This turnkey contract for new sludge handling and dewatering facilities at Thornham Wastewater Treatment Works (located on Thorney Island near Portsmouth) was awarded by Southern Water Services Limited in October 1992 and completed on schedule in April 1993.
The project included provision of sludge screening and dewatering plant with ancillary equipment, control systems and a temporary dewatering facility. An additional contract covered provision of stormwater pumps and controls.
Sludge Screening Inclined rotary sludge screen complete with conveyor and dewaterer with a maximum capacity of 40 l/s, installed above existing tankwork to handle both site generated and imported sludges. Dewatered screenings are discharged into a covered GRP enclosure housing a collection skip mounted on a motorised trolley to facilitate disposal. Hand raked screen facility was provided for the bypass line.
Odour Control In order to minimise odour, all sludge handling plant and tanks were covered and odour treatment was provided by forced draught ventilation units fitted with activated carbon media filters.
Sludge Dewatering The original rotary vacuum sludge filter and associated plant were removed and replaced with a fully automatic centrifuge system capable of handling up to 20 m3/h and producing sludge cake with a 25% solids content. Installation of the new centrifuge brought major space saving as well as big improvements in efficiency and odour control, by comparison with the original system.
Sludge Feed & Polymer Dosing The original sludge feed pumping and polymer-dosing plant was removed and replaced with new equipment arranged for fully automatic control. Final effluent booster pumping equipment was also replaced under this contract.
Temporary Dewatering Facility Minimal disruption to normal plant operation during the installation period was ensured by provision of a temporary, skid mounted dewatering plant.
Instrumentation and Control The original plant control panel was replaced with a new multi-compartment panel housed in a new control room. The system provides fully automatic PLC control of the sludge handling and dewatering operations.
Stormwater Pumping A further contract covered the installation of two submersible stormwater pumps within an underground chamber. These pumps provide both sludge transfer and stormwater return pumping from the new storm water storage tank. Modifications to existing site flow monitoring and control systems were completed and controls housed in an adjacent GRP enclosure
Thornham WTW
