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
Chapel-en-le-Frith is situated in the Derbyshire peak district and required environmental improvement in order to comply with the environmental requirements of the EU Freshwater Fish Directive and river water Quality Objectives for the receiving watercourse, Black Brook, a tributary of the River Goyt. The effluent discharge quality consent was set by the Environmental Agency at 15 mg/l BOD and 2 mg/l ammonia.
The existing works comprising of conventional biological trickling filters, followed by Humus settlement tanks, was unable to meet the new consent standard. Following a feasibility study, a decision was made by United Utilities to add a tertiary treatment stage to the existing process.
The improvements involved de-nitrification of the treated wastewater. The upgrade of Chapel-en-le-Frith Waste Water Treatment Works ensures that the receiving water is of a quality that supports a variety of game fish. Chapel-en-le-Frith WwTW serves a 6000 population equivalent and is capable of treating a daily flow of up to 5.1 MLD.
Veolia Water Solutions & Technologies were awarded the design and build contract to upgrade the wastewater treatment works at Chapel en le Frith, adding a tertiary BAFF using the VWS Biostyr process. A new feed pump station, situated along the route of the existing outfall, incorporating an emergency bypass, was constructed to lift the effluent to the new flow splitting chamber, which splits the flow between the Biostyr cells. The design at Chapel en le Frith incorporates a maturation system allowing potential post wash spikes of BOD and TSS to be ameliorated.
Each of the cells consists of upflow filtration through a fine, floating granular media, retained by a nozzle slab. Bacteria form a film on the Biostyrene® media which break down the pollutants into cellular material which is retained within the bed. The media also acts, simultaneously, 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.
A particular feature of the Chapel-en-le-Frith Works is that the influent frequently contains insufficient amounts of alkalinity to support the autotrophic bacteria necessary to achieve nitrification. Storage and dosing facilities for lime were therefore introduced into the scheme to artificially raise the level of alkalinity to the required levels. Chapel-en-le-Frith also incorporates a maturation system which allows potential post wash spikes of BOD and TSS to be ameliorated.
Biostyr, Chapel-en-le-Firth WwTW