The main water treatment chemicals are used across drinking water, wastewater, and industrial water treatment processes to remove contaminants, disinfect, control corrosion, and condition sludge. They fall into several functional categories:
Purpose: Destabilize suspended/colloidal particles by neutralizing negative charges.
| Chemical | Type | Key Features |
|---|---|---|
| Alum (Aluminum sulfate, Al₂(SO₄)₃) | Inorganic | Traditional, low-cost; narrow pH range (6–7.5); produces high sludge. |
| Ferric chloride (FeCl₃) | Inorganic | Effective over wider pH; good for phosphorus removal; corrosive. |
| Ferric sulfate (Fe₂(SO₄)₃) | Inorganic | Similar to ferric chloride but adds sulfate. |
| PAC (Polyaluminum chloride) | Pre-hydrolyzed inorganic | Broader pH range, less sludge, better cold-water performance than alum. |
| PolyDADMAC | Organic polymer (cationic) | High charge density; no metal residuals; excellent for color/NOM removal. |
✅ Note: PolyDADMAC and PAC are increasingly replacing traditional metal salts due to efficiency and lower sludge.
Purpose: Bridge destabilized particles into large, settleable flocs.
| Chemical | Type | Use Case |
|---|---|---|
| Cationic Polyacrylamide (CPAM) | Organic polymer | Sludge dewatering, wastewater clarification. |
| Anionic Polyacrylamide (APAM) | Organic polymer | Mineral processing, sand-laden water. |
| Non-ionic PAM | Organic polymer | Sensitive pH systems, organic sludges. |
⚠️ Flocculants are typically used after coagulation.
Purpose: Kill or inactivate pathogens (bacteria, viruses, protozoa).
| Chemical | Pros | Cons |
|---|---|---|
| Chlorine (Cl₂, NaOCl, Ca(OCl)₂) | Low cost, residual protection | Forms disinfection by-products (DBPs) like THMs |
| Chlorine dioxide (ClO₂) | No THM formation, effective over wide pH | Must be generated on-site; can form chlorite |
| Ozone (O₃) | Powerful oxidant, no DBPs, improves taste/odor | No residual; high energy cost; complex equipment |
| UV radiation | No chemicals, no DBPs | No residual protection; requires clear water |
Purpose: Optimize pH for coagulation, corrosion control, or disinfection.
| Chemical | Function |
|---|---|
| Lime (Ca(OH)₂) | Raises pH and adds alkalinity |
| Soda ash (Na₂CO₃) | Raises pH without adding calcium |
| Sulfuric acid (H₂SO₄) / Hydrochloric acid (HCl) | Lowers pH |
| Sodium hydroxide (NaOH) | Raises pH quickly |
Purpose: Protect pipes and equipment in distribution systems.
| Chemical | Role |
|---|---|
| Orthophosphates (e.g., H₃PO₄, Na₃PO₄) | Form protective coating on lead/copper pipes |
| Polyphosphates | Sequester metals, prevent scale |
| Silicates | Stabilize iron/manganese, reduce pipe corrosion |
Purpose: Improve dewatering and reduce sludge volume.
| Chemical | Use |
|---|---|
| CPAM | Most common—binds sludge particles for mechanical dewatering |
| Ferric chloride / Lime | Sometimes used to condition biological sludge |
Activated carbon (powdered/PAC or granular/GAC): Removes taste, odor, synthetic organics, and micropollutants.
Antifoaming agents: Control foam in aeration basins.
Defoamers, biocides, algaecides: Used in cooling towers and reservoirs.
| Function | Common Chemicals |
|---|---|
| Coagulation | Alum, Ferric chloride, PAC, PolyDADMAC |
| Flocculation | CPAM, APAM |
| Disinfection | Chlorine, Chlorine dioxide, Ozone, UV |
| pH Control | Lime, Soda ash, Acids (H₂SO₄, HCl), NaOH |
| Corrosion Control | Orthophosphates, Silicates |
| Sludge Dewatering | CPAM, Ferric salts |
| Adsorption | Activated carbon |
Shift from metal-based coagulants (alum) → polymeric coagulants (PAC, PolyDADMAC).
Increased use of hybrid systems (e.g., PAC + CPAM).
Emphasis on minimizing DBPs → ozone/UV + chlorine residual.
Focus on sludge reduction and resource recovery.
These chemicals are selected based on source water quality, regulatory requirements, cost, and treatment goals. Proper dosing and process control are essential for safety, efficiency, and compliance.
