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Dewatering technology optimises dredging operation

As part of its quest to find innovative treatment and reuse solutions for difficult and wet waste materials, Land and Water Services (LAWS) has been using TenCate Geotube technology on a live dredging contract at Anglian Water Services’ Pitsford Water Treatment Works.

TenCate Geotube bags are constructed of high strength, permeable, specially engineered geotextiles designed for containment and dewatering of high moisture content sludge and sediment.

They are available in a variety of sizes, depending on volume and space requirements.

Sludge mixtures are delivered directly to the TenCate Geotube containment system via pipeline. Constant monitoring of the input feed pipes allows the dedicated process engineer to adjust and inject the correct proportion of polymers and coagulants into the pump mix immediately prior to it entering the bag. {{image2-A:R-w:320}}

Once inside the bag, the sludge and flocculent mix causes the rapid binding of the free sludge particles, liberating clean water. The clean water is then ejected from the micro-pores of the bag and returned to the water body, leaving high concentrates of the sludge within the bag.

While up to 99 per cent of the particulates are retained within the bags, the bulk of the water is liberated instantly.

After the final cycle of filling and dewatering, the solids remain in the bag and continue to increase in density due to desiccation as residual water vapour escapes through the fabric. As a result, when the bag is finally opened, the sludge concentration has significantly increased, leaving a dry “soil” to be excavated for recycling or controlled disposal.

Geotube bags can be configured to suit individual sites with minimal space and/or differing sludge make-up using expert technical and installation teams. {{image3-A:L-w:320}}

The containers are arranged on a temporarily lined surface so any clean water that is released from the bags is swiftly returned to the water body through gravity. Where appropriate, drinking water quality polymers are used to ensure the returned water does not negatively affect the original water body.

At Pitsford Water Treatment Works, LAWS successfully completed the dredging and recovery of more than 2500m3 of fine particle sediments, resulting in a final retained volume in the dewatered bags of less than 400m3.

LAWS divisional business manager Steve Massey said: “This method delivers a solution to clients whereby they can dramatically reduce the quantity of sludge for disposal in a quick and safe manner, and with minimal impact on the environment.”

Gary Cunliffe, bio-solids recycling and environmental compliance manager for LAWS, added: “Using the Geotube technology allows us to separate solids from liquid at site and provides savings on haulage and disposal costs, as well as drastically reducing the carbon footprint of lagoon sludge dewatering.”

This article was originally published in the July 2014 issue of Quarry Management (UK) and is reprinted with kind permission.

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