Most industrial ETPs move effluent through a similar sequence of chemical treatment stages, even though the specific chemicals and doses vary by industry and discharge requirement.
pH Correction
Incoming effluent is frequently outside the pH range needed for effective downstream treatment, so it's corrected first — caustic soda or lime to raise pH, or an acid such as sulphamic or hydrochloric acid to lower it. See our guide on pH and how chemicals affect it.
Coagulation and Flocculation
Once pH is in range, a coagulant (alum, PAC or ferric chloride) destabilizes suspended and colloidal particles, and a polyelectrolyte flocculant bridges them into settleable flocs. See our guides on choosing a coagulant and choosing a polyelectrolyte.
Disinfection
Where biological contamination needs to be addressed before discharge or reuse, chlorine-based disinfection (sodium hypochlorite, bleaching powder) is commonly used — see our guide on choosing a chlorination chemical.
Sludge Dewatering
The solids removed during treatment become sludge that needs dewatering before disposal — cationic polyelectrolytes are the standard conditioning chemical ahead of a belt press or centrifuge, since they bind well to the negatively-charged biosolids typical of ETP sludge.
See Cationic Polyelectrolyte — High Molecular Weight.
Meeting Your Discharge Consent
The specific combination and dose of these chemicals should be set against your actual consent order parameters, not a generic target — see our guide on pollution control board consent basics for how that connects to chemical selection.