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Compact Automatic Filter Enables Final Effluent Recycling

Friday, June 03, 2011 by Rotork

A compact Rotork actuated automatic backwashing filter is providing reliable, efficient and economical filtration of final effluent for drum thickener washing duty at a sewage treatment works on the south coast of England. Using filtered final effluent is saving the operator the considerable cost previously incurred by the use of mains water for this duty.

The Cross Phoenix Type R filter is installed at the Wessex Water Weymouth Sewage Treatment Works, a flagship Wessex Water site utilising state-of-the-art activated sludge treatment in a fully enclosed environment. The Cross filter incorporates a Rotork IQTF electric rotary valve actuator to operate the integral backwashing valve, reversing the flow to each of the unit's six stainless steel filter coils in sequence, without interrupting the continuous filtration performance.

Backwashing is triggered automatically by a pressure differential switch that senses the increased pressure drop across the filter caused by the build-up of debris on the filter coils. The filter is rated at two hundred microns and operates at a maximum flow rate of 18l per second. The compact installation at Weymouth incorporates a pump on the inlet from the adjacent final effluent holding tank which supplies the filter.

The pump increases the inlet water pressure to 6 bar, providing enough pressure to ensure both efficient washing of the drum filters and backwashing of the filter coils. Cross filter coils utilise a patented 'zero gravity' design, whereby the coils open evenly along their entire length during backwashing to ensure completely efficient cleaning without any mechanical scrapers or other moving parts.

The Cross Phoenix Type R filter has been developed specifically for the water and waste treatment industry and claims to be the only filter of its type to use a Rotork actuator for this type of application. The IP68 watertight actuator provides a single electrical interface for power and control cabling and offers the proven benefits of Rotork actuation technology as standard, including non-intrusive setting and commissioning, operational data-logging, diagnostics and compatibility with water industry-preferred digital control protocols including Profibus. Unlike other filter designs, installing the Phoenix Type R filter is claimed to be as simple as installing a single motorised valve.