Wastewater Treatment Plants (WWTPs) are no longer solely sanitation facilities; they hold the potential to become energy-active infrastructures, capable of generating, optimizing, and intelligently managing renewable energy. In this context, they are emerging as key components of the future energy system and as a necessary response to the climate crisis and the urgent challenge of decarbonization.
At AIGUASOL, we have contributed to the REGENERA project to explore and demonstrate this potential, focusing on the comprehensive utilization of WWTPs’ intrinsic resources—such as biogas—and their ability to provide flexibility to the electrical grid, with an emphasis on circular economy principles and local energy sovereignty.
Biogas and biomethane: beyond self-consumption
One of the most valuable resources generated at WWTPs is biogas, produced via the anaerobic digestion of sludge. This renewable gas can be used for combined heat and power (CHP) generation, thereby covering the plant’s internal energy needs.
Technical studies conducted by AIGUASOL under the REGENERA project have shown that the heat typically produced during this process exceeds what is required to maintain optimal digester temperature. This presents an opportunity for the alternative valorization of surplus biogas.
Through upgrading technologies, biogas can be purified and converted into biomethane, a gas with characteristics equivalent to natural gas and suitable for injection into the conventional gas grid. This injection directly contributes to decarbonizing the energy mix and enhancing the management of renewable resources.
Additionally, scenarios are being explored where the WWTP’s thermal demand is fully met by external renewable sources, such as local forest biomass. This approach would allow the full amount of biogas to be dedicated to biomethane production, optimizing both its energy and environmental performance while enhancing local resilience.
Demand-side flexibility: turning a challenge into an opportunity
WWTPs can also play a critical role in providing demand-side flexibility, a capability increasingly valued in energy systems with high renewable penetration. Owing to their ability to modulate operations such as sludge recirculation, pumping, or CHP unit activation, these facilities can adjust their energy consumption in response to electricity market conditions—consuming or producing energy at optimal times.
The REGENERA project enabled us to analyze how CHP generation and biomethane injection can be coordinated operations, responding to external signals such as electricity prices or renewable availability.
In parallel, the project has explored the integration of Power-to-Gas (P2G) technologies, such as electrolyzers or electromethanogenesis reactors (EMG), which enable the generation of biogas from surplus electricity—especially from renewable sources. This bioconversion process leverages microorganisms and electrical energy to synthesize methane from CO₂, enhancing microbial performance and expanding the WWTP’s potential for energy self-sufficiency.
Towards intelligent operation: modeling, control, and AI
The evolution of WWTPs into advanced energy hubs requires intelligent management systems capable of real-time resource optimization. At AIGUASOL, we have developed strategies based on energy modeling of the plant, enabling the simulation and prediction of complex behaviors across multiple variables: thermal and electrical demand, biogas generation, photovoltaic output, and electricity market pricing, among others.
Based on this modeling, it is possible to define optimal operational rules that can be integrated into SCADA systems to automate decision-making—such as when to activate CHP, inject biomethane, or adjust energy consumption.
To achieve higher levels of responsiveness and foresight, a layer of artificial intelligence can be added through predictive models and machine learning algorithms. This operational intelligence enables proactive, optimized plant management, maximizing both profitability and sustainability.
The future of WWTPs is circular and decarbonized
WWTPs have the potential to become strategic infrastructures for the energy transition by leveraging their full capabilities as biomethane producers, flexibility providers, and intelligent energy hubs. Realizing this qualitative leap requires a deep understanding of the plant’s energy behavior, as well as tools to optimize its operation under external conditions such as energy demand, pricing, or renewable production.
At AIGUASOL, we have extensive experience and expertise in modeling complex energy systems, designing advanced control systems, and valorizing resources such as biogas, waste heat, and solar energy. With this technical foundation, we support public and private stakeholders in the transformation of conventional WWTPs into strategic, efficient, and climate-aligned facilities.
TRNSYS-Based energy modeling of a real WWTP in the context of the REGENERA Project (AIGUASOL)
