Industrial Water Treatment
Soil Remediation
Tunneling
Mining
Product Three
Application · Gravel, sand and crushed stone
Wash water treatment for gravel, sand and crushed stone plants
Washing gravel and sand sends silt and clay into the process water. The pond fills up, dredging intervals get shorter, and the water permit will not cover more fresh water.
With properly tuned flocculation the fines settle in minutes instead of weeks: clear water returns to the wash circuit, thickened sludge goes to dewatering. We supply the make-down and dosing system for it, retrofittable to your existing separator, for purchase or rent, remotely monitored around the clock.
Sludge flow
0–300 m³/h
Design range per unit
Make-down concentration
0–2 %
Polymer in the make-down unit
Dosing concentration
0–2 %
Relative to sludge flow
Recovery
> 90 %
Wash water kept in the loop, industry benchmark
What actually causes trouble in wash water
Gravel and sand are not the problem. What disturbs is the fine fraction released in the wash: silt from 2 to 63 µm, clay below 2 µm, and in hard rock plants the abrasion fines from crushed sand washing.
The finer the particle, the slower it settles, and clay platelets additionally keep each other in suspension through their surface charge. Without additives, gravel wash water therefore takes weeks to settle.
A flocculant neutralises that charge and binds the particles into millimetre-scale flocs: settling time shrinks to minutes, and the separation fits into a single unit instead of a pond.
Definition in one sentence
Flocculate the fines, return clear water to the circuit and dewater the thickened sludge mechanically, instead of parking it in a pond.
The same pond by other names
Settling pond · settling lagoon · clarification pond · sludge pond · tailings pond · industrial settling facility
The process route in a gravel and sand plant
Flocculation sits between pump sump and separator, the point that decides how clear the return water gets and how dry the sludge.
→ swipe sideways on narrow screens
What FMfloc takes care of
We do not sell separators. We sell the flocculation ahead of them, running on the equipment you already have. That keeps the retrofit in the range of an auxiliary system, not a new plant.
01
Make-down and maturing
Automatic preparation of the polymer at the right concentration, with maturing time. Immature polymer is the most common reason for poor floc formation.
02
Load-dependent dosing
Dosing controlled by flow and turbidity instead of a fixed pump setting. With varying fines load, this decides consumption and effluent quality.
03
Mixing and floc protection
Mixer and dosing point placed so the floc forms and survives all the way to the separation unit. Too much shear destroys what dosing has just built.
04
Flocculant selection
Settling test with your wash water, product selection and concentration setting. Then handover to your staff.
05
Integration with existing units
Mechanical, electrical and control integration with existing clarifiers, thickeners and presses, regardless of manufacturer.
06
Operation and remote monitoring
Readings, thresholds and alarms in the SmartFloc Cloud. On request we take over operation entirely.
Continue to make-down units · mixers · mobile units · remote monitoring
The right flocculant for mineral sludges
Mineral fines are mostly negatively charged, so the standard case is an anionic polyacrylamide of high molecular weight. As the clay share rises, cationic or combined products reach stable flocs faster. The settling test decides, not the catalogue.
| Type | Typical use | Field note |
|---|---|---|
| Anionic, high molecular weight | Gravel and sand wash water dominated by quartz fines | The standard case. Large, fast-settling flocs, good clear water. |
| Cationic | High clay and silt content, swelling clay minerals | Works through charge neutralisation. Overdosing reverses the charge and clouds the effluent again. |
| Combined with coagulant | Very fine abrasion, manufactured sand washing, changing raw materials | The coagulant destabilises, the polymer builds the floc. More effort, but more stable under fluctuating load. |
| Non-ionic | Special cases with high salt load in the loop water | Less sensitive to conductivity, but less effect per gram. |
Powder polymer
Cheaper per kilogram of active agent and long shelf life, but needs a make-down unit with maturing line. The right choice for continuous operation with steady consumption.
Liquid polymer (emulsion)
Ready faster and easier to handle, at a higher price per active agent. Suited to rental, trial operation and small throughputs.
Closed loop: what is realistically achievable
The industry benchmark is recovering over 90 percent of the process water. Measure every offer against that number, including ours.
What your plant achieves depends on the fines in the raw gravel, the residual moisture of the filter cake and the water leaving with the product. Water is lost in product and cake, not in the process.
We meter recovery rate, polymer consumption and cake dry solids and log them in the cloud. From a trial run you know these figures for your plant before you invest.
Design and key figures
Flow and concentrations are design ranges of our units. Suspended solids and dry solids are determined in the settling test at your plant.
