Twist and Shout

Inventor and Engineer David deHoxar on why Spiral Separators should be an integral part of the future for wastewater treatment

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David deHoxar

17th November 2021
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What did I think I’d be doing when I retired?  Well one could say I haven’t!  But there is a very good reason for that – I had unfinished business.

I was due to retire in 2013, however, when Plantwork Systems offered me the opportunity to join the team with a view to developing Spiral Separator technology further and to work with them on various R&D projects, I couldn’t say no.

What became known as the de Hoxar Spiral Separator (Spiral) is an ultra-compact gravity sludge settlement device which has been a real breakthrough in wastewater treatment.  It responds to a very real need for more resource efficiency.

I had invented the Spiral Separator whilst at Southern Water, taking it from concept, all the way to market ready technology. Several Spirals were delivered on sites in the UK and Japan, ranging from small 1.5m diameter units, up to 7m diameter units performing primary settlement for wastewater treatment works serving populations >50,000 PE.

What became known as the de Hoxar Spiral Separator (Spiral) is an ultra-compact gravity sludge settlement device which has been a real breakthrough in wastewater treatment in response to a very real need for more resource efficiency.

The problems associated with conventional means of separating out waste sludge are well known to the industry – traditionally it involves using large settlement tanks taking up huge areas of land. Once the sludge has been settled, it then requires thickening for transport to anaerobic digester sites. The thickening process involves additional equipment and buildings which require large capital and operational investment.

The Spiral solids separating 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 which saves the requirement for additional thickening equipment. The capital investment is greatly reduced – saving money as well as space.

Proof of the Pudding

Our Spiral technology is in operational use on twelve wastewater and potable water treatment sites around the UK and has potential for many other applications.

We are delivering a 1.5m diameter pilot plant to a wastewater treatment plant in Ontario, Canada. The unit will be demonstrated performing three distinct duties – primary settlement, sludge thickening and final settlement for activated sludge. These trials will be carried out concurrently, with the unit moving to different locations on the site. The pilot project is expected to begin in the Spring of 2022, with our Spiral about to commence wet testing as of November 2021.

The footprint of this system is 90% less than the original plant. The nearest competitor was only able to offer a 30% reduction in footprint.

1.5m Spiral plate pack and the unit being mounted in a bespoke container frame
Ontario, Canada November 2021

Our Spiral technology saves money and helps in the delivery of a low carbon future.

Environment & Economy

The economic and environmental benefits of these kind of reductions are significant, and the uses for this technology are many – across municipal, potable and non-municipal wastewater treatment processes.  Applications include washwater recovery at water supply works, use on a range of industrial processes and several different uses within sludge treatment centres.

The technology has also been integrated with PWS’ other flagship technology, a biological nutrient removal (BNR) process called NUTREM®. For this application, it will be used to provide primary settlement to generate fresh sludge to use in the NUTREM® hydrolysing system, as well as a smaller version of the technology being offered to clients to provide SAS thickening.

In addition to the space and cost savings, the reduced visual impact makes the Spiral suitable for urban sites next to areas with public access. It is also an ideal solution for efficient extraction of high calorific primary sludge for Anaerobic Digestion as part of utilities CHP programs.

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.

Saving money and helping to deliver a net zero carbon future.

We have the technology, as they say…

The End ?

Well I suppose I might properly retire one day, but in the meantime I remain truly excited by the huge possibilities for our technology.  I’m very keen to see customers take advantage of them before I hang up my boots just yet.

It’s very nice to have something so innovative and useful to my name and I am proud of what PWS has been able to do with it for future engineering applications.


Article by David deHoxar, PWS Chief Engineer