Wastewater Treatment Plants in Transition: Achieving Energy Neutrality Under the KARL Directive

The Balance Between Treatment Performance and Energy Consumption

Wastewater treatment plants are currently undergoing a fundamental transformation. In addition to safe and efficient wastewater treatment, new requirements—both technical and regulatory – are increasingly coming into focus.
Currently, the focus is particularly on measures such as the introduction of the fourth treatment stage. These measures make an important contribution to water protection, but at the same time are associated with significantly higher energy consumption. This is noticeably changing the situation for operators: The plants are becoming more complex – and more energy-intensive.

New Regulatory Requirements Under the KARL Directive

At the same time, the new EU Urban Wastewater Treatment Directive (KARL) establishes a clear framework for future energy supply. It requires member states to gradually transition the energy supply of wastewater treatment plants to renewable sources.
By 2045, the entire energy demand is to be covered by renewable energy¹. The focus here is not on the procurement of energy, but on its generation – either directly on-site or on behalf of the operators².

When Two Trends Converge

These two trends are occurring simultaneously – and reinforcing one another. On the one hand, energy demand is rising due to new cleaning requirements. On the other hand, there is a growing expectation that this demand will increasingly be met through in-house, renewable energy production.
For operators, this creates a new dynamic: energy is becoming a central component of plant design and day-to-day operations.

Limitations of Existing Energy Sources

Existing solutions, such as photovoltaics or biogas-based systems, already make an important contribution to self-sufficiency today. At the same time, they often face practical limitations.
Land availability, site-specific potential, and the seasonal availability of energy all influence the actual performance of these systems. This makes it clear that additional approaches are needed to meet growing demands.

Energy generation is becoming part of the infrastructure

Against this backdrop, the role of energy within wastewater treatment plants is changing. It is no longer merely being optimized, but is being deliberately developed.
Wastewater treatment plants are thus increasingly evolving from mere energy consumers into integrated energy systems in which generation, consumption, and control are considered as a unified whole.

Wind Energy as a Complementary Component

One possible approach is to supplement existing systems with wind energy. It adds an additional temporal dimension to energy generation and can be particularly useful during periods when other sources are less available.
This results in a more balanced overall energy production profile – an important prerequisite for a stable and predictable energy supply.

Vertical Sky®: Expanding Local Energy Production

With Vertical Sky®, Agile Wind Power is pursuing a strategy to systematically expand local energy production. The technology is designed to integrate into existing infrastructure and make a measurable contribution to renewable energy production.
For operators, this provides an additional option for meeting rising demands – both in terms of energy needs and regulatory targets.

Economic Efficiency and Regulatory Framework

Expanding local energy production also opens up economic opportunities. Increasing self-sufficiency can help reduce reliance on external power sources and make energy costs more predictable.
At the same time, verifiability and documentation are becoming increasingly important. Energy audits and reporting will be key tools in the future for demonstrating progress and evaluating measures³.

From Consumer to Integrated Energy System

The trend is clear: wastewater treatment plants will continue to evolve in the coming years. The combination of different technologies – tailored to the location, demand, and regulatory requirements – will be crucial in this process.
Energy is becoming an integral part of infrastructure and strategic planning.

Outlook: Integrated Solutions Will Be Crucial

The challenge lies not in individual requirements, but in the interplay of multiple developments. Rising energy demand, regulatory targets, and economic conditions are all intertwined.
Solutions that take this interplay into account will become increasingly important. Wind energy can play a key role in this – both as a complement to existing systems and as a building block for a sustainable energy supply.