Reed beds to replace sludge lagoon system

Essex & Suffolk Water, part of Northumbrian Water, is trialling ARM sludge treatment reed beds for the ferric sludge produced in drinking water treatment processes at its Hanningfield Water Treatment Works. Applying this technology to drinking water treatment is "a world first", accord to ARM.

The trials are to see how well reed beds treat sludges generated as a by-product of drinking water production. Plans are now in place to design a full-scale system covering over four hectares. The reed beds will replace Hanningfield’s existing sludge lagoon system.

Paul Grimwood, project manager – Investment Delivery at Essex & Suffolk Water, said: “We see reed beds as a good solution because of their low energy requirements, reduced transportation needs and they use no chemicals for dewatering. Their daily operation will require minimal input creating a significant saving in our annual maintenance and operational budgets.

“The successful delivery and operation of this scheme will provide a sustainable dewatering system which could potentially be rolled out to other treatment sites across the business.”

ARM’s Tori Widdas said: “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.

“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 running a trial on alum sludges.”

Widdas said Denmark has used 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.

“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.”

Widdas continued: “Reaching capacity after ten to 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.”

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