As part of an on-going programme by Anglian Water Services Plc to empty final effluent settlement lagoons, Land & Water Services Ltd received an order to dredge approx 2500m3 of Iron sludge from No.1 lagoon at Pitsford Waste Water Treatment Works, Northamptonshire.
Application: Cleanout of an Iron Sludge Lagoon.
Location: Anglian Water Services Plc. Pitsford WTW—Northamptonshire.
Product: Tencate’s Geotubes®– Dewatering Technology.
Contractor: Land & Water Services Ltd. (LAWS)
The most cost-effective method for this particular project was to use a Tencate Geotube® Dewatering System, this being the most cost effective and simple solution to de-sludge / dewater the lagoon’s difficult wet waste material(Iron Sludge). Anglian Water’s Biosolids team have been keen to find innovative solutions to dredge and dewater Iron sludge’s, reduce volumes, retain and reuse silts for their Biosolids operation, at significant reduced cost.
Prior to any Geotubes® dewatering project a full set of tests are undertaken to establish the suitability of our technology, this enables us to set up the correct methods and to deliver to the client a rapid and successful dewatering operation, that meets all expectations.
Using this type of technology dredging work can be conducted with the water remaining in the lagoon, which negates the need for expensive dewatering, fish rescue and habitat protection measures…..the “Status Quo” is maintained throughout the operation. At Pitsford the bankside access was acceptable and a dipper mounted, high capacity sludge pump was fitted to a LAW’s 52 long reach excavators.
Geotubes® are available in a variety of sizes, depending on your volume and space requirements; on this site we used three 1.83M circumference x 20M long Geotubes®, the tubes were sited within an impermeable bund. The sludge mixture was pumped direct to the Geotubes® containment system through a 150mm modular pipe system. To promote flocculation, specially selected, environmentally friendly polymer and coagulant were added to the sludge just before it is pumped into the Geotubes®; this makes the solids bind together and the water separate.
Constant monitoring of the input feed pipes enables the dedicated process engineer to adjust and inject the correct mix of polymers and coagulants to the pump mix immediately prior to it entering the bag. Once the dewatered sediments have settled the filling process was repeated over and over again until the Geotube® container was full. The dredging process was able to remove all the sludge from within the lagoon over a 7 day period.
Over 99% of the solids were captured within the Geotubes® In the Geotubes® rapid binding of the sludge takes place and through the pumping pressure the rapid dewatering immediately removes the bulk of the water, the clean water is ejected through the micro-pores of the geotextile. The water is captured within the bund and channelled straight back into the lagoon, leaving high concentrates of sludge within the Geotubes®. Water samples are taken for the client’s analysis.
After the final cycle of filling and dewatering the solids will remain in the Geotubes® and continue to increase in density due to desiccation as residual water vapour escapes through the fabric. After 30 days the silts were tested and the majority of the silts had reached a 25% dry solid state. At Pitsford the Land & Water’s specialist team successfully completed the dredging and dewatering of more than 2500m3 of fine particle sediment (iron Sludge), the final result after an 8 week drying period will be a reduction to approximately 750m3.Steve Massey, Land and Water’s Divisional Business Manager commented:
“This method delivers a solution to Clients where they can dramatically reduce the quantity of sludge for disposal with minimal impact to the environment in a quick and safe manner.”
Gary Cunliff, Biosolids Recycling & Environmental Compliance Manager for Anglian Water Services Plc, commented:
“Using the Geotube technology will enable us to separate solids from liquid at site, and provide savings on haulage, and disposal costs and drastically reduce the carbon footprint of lagoon sludge dewatering”
Download Case Study PDF Case Study AWS Pitsford