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The sludge from a treatment plant is largely water. Typically between 90% and 95%.
This means that when transporting a truckload of sludge for disposal, you are transporting—and paying for—mostly water. Dewatering exists to solve this problem. Using geobags is one of the most economical ways to do it.
What is a geobag?
A geobag is a tube made of high-strength geotextile — a permeable synthetic fabric designed to retain solid particles while allowing water to pass through.
The logic is simple: the sludge is pumped into the geobag; the water drains through the pores of the fabric; the solids are retained. Over time, the material inside the geobag progressively concentrates.
Geobags are manufactured in different capacities and are placed in an area prepared with a drainage system to collect the liquid that runs off—the filtrate, which returns to the treatment system.
How does the process work?
The operation follows four steps:
1. Area preparation
The site receives a waterproofed base with a slope and a drainage system, ensuring that all the filtrate is collected and directed back to the treatment process — there is no liquid discharged into the soil.
2. Sludge conditioning
Before entering the geobag, the sludge undergoes chemical conditioning with a flocculant polymer. This step is crucial: the polymer causes the fine particles to aggregate into larger flocs, which are retained by the geotextile instead of passing through the pores.
“The geobag is not just a filter. What defines the result is the chemical conditioning. A poorly dosed polymer means fine solids passing through along with the clarified water — and then you have an expensive geobag that hasn't dehydrated anything. The correct dosage is defined by prior testing with the client's actual sludge, not by a table.”
— Luiz Varandas, Project Coordinator at TSL
3. Filling
The conditioned sludge is pumped into the geobag. Filling is done in cycles: it is partially filled, allowed to drain and consolidate, and then topped off again. This allows for better utilization of the structure's capacity.
4. Dehydration and consolidation
After the final filling, the geobag remains at rest. The water continues to drain by gravity and the material gradually consolidates. This period varies from a few days to a few weeks, depending on the type of sludge and the weather conditions.
Geobag or centrifuge: how to choose
Both technologies deliver the same thing — separating water from solids — but in very different ways.
| Criterion | Geobag | Centrifuge |
|---|---|---|
| Time | Days to weeks | Continuous, immediate result. |
| Required area | Large — needs a yard | Small — compact equipment |
| Cost | Minor | Bigger |
| Energy | Virtually none (gravity) | Continuous electrical consumption |
| Operation | Simple, low labor requirements. | Requires a dedicated operator. |
| High volume at once | Excellent | Limited by the equipment's flow rate. |
| Urgency | Bad | Excellent |
In practice, the choice boils down to two questions: Do you have available space? Do you have time?
If the answer to both is yes, the geobag is almost always the most economical option. If not — if the available area is limited or the deadline is short — the use of decanter centrifuges It is justified.
Where are geobags used?
- Industrial wastewater treatment plants — biological and chemical sludge
- Dredging operations — sediments removed from lagoons and reservoirs.
- Mining — tailings and process sludge
- Sanitation — sludge from wastewater treatment plants and water treatment plants
- Cleaning of stabilization ponds
The application in dredging deserves special mention: the sediment removed from the bottom of a lagoon has a very high water content. Without dewatering, the volume to be transported would be prohibitive. The geobag is often installed next to the lagoon itself, receiving the pumped material directly into the lagoon. industrial dredging.
Frequently Asked Questions
What is a geobag?
It is a high-strength geotextile tube used to dewater sludge. The fabric retains the solid particles and allows water to drain, significantly reducing the volume of the material.
How long does dehydration take in a geobag?
From a few days to a few weeks, depending on the type of sludge, the volume, the chemical conditioning applied, and the weather conditions. It is a gravity-driven process, without mechanical acceleration.
Can the geobag be reused?
No. The geobag is for single use only. At the end of the process, the entire set (geotextile + dehydrated material) is disposed of according to the waste classification.
What happens to the drained water?
The filtrate is collected by the drainage system of the prepared area and returned to the wastewater treatment system. There is no direct discharge into the soil or water body.
Geobag or centrifuge: which is cheaper?
Geobags are less expensive, mainly because they consume no energy and require little labor. On the other hand, they need available space and time. Centrifuges cost more, but deliver immediate results in a smaller space.
Is it necessary to use polymer?
In practice, yes. Without chemical conditioning, fine particles pass through the pores of the geotextile along with the water, compromising solids retention. The correct dosage is determined by prior testing with actual sludge.
TSL Engenharia e Serviços executes sludge dewatering projects with geobags and decanter centrifuges, including preliminary conditioning testing, site setup, and final disposal of the material.
