Questions about Dewatering Products
Below is a small selection of frequently asked questions about dewatering and GEI Works' dewatering products. Our goal is to support customers by providing answers to questions regarding Dewatering Products.
1. What is dewatering?
Dewatering is the removal of water from solid materials, such as soil, sediment, sand, and sludge. There are multiple ways for the dewatering process to occur, including centrifugation, filtration, and other separation processes.
2. Which dewatering products do you have? What do they do?
GEI Works offers three dewatering products. All provide a way to retain suspended solids and sediment, while allowing water to pass through the tiny gaps of the fabric. The dewatering filter rate and effluent quality depends on the sediment, system used, and the operating conditions. While similar in design and use, their applications vary between projects and job sites.
- Dewatering Bags provide standard dewatering filter options for small projects, such as pond dredging and construction site runoff. They are generally square or rectangular in shape.
- Dewatering Socks are specifically designed to filter water runoff from pipes and hoses. They are narrower in size and are an economical choice for smaller jobs.
- Dewatering Tubes are larger in size than regular dewatering bags and socks. They offer filtering for extensive, substantial projects, such as large-scale sludge dewatering jobs for power plants, as well as coastal protection projects used as breakwater tools.
3. What is the difference between dewatering bags and dewatering tubes?
The first difference between dewatering bags and tubes is size. Able to handle lesser dewatering requirements, the bags range in size from 6' x 6' to 15' x 25'. By contrast, dewatering tube sizes start at 50' in length and 15' in circumference. The maximum size available is 250' in length and 90' in circumference.
The second difference between the two dewatering products is their construction materials. Dewatering Bags are made with either 6 oz. or 8 oz. nonwoven geotextiles, depending on the filtering requirements of the job site. Dewatering tubes use a woven polypropylene geotextile with higher tensile strength to handle greater amounts of sediment and sludge.
4. What should I consider when choosing between dewatering products?
Choosing dewatering products depends greatly on the project and location. There are a number of factors to consider:
- Quantity and Type of Sediment
- Water Flow Rate
- Available Space
- Water Volume
- Type of Application
- Timeline and Budget
5. When do I use dewatering socks?
When filtering water directly from hoses or pipes, dewatering socks are the most appropriate choice. Diameters range from 4" to 16" to fit around most pipe sizes. Each pipe sock is secured via clamp, so fitting can be approximate as long as the pipe is smaller than the sock opening. The concentration of sediment and debris is an important consideration, as dewatering socks do not have as much volume for containment as other dewatering products.
6. Why would you to do a hanging bag test?
The hanging bag test is a low cost and low technology approach to assessing the performance of dewatering products in combination with sludge or slurry from a potential site. It can be useful for quick evaluations and demonstrations of the following:
- 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
7. How does the hanging bag test work?
Hanging bag tests identify the dewatering filter characteristics of the sludge. It works using the following steps.
After noting the specifications of the bag, suspend the bag on a suitable structure or frame (eg. tree, fence, brick, and pole arrangement). Place a slurry sample in the 3' x 2.5' bag. The sample is typically 5 gallons of watered-down sediment to replicate the condition of the sludge entering the bag during the project.
Collect the effluent from the bag to evaluate the quality. Note the time to establish the rate of dewatering.
The sludge should be checked regularly for the first few hours before standing for 6 - 8 hours. Leave the sludge for a few days to evaluate how dry it has become and its handling suitability during the removal process.
Performing a pressure filtration test is also recommended to establish the consolidation rate of the selected tube.
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