Frequently Asked Questions about Dewatering. Our goal is to support our customers in their efforts by providing answers to questions regarding Dewatering Bag products.
1. What are Geotextile Tubes?
Geotextile tubes are flexible in their application and can provide benefits over other dredging dewatering options in the area of cost, quality, and ease of use. Physically they are made up of woven Fabric Geotextile Materials that are designed in such a way to retain suspended solids and sediment and allow water to pass through the gaps in the woven fabric. The dewatering rate and effluent quality will depend on the sediment, system used and the operating conditions.
2. Why is it smart to do a hanging bag test before I purchase a Geotextile Tube?
The hanging bag test is a low cost / low technology approach to assessing the performance of geotextile fabric in combination with a sludge from a potential job site. It can be useful for quick on site evaluations. Evaluating the cake formation. Effluent for water quality testing. Water flow rate. Demonstrating the concept to a client. First hand look at the dewatering characteristics of the sludge. Checking the effectiveness of polymer addition.
3. How does the hanging bag test work?
The hanging bag details (fabric) should be noted and it is suspended on a suitable structure / frame (eg tree, fence, brick and pole arrangement). The bag is typically 3 x 2,5 feet in size and a slurry sample is placed in the bag. (the sample is of typically 5 Gal of sediment that is watered down if required to replicate the condition of the sludge that will enter the bag during the project). The effluent from the bag is collected for evaluation to see the quality and also the time is taken to establish the rate of dewatering (this provides a guideline). The sludge should be checked regularly for the first few hours and then left to stand for 6-8 hour and checked again. It can then be left for a few days to evaluate how dry the sludge becomes and is suitability to be handled during the removal process. Hanging bag tests give an indication of the dewatering characteristics of the sludge and a pressure filtration tests using the selected tube should be conducted on a small scale to establish the consolidation rates. They are typically better than the results achieved in the hanging bag test.
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