The deHoxar Spiral Separator (dHSS) is a very compact gravity settlement device, invented by David de Hoxar utilising the operational experience gained working within the UK Water and Sewage Companies. David developed the dHSS in conjunction with Southern Water and the technology is now in operational use on twelve wastewater and potable water treatment sites around the UK.
|Municipal wastewater treatment for Primary settlement of normal domestic sewage / Primary settlement with co-settlement of secondary (or other recycled) sludge / Activated sludge final tank / Humus tank / Other secondary settlement duty / Sludge liquor settlementPotable water treatment as a clarifier or for wash water recoveryNon-municipal wastewater treatment or municipal with a high content of trade waste||3% of the site area is required when compared to conventional tanks and only about 25% when compared to 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 there is typically 1% the volume of air to treat compared to conventional tanks.|
Non-municipal wastewater treatment or municipal with a high content of trade waste 3% of the site area is required when compared to conventional tanks and only about 25% when compared to lamella separators.Potable water treatment as a clarifier or for wash water recovery
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 there is typically 1% the volume of air to treat compared to conventional tanks.
In addition to the above the reduced visual impact makes it suitable for urban sites and 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.
The dHSS takes the rectangular plate packs found in lamella separators and twists them to allow them to fit inside a circular treatment tank. Creating a circular plate pack in a circular tank allows the plates to be rotated to match the upflow rate within the tank. This improves the settled water quality and also minimises wasted space within the tank by virtually eliminating “dead spots”.
This is a true cross flow lamella design. The sludge leaving the plate pack does not pass through the inflow entering the plate pack. Instead it is concentrated in the annular gap between the plate pack and the tank wall. This means that instead of the thin sludge we normally expect from lamellas, the dHSS produces thickened sludge.
As the dHSS is a true cross flow design, there is no process limit to the depth of plate pack that can be used. The depth of plate pack is only limited by what can be practically built. The dHSS can separate any solid from a liquid (or two liquids) as long as there is a difference in specific gravity. If a sample of the mixture will separate by gravity in a laboratory beaker, then PWS can design a dHSS to separate a continuous flow of the mixture.
Whilst the original invention was as a water supply works clarifier, the majority of the applications to date have been on primary settlement of sewage and of these most also cosettle secondary sludge, eliminating the need for a sludge thickening stage.
As a primary settlement tank the dHSS requires about only 3% of the land area required for conventional settlement tanks and less than one third of the land area required for normal counter current lamella separators. Other applications in the reference list of operational Spiral Separators include; washwater recovery at a water supply works, use on a range of industrial processes, applications and different uses within sludge treatment centres.