Essex & Suffolk Water - part of Northumbrian Water Limited - has appointed market-leading ARM to design sludge treatment reed beds for the ferric sludge produced in its drinking water treatment processes at its Hanningfield Water Treatment works.

"Reed beds were compared against traditional mechanical dewatering options - mainly centrifuges - and were preferred because of their lower capital and operating costs and environmental aspects" said Tori Widdas of ARM Ltd.

"We have teamed up with Danish company Orbicon to devise a world first - reed beds designed specifically to treat drinking water sludges. We've proved the technology works on ferric sludges and are currently running a trial on alum sludges," says Tori Widdas.

"Denmark has been using reed beds to treat sewage sludges for 20 years. They use much deeper beds than a standard horizontal sub-surface or vertical flow reed bed. A number of basins are individually dosed - in rotation and with calculated resting periods - with sludges comprising approximately 2.0% dry solids," said Tori Widdas.

"The sludges then dewater leaving a sludge residue on the surface of the bed while the filtrate percolates through the system. The sludge residue mineralizes, reducing by up to 200 times its original volume.

"Reaching capacity after 10-15 years, Denmark has found reed beds make a sustainable long-term solution to treat 80% of all its sewage sludges. Residues are classified as an Enhanced Treated Product, excavated and spread on land as fertilizer. The beds are then ready to be dosed with sludge again," said Tori Widdas.

Applying this technology to drinking water treatment is a world first and will work in a similar manner. The final sludge residue produced can have up to 60% dry solids content. This is achieved through dewatering, evapotranspiration and mineralization.

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