A 5Mld extension to Sandown Water Treatment Works, Isle of Wight comprising coagulation, clarification, filtration and washwater recovery.
Whitewater was retained by the Principal Contractor to provide process design, P&ID development, control philosophy, equipment specification, commissioning support and performance trial review.
The raw water is from the “flashy” river Yar via bankside storage. The new treatment works consists of coagulation with polyaluminium chloride and polyacrylamide followed by mechanical flocculation, clarification in a lamella clarifier, optional sodium hypochlorite dosing for manganese oxidation and rapid gravity filtration. The treated water then mixes with water from the existing Microfloc treatment plant before GAC filtration and chlorination.
Recovery of up to 1.3Mld from both existing and new works is provided by polyacrylamide dosing followed by clarification using duty and standby lamella clarifiers.
The project included a new raw water pumping station, a new GAC filter feed sump and pumping to the existing GAC filters, modifications to the existing dirty backwash water lagoon to allow washwater recovery, and a clarifier sludge holding tank and pumping station to sewer.