Polyacrylamide-based conditioners have become an essential component of the geotextile tube dewatering processes. These conditioners act as flocculants, binding fine sediments through charge neutralisation and particle bridging, resulting in faster dewatering rates and greater retention of fine sediments. Recently, however, momentum has begun to shift towards the use of sustainable materials. Natural flocculants, such as starch and chitosan, are increasingly being tested as an attractive alternative to synthetic polymers. Researchers have identified a number of natural flocculants, polysaccharides and polysaccharide derivatives in particular, as candidates for dewatering applications. In this study, the dewatering performance of four soils (sand, silt, kaolin, and natural organic soil) was evaluated with synthetic and starch-based flocculants. Dewatering performance of five cationic starch-based polymers with charge densities ranging from 0.38 to 0.94 meq/g and molecular weights ranging from 5 3 10 4 g/mol to 5 3 10 5 g/mol were compared with five cationic acrylamide-based polymers with charge densities that ranged from 1 to 3.05 meq/g and molecular weights that ranged from 10 3 10 6 to 20 3 10 6 /mol. The cationic polyacrylamides and cationic starches were selected with a wide range of charge densities and molecular weights in order to study the effect of flocculant properties on the flocculation and dewatering performance of the used soils. The optimum dose of each flocculant was determined using the jar test. Additionally, pressure filtration tests were performed to determine the dewatering rates and filter cake properties. Test results showed that the flocculants' properties, especially charge density, have a significant effect on the optimum dose. The optimum doses of the cationic starch flocculants were two to four times higher than the cationic polyacrylamide polymers. Additionally, it was found that the cationic starches were more effective in minimising the turbidity of the natural organic soils than the cationic polyacrylamides. Finally, the cationic starches allowed for a 900% increase in dewatering rate in comparison with the soil samples that were tested without flocculants.
The use of polyacrylamide (PAM)-based flocculants has become an essential component of most geotextile tube dewatering projects. Although knowledge of the residual flocculant concentration in geotextile tube supernatant and effluent is essential to the safe use of PAM-based flocculants, residual flocculant concentration is not commonly measured in geotextile tube dewatering operations. Furthermore, there is no ASTM standard test method for measuring residual flocculant concentrations in water. This paper presents a comparative study of two different methods that are commonly used to measure residual flocculant concentrations in water: the Streaming Current Detection (SCD) method and the China Clay Settling Rate (CCSR) method, to evaluate their applicability to the geotextile tube industry. The comparison is based on an analysis of measured residual PAM concentrations obtained for five different cationic PAM polymers used to flocculate Tully fines soil. Optimum flocculant doses for the Tully fines soil were determined using the jar test (ASTM D2035-08) for three different solids concentrations by mass (5, 15, and 33 %). The SCD and CCSR methods were performed on the supernatants of Tully fines that were conditioned at their optimum doses and at concentrations 50 % above their optimum dose. Laboratory test results showed that both the SCD and CCSR methods produced similar residual PAM concentration results for the polymer/soil combinations tested. The SCD method, however, produced more consistent and repeatable results in comparison to the CCSR method. The SCD method was also easier to use and could be performed in shorter amounts of time than the CCSR method. Based on the results, it is recommended that the SCD method be standardized and used to measure residual PAM-based flocculant concentrations in geotextile tube supernatant and effluent.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.