While the revised Urban Wastewater Treatment Directive (UWWTD) sets out a clear direction for improving water quality across Europe, some uncertainty remains, particularly for smaller wastewater treatment plants. With questions over the criteria for advanced treatment for micropollutant removal, as well as how future upgrades will be funded, operators need to make decisions about when and how to invest. Waiting for greater clarity may seem the safest option, but understanding the technologies available today can help utilities prepare for a range of future scenarios.
Here, Arne Wieland, Process Engineer Expert at Xylem, explores the growing challenge of micropollutants and explains how advanced treatment technologies such as ozonation can help operators improve environmental performance while delivering long-term operational benefits.
The road ahead
Although the revised Urban Wastewater Treatment Directive (UWWTD) has entered into force, its implementation will be phased in across EU Member States over the coming years. While the requirements for larger wastewater treatment plants (WWTP) are becoming clearer, many smaller facilities await further details.
Member States are responsible for assessing which plants may require quaternary treatment based on local environmental conditions, including the sensitivity of receiving waters and the potential impact of micropollutants. As these assessments and implementation plans develop, many smaller utilities are left balancing the need to prepare for possible future investment against uncertainty over regulatory obligations, project timescales and how advanced treatment upgrades will ultimately be funded.
Why micropollutants matter
Tackling micropollutants is a key pillar of the revised UWWTD, reflecting growing recognition that conventional wastewater treatment alone is not enough to protect Europe's waters from emerging contaminants.
Micropollutants – including pharmaceutical residues, personal care products, pesticides and industrial chemicals – are typically present in wastewater at very low concentrations. Despite this, they can have a significant impact on aquatic ecosystems, with some compounds persisting in the environment and affecting wildlife even at trace levels.
The power of ozone
To effectively remove micropollutants, advanced water treatment is required – and one of the most effective technologies for this is ozone. Ozone degrades persistent compounds via two complementary pathways: direct oxidation and the formation of highly reactive hydroxyl radicals. This dual oxidation mechanism enables the efficient removal of a broad range of micropollutants that are poorly treated by conventional biological processes.
One of the leading ozone technologies for micropollutant removal is Xylem’s Evotide system. It is a pre-engineered system for simplified use. Along with its guided user interface, intuitive features, and seamless digital connectivity, Evotide helps reduce downtime and simplify operation – vital for plant success.
For larger wastewater treatment plants, scalable ozone generation is equally important. Xylem's PDOevoPLUS ozone system is designed to deliver high volumes of ozone reliably and efficiently. At the core of both systems are the Effizon® evo 3G electrodes. They feature Intelligent Electrode Protection (IEP) to prevent premature electrode failures, for zero downtime and 11 percent more energy-efficient ozone production. Building on decades of research and development, both systems deliver critical reductions in energy consumption, operating costs, and maintenance time.
A proven pathway
Ozone has been used in water treatment for more than a century and today more than 100 advanced treatment systems are installed or planned across Europe since 2009. One example is the Werdhölzli WWTP in Switzerland, which treats the wastewater of Zurich with a design flow of 6,000 l/s (137 MGD). The largest installation in Germany, the Aachen-Soers WWTP, treats up to 3,000 l/s (68 MGD).
Installed systems have generated over the years valuable information about implementation, design and operation of ozone systems and this data informs new installations for increased efficiency. While the success of full-scale installations gives operators confidence in the technology, understanding how it can work in each individual scenario is key.
Operators can gain greater confidence ahead of making an investment through feasibility studies. At Xylem utilities can be supported during technology selection through laboratory testing. Wastewater samples are analysed to determine ozone demand, expected micropollutant removal efficiency, and the potential formation of oxidation by-products (e.g., bromate) before proceeding to engineering design.
Preparing with confidence
As implementation of the revised UWWTD progresses, the exact requirements for some smaller wastewater treatment plants will continue to evolve. What is certain now, is that operators can take proactive steps to prepare by understanding the treatment technologies available and working with experienced partners to assess the most effective and efficient solutions for their sites. With proven advanced oxidation technologies, extensive application expertise and a collaborative approach to project development, Xylem helps utilities reduce uncertainty, make informed investment decisions and prepare confidently for the future of micropollutant removal.
