Which method is best for your pond cleaning project- geotextile bags or belt press?
Geotextile bags and mechanical dewatering machines (belt presses, filter presses, or centrifuges) dewater the solids pumped from a hydraulic dredge. Each method has its own advantages & disadvantages.
Geotextile bags generally speaking are cheaper than using a belt press- especially on smaller projects. However, as the volume of solids to be dewatered increases, the costs of the total site work, handling, and final disposal can match or become more expensive than mechanical dewatering. Also, if the dewatering does not occur effectively, extra costs will be incurred to clean up and solids that were not effectively dewatered. Geotextile bags require lots of flat land. If the bags are placed on too great of a slope, they can slide or roll- and there is no way to stop that much weight from moving! Biological sludges that are very old and "light" require large amounts of polymer dosing. Press Rentals has seen many paper mills or municipal WWTP plan pond cleaning projects where the polymer was not dosed right and the bags never dried. This forced the customer to let them sit permanently. Geotextile bags can also tear if pumped too full. Once spilled, extra costs is incurred that was not built into the bid. Press Rentals advises customers that granular solids in ponds such as sand, ash, coal, etc. work easiest with geotextile bag dredging projects.
Mechanical dewatering methods like a belt press or centrifuge allow for finer polymer dosing (useful on biological sludges like paper waste or municipal wwtp sludge). Once the material is pumped thicker or lighter, the press operator can make the effective changes. A belt press dewatering operation requires a much smaller footprint than a geotextile bag. Once dewatered, the filter cake can be loaded straight into a dump truck for disposal. Mechanical dewateirng might have larger up front costs that geotextile bags, but once the project is complete, there is no second guessing that the solids are removed.