Scottish Water has gone out to tender with a contract for the rental of lime treatment equipment at its Allanfearn Waste Water Treatment Works to stabilise dewatered sewage cake with an estimated value of £2.8 million (ex VAT).

The water company has specified that the equipment must ensure effective mixing of lime with sewage cake, precise dose control, and safe handling of materials. The supplier will be required to provide all necessary equipment, training, and maintenance support for the duration of the rental period.

Scope of supply

The supplier will be required to provide a complete lime treatment system for hire, including:

Lime Storage Silo

• A sealed, weatherproof silo with sufficient capacity for lime storage. There should be enough capacity to allow for a full load of quick lime to be added prior to running empty to allow for a continuous operation of the plant.
• Dust suppression and venting to prevent environmental contamination.
• Level indicators to monitor lime quantity.
• A method of delivering the lime to the mixing unit in a controlled dose rate.
• The silo should not interfere or require any adjustment to the infrastructure or buildings.

Cake Import

A method of receiving cake import to the lime treatment plant. This should allow cake to be loaded into the lime treatment plant by a telehandler or other similar type plant.

Twin Screw Auger Mixing System (or similar)

• A twin-screw auger mixer designed to homogenously blend lime with dewatered sewage cake.
• Corrosion-resistant construction suitable for high-pH lime and sewage cake.

Material Conveyance System

• A mechanical conveying system to transfer sewage cake into the mixer. This should ideally be able to be fed automatically from the outlet of the centrifuge.
• A mechanical conveying system to transfer lime into the mixer.
• A mechanical conveying system to transfer treated cake to a clean area that will avoid cross contamination.
• Compatibility with the dewatered cake’s consistency (typically 20 -30% dry solids).
• Minimal spillage and dust generation.

Lime Dosing Control System

• Automated dosing control to regulate lime addition based on sewage cake feed rate.
• Measurement and adjustment of lime dose rate in kg lime per kg dried solids (DS)
• Real-time monitoring with data logging of lime dosing control system.

Safety & Environmental Controls

• Dust extraction/containment systems.
• Emergency stops and safety interlocks.
• Compliance with health, safety, and environmental regulations.

Training Requirements

• Supplier shall provide training to a competent level.
• Operator Training: Hands-on instruction on system operation, dosing adjustments, and troubleshooting.
• Safety Training: Proper handling of lime, PPE requirements, and emergency procedures.
• Documentation: User manuals, maintenance guides, and safety protocols.

Maintenance & Support

• A preventative maintenance plan detailing frequencies and tasks required to be completed by operators.
• Preventive Maintenance: Scheduled inspections and servicing to ensure continuous operation. This should consider the requirements of the WWTW’s and adapt to ensure minimum impact.
• Breakdown Support: Technical support with a guaranteed response time for critical failures. This should include out of hours and weekends.
• Spare Parts: Availability of critical spare parts to minimize downtime.

Performance Requirements

• The system must achieve a homogeneous lime-sewage cake mixture with a consistent dose rate (±5% accuracy). This should be calibrated annually as a minimum, with certificates supplied.
• Capable of processing approximately up to 4 tonnes per hour of dewatered sewage cake.
• Minimal unplanned downtime

Visit https://atamis-scottishwater.my.salesforcesites.comProSpend__CS_PublicLandingPageSearchType=Projects

to access the procurement documents.

Reference number is SW25/WM/1523