How to Use PAC 30% (Polyaluminum Chloride) in Water Treatment

Overview

PAC 30% is the most widely used inorganic coagulant in water treatment, with ≥ 30% Al₂O₃ content. It works by charge neutralization and sweep flocculation to remove turbidity, TSS, color, and partial COD. Effective pH range: 5.0–9.0 with minimal pH depression.

Preparation & Dissolution

PAC 30% is a liquid product — no dissolution needed. For solid PAC (powder/granular), prepare a 10% stock solution:

1. Fill dissolving tank with clean water to 90% volume
2. Slowly add PAC powder while stirring (mechanical mixer at 100–150 rpm)
3. Stir for 30 minutes until fully dissolved — solution should be clear amber
4. Dilute to working concentration (2–5%) before dosing

Equipment: HDPE or FRP dissolving tank, mechanical mixer, metering pump (diaphragm type recommended).

Dosing Guide

Application	Typical Dose (as product)	pH Range
Municipal drinking water	20–40 ppm	6.5–7.5
Municipal wastewater primary	30–80 ppm	6.0–8.0
Industrial wastewater	50–200 ppm	5.5–8.5
River water (low turbidity)	10–25 ppm	6.5–8.0
River water (flood/high turbidity)	40–100 ppm	6.0–7.5

Note: Always confirm by jar test. Dose varies with raw water quality, temperature, and target turbidity.

Application Procedure

1. Measure raw water turbidity, pH, and temperature
2. Set metering pump to target dose based on jar test results
3. Inject PAC at the flash mix zone — ensure turbulent mixing (G value > 300 s⁻¹)
4. Flash mix for 30–60 seconds
5. Transfer to slow mix (flocculation) zone — G value 30–50 s⁻¹ for 15–20 minutes
6. Allow settling in clarifier — typical HRT 2–4 hours
7. Monitor settled water turbidity every 30 minutes
8. Adjust dose based on results — increase 10–20% during cold weather or turbidity spikes

Monitoring & Control

Parameter	Frequency	Target
Raw water turbidity	Continuous or hourly	Baseline tracking
Settled water turbidity	Every 30 min	< 5 NTU (drinking) / < 20 NTU (industrial)
pH after dosing	Hourly	Should not drop > 0.5 units
Residual aluminum	Daily (drinking water)	< 0.2 mg/L (WHO)
Floc appearance	Visual, every hour	Well-formed, fast-settling flocs

Common Mistakes

• Overdosing: Excess PAC can restabilize colloids (charge reversal), making water MORE turbid. If turbidity increases with higher dose, you've passed the optimum.
• Skipping jar tests: Raw water quality changes daily — a dose that worked yesterday may not work today. Run jar tests at least weekly.
• Mixing PAC with anionic PAM simultaneously: PAC (cationic) neutralizes anionic PAM. Always add PAC first, allow 1–2 minutes reaction time, THEN add flocculant.
• Using expired stock solution: PAC solutions older than 3 days lose effectiveness due to hydrolysis. Prepare fresh daily or every 2 days.
• Ignoring temperature: PAC performance drops 30–50% below 5°C. Consider switching to PFS in winter.

Storage & Handling

• Shelf life: Liquid PAC 30% — 12 months in sealed container; solid PAC — 24 months
• Temperature: Store at 5–40°C. Do not freeze (crystallization is irreversible for liquid PAC).
• Container: HDPE, FRP, or rubber-lined steel. Do NOT use bare carbon steel (corrosive).
• Safety: Mildly acidic (pH 3.5–5.0). Wear chemical goggles and acid-resistant gloves. Rinse skin/eyes immediately if contact occurs.