What is Polyaluminum chloride used for?

Polyaluminum chloride at a glance

Polyaluminum chloride (PAC) is a pre-hydrolyzed aluminum salt widely used as a primary coagulant to clarify water and wastewater. Because PAC already contains polymerized aluminum species, it forms flocs quickly, works across a broad pH range, and typically produces less sludge than traditional aluminum sulfate.

Key benefits

• Broad pH window (about 5–9), reducing the need for pH adjustment

• Faster, denser floc formation for improved turbidity and color removal

• Lower alkali consumption and reduced sludge volume compared with alum

• Effective in cold water where coagulation can otherwise be sluggish

Common applications of Polyaluminum chloride

Drinking water treatment

PAC removes turbidity, color, NOM (natural organic matter), iron, and manganese precursors that can later cause taste, odor, and disinfection by-products.

Industrial wastewater

It treats suspended solids and emulsified oils from food and beverage, pulp and paper, textiles, mining, and metal finishing. In many cases it replaces multiple chemicals with a single coagulant step.

Desalination pre-treatment

PAC reduces silt density index (SDI), protecting ultrafiltration and reverse osmosis membranes from fouling.

Swimming pools and aquatics

Used intermittently as a clarifier to help filters capture fine particles and restore water sparkle.

How Polyaluminum chloride works

The coagulation–flocculation mechanism

PAC neutralizes negative surface charges on colloids, then bridges particles to form visible flocs. Because it is partially polymerized, PAC creates stronger flocs faster, improving settling and filtration.

Typical dose ranges

• Surface water: 5–30 mg/L as product

• Heavily colored/turbid water: 20–60 mg/L as product

• Industrial wastewater: jar tests often indicate 50–200 mg/L, sometimes higher depending on load

Always verify with jar testing, then fine-tune on line using turbidity, UV254, zeta potential, or particle counts.

Choosing a Polyaluminum chloride grade

Basicity and Al₂O₃ content

• Basicity (%) reflects the degree of pre-hydrolysis. Medium to high basicity (40–85%) often balances performance and stability.

• Al₂O₃ (%) indicates active aluminum content; common liquids are 10–18% Al₂O₃, powders higher.

Liquid vs. powder

• Liquid PAC simplifies dosing and is favored for continuous plants.

• Powder PAC is economical to ship; make 5–10% solutions in clean water before dosing.

Specialty blends

PAC can be blended with organic polymers (e.g., PACl-polyDADMAC) to enhance charge neutralization and bridging in difficult waters.

Polyaluminum chloride vs. alum

When PAC has the edge

• Less pH depression, reducing caustic/lime demand

• Lower sludge volume and better dewaterability

• Faster settling and improved cold-water performance

When alum may still fit

• Extremely tight budgets where chemical price outweighs sludge and alkali savings

• Legacy systems tuned specifically for alum characteristics

Best-practice dosing and control

Jar testing workflow

1. Screen doses (e.g., 10, 20, 30, 40, 60 mg/L PAC).

2. Rapid mix 30–60 seconds to disperse.

3. Flocculate 10–20 minutes at gentle G values.

4. Settle 10–15 minutes; measure turbidity, color, UV254.

5. Check pH after dosing; target within 6–8 unless your process requires otherwise.

Inline optimization tips

• Track influent turbidity/color and adjust dose with feed-forward control during storms or process upsets.

• Combine PAC with a low-dose anionic flocculant to strengthen flocs before sedimentation or DAF.

• Monitor filter headloss and backwash intervals; improved floc often lengthens run times.

Storage, handling, and compatibility

Safe storage

• Keep sealed in corrosion-resistant tanks (HDPE, FRP, lined steel).

• Store cool and out of direct sun; avoid freezing of liquid PAC.

• Maintain dedicated transfer lines to prevent contamination.

Handling and PPE

• Wear gloves, goggles/face shield, and protective clothing.

• Rinse spills with plenty of water; PAC is acidic and can corrode some metals.

Compatibility notes

• Do not premix PAC with strong alkalis; add separately into the rapid-mix zone.

• Compatible with most anionic flocculants when dosed sequentially.

Regulatory and safety considerations

Drinking-water suitability

Select Polyaluminum chloride grades certified for potable use where required. Review product technical data sheets (TDS) and safety data sheets (SDS) for local compliance and handling instructions.

Environmental aspects

Lower sludge volumes and reduced alkali demand can cut downstream handling and carbon impacts. Dispose of treatment sludges according to local regulations.

Troubleshooting with Polyaluminum chloride

Poor floc formation

• Dose may be too low or too high—re-run jar tests in narrower steps.

• pH out of range—adjust alkalinity or acid feed.

• Shear too high in flocculation—reduce mixing intensity.

Carryover or filter fouling

• Increase flocculation time or add a small dose of an anionic polymer.

• Check for coagulant under-mixing at the rapid-mix stage.

Seasonal changes

• In cold water, lengthen flocculation time and consider a slightly higher PAC basicity.

Quick FAQs on Polyaluminum chloride

Is Polyaluminum chloride safe for drinking water?

Yes—when you choose a grade approved for potable applications and follow dosage guidelines, Polyaluminum chloride is commonly used to produce safe, clear drinking water.

What is the ideal pH for Polyaluminum chloride?

PAC performs across roughly pH 5–9, with many plants operating between 6 and 8 for optimal coagulation and minimized corrosion risk.

Can Polyaluminum chloride replace alum directly?

Often yes, but you should run jar tests to confirm equivalent or improved performance and to set the new dose, which is frequently lower than alum on an active-aluminum basis.

Does Polyaluminum chloride increase aluminum residuals?

Properly optimized coagulation and filtration keep residual aluminum low. If residuals rise, check dose, pH, and filter health.

Takeaway

Polyaluminum chloride delivers fast, robust coagulation, broad pH performance, and lower sludge—making it a strong first choice for clarifying drinking water, industrial wastewater, and membrane pre-treatment. With the right grade, dose, and controls, Polyaluminum chloride can improve water quality, reduce operating costs, and simplify plant chemistry year-round.