Polyamine is a highly effective cationic organic coagulant widely used for turbidity removal in surface water treatment. Surface water sources such as rivers, lakes, reservoirs, and canals often contain suspended solids, clay particles, organic matter, algae, and microbial contaminants. These impurities cause turbidity, color, and instability in raw water, making it unsuitable for direct consumption. Polyamine plays a critical role in destabilizing these particles, accelerating floc formation, and improving clarification efficiency in drinking water treatment plants.

1. Characteristics of surface water turbidity

Surface water turbidity is mainly caused by fine suspended and colloidal particles, including:

• Clay and silt particles
• Organic debris (decayed vegetation, humic substances)
• Algae and plankton
• Microbial particles
• Industrial or agricultural runoff contaminants

These particles are typically very small (colloidal size) and carry negative surface charges, which keep them stable in suspension due to electrostatic repulsion. This stability makes natural settling extremely slow without chemical treatment.

2. Properties of polyamine for turbidity removal

Polyamine is synthesized from amine-based monomers, forming a water-soluble polymer with high cationic charge density and moderate molecular weight.

Key properties include:

• High cationic charge density: Strong ability to neutralize negatively charged particles
• Rapid reaction kinetics: Immediate destabilization of turbidity-causing particles
• Wide pH adaptability: Effective across pH 4–10
• Liquid form: Easy dosing and mixing in water treatment systems
• Low sludge production: Compared with inorganic coagulants

These properties make polyamine particularly suitable for treating variable and low-to-medium turbidity surface water.

3. Mechanism of turbidity removal

Polyamine removes turbidity through several key mechanisms:

(1) Charge neutralization
Most suspended particles in surface water are negatively charged. Polyamine neutralizes these charges, eliminating electrostatic repulsion and allowing particles to come together.

(2) Coagulation of colloids
Fine colloidal particles such as clay and organic matter are destabilized and aggregated into microflocs.

(3) Adsorption and bridging
Polyamine adsorbs onto particle surfaces and binds multiple particles together, forming larger aggregates.

(4) Enmeshment in flocs
During floc formation, small particles and organic matter become trapped inside larger flocs, improving removal efficiency.

4. Application process in water treatment plants

Polyamine is typically used in the coagulation stage of surface water treatment:

(1) Raw water intake

Surface water is pumped into the treatment plant and screened to remove large debris.

(2) Rapid mixing (coagulation stage)

Polyamine is added into the rapid mixing tank where it immediately interacts with suspended particles, destabilizing colloids and initiating floc formation.

(3) Flocculation stage

Gentle mixing allows microflocs to grow into larger, settleable flocs. In many systems, a flocculant such as polyacrylamide may be added to enhance floc strength.

(4) Sedimentation or flotation

Flocs are removed through sedimentation tanks or dissolved air flotation (DAF) systems.

(5) Filtration

Remaining fine particles are removed through sand filters, activated carbon filters, or membrane systems.

5. Advantages of polyamine in turbidity removal

(1) High turbidity removal efficiency
Polyamine effectively reduces turbidity even at low concentrations of suspended solids.

(2) Fast reaction speed
Rapid destabilization leads to quick floc formation and shorter treatment times.

(3) Low dosage requirement
High charge density allows effective treatment with relatively small amounts.

(4) Reduced sludge production
Compared to aluminum or iron salts, polyamine generates less sludge.

(5) Stable performance under varying conditions
Effective in fluctuating water quality conditions common in surface water sources.

6. Dosage and influencing factors

The optimal dosage depends on raw water quality and environmental conditions.

Typical dosage range:

• 1–20 mg/L for surface water turbidity removal

Key factors influencing dosage:

• Turbidity level (low, medium, high)
• Seasonal variation (rainy season increases turbidity)
• Organic matter content
• Algae concentration
• Water temperature
• pH level

Jar testing is essential to determine optimal dosage under specific conditions.

7. Combination with other treatment chemicals

Polyamine is often used in combination with other coagulants and flocculants:

(1) Polyaluminum chloride (PAC):
Used together to improve coagulation strength and reduce cost.

(2) Polyacrylamide (PAM):
Enhances floc size and settling speed after coagulation.

(3) Activated carbon:
Helps remove organic matter, odor, and color.

(4) Chlorine or ozone:
Used in disinfection and oxidation processes after turbidity removal.

This combined approach ensures comprehensive water purification.

8. Performance in different surface water conditions

(1) Low turbidity water
Polyamine works efficiently at low dosages, producing clear water with minimal sludge.

(2) High turbidity water (rainy season)
Higher dosage is required to handle increased suspended solids and clay particles.

(3) High organic matter water
Polyamine helps remove natural organic matter, reducing color and improving taste.

(4) Algae-rich water
Effective in destabilizing algal cells and improving removal in flotation systems.

9. Limitations and considerations

(1) Overdosing risk
Excess polyamine may cause charge reversal and reduced turbidity removal efficiency.

(2) Water quality variability
Surface water conditions change frequently, requiring continuous adjustment.

(3) Cost considerations
More expensive than traditional coagulants, though often more efficient at lower doses.

(4) Operator control required
Proper monitoring is essential for stable performance.

10. Operational best practices

To achieve optimal turbidity removal:

• Conduct regular jar tests
• Adjust dosage based on seasonal water quality changes
• Maintain proper rapid mixing intensity
• Combine with flocculants when necessary
• Monitor effluent turbidity continuously

11. Future trends

The use of polyamine in surface water treatment is expected to increase due to:

• Demand for higher drinking water quality standards
• Increasing variability in surface water quality due to climate change
• Expansion of water reuse systems
• Development of hybrid coagulant formulations

Future products will likely focus on improved efficiency, lower dosage, and better environmental performance.