Going underground: Innovative DAF system supports stylish exterior in Swansea

The underground lamella tanks presented a challenge from an installation point of view, requiring the use of a bespoke gantry.

Wastewater technology and services expert Jacopa has completed the £2.5m design and installation of a DAF system for Dŵr Cymru Welsh Water’s landmark Swansea wastewater treatment plant.
Billed as a “zero nuisance plant” when it went into operation in 1996, the Swansea works was buried underground with extensive landscaping to disguise its existence from the landward side. The DAF system was provided for Jacopa client Imtech Process and is said to offer an innovative solution.
The original facility treatment train comprised screening, fat, oil, grease and grit (FOGG) removal lanes; primary settlement tanks (PSTs) fitted with lamella plates; a four-lane activated sludge process; final settlement tanks (FSTs), also fitted with lamella plates; UV disinfection and sludge treatment. The system had to be designed to support reduced operating costs and compliance with the tightened effluent discharge consent for Swansea Bay.
To accomplish these goals, the works has been undergoing a substantial upgrade since 2011, modernising many of its treatment systems. Developing innovative process solutions to meet the identified needs for improvements has been challenging because of the restricted underground site, says Jacopa.
With the aim of ensuring long-term compliance Jacopa changed the process from the current activated sludge plant with final lamella settlement to moving bed biofilm reactors (MBBRs), and dissolved air flotation (DAF).
Jacopa’s remit to convert 11 FSTs to DAFs faced several challenges, not least that the lamella tanks were underground with access and lifting operations severely hindered. The chosen solution involved designing a frame and chain scraper to be positioned halfway along the tank – flow velocities at the surface are sufficient for the float sludge to reach the scraped section, making this feasible.
Given the tight working space available for installation, the developers had to devise a novel lifting gantry. Components were manufactured in sub-assemblies and put together in situ with expert input from the company’s Chippenham office.
Project manager Graham Fife noted: “It was not an easy task – the tanks are colossal, two storeys deep. Installing the equipment safely was priority. With the aid of the bespoke lifting gantry system, the install was achieved.”
Another key challenge for the £2.5 million contract was the changeover methodology. Two tanks had to be changed at a time to ensure the processes continued to provide full treatment for Swansea’s wastewater.
The plant is now operational and is in compliance with the tightened consents. The 112,000m3/day, 225,000 PE DAF plant has to achieve an effluent total suspended solids (TSS) limit of 30mg/l on average throughout the year.