For councils and communities, this creates a difficult challenge. Wastewater infrastructure is mostly hidden from sight, expensive to replace, and often taken for granted. The Water Services Authority puts it bluntly - upgrading and renewing aging wastewater treatment systems is one of the biggest infrastructure challenges facing the country.
The result of long‑term lack of investment is a growing number of plants operating at or beyond their limits, just as new wastewater environmental performance standards have come into force.
WSP work group manager for water Larey-Marie Mulder says in most cases upgrading existing, or ‘brownfield’, wastewater sites is more realistic than building new. It's far more complex, but, by applying some project smarts, is absolutely achievable.
Why brownfield upgrades are different
Unlike new plants, existing wastewater facilities have to keep running during construction upgrades.
“What makes brownfield upgrades challenging is staying online,” says Larey. “From day one, you have to design how the new works will integrate with the existing plant, while keeping everything operating and compliant.”
Space is another constraint. Many sites are tightly packed, with little room to expand. Designers must fit new treatment processes into limited footprints without creating long, inefficient pipe runs or compromising safety. At the same time, construction teams are working in live environments that can include biological hazards, hot surfaces, or explosive gases.
“And on wastewater plants, you often can’t have systems offline for more than six to eight hours. That gives you a very small window to work in.”
Designing for success from the start
Larey-Marie says successful upgrades begin long before construction starts. One of the most important principles is designing with commissioning in mind from the outset.
“You have to think about how you’re going to bring the plant into service on day one. Sometimes that means adjusting the design early or installing temporary pipework or equipment that will later be removed, just to make commissioning safer and smoother.”
Equally important is early and ongoing engagement with plant operators. Operators understand their facilities better than anyone, and their support can make or break a project.
“If operators don’t buy into the solution, it can derail things,” says Larey. “You rely on them to bring the plant into service. They need to be involved early, not after the design is finished.”
Taking a big-picture view of the entire treatment process is essential. Even small changes in one part of the plant can have unintended impacts elsewhere.
The role of digital engineering and staging
Digital tools play a big role in making brownfield upgrades safer and more efficient. Laser scanning and 3D models let teams understand existing sites in detail, reduce repeat site visits, and identify clashes between structures, pipes, and equipment early in the design process.
“Having a single 3D model that everyone works from avoids a lot of confusion later,” says Larey-Marie. “If you change something in the model, it can automatically flow through to drawings, which makes delivery much faster.”
Construction staging is another key success factor. Where possible, opportunities to build components off‑site should be taken. These can then be installed in a single, well‑planned cut‑over, rather than carrying out multiple disruptive shutdowns.
Early contractor involvement adds further value. Contractors often have really good ideas about how things can be built safely and efficiently and bringing them in early can significantly improve construction staging.
Designing for today and tomorrow
While upgrades must address immediate compliance and capacity issues, Larey-Marie says good design also considers future growth. Staged designs, modular systems, and flexible layouts can allow plants to expand over time without major rework.
“Innovation doesn’t always mean newer or more costly. Sometimes it’s about finding elegant, practical solutions that meet the brief, the budget, and the timeframe.”
Ultimately, upgrading wastewater infrastructure is about balancing risk, cost, and performance - while keeping essential services running for communities every day. With the right planning, collaboration, and technical insight, brownfield upgrades can extend the life of existing assets and help plants meet future expectations.
And for those working in the field, Larey-Marie says there's a deeper motivation too.
“Wastewater engineers are passionate about what they do. It’s the mix of biology and engineering and working to get the best outcome for communities and the environment. That’s what makes it so rewarding.”
