Energy Audits and Energy Efficiency of Urban Wastewater Systems, Following UWWTP Directive 2024/3019

The recent Directive EU/2024/3019, a recast of the previous 1991 Directive 91/271/EEC concerning urban wastewater treatment, introduces new obligations concerning effluents requirements and overall energy management in urban wastewater systems. In addition to increased levels of treatment (including extended tertiary and quaternary pollutants removal), the Directive introduces the obligation for treatment facilities to become “energy neutral” at the national sectoral level, increasing reliance on energy optimization and recovery from internal processes and external renewable energy sources. In order to achieve this objective, an obligation to periodically conduct energy audits is introduced; however, while this practice is commonly carried out in residential and industrial buildings, guidelines for its implementation in treatment facilities are currently not precisely defined. The paper summarizes current issues on wastewater sector energy audits, discussing the current state-of-the-art and the expected requirements to conduct such audits. It then discusses the causes of possible facility inefficiencies and their possible solutions from both permanent and transient perspectives. Finally, it addresses the issue of energy neutrality requirement, and the role of renewable energy sources contribution, both natural and internal (process-related) to the sector’s energy efficiency.