Many peers in the water treatment industry, especially newcomers, often get confused by chemical abbreviations such as PAC and PFS, unsure how to select and apply them properly.
As a professional water treatment technology enterprise, Chengda sorts out core information of 9 commonly used chemicals today, covering applications, suitable working conditions, advantages and drawbacks. This article elaborates all key points; feel free to bookmark it for reference!
I. Primary Flocculants (For Water Purification & Impurity Removal)
1. Polyaluminium Chloride (PAC) – The Versatile All-Rounder
Application Scenarios: Tap water purification, municipal wastewater, industrial circulating water, initial rainwater treatment; compatible with water of high and low turbidity.
Optimum pH: 6.0–8.0 (effective range: 5.0–9.0). Lime dosing is required if pH is too low; PAC loses efficacy under excessive pH.
Core Advantages:Fast hydrolysis; visible flocs form within 1–3 minutes. Required dosage is 30%–50% lower than aluminum sulfate; low residual aluminum in effluent;
low corrosion to equipment and easy operation.
Limitations: Performance declines at low temperature (<5℃); flocs are lightweight with slow sedimentation.
Treatment Performance (Domestic Wastewater, Dosage: 30–60 mg/L):Turbidity removal: 85%–98%; COD removal: 40%–60%; Total Phosphorus (TP) removal: 60%–80%.
2. Polyferric Sulfate (PFS) – Specialist for Phosphorus Removal & Decolorization
Application Scenarios:Advanced phosphorus removal for wastewater, textile wastewater decolorization, demulsification of oily wastewater, heavy metal wastewater treatment; particularly suitable for
low-temperature & low-turbidity water.
Optimum pH: 6.0–9.0 (effective range: 4.0–11.0). Better phosphorus removal under alkaline conditions.
Core Advantages: Dense flocs; sedimentation speed 1.5–2 times faster than PAC. Outperforms aluminum salts in phosphorus removal, decolorization and COD reduction; stable performance under low temperature.
Limitations: Effluent may carry slight yellow tint; highly corrosive to carbon steel, anti-corrosion dosing equipment is necessary.
Treatment Performance (Primary Treatment of Municipal Wastewater, Dosage: 20–50 mg/L):
TP removal: 85%–95%; Turbidity removal: 90%–98%; Decolorization rate for textile wastewater:70%–90%.
3. Aluminum Sulfate – Traditional Low-Cost Option
Application Scenarios: Small-scale water plants, low-turbidity industrial circulating water, fluoride removal for fluoride-containing wastewater; ideal for small projects with limited budget.
Optimum pH: 6.0–7.8 (narrow effective range). Treatment efficiency drops sharply outside this range; pH adjustment is mandatory.
Core Advantages: Mature technology, stable supply and competitive price.
Limitations: Almost ineffective under low temperature; light flocs settle slowly and auxiliary coagulant is required. Higher dosage leads to larger sludge output.
Treatment Performance (Low-turbidity Surface Water, Dosage:40–80 mg/L):
Turbidity removal:70%–90%; Fluoride removal rate exceeds 90% (pH controlled at 5.5–6.5, dosage:200–300 mg/L).
4. Ferric Chloride – High-Strength Ferric Salt Coagulant
Application Scenarios: Steel pickling wastewater, acidic mine wastewater, sulfide-containing wastewater, pretreatment of high-concentration organic wastewater.
Optimum pH: 6.0–9.0 (effective range:4.0–11.0). Functions vary at different pH levels; primary working range:6.0–9.0.
Core Advantages: Large, heavy flocs with excellent sedimentation; reliable treatment effect for low-temperature and high-turbidity water.
Limitations: Extremely corrosive; dedicated anti-corrosion equipment required. Causes high color in effluent, subsequent decolorization needed. Solid material is highly
hygroscopic with strict handling requirements.
Treatment Performance (Steel Pickling Wastewater, Dosage:100–300 mg/L):
SS removal:85%–95%; Heavy metal removal:80%–90%; Sulfide removal rate >95%.
5. Ferrous Sulfate (Green Vitriol) – Low-Cost Multi-Functional Agent
Application Scenarios: Textile wastewater decolorization, reduction treatment of chromium-containing wastewater, precipitation of phosphorus-containing wastewater.
Widely available as by-product from titanium dioxide plants and steel factories with ultra-low cost.
Optimum pH: pH 2.5–3.0 for chromium reduction; oxidation is required before coagulation, optimum oxidation pH:8.0–9.0.
Core Advantages: Price is only 1/3 of PAC. Works as both reducing agent and coagulant (oxidation required).
Limitations: Insufficient oxidation causes green/yellow discoloration in effluent and consumes dissolved oxygen in water.
Treatment Performance (Textile Wastewater, Dosage:200–400 mg/L, pH adjusted to 9 with lime):
Color removal:60%–85%; Chromium reduction rate >99%; TP removal:70%–85% (after oxidation).
6. Polyaluminum Ferric Chloride (PAFC) – Aluminum-Iron Composite Coagulant
Application Scenarios: High-turbidity flood-period water, low-temperature low-turbidity water, industrial wastewater with fluctuating water quality, upgrading of municipal wastewater treatment.
