Poly Aluminium Chloride (PAC): Dosing, Specs, and Use Guide

Direct answer: how to use poly aluminium chloride effectively

To get reliable results with poly aluminium chloride (PAC), do three things in order: (1) pick a grade by Al₂O₃ (%) and basicity (%), (2) confirm the working pH window, and (3) lock the dose with a jar test before you scale. In published coagulation studies using PAC on typical raw waters, optimal doses commonly fall around 15–25 mg/L when pH is controlled near neutral, but the right dose still depends on turbidity, alkalinity, temperature, and organic load. :contentReference[oaicite:0]{index=0}

Practically, PAC is often chosen because it can perform across a relatively broad pH band (frequently cited as roughly pH 5–9 in supplier guidance) and can form denser floc faster than conventional alum in many waters—reducing settling time and, in some cases, sludge volume. :contentReference[oaicite:1]{index=1}

What PAC is and what it is best used for

PAC (also written PACl) is a pre-hydrolyzed, polymeric aluminium coagulant. Compared with “single-salt” aluminium coagulants, PAC contains a distribution of aluminium species that can neutralize particle charges and build floc efficiently, especially when raw water quality swings (storm turbidity, seasonal color, etc.).

Common applications

• Potable water: turbidity and color reduction, improved filter run stability
• Wastewater/industrial: suspended solids removal, partial COD/BOD reduction, phosphorus reduction when optimized
• Clarification ahead of membranes: lower SDI and reduced fouling risk when dose and mixing are well controlled

A practical pH note

Many operations see strong performance around near-neutral pH, and research commonly reports effective coagulation for PAC in the pH ~6.0–8.0 zone (with the exact window shifting with raw water chemistry and PAC basicity). :contentReference[oaicite:2]{index=2}

How to choose a PAC grade from the spec sheet

PAC products vary widely. Your job is to match the product to your process constraints (drinking vs. wastewater, solids load, temperature, residual aluminium limits, and chemical feed equipment).

Rule of thumb for matching grade to use case

• Potable water: prioritize low insolubles, consistent Al₂O₃, verified impurity limits
• Industrial/wastewater: prioritize cost-per-kg Al₂O₃, robustness under variable solids and pH, equipment maintainability

Dosing PAC: a jar-test workflow that scales cleanly

PAC dosing should be treated as an optimization problem, not a fixed recipe. A jar test gives you the fastest, lowest-risk path to a stable setpoint.

Step-by-step jar test (practical baseline)

1. Prepare a diluted PAC stock that your pipettes can dose accurately (commonly 0.1–1% by mass).
2. Set 6 beakers across a dose ladder (for example: 10, 20, 30, 40, 50, 60 mg/L) and keep raw water temperature representative.
3. Rapid mix (flash mix), then slow mix to grow floc; settle and measure settled turbidity and/or filtered turbidity.
4. Select the lowest dose that produces strong, settleable floc and the lowest stable turbidity without carryover.

Dose math you can trust (example)

If you use a 1% stock solution, a common approximation is: 1 mL dosed into a 1-liter jar delivers 10 mg/L. That makes dose ladders simple and repeatable during testing. :contentReference[oaicite:8]{index=8}

What “good” looks like in measured results

• Settled turbidity drops sharply, then plateaus (your target is near the knee of the curve, not the maximum dose).
• Floc is compact and settles cleanly (not “pin floc” that stays suspended).
• Finished water pH stays in your permitted/desired range without excessive alkalinity addition.

Real-world reference points: one study reported an optimum PAC dose of 15 mg/L within pH 6.5–8.0 for effective coagulation in their test water; another reported ~25 mg/L as optimal in their specific conditions. Use these as sanity checks—not as setpoints. :contentReference[oaicite:9]{index=9}

Troubleshooting PAC problems with targeted adjustments

Most PAC “failures” come from mismatched mixing energy, unmeasured pH/alkalinity limits, or overdosing. Use symptoms to narrow the root cause quickly.

If you see pin floc or carryover turbidity

• Reduce dose slightly and retest: overdosing can restabilize colloids.
• Increase slow-mix time or optimize G-value (floc needs time and gentle collisions).
• Check raw water alkalinity; insufficient buffering can shift pH out of the effective coagulation zone.

If pH drifts too low or alkalinity demand is high

• Use a higher-basicity PAC grade (often less alkalinity consumption at equal performance).
• Add alkalinity strategically (e.g., upstream carbonate/bicarbonate addition) and verify with jar tests.
• Confirm your effective pH band; many users target near-neutral conditions even if wider ranges are possible. :contentReference[oaicite:10]{index=10}

If performance drops in cold water

• Increase flocculation time before increasing dose (kinetics slow down first).
• Confirm rapid-mix intensity (insufficient dispersion is common when viscosity rises).
• Re-run jar tests at the actual cold temperature; the optimal dose can shift materially.

Handling, storage, and feed-system design notes

PAC solutions are typically acidic and can be corrosive to incompatible metals. Design for safe transfer, accurate metering, and easy flushing.

Operational best practices

• Use compatible wetted materials (confirm with supplier) and avoid dead legs where sediment can accumulate.
• Provide secondary containment and PPE appropriate for acidic chemicals.
• Flush injection points and quills routinely; insolubles can build up over time.
• If you dilute on-site, standardize your dilution procedure and record batch strength to reduce dose drift.

For potable systems, request documentation aligned with recognized standards for liquid PACl used in water treatment, and insist on consistent product characterization (active Al as Al or Al₂O₃, basicity, and impurity disclosure). :contentReference[oaicite:11]{index=11}

Bottom line

Poly aluminium chloride delivers the best, most repeatable results when grade selection (Al₂O₃ and basicity) is paired with jar-test dose optimization and pH/alkalinity control. Use published dose ranges (often ~15–25 mg/L in example studies) only as a starting point, then validate under your actual raw water conditions to minimize chemical cost, sludge, and downstream turbidity risk. :contentReference[oaicite:12]{index=12}