A simple, cost effective new method of dewatering sludge is now available in Australia, writes Bill Kelly from CRS Industrial Water Treatment.
The use of geotextilcs for containment and dewatering came about as a result of a major flood event in Holland in the 1950s. It prompted Dutch marine engineers to seek new methods and materials to build structures for coastal defences.
The ensuing development of geotex-tiles for reinforcement and erosion control lead to the application of geoCOfl-tainment technology using high strength geotextiles for containment, dewatering and consolidation of a range of different types of sludge.
High strength permeable membranes with uniquely designed retention properties are fabricated into Geotubes that can be filled with fine grain sludge, hazardous contaminated soils or dredged waste materials. The geotextile's unique weave and fabrication creates small pores that confine the fine grains of the contained material.
Excess water drains from the small pores in the geotextile resulting in effective and efficient volume reduction Of the contained material and allowing the Geotube to be repeatedly filled. In many cases the decanted water is ol a quality that can be returned to natural watercourses or reused.
After the final cycle of filling and dewatering, the retained fine grain materials can continue to consolidate by desiccation because the residual water vapour escapes through the gco textile. Dried solids of up to 35 per cent an attainable depending on sludge conditioning, ambient conditions and length of time the material is left in theGeotube. Once dewatered the large lube should be opened, the contents removed with a front-end loader and shipped to a landfill via dump trucks.
Using Gcotubes eliminates the need for expensh e capital equipment and associated labour and maintenance, and does away with periodic tendering for dewatering contractors by allowing clients to effectively control their dewatering and disposal costs.
Some of the main applications of this new technology are to be found in municipal sewage treatment plants, the paper and pulp industry, industrial sludge and contaminated marine sediment dewatering.
In municipal sewage treatment plants Geotubes are used to dewater consolidated sludge from digesters and lagoons. In most cases the dewatered effluent is clear and safe enough to be returned to the plant. This greatly reduces the volume of sludge and the cost of disposal, while allowing the continual operation of digesters and lagoons. Municipal users of Georubes in Australia include Water Corporation in WA, South Gippsland Water in Victoria and numerous councils in NSW.
Brian Ashworth, the operations manager at South Gippsland Water, has used Geotubes at its drinking water plant at Fish Creek and for sewage sludge dewatering at its Leongatha and Korrumburra sewage treatment plants.
'In my experience of the water and wastewater industry this is one of the only technologies to exceed my expectations/' he said. 'By using the bags I have Baved thousands of dollars in cartage of alum sludge over the last few months (at fish Creek).'
Similar results have been experienced overseas in (he power industry and paper and pulp market, with lleotubes being used to dewater large volumes of accumulated sludge without impacting upon plant operation. They have yielded tremendous operational cost savings.
It has also been used successfully to dewater fine grained, contaminated dredged material th.it contained dioxins, PCBs, PAHSj pesticides and heavy metals. Users include the Port Authority of New York and New krscv, the Miami River Marine GfOUp and the Port of' Oakland.