new facilities. The
existing models in the literature are focused on the influence of the capacity of plant, expressed as inhabitants or flow rate, on the cost of treatment. We propose a new approach for the operating cost function that includes the most representative variables in the process. The idea is that the modelling of treatment costs enables us to understand the key role of the economies of scale in this context; and also the influence of other variables such as contaminants removed, or the age of the facility. The calculation of these extended cost functions also enables a detailed comparison to be made of the various treatment technologies from an economic point of view. In this sense, an extensive knowledge of the structure of the costs associated with each of the available treatment technologies is a basic issue in the planning of treatment processes and water reuse projects. This research applies a cost modelling methodology using statistical information from a sample of 341 wastewater treatment plants in Spain.
