ETP Chemicals — Uses, Purpose & Typical Dosage

Comprehensive reference for coagulants, flocculants, pH correctors, oxidants, dechlorinants, membrane care chemicals and specialty reagents.

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Quick Summary

This page lists common ETP chemicals, their primary purpose, the stage where they are used and indicative dosage ranges. Dosages are indicative — final dosing requires jar tests/pilot trials and will vary with influent characteristics (pH, TSS, BOD, COD, conductivity, temperature).

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Primary Chemical Reference

#	Chemical Name	Primary Purpose / Role	Typical Dosage (Indicative)	Stage of Use
1	Lime (Calcium Hydroxide)	pH correction (raise); heavy metal precipitation (as hydroxides)	50–500 mg/L (depends on acidity)	pH Adjustment / Neutralization
2	Caustic Soda (NaOH)	pH increase, neutralization, break oil emulsions	5–200 mg/L	pH Adjustment / Equalization
3	Sulphuric Acid (H₂SO₄)	pH reduction, acid dosing for neutralization	0.5–200 mg/L (as H₂SO₄)	Neutralization Tank
4	Hydrochloric Acid (HCl)	pH reduction, descaling, metal cleaning	0.5–200 mg/L	Neutralization / CIP
5	Aluminium Sulfate (Alum)	Coagulation — turbidity, colloidal removal	10–100 mg/L (as Al₂(SO₄)₃)	Coagulation Tank
6	Ferric Chloride (FeCl₃)	Coagulation, phosphate removal, colour reduction	5–80 mg/L (as Fe³⁺)	Coagulation / Primary Treatment
7	Ferrous Sulphate (FeSO₄)	Coagulation, COD reduction in some streams	5–80 mg/L	Coagulation
8	Poly Aluminium Chloride (PAC)	High-efficiency coagulation with less sludge	5–50 mg/L	Coagulation Tank
9	Polyelectrolytes / Polymers (Anionic / Cationic / Non-ionic)	Flocculation — increase floc size & improve settling; sludge dewatering aid	0.1–5 mg/L (flocculation) / 50–500 g/t DS for dewatering	Flocculation / Sludge Handling
10	Activated Carbon (GAC / PAC)	Adsorption of organics, odour, colour	PAC: 5–50 mg/L; GAC: bed contact time design	Tertiary Polishing
11	Sodium Hypochlorite (NaOCl)	Disinfection (microbial control)	1–5 mg/L (free chlorine) typical dosing	Post-Treatment Disinfection
12	Chlorine Gas / Bleaching Powder	Disinfection (industrial scale)	Calculated to achieve 1–5 mg/L residual	Post-Treatment
13	Sodium Metabisulphite (SMBS)	Dechlorination (removes residual chlorine before RO)	1–5 mg/L (as available SO₂ equivalent)	Before RO / UF
14	Antiscalants (RO Antiscalant)	Prevent scale formation on membranes (CaCO₃, CaSO₄, silica)	1–5 mg/L (product dependent)	RO Feed
15	Biocides (RO & Cooling)	Control biofouling in membranes & pipelines	0.1–5 mg/L (product dependent)	Membrane Care / Cooling Systems
16	Hydrogen Peroxide (H₂O₂)	Oxidation, colour & odour reduction, AOP feed	5–200 mg/L (AOP varies)	Advanced Oxidation
17	Fenton's Reagent (H₂O₂ + Fe²⁺)	Strong oxidation for high COD/BOD reduction & colour removal	Site-specific; H₂O₂ 50–500 mg/L range	AOP / Pre-treatment for refractory organics
18	Defoamer / Antifoam	Control foam in aeration tanks & clarifiers	0.5–10 mg/L (as needed)	Biological Stage
19	Nutrient Dosing (Urea, DAP, Ammonium Sulphate)	Supply N & P for heterotrophic biomass (if nutrient-deficient)	BOD:N:P ~ 100:5:1 (dosing to achieve ratio)	Aeration / Biological Tank
20	Soda Ash (Sodium Carbonate)	pH correction / hardness adjustment	5–200 mg/L	Pre-treatment / pH control
21	EDTA / Complexing Agents	Chelation of metals (special cases)	Low mg/L (case-by-case)	Specialised Chemical Streams
22	Citric Acid / Oxalic Acid	Membrane cleaning (acid cleans for scaling)	1–5% w/w cleaning solutions	Membrane Cleaning (CIP)
23	Sodium Hydroxide / Sodium Hypochlorite Cleaners	Membrane & pipe cleaning (alkali clean for organics)	1–2% w/w cleaning solutions	CIP / Membrane Cleaning
24	Ozone (O₃)	Strong oxidant for colour, organics, odour (non-chemical residual)	mg/L as per design (on-site generation)	Tertiary / AOP

Note: Dosage values above are indicative ranges. Always perform lab jar tests or pilot trials to confirm exact dosing and sequence. Chemical compatibility and safety must be verified on a site-specific basis.

Application Guidance & Dosing Tips

Jar tests are mandatory: For coagulant & polymer selection and optimization — try multiple doses and mix regimes.
Sequence matters: pH adjustment → coagulant → rapid mix → slow flocculation → clarification → polymer aid → filtration
Polymers: Use correct ionic type: anionic for cationic coagulants, cationic where negatively charged colloids need bridging. Avoid overdosing — it reduces settling.
RO protection: Remove free chlorine (SMBS) before RO; apply antiscalant based on Langelier / silt density index analyses.
AOP caution: Fenton / H₂O₂ dosing must be controlled (pH, catalyst) — residual H₂O₂ harmful to biology and membranes.
Safety & handling: Acids & caustics require secondary containment, PPE, and neutralization plans. Chlorine handling needs trained staff & ventilation.

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