Wastewater Gravity Solution – Benefits Spiralling Out of Control!

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Alec Bond

17th October 2023

The de Hoxar Spiral Separator is an ultra-compact gravity settlement device requiring as little as 3% of the space of traditional technologies.

Invented by Plantwork Systems’ Chief Engineer, David de Hoxar, and developed in conjunction with Southern Water, our spiral separator represents a significant advance on conventional means of separating out waste sludge. Traditionally plants consist of large settlement tanks with a large footprint; once the sludge has been settled, it then has to be thickened for transport to the anaerobic digester sites. This requires additional equipment and buildings.

Our technology performs the same task as traditional settlement tanks but requires as little as 3% of the space. It also has the added advantage of producing thickened sludge, eliminating the need for additional thickening equipment.

The Spiral technology is now in operational use on several wastewater and potable water treatment sites in the UK, and has potential for many other applications, including use on a range of industrial processes.

Further design updates are in progress to reduce the cost of production and improve the accessibility for maintenance and repair. Mobile units have also been designed to enable efficient installation and significantly reduce the time spent on site during the construction period.

Key Benefits


Requires only 3% of the site area of conventional tanks, and about 25% of the site area of lamella separators.


Thicker sludge is produced – typically 6% dry solids (thicker can be produced if required). In many cases, this saves one stage of sludge treatment.


Low cost to cover for odour control – once covered, the volume of air requiring treatment is typically 1% compared to conventional tanks.


Reduced visual impact makes it suitable for urban sites and sites next to areas with public access.


Anaerobic Digestion – ideal solution for efficient extraction of high calorific primary sludge for Anaerobic Digestion as part of utilities CHP programs.

Trials in Canada

As well as UK projects, Plantwork Systems is also installing a Spiral Separator in the City of London, Ontario, Canada. The project is being delivered as a Joint Venture between Plantwork Systems and Canadian construction company Aquicon, through a newly formed division (Aquicon Water), to introduce innovative sustainable wastewater treatment solutions in Canada.

Pottersburg is one of five substantial treatment works serving the Eastern part of the rapidly expanding City of London, Ontario. The Spiral Separator will demonstrate three distinct duties: primary settlement, sludge thickening, and final settlement for activated sludge. These trials will be carried out consecutively, with the unit being moved to different locations on the site.

Plantwork Systems Spiral Separator being assembled and shipped to Canada

How might we help you?

The Spiral Separator is just one of Plantwork Systems’ innovative products which offer lower cost, environmentally friendly and sustainable solutions compared to others on the market. Our commitment as a business is to make a positive contribution to a sustainable, clean environment whilst delivering exceptional value to our customers.

We do this by using our technical expertise and unique experience to create, supply and promote innovative products and services to both the wastewater treatment industry and the commercial sector.

For more information on the Spiral Separator or any other Plantwork Systems wastewater treatment products, please contact [email protected].

Article by Alec Bond, Sustainability and Environment Manager