Lower Gornal STW

About This Project

As part of Severn Trent’s AMP7 programme, Lower Gornal Sewage Treatment Works (STW) underwent significant upgrades to meet tighter phosphorus and ammonia discharge limits. Initially planned for closure with flows redirected to Roundhill STW, an early contractor involvement (ECI) approach led by Mott MacDonald Bentley (MMB) resulted in a revised, more cost-effective solution that retained the site and saved over £20 million. The upgrade included the demolition of four biofilters and installation of a new moving bed biofilm reactor (MBBR) and tertiary solids removal (TSR) plant to meet the new discharge consents of 0.3 mg/l for phosphorus and 1.5 mg/l for ammonia. Chemical dosing systems were added to manage pH and phosphate removal, while a new recirculation pumping station—installed using trenchless augerbore methods—enhanced flow management without disrupting existing services. Sustainable practices such as reusing 2,000m³ of biofilter media and existing civil structures helped minimise carbon impact. The project was delivered three months ahead of schedule and below target cost, showcasing the benefits of collaborative working, innovative procurement, and MMB’s expertise in advanced wastewater treatment solutions.