The objective of this paper is to demonstrate the importance of incorporating more realistic energy cost models (based on current energy tariff structures) into existing water resource recovery facilities (WRRFs) process models when evaluating technologies and cost-saving control strategies. In this paper, we first introduce a systematic framework to model energy usage at WRRFs and a generalized structure to describe energy tariffs including the most common billing terms. Secondly, this paper introduces a detailed energy cost model based on a Spanish energy tariff structure coupled with a WRRF process model to evaluate several control strategies and provide insights into the selection of the contracted power structure. The results for a 1-year evaluation on a 115,000 population-equivalent WRRF showed monthly cost differences ranging from 7 to 30% when comparing the detailed energy cost model to an average energy price. The evaluation of different aeration control strategies also showed that using average energy prices and neglecting energy tariff structures may lead to biased conclusions when selecting operating strategies or comparing technologies or equipment. The proposed framework demonstrated that for cost minimization, control strategies should be paired with a specific optimal contracted power. Hence, the design of operational and control strategies must take into account the local energy tariff

The authors would like to thank the Spanish Ministry of Economy and Competitiveness for funding (RYC-2013-14595 and CTM2012-38314-C02-01), and the European Union Marie Curie Career Integration Grant PCIG9-GA-2011-293535. ICRA was recognised as consolidated research groups by the Catalan Government with the code 2014-SGR-291. The usefulness of the energy cost model is now being demonstrated within the framework of the R3water project funded by EU (FP7, Grant agreement no: 619093)