ABSTRACT
Extended statistical entropy analysis (eSEA) is used to evaluate the nitrogen (N) budgets of 13 Austrian wastewater treatment plants (WWTPs). The eSEA results are then compared to the WWTPs specific N-removal rates. Among the five WWTPs that achieve a removal rate of 75% the eSEA detects significant differences in the N-performance. The main reason for this is that eSEA considers all N-species and seems to be more discriminating than the N-removal rate. Additionally, the energy consumption and the costs of the mechanical-biological treatment process are related to the N-performance according to the eSEA. The influence of the WWTP size on the energy- and cost-efficiency of the N-treatment is investigated. Results indicate that energy-efficiency does not necessarily coincide with cost-efficiency. It is shown that smaller WWTPs between 22,000 PE (population equivalents) and 50,000 PE can be operated as energy-efficiently as larger WWTPs between 100,000 and 1,000,000 PE. On average, the smaller plants operate less cost-efficiently than the large ones. This research offers a new method for the assessment of the N-performance of WWTPs, and suggests that small WWTPs are not necessarily less energy- and cost-efficient than large ones.