Flocculants are generally divided into inorganic flocculants and organic flocculants. Choosing the right flocculant depends on the characteristics of the wastewater and the treatment process where the flocculant will be added.
Before selection, it is important to clearly understand:
- The treatment stage where the flocculant is used
- The purpose of flocculation
- The concentration of colloids and suspended solids in the water
Flocculant Selection Based on Colloids and Suspended Solids
When pollutants exist mainly in a colloidal state, inorganic flocculants are usually preferred. They help destabilize colloids and promote floc formation.
If the flocs formed are too small:
- Add a high molecular weight organic flocculant
- Or use activated silica gel as a coagulant aid
Using inorganic flocculants together with organic flocculants can significantly improve coagulation efficiency and expand the application range.
High molecular flocculants have:
- Higher charge density along the polymer chain
- Better chain extension in water
- Stronger adsorption and bridging ability
As a result, flocculation performance is improved.
Flocculant Selection for Tailing and Industrial Wastewater
When selecting inorganic flocculants, always consider:
- Wastewater composition
- pH value
Then choose the most suitable product type.
For organic flocculants (PAM), selection depends on ionic type:
- Anionic PAM
- Cationic PAM
- Nonionic PAM
Anionic PAM Selection
Anionic PAM can be classified into:
- Weak anionic
- Medium anionic
- Strong anionic
This classification is based on hydrolysis degree.
Cationic PAM Applications
Cationic PAM is mainly used for sludge dewatering. Selection tests are very important.
Typical applications include:
- Municipal wastewater treatment → Medium or strong cationic PAM
- Papermaking and dyeing wastewater sludge → Weak cationic PAM
- Medical wastewater treatment → Strong cationic PAM
Key Factors for Choosing the Right Flocculant
- Molecular Structure
The molecular structure should match the required dewatering performance.
- Linear structure
- Low dosage
- Good dewatering efficiency when molecular weight is suitable
- Dendritic structure
- Medium dosage
- Stable and effective dewatering performance
- Cross-linked structure
- Higher dosage
- Excellent shear resistance and special filtration performance
- Molecular Weight
Molecular weight represents the length of the polymer chain and should match the dewatering equipment.
- Centrifuge dewatering
- High molecular weight recommended
- Better resistance to strong shear forces
- Filter-type equipment
- Low to medium molecular weight
- Better filtration and drainage performance
- Flocculant Charge Type
Choose flocculant charge based on particle characteristics:
- Inorganic particles → Negatively charged flocculants
- Organic particles → Positively charged flocculants
Final selection should always be confirmed through:
- Jar tests
- On-site equipment trials
- Charge Density (Ionic Degree)
Charge density refers to how much positive or negative charge the flocculant carries to achieve the best flocculation effect with the lowest dosage.
Charge density depends on:
- Sludge type
- Organic matter content
- Volatile solids (VS) content
In general:
- Higher volatile content → higher required charge density
Special Notes on Nonionic PAM
Nonionic polyacrylamide is mainly used under acidic conditions. It is commonly applied in:
- Printing and dyeing wastewater treatment
Each wastewater type has unique characteristics. The final flocculant model must be confirmed by selection tests, considering:
- Dosage
- Floc size and strength
- Settling speed
- Overall treatment cost
Conclusion
Choosing the right flocculant requires a systematic evaluation of wastewater characteristics, treatment process, and equipment conditions.
Key steps include:
- Understanding colloid and particle properties
- Selecting suitable ionic type and molecular structure
- Matching molecular weight to dewatering equipment
- Verifying performance through selection tests
Only through proper testing and optimization can the most economical and effective flocculant be selected for stable wastewater treatment.
