Fibertex geotextile bags (geobags) for use in on-site desludging wastewater projects, have advantages over conventional methods, which are often unaffordable to authorities and contractors with limited budgets.
Benefits of using geobags for sludge removal include ease of operation, efficient retention of solids, compliance with environmental regulations and cost optimisation. A further advantage is this dewatering system is passive and does not require constant monitoring and maintenance of equipment.
The filtration properties of geotextiles - which are effective in retaining the fine-grained materials found in sewage sludge, while allowing the water to filter through - make these materials suitable in desludging wastewater ponds. The effluent that passes through the woven fabric can then be transferred to a designated safe disposal site, given that it meets the regulations set by the Department of Water Affairs (Policy and Strategy for Groundwater Quality Management in South Africa).
‘When wastewater treatment ponds reach their capacity, the options available are to either build new facilities or to empty the existing ones to make additional space available for waste. Traditional methods of waste containment, which usually require large amounts of space, stringent environmental permits and frequent dredging, are normally unaffordable to municipalities,’ explains Johnny Oriokot, geotechnical engineer, Fibertex SA. ‘A feasible solution needed to be found to dispose of extracted material through the desludging process, which is not restricted by budget constraints and the limited space available at existing wastewater facilities.
‘The use of geotextile dewatering bags is recognised globally as the most efficient and economical method to achieve the required desludging process, to improve the functionality and safety of wastewater treatment works.’
Minimal environmental impact
Fibertex geobags, manufactured from UV-stabilised woven Polypropylene (PP) geotextile materials, are incorporated in the desludging process in wastewater treatment - the process used to convert wastewater into an effluent that can be returned to the water cycle with minimal environmental impact.
Solid particles (sludge) are then separated from the effluent and transported to a designated safe disposal site, or stored in a tailings storage facility at the wastewater treatment plant.
Fibertex geotextile dewatering bags, with high strength seams for a strong and durable dewatering system, are used to capture dredged sludge, whilst minimising water loss. The thread used to stitch the bags has a higher breaking strength than the geotextile itself, providing sufficient tensile strength to the geobags, to withstand the stresses associated with pumping the material at high pressures.
Effective retention of solids
Dewatering bags allow water to flow out through the porous geotextile fabric of the bags, while filtering any solids. The concern of the woven fabric opening size appearing to be slightly larger than the particle size of the dredged sludge material is countered by the formation of a filter cake on the inside of the fabric, with a resultant effective retention of the solids. This creates an equivalent two-stage filter, with filtration efficiencies above 98 percent for fine-grained material filtered through the high-strength woven geotextile bags. Certain geotextile designs are able to retain all particles larger than 10 microns.
In recent local projects, where wastewater treatment plants had reached their maximum storage capacities, the Fibertex solution was to remove sludge from the existing tailings facilities by using geotextile dewatering bags on-site. Fibertex also provided the geosynthetic products required to carry out repairs to existing lining systems that were damaged, and for installation of new lining systems in facilities which previously had none.