Water treatment in tunnelling by flocculation

Bentonite is a swelling clay mineral with a strongly negatively charged surface. It binds water and forms stable suspensions, which is exactly why it is used for face support. For dewatering, that stability has to be broken deliberately.

With bentonite-rich slurry, cationic polymers or a combination of coagulant and polymer often work best. Where rock flour from sandstone or limestone dominates, an anionic polyacrylamide is often sufficient. Polymer demand tends to be higher with bentonite than with pure rock flour. Which product works, and at what dose, is shown by the lab test on your sample, not by a data sheet.

The chamber filter press produces a stackable cake that is removed by skip or tipper. Bentonite-rich cake holds more water than cake from pure rock flour, so the achievable dry solids content depends heavily on the bentonite share.

Before removal, the landfill or recycler will usually ask for a waste classification analysis. They often also ask which flocculant was used, so keep the safety data sheet on site. Whether the cake can be reused, for instance in earthworks, is decided case by case on the basis of that analysis. Either way, a stackable, transportable consistency is the precondition.

Whether site water goes to a watercourse or to the sewer is governed by the local discharge permit or the sewer operator's consent. That is where the limits are set. Suspended solids or turbidity and pH are typically regulated, with further parameters depending on the site.

The SmartFloc Cloud continuously records flow, dose, tank levels and alarms of the FMfloc unit. Turbidity and pH measurement can be added as options. The result is an operating record that shows client and authority when the unit ran and how. Meeting the limits themselves depends on the whole process chain, not on flocculation alone.

Surplus bentonite suspension is the classic case for flocculation: high solids content, very fine particles, hardly separable without treatment. The distinction matters: the support slurry circulating through the machine is not flocculated, only the portion bled off and replaced.

Groundwater ingress usually carries little solid matter. Settling containers are often enough; flocculation only pays off when fine turbidity will not settle.

Water from sprayed concrete and cement works is strongly alkaline and contains cement fines. The fines can be flocculated, the pH cannot. Neutralisation needs its own stage from existing equipment or a partner; the cloud can optionally log the pH measurement.