Polyaluminium Chloride (PAC) is a widely used inorganic polymer coagulant in water and wastewater treatment. It is a water-soluble polymer positioned between aluminium chloride and aluminium hydroxide, offering strong coagulation efficiency with relatively low dosage.
However, during actual operation, many plants experience clogging in PAC dosing lines, filters, or mixing tanks, especially in industrial wastewater systems. This issue not only disrupts continuous operation but also increases maintenance cost and chemical waste.
Below we explain the main causes of PAC dosing clogging and how to solve them effectively.
1. Overdosing of PAC
One of the most common causes of clogging is excessive PAC dosage. PAC dosage should always be determined through jar testing based on raw water quality.
If PAC is overdosed:
- The product may not fully dissolve
- Excess polymer forms gel-like aggregates
- Undissolved material accumulates in pipes and filters
This often results in:
- Blocked dosing lines
- Clogged filter tanks
- Inconsistent coagulation performance
👉 For stable performance, dosage should align with PAC dosage guidelines for water treatment rather than relying on experience alone.
2. Improper Dilution Ratio and Dissolution Conditions
PAC requires sufficient water and proper mixing to fully dissolve. In practice, a dilution ratio of 1:3 (PAC : water) is commonly recommended for liquid PAC preparation.
If dilution water is insufficient:
- PAC dissolves incompletely
- Insoluble particles settle inside tanks
- Blockage gradually forms in metering pumps and pipelines
Recommended corrective actions:
- Increase dilution water volume
- Improve mixing intensity during dissolution
- Extend dissolution time before dosing
If the system design does not allow better dilution, replacing the metering tube or dosing line may be necessary.
3. PAC Quality and Insoluble Matter Content
All PAC products contain a certain amount of insoluble matter, which normally does not affect system operation.
However:
- Lower-grade or low-content PAC contains higher insoluble residues
- Economically driven product selection often increases clogging risk
- Poor filtration of PAC solution accelerates deposition
In general:
The lower the Al₂O₃ content, the higher the insoluble fraction.
When using lower-cost PAC products, it is critical to:
- Increase stirring speed
- Use finer solution filtration
- Increase dilution water volume
👉 Choosing high-purity PAC for wastewater treatment significantly reduces clogging frequency and maintenance cost.
4. Inadequate Mixing and System Design
Even with correct dosage and quality PAC, poor system design can still cause clogging.
Common issues include:
- Low-speed or inefficient mixers
- Dead zones in dissolution tanks
- Long dosing pipelines without flushing
To improve system reliability:
- Use continuous stirring during PAC preparation
- Avoid sharp bends and dead ends in pipelines
- Implement regular water flushing routines
For large systems, combining PAC with a suitable polyacrylamide flocculant downstream can reduce PAC dosage demand and improve overall stability.
Practical Checklist to Prevent PAC Dosing Clogging
✔ Confirm PAC dosage via jar test
✔ Maintain proper dilution ratio
✔ Ensure sufficient mixing energy
✔ Select PAC with suitable Al₂O₃ content
✔ Flush dosing lines regularly
✔ Avoid long-term use of low-grade PAC
Conclusion: Stable PAC Dosing Starts with the Right Choices
PAC dosing system clogging is rarely caused by a single factor. It is usually the result of dosage, dilution, product quality, and system design combined.
By optimizing these variables, treatment plants can:
- Reduce downtime
- Improve coagulation efficiency
- Lower long-term operating costs
If clogging occurs frequently, reviewing PAC selection and dosing design is more cost-effective than repeated mechanical maintenance.
👉 Learn more about PAC applications in industrial wastewater treatment or how to choose the right coagulant for your plant.
