One Liquid Lime and One Powder Dosing Plants for South West Water

Countess Wear STW at Exeter required process enhancements (additional Biological Aerated Flooded Filter {BAFF} cell, alkalinity dosing, sludge enhancements and ancillary items) which entailed the provision of one alkalinity and one Powder Lime Dosing Plant as part of the Sludge De-watering Scheme.

The contract for the two plants was managed by Balfour Beatty Construction Services Ltd.

Alkalinity Plant. This plant is designed to make up the required liquid lime solution at the designated concentration and alternate the mixing/batching process between two tanks so that the liquid lime solution was always available for dosing as required. The delivery from the tanks to the plant was supplied by others.
The plant was designed to provide:

  • Continuous unattended operation – 24 hours/day for 7 days/week;
  • Automatic control of the lime dosing operations to optimise lime usage;
  • Plant availability in excess of 95% based on continuous operation over a three-year period;
  • A design life of the plant in excess of 25 years.

Powder Dosing Plant. This plant is designed to provide a consistent quantitative delivery in the selected ratio of lime powder and cake to the mixing vessels and a thorough, homogeneous mixture as it leaves the final ploughshare mixer for distribution by others.

The plant was designed to provide:

  • Continuous unattended operation – 24 hours/day for 7 days/week;
  • Automatic control of the lime dosing operations to optimise lime usage;
  • Plant availability in excess of 95% based on continuous operation over a three-year period;
  • A design life of the plant in excess of 25 years.