The study conducts hanging bag tests for understanding the filter behaviors of fine soil particles flowing through geotextiles. Four types of fine particles including reservoir sediment, sludge from sewage plant, river bed sediment and laterite are tested in this study. The study starts with jar tests to select the appropriate polymer coagulants. Different sizes of hanging bags composed of different geotextiles are subsequently used for fine particles filtering through. Moreover, the backwashing and refilling process is also conducted to study its effect on the filtering behaviors. During the tests, the flow rate, sludge water content and water quality of leachate are monitored. Some conclusions are reached from these tests. The hanging bag of multifilament plain weave geotextile retains sludge particles more than the hanging bag of monofilament geotextile does because the multifilament plain weave geotextile is characterized with a smaller pore opening ratio that provides more contact area with sludge particles. The water quality of leachate filtering through multifilament plain weave geotextile is better but the dewatering ability is worse because the clogging phenomenon is more significant. The dewatering effect for reservoir sediment and river bed sediment filtering through geotextiles is significant for the water content of the filter cake deposits in hanging bags reduces considerably. The water content of filter cake is even less than the water content of the sediment processed by belt press device. However, the dewatering effect for sludge from sewage plant filtering through geotextiles is poor for its fine particle has an affinity for water which is too strong to be expelled from gravity drainage. Geotextiles are functional to cleanse water quality of sludge as the suspended solid (SS) is reduced by more than 90 % while the chemical oxygen demand (COD) is reduced by about 75 % to 80 %. The backwashing process that pours water on the outer surface of hanging bags can break the sludge membrane that adheres on the surface of geotextile. Consequently, the service life of hanging bags can be prolonged to some extent. However, the effect of backwashing process is limited because the filter cake deposits in hanging bags basically remain there.
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