Optimum pH:6.5–8.5 (effective range:5.5–9.5), combining the adaptability of aluminum salts and ferric salts.
Core Advantages:Integrates strengths of PAC and PFS, strong resistance to water quality fluctuation. Flocs denser than PAC; sedimentation speed between PAC and PFS;
stable performance at low temperature.
Supplementary Note: Solid products generally contain ≥28% Al₂O₃ (national standard requirement), iron content 2%–5%. It is a copolymerized aluminum-iron composite flocculant.
Treatment Performance (Domestic Wastewater, Dosage:35–50 mg/L):
TP removal:75%–90% (10%–15% higher than PAC); Turbidity removal:85%–95%; High retention of sedimentation speed under low temperature.
II. Auxiliary Chemicals (pH Adjustment, Coagulation Aid, Precipitation)
7. Lime (Quicklime / Slaked Lime) – Economical Regulator
Application Scenarios: Neutralization of acidic wastewater, chemical phosphorus removal, water softening, heavy metal precipitation, sludge dewatering conditioning.
Optimum pH: Neutralization adjusts pH to 7.0–12.0; optimum pH for phosphorus & heavy metal removal:9.5–11.5.
Core Advantages: Low price, serves both pH adjustment and pollutant precipitation.
Limitations: Generates massive sludge and increases sludge disposal pressure; produces dust during operation, dust removal facilities required.
Treatment Performance (Phosphorus Removal, Dosage depends on phosphate concentration):
TP removal:90%–98%; Heavy metal removal:90%–99%; Rapid neutralization of acidic wastewater.
8. Calcium Chloride – Excellent Coagulation Aid for Low-Temperature Conditions
Application Scenarios: Accelerate sludge sedimentation under low temperature, demulsification of oily wastewater, cooling water stabilization, fluoride removal for fluoride wastewater.
Optimum pH:6.0–9.0; performance barely affected by pH.
Core Advantages: Improves sludge settling performance under low temperature (sedimentation speed increased by 30%–50%); capable of oil demulsification.
Limitations: Limited coagulation effect when used alone; must be combined with PAC or PFS.
Treatment Performance (Low-Temperature Sludge Sedimentation, Dosage:10–30 mg/L):
Combined with PAC, oil removal rate rises to 60%–80%; sludge volume index reduced by 20%–40% under low temperature.
9. Magnesium Salts (Magnesium Hydroxide, Magnesium Chloride, etc.) – Safe & High-Efficiency Heavy Metal Remover
Application Scenarios: Electroplating wastewater containing heavy metals, textile wastewater decolorization, advanced phosphorus removal at the tail end of wastewater treatment.
Optimum pH: Flocculation takes effect only at pH9.5–11.5; ineffective at lower pH.
Core Advantages: Non-toxic, no impact on effluent biotoxicity; low sludge output and easy filtration, high precision for heavy metal removal.
Limitations: Large dosage of alkali required for pH adjustment, raising chemical cost.
Treatment Performance (Nickel-Containing Electroplating Wastewater, Dosage:80–150 mg/L, pH 10.5–11.0):
Nickel removal rate:95%–99%; Textile wastewater decolorization rate:80%–95%; TP removal:80%–90%.
III. Quick Selection Guide (Direct Matching)
·Conventional surface water (Turbidity < 500 NTU): PAC first choice; aluminum sulfate for low-cost alternatives
·Low-temperature low-turbidity water (<5℃): PFS or PAFC preferred
·High-turbidity flood-period water (>1000 NTU): PAFC first choice; PAC + PFS combination also applicable
·Advanced phosphorus removal for municipal wastewater (TP <0.5 mg/L): PFS preferred; add lime if alkalinity insufficient
·Textile wastewater decolorization: Ferrous sulfate (reduction) + PFS (coagulation); magnesium salt as alternative
·Heavy-metal-containing wastewater: PFS (weak alkaline environment), magnesium salt (strong alkaline, high precision)
·Acidic wastewater (pH<5): Lime first choice; sodium hydroxide as alternative (higher cost)
·Poor sludge sedimentation under low temperature: Calcium Chloride + PAC combination
IV. Tips for Combined Chemical Dosing
Single chemical hardly achieves all treatment targets; combined dosing delivers higher efficiency:
1.PAC + Calcium Chloride: Classic combination to improve sedimentation under low temperature
2.Ferrous Sulfate + PFS: Top option for decolorization & impurity removal of textile wastewater
3.PAC + PFS: Complementary effect to cope with fluctuating water quality
4.Lime + PFS: Adjust pH first before coagulation when alkalinity is inadequate
5.Ferrous Sulfate + Hydrogen Peroxide (Fenton Process): Treat refractory organic wastewater
Note: Dosing sequence and interval directly affect treatment efficiency. Jar tests with actual wastewater are recommended to confirm optimal solutions.
If you need support on chemical selection or process optimization, feel free to consult the professional team of Chengda Water Treatment!
