180 week - Programme
United Utilities are the 2nd largest water company in England / Wales. They are responsible for an area in the north west of the UK, which includes major cities such as Manchester and Liverpool.
The Client's Needs
Davyhulme is the largest treatment works operated by United Utilities and is located near Trafford Park in Manchester handling a flow rate of 785MLD from a population equivalent of 1.5m.
The project requirement was for the provision of a nitrification plant for the removal of ammonia to comply with EA directives. United Utilities originally intended to extend the existing aeration streams (ASP1 and ASP2) to achieve the new consents.
VWS secured the project by designing an upflow BAFF BiostyrTM plant to fit within the existing area already excavated for the new ASP1 lane and therefore meet the small footprint requirement. The treated effluent discharge consent is 5mg/l N-NH4, 95%-tile. The BiostyrTM is made up of 36 filter cells, each providing a total filter surface area of 113 m2.
Each of the BiostyrTM cells consists of upflow filtration through a fine, floating granular media, retained by a nozzle slab. Bacteria form a film on the BiostyreneTM media which break down the pollutants into cellular material which is retained within the bed. The media also simultaneously acts as a filter to remove solid particles. Air is injected into the base of each cell to provide the necessary environment for nitrification to occur.
Each cell is periodically backwashed to remove trapped solids and excess biological growth, using the head of water stored above each cell. This eliminates the need for separate clean backwash storage and the pumping facilities required in conventional BAFF plants.
A dirty washwater tank was constructed to contain and balance the backwash flows prior to their return to the head of the existing treatment process.