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.”