MBBR and DAF solution: an innovative process solution to enhance performance for Dwr Cymru Welsh Water

Originally designed to treat a population of 165,000 Swansea Bay WwTW now serves a growing population in South Wales that has reached a PE of 185,000. The existing facility comprised screening, FOGG (FOG and grit removal) lanes, lamella PSTs, ASP utilizing lamella FSTs and UV disinfection. There is also a sludge digestion facility on site with an associated centrifuge. The majority of the works is located in an underground building that is covered with landscaping. At the back of the works runs Fabian Way, one of the main roads into Swansea and the front of the works is the proposed location for a new campus area for Swansea University. Dŵr Cymru Welsh Water identified a need to improve the treatment performance of the Swansea Bay WwTW as there was a large cost in operating the asset in order to maintain compliance. The areas of the works that Welsh Water wanted to focus on were the screens, FOGG lanes, lamella FSTs and the UV plant and the basis of design was to ensure that the facility was capable of treating 215,000 PE.
Developing a sustainable solution
Swansea Bay WwTW is a key works for Welsh Water and it is vital that the water quality in Swansea Bay is maintained, particularly as it is a designated Bathing Water. Imtech has worked closely with Welsh Water and its operations team on a proactive basis since AMP4 to implement mitigation plans to ensure short-term compliance and to develop a long- term sustainable solution. The taskforce set up in AMP4 reviewed a number of different options for the site. Developing an innovative process solution to meet the identified improvement needs was not straightforward as there were difficulties associated with extending beyond the existing site boundaries.
The FOGG lanes were upgraded in 2011, the UV plant in 2013/14 and the screens are being upgraded in a separate scheme. The focus of the scheme described within this article is the activated sludge plant and lamella FSTs.
Looking at conventional solutions would have meant the following:
• Large scale customer impact both with the local and wider community.
• Challenging planning conditions that may have been prolonged and costly.
• Replacement of the existing final lamella settlement tanks: Capital cost in excess of £30m.
• Replacement of the existing works: Capital cost in excess of £200m.
It was concluded that the best solution to secure long term compliance was a change of process from the current activated sludge plant and lamella clarifiers to moving bed biofilm reactors (MBBR) and dissolved air flotation (DAF). The use of the MBBR wastewater treatment process allows the provision of a higher level of wastewater treatment within the
existing structures of a treatment works. The process increases the population of active biomass within a tank to give higher levels of treatment and can be retrofitted into existing structures.

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