Yorkshire Water - St. Aidans


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St Aidans Water Treatment Works was a 30ML/day plant utilising reverse osmosis technology to treat water from an open cast mine site for drinking water purposes. The site was flooded in 1988 when the River Aire, to the south west of Leeds, burst its banks.

Following an accelerated tender period of only four working days, ACWA Services were awarded the project as main contractor, responsible for the detailed design, construction and operation of the plant.

The complete programme from this fast track project was as follows:

  • 4th to 12th April Tender period including Good Friday and Easter Monday.
  • 16th April Presentation to Yorkshire Water.
  • 19th April Notice to Proceed.
  • 26th April Order received.
  • 27th May Site establishment completed.
  • 7th June Raw water, backwash and 1st settlement tank completed.
  • 14th June 1st filter skid on site, 2nd & 3rd settlement tanks completed.
  • 21st June 2nd & 3rd filter skids on site, 1st 3 RO containers on site.
  • 28th June Treated water tank completed.
  • 12th July 4th & 5th filter skids and Diesel generators on site.
  • 19th July All filters, RO plants, MCC and dosing equipment on site.
  • 26th July MCC and Dosing buildings completed. Site offices and welfare completed.
  • 5th August All filter sets commissioned. 1st RO commissioned.
  • 7th to 22nd August Remaining RO plants commissioned & toxicology test period completed.
  • 23rd August Complete WTW put into supply.

2 weeks to Tender and negotiate the contract with Yorkshire Water
9 weeks to design and procure all items and complete off site fabrications.
13 weeks from site establishment to completing the project and going into supply

Because the water source at St Aidans was finite, Yorkshire Water required that the plant, in part or in whole, could be moved to other locations when the supply was exhausted. Consequently, the St Aidans treatment plant was constructed in modular form, allowing rapid de-commissioning and removal.

Plant Description

The process comprised:-

Raw water pumps located on a floating pontoon, 500m of raw water pipe, raw water storage tanks, forward feed pumps, iron removal by multi-media filters, settling tanks, ultraviolet disinfection, cartridge filters, reverse osmosis, remineralisation, chlorination, treated water storage, treated water transfer. The plant produced 30 MLD of treated water into supply.

A total of 33ML/day was pumped out of the flooded mine workings over approximately one year. All of this was filtered through the multi-media filtration system with 25 ML/day passing on to the Reverse Osmosis plants. 8ML/day was used for filter backwash water and for dilution of RO concentrate (5 ML/day).

The filter backwash water was transferred from the backwash sump to 1 of 3 tanks for 24hours settlement prior to release of the supernatant in order to minimise the suspended solids discharge to the river.

This 13 ML/day (Backwash water and concentrate) was clean enough to discharge to a local river with Environmental Agency Approval.

Of the 25 ML/day feed to the Reverse Osmosis stage, 80% (20 Ml/day) was converted to useable permeate, all undesirable impurities having been removed by the RO plant.

The 20 ML/day permeate was dosed with lime and CO2 to remineralise and correct the pH and sodium hypochlorite to provide residual disinfection in Yorkshire Water’s distribution network.

After 20 minutes residence time in an annular chlorine contact tank, high lift pumps discharged the water directly into Yorkshire Water’s pressurised mains serving customers in the Yorkshire area.

The St Aidans Water Treatment Works was fully automated, controlled by a PLC and continuously monitored by a sophisticated SCADA system. A direct link to Yorkshire Waters telemetry system ensured that the water quality was monitored for four key parameters 24 hours a day, guaranteeing that only water of the highest purity was delivered into the service reservoirs.

Project Details

Client: Yorkshire Water - St. Aidans, St. Aidans

Industry: Water Treatment Works

Application: Temporary Water Supply during a drought