Source Of Silt Research Articles

Predicting colloidal fouling of tap water by silt density index (SDI): Pore blocking in a membrane process

Colloidal fouling of reverse osmosis (RO) elements can seriously impair the performance of membranes resulting in loss of productivity. The source of silt in water is varied and often includes bacteria, clay, colloidal silica, and corrosion products. Various pre-treatment chemical can be used to agglomerate the fine colloidal particles which in-tern can be removed easily however if the incorporation of pre-treatment chemicals with the fine colloidal particles fails then these pre-treatment chemicals can also become a source of membrane fouling. In addition, cationic polymers may co-precipitate with the negatively charged anti-scalants resulting in membrane fouling. Several methods have been proposed to predict the colloidal fouling potential of feed water such as the modified fouling index (MFI) and the most commonly used silt density index (SDI). SDI is an important design parameter for an RO membrane water treatment process. In this investigation the effect of SDI index was investigated to predict the fouling tendency of different pore size membranes. The SDI index showed elevated values (~12) with big pore size (2, 3, 5, 10μm) membranes however lower fouling index values (~6) were recorded with membrane pore sizes near to 0.45μm even with different kind and make of membranes.

Provenance and Geochemical Characteristics of the Silt and Clay Fraction in the Taklamakan Desert, Northwestern China

To advance understanding of the provenance of the silt and clay fraction (particles <0.063 mm in diameter) in the Taklamakan Desert, where dust events occur frequently, we have investigated the spatial distribution and geochemical characteristics of the silt and clay content of surface sediment in the region. The mean PM10 (particles <0.01 mm in diameter) and PM50 (particles <0.05 mm in diameter) content of the surface sediment of the mobile desert were <0.97% and <3.98%, respectively, which was lower than for the Gobi Desert (PM10 = 2.13–6.46%, PM50 = 7.94–20.86%) and the degraded land surrounding the Taklamakan Desert (PM10 = 3.71–13.70%, PM50 = 12.33–32.29%). These results indicate that the Taklamakan Desert is surrounded by potential sources of silt and clay. The relationships between TiO2 and Fe2O3, MgO, V, and Zr confirm that the geochemical composition of the silt and clay fraction have striking spatial differences in the interior of the Taklamakan Desert. Three regions with different silt and clay fraction provenances were identified: the Southeastern (I), Northeastern (II), and Western (III) deserts. Homogeneous geochemical characteristics of the silt and clay fractions from the Southeastern (I) Desert, Gobi Desert and degraded land surrounding the Taklamakan Desert, under prevailing wind conditions, means that the same sources of silt and clay fraction source existed among these areas. The significant differences in the geochemical characteristics of the silt and clay fraction from upwind degraded land, the Western (III) Desert and the Northeastern (II) Desert, indicate that they are sourced from different locations.

Collapse Mechanisms of Low Cohesion Compacted Soils

Despite the knowledge of collapse phenomena, there have been many documented cases presented in the literature of compacted fills, earth dams, and road embankments which failed at least partially as a result of wetting-induced collapse. Two aspects of wetting-induced collapse not fully explored for compacted silty-sands are the magnitude of collapse and the fabric alteration after wetting. This paper presents the results of two studies of collapse potential of such soils using Double-Oedometer Tests and Scanning Electron Micrographs (SEM's). In one study, silty-sand soils compacted dry of (less than) optimum water content at 90 percent of Modified Proctor maximum dry density showed appreciable magnitude of collapse upon wetting. In the second study, similarly prepared soils with a lower clay content indicate little to no collapse. The sand component of each soil is similar; however, different sources of silt were used in each study. SEM's showed that the silt of appreciably collapsible soils is more angular. Also, clay binds silt grains together leading to a more open structure. The clay quantity triggers the collapse of these soils more than the removal or reduction of capillary force.