Ferrovial to Upgrade Slough Sewage Treatment Works

Ferrovial will deliver the upgrade of the Slough Sewage Treatment Works (STW) under an integrated joint venture between Ferrovial Construction and Cadagua. The scheme, valued at approximately £80 million, is designed to enhance treatment capacity and ensure compliance with updated wastewater quality requirements set by the Environment Agency.

Capacity Expansion and Stricter Effluent Standards
The Slough STW upgrade aims to meet more stringent discharge permits, including tighter limits for ammonia and phosphorus concentrations. Nutrient removal is a critical factor in reducing eutrophication risks in receiving water bodies and maintaining ecological balance.

The project will expand treatment capacity to accommodate increased flows while improving process control for high-strength return streams. Enhanced management of storm flows will support compliance with storm permit requirements, reducing the risk of untreated discharges during peak rainfall events.

By increasing hydraulic and biological treatment performance, the scheme targets improved effluent quality and greater operational stability.

Power Supply and Operational Resilience
The works include installation of a new power supply and standby systems to improve plant resilience. Redundant power configurations are essential for wastewater treatment facilities, where continuous operation is required to maintain biological treatment processes and prevent environmental incidents.

Upgraded electrical infrastructure also supports long-term sustainability by enabling integration of energy-efficient equipment and future process enhancements.

Design for the scheme began in November 2025, with construction scheduled to commence approximately 15 months later. Phased implementation is expected to allow continued plant operation during construction.

Integrated Delivery Model and UK Infrastructure Context
The project will be delivered through an integrated joint venture combining Ferrovial Construction’s UK infrastructure experience with Cadagua’s technical expertise in water and wastewater treatment.

Ferrovial Construction has previously delivered major UK infrastructure projects, including the Thames Tideway Tunnel, the Silvertown Tunnel, and the Northern Line Extension. Cadagua contributes more than five decades of experience in water, wastewater, and desalination plant engineering.

Environmental and Community Impact
Upgrading Slough STW forms part of broader efforts to strengthen UK water infrastructure in line with evolving environmental standards. Improved ammonia and phosphorus removal will contribute to cleaner receiving watercourses and healthier aquatic ecosystems.

By combining treatment capacity expansion, enhanced nutrient removal, and resilient power systems, the scheme addresses regulatory compliance, operational efficiency, and long-term environmental performance within the UK wastewater sector.