Drinking & Process Water
Surface water clarification at 40–80 m/h, carbonate softening, colour and natural organic matter removal, and algal bloom response — with the stability a potable plant has to have.
Raw water changes; the plant should not
A drinking water plant is judged on the worst day, not the average one. Spring turbidity peaks, autumn algal blooms, colour after heavy rain and seasonal organic carbon all arrive without notice, and a clarifier that only performs at design conditions is not much use.
Both high-rate platforms handle that variability structurally rather than by operator intervention. In high-rate clarification the solids inventory in the flocculation zone comes from recirculated sludge, so it barely changes when the raw water does. In ballasted flocculation the floc density comes from the sand, so settling velocity is largely decoupled from the incoming solids concentration. In both cases the process rides through a turbidity spike that would upset a conventional clarifier.
Clarification
Surface water, reservoir water, river abstraction and seawater intake are all standard duties. Ballasted flocculation at 40–80 m/h is the usual choice on larger plants where land is expensive and raw water is variable; high-rate clarification is often preferred where the sludge has to be thickened on site anyway.
Softening
Lime, or lime with soda ash, precipitates carbonate hardness as calcium carbonate. The precipitate is dense and settles well, but the volumes are large. High-rate clarification with integrated thickening is a natural fit here: the process both handles the high solids loading and discharges the carbonate sludge concentrated. Where hydraulic rate matters more, the softening configuration of the ballasted platform does the same job in a smaller reactor.
Colour, organics and micropollutants
Natural organic matter is the precursor to disinfection by-products, so removing it upstream is usually cheaper than managing them downstream. Enhanced coagulation at a controlled pH takes out a large fraction. Where taste and odour compounds, pesticides or trace micropollutants also have to be addressed, powdered activated carbon is dosed ahead of coagulation and is captured with the floc — adding an adsorption stage without adding a vessel.
Algal blooms
Algae are difficult for conventional clarifiers because the cells are close to neutral buoyancy. Ballasting solves that directly: attached to a sand or magnetite grain, an algal cell settles like the grain. Because these events are seasonal and sudden, the fast start-up of a ballasted unit matters — it can be brought online for the duration of the bloom and stood down afterwards.
Backwash and washwater recovery
Filter and membrane backwash can be clarified and returned to the head of the works rather than discharged, recovering 2–5 % of plant throughput. The duty is intermittent and the solids concentration high, which suits a high-rate unit with integrated thickening.
| Design parameter | Typical range |
|---|---|
| Rise rate — ballasted | 40–80 m/h |
| Rise rate — high-rate clarification | 15–40 m/h |
| Raw water turbidity range handled | < 5 to > 1,000 NTU |
| Settled water turbidity | < 1–2 NTU |
| Colour removal | 80–95 % with enhanced coagulation |
| Dissolved organic carbon removal | 40–70 %, water dependent |
| Algae removal | > 90 % with ballast |
| PAC dose for taste, odour, micropollutants | 5–30 mg/L |
| Softening — carbonate hardness reduction | to 30–60 mg/L as CaCO₃ |
| Washwater recovery | 2–5 % of plant throughput |
| Materials in contact with potable water | Certified to NSF/ANSI 61 or local equivalent |
Removal efficiencies are strongly water-specific. Jar testing establishes coagulant type, dose and pH before a design is fixed.
For drinking water duty we specify ballast media, coatings, gaskets and wetted components certified to the relevant standard for contact with potable water, and the certification is named in the supply documentation rather than assumed.
Clarifying a difficult surface water?
Send a raw water analysis covering the seasonal range, the plant flow and the treated water target. We will propose a configuration and tell you what needs pilot testing.