How to Optimize PAC Usage in Industrial Wastewater: Real Insights & Best Practices
Engineer-focused guidance for getting the most from Polyaluminium/Polymeric Aluminum Chloride (PAC): grade selection, dosing math, PAM pairing, and field-proven tweaks for Southeast Asia & MENA plants.
PAC at a Glance
Polyaluminium Chloride (PAC) is a high-charge-density, pre-hydrolyzed inorganic coagulant that destabilizes colloids and accelerates solid–liquid separation. For technical background and purchasing specs (28–30% Al2O3, basicity ranges), see our PAC product page and this practical uses guide.
Common Pitfalls That Increase Cost
1) Over-diluted or over-aged stock
Very low concentration (<1%) or long holding time reduces effective charge. Keep dilution consistent (typ. 5–10%) and use fresh batches. See our comprehensive PAC guide.
2) Wrong basicity for the matrix
High-basicity PACs improve charge neutralization at neutral pH; low-basicity grades can help with highly colored or low-alkalinity waters. Match grade to matrix (details below).
3) Suboptimal injection point
Feed into a zone with vigorous initial mixing (G-value high), followed by tapered flocculation. Poor mixing wastes coagulant and generates fragile flocs.
4) Ignoring PAM synergy
PAC handles destabilization; a tailored PAM flocculant bridges particles for faster settling and denser sludge—often reducing total chemical cost.
Dosing Strategy & Quick Math
Start with jar tests, then confirm on-line with stepped trials. Typical starting points for industrial wastewater:
| Matrix | Starting Dose (as PAC) | Notes |
|---|---|---|
| Colored, humic-rich (textile/dye) | 30–80 mg/L | Consider lower basicity PAC for color; add an anionic PAM for bridging. |
| Oily/metal-bearing (machining, plating blend) | 40–100 mg/L | pH 6.0–7.5 typical. Follow with CPAM if sludge shear is high. |
| Mining/aggregate high-TSS | 20–60 mg/L | Coarse solids settle; optimize mixer time, then low-dose PAM for compaction. |
Working Example
Plant flow: 500 m³/h; trial dose: 50 mg/L PAC (as product).
Hourly PAC mass = 500 × 50 g = 25,000 g/h = 25 kg/h.
If using 10% w/w solution, solution flow ≈ 250 kg/h (≈250 L/h).
Choosing the Right PAC Grade (Basicity & Al2O3)
Basicity reflects the degree of pre-hydrolysis. In practice:
Low basicity (≤40%) — stronger acid neutralization; effective for high color/low alkalinity waters (textiles, surface color).
Medium basicity (45–65%) — balanced CT removal; good general-purpose coagulant for mixed industrial effluents.
High basicity (≥70%) — efficient at near-neutral pH, lower sludge volume, often better cold-water performance.
Compare specs and certificates on the PAC 28–30% Al₂O₃ page, and see deep dives here: PAC Water Treatment Guide.
Pairing PAC with PAM for Faster, Denser Clarification
PAC neutralizes particle charge; polyacrylamide (PAM) creates polymer bridges for robust flocs. Best practice:
Order of addition: PAC first in high-G rapid mix (<30 s), then PAM in tapered flocculation zones.
PAM type: Anionic PAM for mineral/neutral surfaces; cationic PAM for organic-rich or biological sludges.
Make-down: PAM at 0.1–0.2% w/w; age 30–60 min before dosing to maximize chain extension.
Industry Snapshots (SEA & MENA)
Textile & Dyeing (Color + COD)
Switch from alum to medium-basicity PAC cut dose ~25% and improved color removal (>90%). Final polish achieved with low-dose anionic PAM.
Food Processing (Fat/Oil/Grease)
PAC at neutral pH improved organics capture; adding CPAM (0.5–1.5 mg/L) produced shear-resistant flocs for DAF + clarifier trains.
Mining & Aggregates (High TSS)
Low–mid dose PAC stabilized fines; small PAM trim dose increased settling velocity and raised underflow solids for faster dewatering.
Troubleshooting Cheatsheet
| Symptom | Likely Cause | Action |
|---|---|---|
| Flocs too small / slow settling | Under-dosing PAC; PAM added too early or too diluted | Increase PAC in small steps; move PAM downstream; check PAM make-down age |
| Pin-floc carryover | Excess shear; wrong PAM charge type | Reduce mixer G; trial anionic vs cationic PAM; verify pH 6–7.5 |
| Rising sludge / blanket | Gas formation; sludge too light | Improve sludge withdrawal; add PAM trim; check nutrient/biogas disturbance |
| Seasonal performance drop | Cold water viscosity; low alkalinity | Consider higher-basicity PAC; ensure alkalinity support; insulate lines |
For full mechanisms and selection flowcharts, review the Comprehensive PAC Guide.
Need a PAC–PAM dosing plan tailored to your plant?
Share your flow, pH/alkalinity, turbidity/SS, and current chemicals. We’ll return a jar-test matrix and starting setpoints.
FAQ
What is the typical pH window for PAC?
Most industrial matrices perform well around pH 6.0–7.5. Low alkalinity streams may need lime/soda support.
Should I pick liquid or powder PAC?
Powder eases long-distance logistics; liquid saves handling time onsite. See spec and logistics notes on the PAC product page.
Do I always need PAM with PAC?
No, but PAM often delivers faster settling and drier sludge. Explore anionic PAM options for mineral-rich waters.
