Introduction
PAC, or Poly Aluminum Chloride, is an aluminum coagulant used to clarify water and wastewater by neutralizing colloidal particles, forming flocs, and making them easier to settle or filter. For WTP and WWTP operators, PAC is selected when the main target is reducing turbidity, TSS, color, and part of the organic load before a clarifier, DAF, filter, or biological process.
This article explains the definition, working mechanism, product forms, applications, and process data to prepare before selecting PAC, industrial liquid PAC, or a combined coagulants and flocculants program.
What is PAC?
PAC stands for Poly Aluminum Chloride, an aluminum-based coagulant that destabilizes colloidal particles so they can form floc. Products are supplied as powder or liquid, with active content, basicity, pH, and density varying by grade.
PAC and alum both need testing on the actual water. Compare pH and alkalinity change, effective dose, floc strength, separation rate, and sludge production before changing coagulants.
History and Background of PAC
The use of coagulants in water treatment is not new. Since ancient times, humans have used alum to purify water. However, the need for efficiency and better results encouraged chemists to develop new compounds. This is how PAC became known and mass-produced in the 20th century.
PAC later gained broad use in water treatment and industrial processes. Comparisons with alum should not be generalized: dose, pH shift, floc-formation rate, and sludge production depend on coagulant grade and the water being tested.
Composition and Characteristics of PAC
PAC is usually available in two main forms: powder and liquid.
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PAC Powder
- Pale yellow to beige in color.
- Requires a controlled dissolving or make-down system.
- Provides a higher mass concentration for storage and shipping.
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Liquid PAC
- Light yellow to brown in color.
- Can be fed continuously without a powder-dissolving step.
- Requires compatible storage, piping, and pumping materials.
Important characteristics of PAC:
- Al₂O₃ content and basicity confirmed in the product specification.
- pH and density that vary by form and grade.
- Insoluble matter checked for product quality and dosing-system reliability.
- Coagulation performance demonstrated on the actual water by jar testing.
How PAC Works in Water Treatment
PAC works through two main processes:
- Coagulation
Aluminum ions in PAC neutralize the negative charge on colloidal particles. Because the charge is gone, the dirt particles no longer repel, but instead draw closer to each other. - Flocculation
Once the charge is neutralized, the particles will combine to form large clumps (flocs). These flocs are heavier and settle easily, so they can be separated from the water.
With this mechanism, murky water can turn clear in a short time.
Benefits of PAC in Various Sectors
1. Drinking Water Treatment
PAC is widely used by PDAMs and private drinking water companies to produce clean water that is suitable for consumption.
2. Industrial Liquid Waste Treatment
For textile, paper, food, or petrochemical wastewater, PAC can be tested to capture TSS, color, emulsified oil, or the coagulable organic fraction. COD/BOD reduction depends on wastewater composition and must be demonstrated by testing. Review the available wastewater treatment equipment only after defining the separation target.
3. Household Wastewater Treatment
In domestic wastewater, PAC only addresses the fraction that can be separated by coagulation; biological treatment and disinfection are still selected from wastewater characteristics and the effluent target. A compact sewage treatment plant therefore needs a complete process review, not a coagulant decision alone.
4. Paper and Textile Industry
PAC can be tested for process-water clarification, fine-solids control, or fiber separation according to the mill’s process need.
5. Oil and Gas Industry
In oil and gas wastewater, PAC can be part of pretreatment when jar testing shows that fine solids or emulsions can be separated before downstream units.
