Eign and Rotherwas Wastewater Treatment Works phosphorus removal upgrades 

Welsh Water’s £30m upgrade of Eign and Rotherwas Wastewater Treatment Works (WwTWs) is cutting phosphorus levels in the River Wye, protecting local ecosystems, and preparing Hereford’s treatment network for future population growth. 

Project overview

Welsh Water invested £30 million to upgrade the Eign and Rotherwas treatment works in Hereford to help reduce the amount of phosphorus entering the River Wye. This is a  key step in protecting the local river water quality and wildlife.  

At Rotherwas, the improvements included:

• A new advanced filtration system with 16 vertical filters
• Upgraded chemical dosing equipment
• A new pumping station
• A high-voltage power supply 

At Eign, the improvements included:

• Upgrade chemical system
• Refurbishment to optimise phosphorus removal

The team worked within tight site boundaries, navigated around live pipework, and kept both sites fully operational throughout construction. At Rotherwas, this meant over-pumping up to 600 litres of water per second, 24 hours a day, 7 days a week. With duty and standby pumps, on-site pump attendants, and on-call support in place to ensure there was no risk of breaching the Environment Agency’s discharge permit – a legal requirement that sets limits on what can be released into the environment. 

Innovative engineering and design played a key role in overcoming any challenges. 

A prefabricated 2.5m high and 5.6m wide concrete wall, know as a baffle wall, was lowered into the 8-metre-deep wet well shaft by a 200-tonne crane. This reduced the amount of time the team needed to spend in confined spaces and helped improve the quality of the build. 

Another solution was removing a clean water tank for the backwash process. After a risk-based analysis with Bluewater Bio and Welsh Water’s operations team, the existing filter system was confirmed to provide sufficient capacity, which saved space, time, and cost without compromising performance. 

The project was completed on time, met new environmental permit requirements, and has contributed valuable lessons to Welsh Water’s wider programme of river quality improvements.