Exploring the Role of Tertiary Treatment in England's Wastewater Management Systems

Recent Trends in Wastewater Treatment Upgrades

In recent years, English water companies have increasingly turned to tertiary treatment to meet tightening environmental standards. Driven by public concern over river health and new regulatory pressures under the Environment Act, many treatment works now add advanced filtration or nutrient-removal stages beyond conventional secondary treatment. These upgrades target phosphorus, nitrogen, and micro-pollutants that escape secondary processes.

• Phosphorus removal – increasingly mandated in sensitive catchments to reduce eutrophication.
• Microplastic and chemical contaminant reduction – emerging focus for newer installations.
• Ammonia polishing – to protect receiving waters during low-flow summer conditions.

Background: How Tertiary Treatment Fits into England’s System

England’s wastewater infrastructure largely relies on primary sedimentation and secondary biological treatment. Tertiary treatment is an additional stage that can include sand filters, membrane bioreactors, constructed wetlands, or chemical dosing for nutrient stripping. Historically, many coastal treatment works provided only primary or secondary treatment, with long sea outfalls diluting effluent. Today, inland works near bathing waters or ecologically sensitive rivers are being retrofitted or redesigned to include tertiary processes.

• Typical tertiary technologies: rapid gravity filters, disc filters, reed beds, UV disinfection.
• Cost and space constraints: upgrading existing sites near housing or protected land is often expensive.
• Regulatory drivers: Water Framework Directive and emerging Levelling Up agenda push for higher standards.

User Concerns: Costs, Effectiveness, and Trade-Offs

Households and businesses face potential bill increases as water companies invest in tertiary treatment. Consumer groups question whether the benefits justify the expense, especially in catchments where effluent makes up a small fraction of river flow. Meanwhile, environmental advocates argue that current secondary treatment insufficiently protects biodiversity and that tertiary solutions are essential.

• Bill impact: typical upgrades can add between 3% and 8% to annual water bills over a five-year price-review period.
• Performance variability: nutrient removal efficiency depends on influent load, temperature, and plant design.
• Byproduct concerns: chemical flocculants may increase sludge volumes or introduce metals into residuals.

Likely Impact on Water Quality and Regulation

Phased adoption of tertiary treatment is expected to reduce phosphorus loads in rivers by 40-70% in targeted areas, improving compliance with statutory targets. However, the overall impact will be gradual because only a portion of treatment works have committed to upgrades within current asset management plans. Combined with ongoing storm overflow reduction efforts, tertiary treatment will help meet storm and dry-weather effluent standards, but legacy infrastructure and high capital costs limit the pace of change.

• Locally: visible improvements in clarity and reduced algal blooms in downstream water bodies.
• Regionally: cumulative effects will take a decade or more to be measurable in larger river basins.
• Regulatory: expected to align with 2027 and 2035 nutrient neutrality deadlines in sensitive catchments.

What to Watch Next

Industry observers are monitoring the next water industry price review (PR24/AMP8) due to set investment levels for 2025–2030. Key indicators include how many treatment works receive funding for tertiary upgrades, whether nature-based solutions (constructed wetlands) are favoured over engineered systems, and how emerging concerns such as PFAS (‘forever chemicals’) drive new treatment requirements. Also worth watching: the role of independent catchment partnerships in prioritising sites and technologies.

• Funding allocations in the upcoming regulatory settlement from Ofwat.
• Pilot projects for advanced oxidation or granular activated carbon at tertiary sites.
• Parliamentary committee reports on river quality and wastewater treatment expenditure.
• Innovation in low-energy nutrient removal technologies (e.g., algal turf scrubbers, partial nitritation).