MacRobert Award

2001 Finalist

Southern Water plc - putting sludge in a spin

[News Release]

David de Hoxar of Southern Water plcDavid 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

Diagram of how the Spiral separator operatesWastewater 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

A group of engineers looking at an in situ assembly of the lamella plate packsThe 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.

 

 

Updated July 2012

/prizes/macrobert/finalists/2001/southernwater.htm