Skipping the settling pond: the maths
A settling pond does not just cost area. It costs dredging, disposal, evaporation and permitting effort, every year. In most plants the retrofit pays for itself from dredging and water costs alone.
| Item | With settling pond | With flocculation and dewatering |
|---|---|---|
| Footprint | Pond area, permanently tied up | Floor space for clarifier, press and make-down unit |
| Dredging | Cyclical excavation, external equipment and downtime | Not needed, cake is produced continuously |
| Sludge transport | Wet sludge, high tonnage due to water content | Stackable filter cake, lower mass |
| Fresh and groundwater | Continuous abstraction, limited by permit | Only make-up for adherent and evaporated water |
| Evaporation losses | Open water surface, substantial in summer | Closed loop |
| Recultivation | Dismantling and securing after closure | Area stays usable |
| Fine sludge | A cost item | Filter cake with a recovery path |
Filter cake: cost item or raw material?
The dewatered fine sludge is a clayey-silty material with a defined grain size, not necessarily waste. The brick industry uses filter cake at 10 to 30 percent by mass, preferably in floor tiles and roof tiles.
Other routes are haul road construction, recultivation and backfilling on site. The prerequisite is a uniformly dry cake, and exactly that is set by the flocculation ahead of the press.
Recovery paths
Permitting
Water law and discharge
Abstracting water for washing requires a permit and is limited in volume. Closing the loop cuts the abstraction, often the decisive argument when a water permit is renewed or extended.
Discharged surplus water has to meet the TSS limit set in the permit. A stably controlled flocculation keeps it through load changes. We do not give legal advice, but we deliver the measurements for your case towards the authority.
What the permit is about
- Abstraction volume for ground and surface water
- Discharge point and volume into the receiving watercourse
- Suspended solids and turbidity in the effluent
- Record keeping and documentation duties
- Handling of the fine sludge after closure
Crushed stone, ballast and manufactured sand
In a quarry the fines come from crushing, not from washing out a natural deposit. That changes grain shape, abrasiveness and volume, and with it flocculant choice and pump design.
Manufactured sand washing
Freshly crushed ultra-fines with sharp edges, in larger quantities than in a gravel plant. The floc has to be built correspondingly more robust.
Chippings and ballast works
Washed crushed sand for asphalt and concrete keeps tight limits on fines in the product. That loads the wash water and makes the circuit more demanding.
Abrasiveness in plant design
Quartzitic and basaltic abrasion attacks pumps, pipe bends and dosing points. Material choice and dosing point decide service life.
Buy, rent or test first
Not every situation justifies an investment. Our units come as containers and trailers, wired ready for operation and with cellular connectivity ex works.
Test run
Proof before the investment
A few weeks at your plant, with your wash water. The result is solid figures for consumption, clear water quality and cake dryness.
Rental
Seasonal peaks and rebuilds
A bridge while the pond is being dredged, an order comes in at short notice or the existing plant is being rebuilt. See rental units
Purchase
Continuous operation
Stationary make-down and dosing unit, sized for your throughput and integrated into the plant control system.
SmartFloc Cloud
Monitored around the clock, even with nobody on site
Many plants run unstaffed at night and on weekends. A dosing fault would go unnoticed until Monday: circuit turbid, cake too wet, polymer used up.
Our units report readings to the cloud every second, with thresholds and alarms by e-mail or push. Several plants can be run from a single location. About remote monitoring
Gravel plant · Line 2
OnlineSludge flow
– m³/h
Flocculant
– l/h
Effluent turbidity
– NTU
Feed tank
– %
Schematic view, live view in the customer account
Reference
Gravel plant in southern Germany, 180 m³/h sludge flow
The settling pond needed dredging at short intervals and the permitted abstraction volume was exhausted. The existing lamella clarifier stayed; our make-down and dosing system with load-based control went in ahead of it.
Result after commissioning: closed wash circuit, stackable filter cake for recovery, documented effluent readings for the authority.
Plant data
Frequently asked questions
How much fresh water does a gravel washing plant need?
Without recirculation, several cubic metres per tonne of product. With flocculation and clear water return, make-up water drops to what leaves in product and filter cake plus evaporation.
Which flocculant suits gravel wash water?
Usually an anionic polyacrylamide of high molecular weight. With high clay content, cationic or combined products are used. The settling test with your wash water makes that call, not the catalogue.
Can I retrofit my existing plant?
Yes. The make-down and dosing system is installed ahead of your existing separator, independent of its manufacturer. You need footprint, power, a water connection and a dosing point in the pipe.
How often does a settling pond need dredging?
That depends on fines content, throughput and pond volume. With a closed loop, flocculation and mechanical dewatering the dredging cycle disappears, because the fine sludge is produced continuously as a stackable filter cake.
Is a closed loop worthwhile at small throughputs too?
Yes, as soon as dredging costs, disposal or a capped abstraction volume constrain the operation. For small and seasonal throughputs there are rental units, so no upfront investment decision is needed.
What does wash water treatment cost?
Retrofitting flocculation to an existing separation unit costs far less than building a new plant. Price is driven by throughput, fines content, degree of automation and whether you buy or rent.
Send in a sludge sample or book an on-site settling test
Two litres of wash water are enough. You get a product recommendation, expected consumption and an assessment of what your existing separator can do with proper flocculation, free of charge.
FMfloc GmbH · Frankfurt · info@fmfloc.de