Soil drainage clogging mechanism under vacuum preloading: A review
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Clogging
Consolidation
Clogging
Subsurface Flow
Constructed wetland
Filtration (mathematics)
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The recharge efficiency during artificial groundwater recharge (AGR) is reduced primarily by clogging that is triggered by suspended particles. However, there are loopholes in the current standards of recharge-water quality for clogging control during AGR, and the threshold values of turbidity to prevent clogging have not been reasonably determined. In this study, secondary effluents from wastewater treatment plants (WWTPs) were injected into saturated sand columns to simulate the process of AGR. Batch experiments under different turbidity conditions were conducted, and the numerical modeling of particle transport and deposition was performed to assess the clogging processes. Theories of single-collector contact and interfacial interaction energy were applied to elucidate possible microcosmic mechanisms. The results showed that the diluted secondary effluent (SE) with turbidities of 0.540 ± 0.050, 1.09 ± 0.050, and 1.84 ± 0.060 NTU caused considerable clogging in the porous media, which decreased the relative hydraulic conductivities (K/K0) by 13.2%, 17.6%, and 83.6%, respectively. The filtered SE with a turbidity of 0.160 NTU did not cause clogging, and K/K0 was reduced by only 1.70%. The clogging was attributed to the deposition of suspended particles in the sand matrix because they have a high collision efficiency (0.007–1.98) and attachment efficiency (0.029–0.589 kBT). Finally, this paper recommends that the turbidity of the recharge water should not exceed 0.500 NTU during AGR practices.
Clogging
Turbidity
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Filtration is a very basic and primitive technique of water treatment. For many remote, under-privileged and poor communities, this is the only pre-treatment of drinking water prior to boiling. With the emergence of arsenic contaminations in many groundwater aquifers, the filtration became imperative for many communities around the world. However, after repetitive/continuous uses, clogging of the filter media is obvious, which eventually causes poor performance of the filtration process. Backwashing is a common technique being used for the recovery of the filtration capacity of clogged filter media. This study presents development of a simple clogging and backwashing efficiency model for a special filter media. "3rd generation IHE family filter" was developed by UNESCO-IHE Institute for Water Education and widely used for treating arsenic-contaminated water in many countries including Bangladesh. Several field tests were conducted in three different sites in Bangladesh having different qualities of influent water. Developed model coefficients were derived using the collected data on flow measurements through the device during successive clogging and backwashing periods up to four months. Developed model with the selected model coefficients can simulate field measurements on flow retardation and recovery with good accuracy. Eventually, selected model coefficients for three sites were correlated with the respective influent water quality. It was found that the coefficients are linearly correlated with the iron and ammonium contents of inflow water.
Backwashing
Clogging
Filtration (mathematics)
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Since groundwater is one of the main factors that affect the stability of highway slopes in mountainous regions, a smooth drainage is of importance for the safety of cut slopes. After years of service, the cut slopes of highway are often characterized with drainage problems or even drainage failures that threaten the stability and safety. In this paper, the clogging mechanism of drainage holes in highway cut slopes is firstly clarified through on-site survey. The soil and blockage samples are collected from typical slopes for laboratory tests and analysis, and the results reveal that all the blockages are made of fine-grained particles from the slopes. Scanning electron microscope (SEM) images indicate that the blockages penetrate the drainage pipe wrappings to form the clogging. The combined effect of clayey soil, chemicals, and biological clogging exacerbate the clogging process around the drainage pipes. Laboratory tests are also performed to simulate the CaCO 3 crystal clogging around the drainage holes, and the microstructure of the clogged geotechnical screens and geotextiles is observed by scanning electron microscope as well. The results confirm that the amount of CaCO 3 crystal attached to the drainage pipe surface increases with the time. The single-layer structure of screens does not facilitate the three-dimensional clogging as in the case of geotextiles. After soaking in diluted hydrochloric acid at a pH of 5.0, there is no significant decrease of CaCO 3 crystals attached on the screens and geotextiles. However, the CaCO 3 decrease is apparent after soaking in the hydrochloric acid at a pH of 3.0. The clogging of drainage holes can be classified into two stages according to the laboratory tests and acid soaking, and the relationship and characteristics between the two stages are summarized.
Clogging
Watertable control
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