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.
This study aims to assess the impact of time on sawdust usage to enhance the behavior of the clay used in landfills. The soil used in this paper was brought from Büyükçekmece region / Istanbul. Four proportions (1, 2, 3 and 5) of the sawdust were added as a percentage of the dry weight of the soil. Soil-sawdust mixtures were compacted with the optimum water content corresponding to each percentage and samples were extracted. The extracted samples were divided into two groups, the immediate tests were performed on the first group while the second group was kept in special containers for long-term tests after 90 days. A series of undrained unconsolidated triaxial tests (UU) and unconfined compression tests (UCS) were performed on the specimens and compared with the row soil, in the immediate tests, the results from the UU triaxial test showed that the undrained shear strength was increased as the sawdust content increased and then decreased, it was conducted that the optimum sawdust content was 3%, it was increased the undrained shear strength by (39.5%) and (41.44%) for UU triaxial and Unconfined compression tests respectively. After 90 days of the curing period, it found that 2% is the optimum sawdust content, it was increased the undrained shear strength by (202.51%) and (176.64%) for UU triaxial and unconfined compression test respectively. In the immediate and long-term tests, the coefficient of permeability increased by (66.66) and (94.44%) as the sawdust increased from 0 to 5 % respectively. Sawdust increases the hydraulic conductivity of the clay. It can be concluded that the sawdust usage has a remarkable effect on the shear strength of the clay for both immediate and long-term tests.
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