How to Use Poly Ferric Sulfate (PFS) in Water Treatment

Overview

Poly Ferric Sulfate (PFS) is a high-performance inorganic coagulant with ≥ 19% Fe content. It outperforms PAC in cold water (< 5°C), high-color applications, and heavy metal co-removal. PFS produces denser flocs with faster settling. Working pH range: 4.0–11.0.

Preparation & Dissolution

PFS is supplied as a dark reddish-brown liquid (specific gravity ~1.45). No dissolution needed — dose directly or dilute to 5–10% working solution.

For solid PFS (less common):

1. Fill tank with clean water
2. Add PFS granules slowly with agitation
3. Stir 20–30 minutes
4. Working solution concentration: 5–10%

Equipment: PVC, HDPE or FRP tanks and piping. Avoid stainless steel 304 (chloride stress corrosion). Metering pump with anti-siphon valve.

Dosing Guide

Application	Typical Dose (as product)	Notes
Municipal wastewater	30–80 ppm	Better color removal than PAC
Cold water (< 5°C)	20–50 ppm	Does not slow down like PAC in cold
Textile wastewater	80–150 ppm	Superior for reactive dye removal
Heavy metal co-removal	50–150 ppm	Fe(OH)₃ co-precipitates Cu, Zn, Pb
Phosphorus removal	10–30 ppm as Fe	Fe:P molar ratio 1.5–2.5:1

Application Procedure

1. Measure raw water turbidity, color, pH, temperature, and target metals
2. Set metering pump to target dose
3. Inject at flash mix zone with vigorous agitation (G > 300 s⁻¹) for 1 minute
4. Slow mix at 30–50 s⁻¹ for 15–20 minutes
5. Settle in clarifier (HRT 2–4 hours)
6. Monitor settled water quality
7. Check for iron residual in effluent — if yellowish tint, dose is too high

Monitoring & Control

Parameter	Frequency	Target
Settled water turbidity	Every 30 min	< 5 NTU
Effluent color	Hourly	< 40 Pt-Co
pH after dosing	Hourly	Note: PFS depresses pH more than PAC
Iron residual	Daily	< 0.3 mg/L
Phosphate (if P removal)	Daily	< 0.5 mg/L TP

Common Mistakes

• Forgetting pH impact: PFS drops pH more than PAC (0.5–1.5 units). May need NaOH co-dosing for low-alkalinity water.
• Iron staining: Overdosing causes yellowish effluent from residual Fe³⁺. Reduce dose or add polymer to settle iron flocs.
• Mixing with phosphonate inhibitors: PFS reacts with HEDP/ATMP, reducing both coagulant and inhibitor effectiveness. Dose at separate injection points.
• Using in drinking water without monitoring: Iron residual must be < 0.3 mg/L to avoid taste/color issues.

Storage & Handling

• Shelf life: 12 months (liquid)
• Temperature: Store above 0°C. PFS may crystallize below -5°C but can be reconstituted by warming to 20°C with agitation.
• Container: HDPE, PVC, FRP. Avoid bare metals.
• Safety: Acidic (pH 2–3). Strong oxidizer hazard if concentrated. Wear acid-resistant PPE. Stains skin and clothing brown — wash immediately.