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Veolia Water Solutions and Technologies has announced that Severn Trent Water is using Hydrotech Discfilter technology for tertiary sewage treatment.

The packaged filtration plant has been included on Severn Trent’s tertiary solids filtration framework and the first unit has been supplied to Craven Arms sewage treatment works.

The Hydrotech Discfilter consists of a series of hollow segmented discs that supports a woven polyester or stainless steel mesh.

The discs are mounted on a central shaft.

Influent liquor enters along the centre line of the unit and is distributed radially on the inside of the discs.

The flow passes through the mesh, leaving suspended solids retained on the inner face of the filter elements.

Filtered water is collected in the chamber around the Discfilter and an outlet weir, which is part of the structure, maintains the filtered water level so that the discs are approximately 65 per cent submerged.

This retained volume provides backwash water for filter cleaning.

Filtered water flows over the weir and away to the outfall.

As the retained solids start to blind the filter mesh, the head loss across the Discfilter increases up to a maximum of about 250mm, and the influent liquor level rises.

At a predetermined level a backwash cycle is initiated, which rotates the Discfilter and presents clean mesh to the influent liquor.

At the same time, filtered water from the integral reservoir is pumped at high pressure to jet-wash the dirty mesh.

The dirty backwash water is collected in a trough within the centre of the Discfilter and flows away by gravity to a pump sump for return to the head of the works.

The backwash water volume is typically between one per cent and three per cent of the maximum design flow.

Filtration is continuous throughout the backwash cycle and, once the cycle is completed, the Discfilter stops rotating and awaits the next backwash.

Hydrotech Discfilter modules, in four ranges up to 1,000 L/s, can be supplied on steel frames for building into concrete chambers or as standalone stainless steel tank units.

The modular design is said to make filter selection simple and allows for planning for future expansion.

It also allows flexibility in choice of materials – ABS plastic or stainless steel for the discs, 304 or 316 stainless steel for frames and tanks, and a choice of 10, 20 or 500 micron mesh depending on the application.

Veolia said the small footprint, low headloss, low backwash water volumes, low power consumption and minimum maintenance make the Hydrotech Discfilter a cost-effective and sustainable option.

Veolia Water Solutions & Technologies

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