|
MacRobert Award
2001 Finalist
Southern Water plc - putting sludge in a spin
[News Release]
 David de Hoxar of Southern Water plc is the inventor of the de Hoxar Spiral Separator - a novel, compact gravity settlement device that is now being used on wastewater and potable water treatment works run by some of the UK's most innovative water companies.
Innovation
David de Hoxar first mooted the idea of a lamella separator with moving parts in the late 1980s but it was only after he began to work for Southern Water Services Ltd. that he was able to turn the concept into reality. In the 1990s Southern Water funded David's research, which culminated in the development of the de Hoxar Spiral Separator.
The spiral separator offers important benefits to the wastewater treatment industry including:
-
Very small footprint (taking up between 1/3 and
1/2 of the site area of conventional separators), making it ideal for compact sites;
-
Excellent sludge thickening which in turn results in cost savings downstream at sludge treatment plants
The EC Urban Wastewater Treatment Directive (UWWTD) has been the driving force behind attempts to clean up
Britain's beaches and reduce the level of waste discharged. A number of UK water companies, led by Southern Water, have decided to upgrade their treatment works, many of which are on confined sites, with the addition of de Hoxar Spiral Separators.
Design
The de Hoxar spiral separator comprises a spiral plate pack, in the shape of a helical core, installed within a tall circular tank. Each plate pack consists of a large number of platelets made of glass reinforced plastic. The shape of the plates provides built in strength and stiffness, and no spacers or structural connections are required between the plates, other than the core, to keep the whole plate pack in shape.
Operation
 Wastewater
enters the separator via an inlet pipe in
the side of the tank, which passes up the
central core of the plate pack. The dirty
water flows down the central core, which
acts as a baffle, before flowing up through
the plate pack. The suspended particles,
which are heavier, settle onto the plates
whilst the water passes up through the plate
pack and leaves the separator. The settled
solids coalesce forming a sludge, which then
slides down between the rotating plate pack
and the tank wall onto the floor of the
tank.
The continuous rotation of the plate pack increases the relative velocity of settling particles on the plate and improves the solids removal efficiency. The deHoxar spiral separator is a true cross-flow device in that the movement of the sludge down the annular gap between plate pack and the tank wall ensures that the sludge does not mix with the water entering at the bottom of the plate pack.
Commercial success and the future
 The development of resin transfer moulding techniques to produce the individual platelets and the in situ assembly of the lamella plate packs are significant engineering developments which are assisting in the commercialisation of the process.
Southern Water has issued marketing licenses to Purac Ltd (an Anglian Water company) and OTVB Ltd. (part of the Vivendi group). Although the main application at the moment is in water and wastewater treatment, there is the potential for the spiral process to be used outside the water industry.
Current trials indicate that the deHoxar spiral separator could be an effective means of final sedimentation on works using the activated sludge process. This would open up considerable opportunities both on compact new build and existing sites undergoing upgrading and extensions.
|
