The present work provides a structured examination of approaches for improving the energy efficiency of municipal and industrial wastewater treatment plants (WWTPs) under conditions of deep reconstruction. Against the backdrop of pronounced volatility in energy markets in 2022–2023—when EU electricity prices reached record levels in the first half of 2023—the reduction of operating expenditures became a priority engineering and economic objective. Within the study framework, a benchmarking methodology based on specific indicators (kWh/m³, ) is considered; a comparative analysis of technological solutions for CAS and MBR configurations is carried out; and the attainability of partial energy self-sufficiency through biogas cogeneration is assessed. Scientific novelty is associated with the development of an integrated model for selecting a modernization strategy that accounts for equipment performance, operational constraints, and the digitalization potential embedded in the “water sector digital transformation / Water 4.0” logic. The results indicate that advanced control (including AI/ML-based decision support where data quality allows) and modern membrane technologies can enable a 20–30% reduction in energy consumption while maintaining compliance with stringent environmental requirements. The material is oriented toward chief engineers of design organizations, specialists of utility operating services, and developers of environmental protection equipment.

energy efficiency, wastewater treatment plant reconstruction, membrane bioreactor, specific energy consumption, biogas, aeration, digital twin, environmental standards, sewerage.

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