Frequently Asked Questions

All three make chemical floc settle faster. High-rate clarification does it by recirculating thickened sludge so the floc is grown around existing dense solids. Ballasted flocculation does it by injecting silica microsand so the floc is grown around a heavy grain. Magnetic separation does the same with magnetite, which is twice as dense and is recovered by magnets rather than by a cyclone. The first produces the most concentrated sludge, the second the highest hydraulic rate, the third the cleanest effluent. The comparison table sets out the numbers.

Between one fifth and one twentieth of the plan area, depending on the platform and the duty. A conventional clarifier is loaded at roughly 0.5–1.5 m/h; a lamella high-rate unit runs at 15–60 m/h and a ballasted unit at 40–120 m/h and above. The saving is not proportional to that ratio, because reactor volume and sludge handling do not shrink at the same rate, but a factor of five to ten on the clarifier itself is normal.

No. They are physical–chemical separation processes. They remove suspended and colloidal material, coagulable organics, phosphorus and precipitated metals. They do not remove soluble BOD, ammonia or nitrate, which need a biological stage. What they do very effectively is reduce the load reaching that stage, or polish what leaves it.

Jar testing, always. A pilot trial, where the water is unusual, where several process streams combine before the treatment point, where the effluent guarantee is tight, or where the client or regulator requires demonstrated performance before approval. On a straightforward municipal duty with a well-characterised influent, jar testing is normally enough.

Less than a conventional clarifier of the same duty, because the process is buffered against feed variation and the control loops are simple: flow-paced coagulant with feedback trim, polymer proportional to coagulant, and recirculation on a fixed ratio. The routine attention is chemical stock, ballast make-up where applicable, and inspection of the wear parts on the recirculation loop.

All three carry a large solids inventory in the reaction zone relative to what the incoming water brings, so a step change in influent solids has much less effect than it would on a conventional clarifier. Effluent quality is normally maintained. The limit is hydraulic rather than chemical — the unit is sized for a stated peak flow and will carry over above it.

Ballasted platforms reach full effluent quality in five to fifteen minutes, which is why they suit intermittent duty. High-rate clarification takes twenty to forty minutes because the sludge blanket and recirculation inventory have to re-establish.

On ballasted platforms: recirculation pump wet ends, cyclone liners and the injection nozzles. On all platforms: mixer seals and gearboxes, scraper drives, dosing pump diaphragms and instrument sensors. All of these are identified with an expected life in the spares schedule issued at supply, not discovered in service.

A metal salt coagulant — ferric chloride, ferric sulphate, aluminium sulphate or polyaluminium chloride — and an anionic polymer. Lime or caustic where pH correction or softening is required, and powdered activated carbon where adsorption is part of the duty. Doses are established by jar testing; they are generally comparable to a conventional process on the same water, sometimes slightly lower because floc formation is more efficient.

Mass production is set by the influent solids plus the chemical solids from coagulation, and is essentially the same for all three platforms. Concentration differs a great deal: 2–4 % dry solids from high-rate clarification with integrated thickening, against 0.3–1.5 % from a ballasted clarifier. That difference decides whether a separate thickener is needed and drives the size of the dewatering plant.

Only through attrition and carry-over. Recovery exceeds 99 % for both microsand and magnetite. Typical make-up is 1–3 g per cubic metre treated for microsand and below 1 g/m³ for magnetite. Both are inert commodity materials with no disposal implication.

A small quantity does — that is the make-up consumption. Silica and magnetite are both inert and non-hazardous, so the sludge disposal route is unaffected.

Design and peak flow; a raw water or influent analysis covering the seasonal or process range; the effluent consent or target; the site constraints and any tankage to be reused; and the operating pattern — continuous, intermittent or storm duty. The enquiry checklist sets this out in full.

Both. Equipment and internals for a contractor-built concrete structure, or a complete pre-assembled skid or containerised unit for smaller duties. The scope boundary is set out in writing in the offer — that is where most equipment disputes originate, so it is worth agreeing early.

Often, and it is usually the cheapest route to added capacity. Rectangular and circular concrete tanks of sufficient depth can take lamella modules and the necessary internals; magnetite ballasting can frequently uprate an existing clarifier with no change to the tank at all. Send the tank drawings and the target duty and we will confirm feasibility before any commercial discussion.

Performance against a defined feed envelope and a defined chemical dose, both stated in the contract. We will not guarantee an outlet figure without a defined inlet, and we will not guarantee performance that jar or pilot testing has not supported.