The Value of Chemical Conditioning with Geotextile Tube Dewatering

Many types of high moisture content slurries are dewatered in geotextile tubes. Slurries can include dredged sediment from waterways and waste from industrial processes. Tubes can also be very useful for dewatering and containing contaminated sediments. Geotextile tubes have been successfully employed in several large remediation projects. Chemical conditioning of the slurry with polymers can provide many benefits to a dewatering project. The category of polymers covers a wide range of chemical additives including flocculants and coagulants. Polymers can dramatically reduce turbidity in the decant water and can bind solid contaminants with the material being retained. There are many chemicals designed for treating waste streams, having a variety of charges, weights and chemical properties. These will be discussed in this paper, as specifically related to their use with geotextile tubes. The effectiveness of a tube dewatering project is often measured by the retention of solids particles and the rate at which clean water is released. The correct dosage of polymers can control the permeability of the filter cake, which in turn, impacts these two measures of effectiveness. Decant water resulting from the dewatering process must be also accounted for in the project design. If the decant water is contaminated or excessively turbid, chemical conditioning of the slurry prior to being pumped into the tube can be a very effective solution. In the design phase, bench-scale tests are conducted to determine the optimal chemicals and their dosage rate. The use of Buchner funnel tests and hanging bag tests will be described. Case histories will also be presented which describes the use of chemical conditioning with geotextile tube dewatering. Results from several years of testing a wide range of slurries will be compared and contrasted to other literature on the subject. Quantitative results from the bench scale tests will be compared to the full scale results.