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Written by the HyChron Technical Team — water treatment specialists with over 15 years of field experience in municipal and industrial systems. Last reviewed: April 2026
The most common objection to PAC is its unit price. Per kilogram, PAC costs more than alum — and that single data point stops many procurement decisions before the full cost picture is considered.
The problem is that cost-per-kilogram is the wrong metric for evaluating coagulant economics. The correct metric is cost-per-cubic-meter-treated — and when the full treatment cost is calculated, PAC consistently delivers a lower total cost than alum in the majority of applications.
This article provides a structured cost analysis framework that accounts for all the relevant cost drivers, with worked examples that show where and how PAC delivers its cost advantage.
Why Cost-Per-Kilogram Is the Wrong Metric
A coagulant’s total cost impact on a treatment plant includes:
- Chemical purchase cost — price per kg × quantity used
- Sludge handling cost — dewatering, transport, and disposal
- Auxiliary chemical cost — pH adjustment chemicals, PAM for flocculation
- Equipment maintenance cost — corrosion-related wear on dosing and treatment equipment
- Energy cost — dewatering energy, aeration (for biological load reduction)
- Compliance risk cost — cost of non-compliance events, fines, or permit violations
PAC costs more on metric 1 but delivers savings on metrics 2, 3, 4, and 5. In most plants, the savings on these metrics exceed the premium on metric 1 — often significantly.
Root Cause of Cost Advantage: Lower Effective Dosage
PAC’s cost advantage starts with dosage. At 30–50% lower dosage than alum for equivalent turbidity removal, the chemical purchase cost per cubic meter treated is substantially lower than the unit price difference suggests.
Example:
- Alum: $0.18/kg, dose 40 mg/L → Chemical cost = 40 × $0.18 / 1,000 = $0.0072/m³
- PAC: $0.35/kg, dose 22 mg/L → Chemical cost = 22 × $0.35 / 1,000 = $0.0077/m³
At these parameters, PAC’s chemical purchase cost per m³ is only 7% higher than alum — despite a 94% higher unit price. And this is before any other cost factors are considered.
Adjust the dosage ratio and unit prices for your specific situation — the calculation framework is the same.
Step-by-Step Total Cost Analysis
Step 1 — Calculate Chemical Purchase Cost Per m³
Chemical cost per m³ = Dose (mg/L) × Unit price ($/kg) / 1,000
Run this calculation for both PAC and your current coagulant at their respective optimal doses (confirmed by jar test).
Step 2 — Calculate Sludge Handling Cost Per m³
Sludge cost per m³ = [Dose (mg/L) × Sludge factor × Disposal cost ($/tonne)] / 1,000,000
Where sludge factor ≈ 2.5 (accounts for coagulant precipitate plus captured suspended solids at typical raw water quality).
Example:
- Alum: 40 mg/L dose, $150/tonne disposal → Sludge cost = (40 × 2.5 × 150) / 1,000,000 = $0.015/m³
- PAC: 22 mg/L dose, $150/tonne disposal → Sludge cost = (22 × 2.5 × 150) / 1,000,000 = $0.0083/m³
- Sludge saving with PAC: $0.0067/m³
Step 3 — Calculate pH Adjustment Chemical Cost Per m³
If your raw water requires pH adjustment before PAC (pH adjustment is rarely needed within PAC’s wide pH range of 5.0–9.0 but may be needed for industrial applications), include acid or alkali dosing cost.
If switching from alum to PAC eliminates a pH adjustment step currently required for alum (alum requires pH 6.5–7.5, PAC does not), this is a direct cost saving.
Step 4 — Estimate Equipment Maintenance Differential
Alum and ferric sulfate are corrosive due to sulfate content. PAC is significantly less corrosive. While maintenance cost differences are harder to quantify precisely, plants switching from alum to PAC consistently report reduced dosing pump maintenance frequency, longer pipe and fitting service life, and reduced chemical storage tank inspection frequency.
Conservative estimate for plants with corrosion-related maintenance history: $0.001–0.003/m³ saving.
Step 5 — Sum the Total Cost Differential
Total cost per m³ = Chemical cost + Sludge cost + pH adjustment cost + Maintenance cost
Continuing the example:
| Cost Component | Alum | PAC | Saving with PAC |
|---|---|---|---|
| Chemical purchase | $0.0072/m³ | $0.0077/m³ | −$0.0005/m³ |
| Sludge handling | $0.0150/m³ | $0.0083/m³ | +$0.0067/m³ |
| pH adjustment | $0.0010/m³ | $0.0000/m³ | +$0.0010/m³ |
| Equipment maintenance | $0.0020/m³ | $0.0005/m³ | +$0.0015/m³ |
| Total | $0.0252/m³ | $0.0165/m³ | +$0.0087/m³ |
Net saving with PAC: $0.0087/m³ — a 35% reduction in total treatment cost.
At 5,000 m³/day plant flow: Annual saving = $0.0087 × 5,000 × 365 = $15,878/year
Expected Cost Savings: Reference Ranges
| Plant Type | Daily Flow | Typical Annual Saving (PAC vs Alum) |
|---|---|---|
| Small municipal plant | 500–2,000 m³/day | $2,000–$8,000/year |
| Medium municipal plant | 5,000–20,000 m³/day | $15,000–$65,000/year |
| Large municipal plant | 50,000+ m³/day | $150,000+/year |
| Industrial wastewater | 500–5,000 m³/day | $5,000–$50,000/year |
Estimates based on typical dosage reduction, sludge disposal costs of $100–200/tonne, and moderate equipment maintenance savings. Actual savings depend on local chemical prices, disposal costs, and current alum dosage.
For detailed sludge cost calculations: Sludge Production When Using PAC
Frequently Asked Questions
My PAC supplier quotes a much higher price per kg than alum — how can PAC be cheaper overall?
The answer is in the dosage. If PAC requires 40% lower dose than alum, and you are paying 50% more per kg, the chemical cost per m³ is only 10% higher (1.5 × 0.6 = 0.9 — actually cheaper). Add sludge reduction and you are almost certainly ahead on total cost. Use the Step 1 calculation with your actual prices and jar-test doses to confirm.
How do I account for the capital cost of switching to PAC (new storage tanks, dosing equipment)?
In most cases, switching from alum to PAC requires only dosage recalibration — the same storage and dosing equipment is compatible. If new bulk storage is needed for liquid PAC, amortize the capital cost over the expected equipment life and add it to the annual cost comparison. At typical savings levels, capital payback is usually 1–3 years.
Our sludge disposal cost is very low — does the PAC cost advantage still hold?
If disposal cost is very low (below $50/tonne), the sludge saving from PAC is smaller. The cost advantage then depends more heavily on dosage reduction and maintenance savings. Run the full five-step calculation with your actual costs. In some very-low-disposal-cost situations, the economics are approximately neutral — PAC’s advantage then comes from performance rather than cost.
Conclusion
The cost case for PAC is built on total treatment cost per cubic meter — not unit purchase price. When chemical purchase cost, sludge handling, pH adjustment, and equipment maintenance are all included, PAC delivers total cost savings of 20–40% versus alum in most applications.
The five-step framework in this article provides the structure to calculate this precisely for your plant using your actual costs, flows, and jar-test-confirmed dosage data.
Contact our technical team today for a free cost analysis tailored to your plant — we will calculate the PAC versus alum cost comparison using your actual flow, disposal costs, and water quality data. We respond within 24 hours.