Advantages of PAC Over Other Coagulants
PAC is not automatically better than alum, ferric chloride, or another coagulant. The defensible choice is the product that meets the treated-water target at a manageable total cost and sludge load. Compare candidates on the actual water rather than relying on a catalogue dose.
| Decision criterion | PAC | Alum | How to verify on site |
|---|---|---|---|
| pH and alkalinity impact | Depends on product basicity, grade, and water chemistry | Depends on dose and water alkalinity | Record pH and alkalinity before and after treatment in every beaker |
| Effective dose | No universal value | No universal value | Find the lowest dose that meets turbidity/TSS targets and forms separable floc |
| Sludge | Depends on dose, captured solids, and polymer aid | Depends on the same factors | Measure settled-sludge volume and dewaterability, not supernatant clarity alone |
| Supply form | Powder or liquid | Commonly solid or solution | Compare make-down, storage, pumping, safety, and cost per cubic meter treated |
Indonesia’s SNI 3822:2018 for polyaluminium chloride sets quality requirements and test methods for liquid and solid PAC used in water clarification, paper, and cosmetics. Request the relevant product specification and lot test results; compliance with a product standard does not replace a jar test on site water.
Dosage and How to Use PAC
PAC dose must be adjusted to the water conditions. Convert the jar-test result into a feed rate using plant flow and confirmed product strength, then verify it again when influent quality changes.
Dry-product mass-feed formula: dose (mg/L) × flow (m³/h) ÷ 1,000 = kg/h. As a calculation example, 10 mg/L at 50 m³/h requires 0.5 kg/h of dry product. For liquid PAC or a made-down solution, divide the active requirement by the confirmed mass fraction in the product specification; do not substitute color or assumed density for supplier data.
- Initial analysis
Test the water quality to determine the correct dosage. - Rapid mixing
PAC is mixed into the water with rapid agitation to mix well. - Flocculation
After that, do slow stirring so that the particles agglomerate. - Settling
Allow the flocs to settle to the bottom of the tank. - Filtration
The clear water is filtered for cleaner results.
Record initial and final pH, dose, floc-formation time, supernatant turbidity or TSS, settled-sludge volume, and floc behavior during mixing and separation. The selected dose must remain workable across realistic influent variation, not merely produce the clearest beaker from one sample.
Quick Questions Before Selecting PAC
| Operating question | Practical answer | Related pages |
|---|---|---|
| Is the raw water turbid or high in TSS? | PAC is a practical first coagulant to test for forming flocs before sedimentation, clarification, or filtration. | PAC, coagulants, clarifier |
| Does the industrial wastewater contain color, oil, or fine suspended solids? | Start with a jar test to compare liquid PAC, powder PAC, and polymer aid so the dose is not guessed from the product name alone. | industrial liquid PAC, flocculants |
| Does influent quality change from day to day? | Prepare pH, alkalinity, turbidity/TSS, COD/BOD, and flow data so product selection, solution strength, and dosing equipment can be sized. | dosing pump, contact Beta |
Read more about chemical dosing pumps.
Environmental Impact and Safety of PAC
PAC risk depends on product form, concentration, exposure, and handling. Use personal protection, compatible tanks and pumps, spill containment, and procedures from the supplier’s safety data sheet. Overdosing can worsen treated-water quality and increase sludge load; verify pH, turbidity/TSS, required residuals, and separation performance after a dose change.
Tips for Choosing Quality PAC
- Match the lot certificate of analysis to the purchase specification and relevant SNI 3822:2018 quality parameters.
- Confirm Al₂O₃ content, basicity, insoluble matter, pH, liquid-product density, and shelf life; do not assume that all PAC grades are equivalent.
- Select powder or liquid according to usage volume, make-down facilities, storage, pumping, and operator capability.
- Follow the supplier’s safety data sheet and storage instructions, and protect powder PAC from moisture.
Challenges in Using PAC
Although there are many advantages, there are some challenges:
- Compare product cost as total cost per cubic meter treated, including sludge, energy, and treatment aids.
- Adjust dose and injection point when pH, alkalinity, temperature, or solids loading changes.
- Select tanks, piping, seals, and pumps from product compatibility data and the safety data sheet.
Conclusion
PAC, or Poly Aluminum Chloride, is one coagulant option for raw water, process water, and wastewater. Suitability depends on product quality, jar-test results, pH impact, the floc-separation unit, sludge production, handling safety, and total operating cost.
Prepare water-quality and flow data, compare candidates on an equal basis, and convert the selected dose into a feed rate using confirmed product strength. For product and coagulation-program evaluation, use the PT Beta Pramesti Asia contact page.