Cost Savings in Wastewater Treatment Processes: the Role of Environmental and Operational Drivers

In this study, 139 Tuscan Wastewater Treatment Plants (WWTPs) were analyzed with the aim of evaluating their efficiency and highlighting the main efficiency drivers, as well as distinguishing among wastewater features, WWTP technology, other features of WWTPs, output variables, and sludge disposal. From a methodological point of view, the proposed method includes an ordinary least squares analysis of total plant costs regressed on a set of 28 exogenous variables and a two‐stage Data Envelopment Analysis model, where efficiency scores are obtained through weight restrictions. Moreover, the results of this study demonstrate that, with the exception of the ‘other features of WWTPs’, all other clusters of variables exert a negative effect on cost savings; in other words, larger scale of operations and higher usage of the productive capacity (grouped as ‘other features of WWTPs’) can improve cost efficiency.