Kew STW Transfer

The contract for the complete Mechanical and Electrical works for the Kew STW Transfer project was awarded to Naston in March 1998. The complete project included the closure of the old sewage works at Kew and the transfer of flows up to 2700 m3/h via the Chiswick low level sewer system to the Thames Water regional treatment works at Mogden.

lncoming sewage to the original plant was diverted through a 2.4m diameter tunnel to the new pump and storage chambers, then pumped through a 700mm diameter pipeline under the Thames to the sewers on the other side of the river. The ?1.73 million contract was successfully completed in January 2000.

Model Test & Chamber Designs
Design of the two 15m diameter by 15m deep pump and storage chambers had to satisfy a wide range of varying requirements:

- At low (dry weather) flows the configuration had to provide for equal supply to all pumps with no grit deposition to any part of the chamber.

- Safe entry to the chamber for maintenance with 50% of the system working.

- In high (storm) flow conditions, the storage capacity had to be large enough to minimize discharge to the river.

The total system was model tested on a scale of 1 to 5 and included studies of the vortex drop shaft and effects of air entrapment within the pipeline under the Thames.

Penstocks
Isolation of the main pump chamber and its compartments was achieved by a series of electrically actuated penstocks.

Submersible pumps
The 16 Flygt submersible pumps installed were arranged to provide transfer of dry weather flows, storm water overpumping, return pumping and drainage. The pumping system is totally computer controlled to achieve any flow and any permutation of transfer, storage or re-cycling.

Automatic control
The MCC is situated in a new control building with power supplied via a new transformer or from the 800kVA standby generator. The ICA panel was connected via a Serck outstation for alarm signals and a plc for control to the District HQ at Mogden, three miles away. Data acquisition from the SCADA system was used to produce mimic diagrams, trends and reports.

Further equipment
Other items of equipment installed included electrical maintenance hoists, flow meters, ultrasonic level controllers, CCTV, alarm systems, discreens and biothane transfer pumps from existing local effluent treatment facility.