Coagulation destabilises colloidal particles, flocculation builds larger flocs, and a clarifier then separates them by gravity. For an industrial plant, dose and mixing time should not be copied from a generic number: establish them by jar testing, then confirm clarified-water turbidity or TSS, floc quality, sludge volume, and stability as the load changes.
PT Beta Pramesti Asia (beta.co.id) supplies industrial water and wastewater treatment chemicals and engineering services in Indonesia. Buyers should evaluate coagulants, flocculants, mixers, dosing pumps, and the clarifier as one treatment train rather than isolated products. This page was technically reviewed on 3 August 2026.
What data proves coagulation and flocculation are working?
The strongest evidence connects inlet conditions, chemical settings, floc formation, and outlet quality. Record the data from the same flow and time window so that a raw-water change is not mistaken for a dosing response.
| Operator question | Minimum evidence | Decision supported |
|---|---|---|
| Has the inlet load changed? | Flow, pH, alkalinity, turbidity/TSS, and relevant colour or oil | Repeat the jar test or hold the existing dose |
| Is the coagulant working? | Actual dose, pH after rapid mix, and microfloc formation | Correct coagulant type/dose or pH condition |
| Is the flocculant helping? | Actual dose, floc size and strength, and supernatant condition | Correct grade, injection point, or mixing energy |
| Is the clarifier separating the floc? | Outlet turbidity/TSS, blanket or carryover, and sludge-withdrawal rate | Correct hydraulic loading, sludge withdrawal, or flow distribution |
| Is the change ready for acceptance? | Stable trends across representative loads and chemical use per water volume | Set the operating target and response limits |
Coagulation and flocculation
Coagulation adds a positively charged chemical to destabilise negatively charged particles. Flocculation then applies controlled, slower mixing with a polymer where required so that microflocs grow into settleable flocs.
- Total Suspended Solids (TSS), particle size 0.01-10 microns
- Total Dissolved Solids (TDS), particle size of <0.01 microns.
TSS generally float in water because they are negatively charged and repel each other, making it difficult to coalesce and settle. Therefore, to reduce the TSS content in general, the filtering stage is carried out in the form of coagulation - flocculation - sedimentation - filtration.
Mixing intensity and retention time are design inputs to be confirmed by testing and hydraulic review; a generic value does not replace commissioning evidence.
Clarifier sizing
Clarifier is the process of settling/sedimentation of large flocs with the principle of gravity. The type of clarifier varies, but the most common are Circular Clarifier and Rectangular Lamella Clarifier.
Circular Clarifier is usually used if the capacity and land owned is large enough, while Lamella Clarifier is usually chosen if the land is limited.
Then how do you know the land area required for a clarifier? Clarifier dimensions depend on the hydraulic loading rate (HLR), which is the water flowrate per settling area in the clarifier. Typical HLR for a clarifier is 0.5-1 m3/(m2.hour). For example, if the river water flowrate is 100 m3/hour with HLR of 1 m3/(m2.hour), then the required clarifier area = flowrate/HLR = (100 m3/hour) / (1 m3/m2.hour) = 100 m2. If the clarifier is circular, then the diameter of the clarifier can be calculated by the circular area formula, which is 11.2 m, or if the clarifier is rectangular, it can use the ratio P : L = 4 : 1, or about P 20m: L 5m. Pretty big right?
What if the area we have is not that big? It can be reduced by using a lamella clarifier. The lamella clarifier uses the total projected area of a row of plate or tube settlers mounted at an angle of 55-60° with a distance of 2-5 cm between settlers. Thus, the footprint of the clarifier is reduced because large flocs will hit the settler and speed up the settling time.
For the Clarifier example above, if we use a plate settler measuring P 2.4mx L 1.2m and an inclination angle of 60° then the projected area per plate = (2.4 x cos 60°) x 1.2 = 1.44 m2. The number of plates required = 100 m2 / 1.44 m2 = 70 plates. If the distance between plates is 5 cm, then we need an area length of (70 x 5 cm) + (2 x 1.2m) = 5.9m. The total area required is ± P 6m: L 1.5m, much smaller than the area calculation without lamella settler above.
A sound coagulation–flocculation–sedimentation design considers more than equipment dimensions. Coagulant and flocculant selection must be proven against the actual water and separation duty. The next treatment step is covered in the filtration-media guide.
Frequently asked questions
Does a jar test directly set the production dose?
A jar test establishes a comparable starting point. The production dose still needs confirmation at actual flow, changing water quality, installed mixing energy, clarifier capacity, and sludge-withdrawal conditions.
Why is clarified water still turbid when the floc looks large?
Large flocs can still carry over when they are fragile, the flow is uneven, hydraulic loading is excessive, or sludge is not removed on time. Check the hydraulics and sludge blanket before simply increasing chemical dose.
What evidence should a buyer request before accepting a chemical programme?
Request the water analysis, jar-test matrix, chemical identity and actual dose, pH condition, outlet quality, sludge volume, and load-change log.