ACH vs PAC: Why Aluminum Chlorohydrate Is Considered a High-End Coagulant in Water Treatment

In water and wastewater treatment, aluminum-based Coagulants play a critical role in removing turbidity, color, suspended solids, and organic contaminants. Among them,Aluminum Chlorohydrate(Ach) and Polyaluminum Chloride (PAC) are two widely used products.

Although both belong to pre-hydrolyzed aluminum salts, Ach is generally regarded as a more advanced and premium coagulant. But why?

This in-depth guide explains the technical differences, performance advantages, and application positioning of Ach compared to PAC.

1. Chemical Structure and Basicity: The Core Difference

PAC (Polyaluminum Chloride)

• Al₂O₃ content: typically 18–30%
• Basicity: 45–90%
• Mixed polymeric aluminum species
• Medium polymerization level

PAC is partially pre-hydrolyzed, making it efficient and cost-effective for a wide range of industrial and municipal applications.

ACH (Aluminum Chlorohydrate)

• Al₂O₃ content: typically 23–24% (liquid grade)
• Basicity: 80–90% (very high)
• Structure close to Al₂(OH)₅Cl
• Highly polymerized and more uniform molecular distribution

2. Lower pH Impact and Better Alkalinity Stability

When aluminum salts hydrolyze in water, they consume alkalinity and may reduce pH.

Ach has:

• Higher basicity
• Lower acidity impact
• Reduced need for lime or alkali adjustment

• Low-alkalinity raw water
• Soft water systems
• Drinking water treatment plants
• Cold climate regions

In contrast, PAC may require additional pH correction in sensitive systems.

3. Superior Low-Temperature Performance

Low temperatures slow down hydrolysis reactions.

At 5–10°C:

• PAC floc formation can slow significantly
• Ach maintains faster floc formation and stronger aggregation

• Northern Europe
• Russia
• North America
• Winter-season municipal treatment plants

Stable winter performance is one reason many high-end utilities prefer ACH.

4. Lower Sludge Volume and Higher Efficiency

Due to its higher polymerization level:

• ACH often requires lower dosage for the same turbidity removal
• Produces denser flocs
• Generates less sludge volume
• Improves sedimentation and filtration efficiency

Over time, this translates into:

• Lower disposal costs
• Improved operational stability
• Reduced chemical handling frequency

5. Purity and Drinking Water Applications

Premium-grade ACH typically features:

• Very low iron content
• Low insoluble matter
• Clear liquid appearance
• Stable quality control

• Drinking water treatment
• High-standard municipal plants
• Process water systems
• Electronics and specialty industries

PAC remains an excellent choice for:

• Industrial wastewater
• Textile effluent
• Mining water
• Cost-sensitive projects

6. Market Positioning: Performance vs Cost

In summary:

• PAC = Cost-effective and versatile
• ACH = High-performance and process-optimized

7. When Should You Choose ACH?

ACH is recommended when:

• Treating drinking water with strict standards
• Operating in cold environments
• Managing low-alkalinity raw water
• Seeking reduced sludge and chemical adjustment
• Running continuous high-stability municipal systems

For industrial wastewater with fluctuating conditions and budget constraints, PAC remains a practical solution.

Final Conclusion