Understanding Coagulation and Flocculation
Coagulation and flocculation are the most widely used processes in water and wastewater treatment for removing suspended solids, colloidal particles, and dissolved organic matter. Hydrochemix provides complete chemical solutions optimized for municipal and industrial applications worldwide.
The Science of Coagulation
Coagulation destabilizes colloidal suspensions through four mechanisms:
- Double Layer Compression: Adding electrolytes compresses the electrical double layer around particles, reducing zeta potential
- Charge Neutralization: Positively charged coagulants (Al3+, Fe3+) neutralize negatively charged colloids
- Sweep Coagulation: Metal hydroxide precipitates (Al(OH)3, Fe(OH)3) enmesh particles as they settle
- Bridge Aggregation: Polymer chains adsorb onto multiple particles, forming bridges
Coagulant Selection Guide
| Coagulant | Best For | pH Range | Notes |
|---|---|---|---|
| PAC 30% (Spray Dried) | General purpose, wide application | 5.0-9.0 | Best overall performance, low sludge |
| PAC 28% (Powder) | Cost-sensitive applications | 5.0-8.5 | Good performance, economical |
| Aluminium Sulphate | Traditional plants | 6.5-8.0 | Higher dosage, more sludge |
| Ferric Chloride | High-color, low-pH waters | 4.0-11.0 | Corrosive, stains equipment |
| Polyamine (Organic) | Oily wastewater, emulsions | 4.0-9.0 | Liquid, easy to handle |
Jar Testing Protocol
- Fill 6 beakers with 1L of raw water sample
- Add different coagulant doses to each beaker (e.g., 10, 20, 30, 40, 50, 60 mg/L)
- Rapid mix at 150-300 RPM for 1-2 minutes
- Slow mix at 20-40 RPM for 15-20 minutes
- Allow 30 minutes settling time
- Measure supernatant turbidity, pH, and residual metal concentration
- Select dose achieving target turbidity with lowest chemical consumption
Common Operating Issues
- Pin Floc: Too much rapid mixing energy, increase slow mix time
- Carryover: Insufficient settling time or hydraulic overload
- High Residual Al: Overdosing or pH outside optimal range
- Seasonal Performance Changes: Adjust dose for temperature and raw water quality
Contact jingshuicc@gmail.com for jar testing kits and technical support.