At a Glance
- The core difference in poly aluminium chloride vs alum: PAC is a pre-hydrolyzed polymeric coagulant, while alum hydrolyzes only after it is dosed into water. That single difference drives most of the performance gap between them.
- Dosage: PAC typically requires 30 to 50% lower dosage than alum for the same turbidity removal.
- Sludge: PAC generates noticeably less sludge, cutting downstream disposal costs.
- pH range: PAC works effectively across roughly pH 5 to 9, a wider window than alum’s more pH-sensitive range.
- Cost: Alum is cheaper per kilogram, but PAC’s lower dosage and sludge volume often close, or reverse, the total cost gap.
What you’ll learn: how PAC and alum differ chemically, how they compare on performance and cost, how to convert your dosing when switching from alum to PAC, and how to decide which coagulant fits your application.
Introduction
When evaluating poly aluminium chloride vs alum, this comparison comes up in nearly every water treatment procurement conversation. If you’re dosing alum today and considering a switch, or specifying a coagulant for a new plant, understanding how they differ is crucial.
Both are aluminium-based coagulants used to remove turbidity and suspended solids, but they behave differently in the water, and that shows up directly in operating costs.
The global market for water treatment coagulants is projected to grow at a 4 to 6% CAGR between 2026 and 2035, driven by tightening discharge standards and rising industrial water reuse mandates, according to industry market research.
PAC and alum together still make up the bulk of that demand, which is exactly why this comparison matters for procurement teams right now.
This guide covers the chemistry, the performance data, and a practical dosing conversion guide for plants switching from alum to PAC. Ready to move forward? Buy poly aluminium chloride with full specifications and certified grades.
What Is the Difference Between PAC and Alum?
The short answer: what is poly aluminium chloride comes down to structure. PAC is a partially pre-formed polymer, while alum is a simple salt that builds its coagulating structure only after it hits the water.
Alum, or aluminium sulphate (alum) in water treatment, dissolves and then hydrolyzes in situ, forming aluminium hydroxide flocs as a reaction with the water itself. That step takes time, is sensitive to pH and temperature, and produces more byproduct.
PAC arrives already partially hydrolyzed and polymerized at the point of manufacture. Its aluminium species are pre-formed into larger, positively charged polymer chains, so it reacts almost immediately on dosing, neutralizing particle charge and forming flocs faster with less chemical needed.
That structural difference is why PAC generally outperforms alum on dosage, sludge volume, pH tolerance, and settling speed. The tradeoff is unit price.
Chemistry Compared
| Factor | PAC | Alum |
| Chemical form | Pre-hydrolyzed polymeric aluminium chloride | Simple aluminium salt |
| General formula | [Al₂(OH)ₙCl₆₋ₙ]ₘ | Al₂(SO₄)₃·xH₂O |
| Hydrolysis | Occurs during manufacturing | Occurs after dosing |
| Reaction speed | Near immediate | Slower, temperature dependent |
PAC vs Aluminium Chlorohydrate
Not quite the same thing. Aluminium chlorohydrate (ACH) is a very high basicity member of the same polyaluminium chloride family. Standard water treatment PAC generally runs lower basicity, commonly in the 40 to 70% range, while ACH’s higher basicity suits specialty uses like antiperspirant formulation alongside high-performance coagulation. If a supplier quotes PAC and ACH at the same price, check the basicity spec before assuming they’re interchangeable.
Poly Aluminium Chloride vs Alum: Performance and Cost Evaluation
| Metric | PAC | Alum |
| Typical dosage | 30 to 50% lower for equivalent removal | Baseline |
| Sludge generated | Less | More |
| Effective pH range | ~5 to 9 | Narrower, more pH sensitive |
| Settling speed | Faster | Slower |
| Residual aluminium | Generally lower | Can be higher outside optimal pH |
| Cold water performance | More consistent | Often underperforms |
| Unit price | Higher per kg | Lower per kg |
| Total treatment cost | Often 10 to 30% lower overall | Varies by scale and sludge disposal cost |
PAC advantages: lower dosage, less sludge, wider pH tolerance, faster settling, better cold-water performance, and lower residual aluminium (relevant for drinking water compliance).
Alum still holds ground where budgets are tight, raw water is warm and low turbidity, and existing infrastructure is already built around alum dosing and sludge handling.
On cost, per-kilogram price isn’t the number that matters. What matters is cost per unit of treated water, which factors in dosage required, sludge disposal cost, pH correction chemicals, and operational consistency.
Across most published case comparisons, switching from alum to PAC reduces total treatment cost by roughly 10 to 30%, though the actual figure depends on your raw water and sludge handling setup.
This isn’t just supplier marketing. A full-scale drinking water treatment plant study published in Separation Science and Technology found that PAC achieved lower turbidity and residual aluminum than alum at meaningfully lower dosages, confirming the lab-scale numbers hold up under real operating conditions.
See these numbers hold up against your own water. Request a quote or request a sample to test PAC against your current alum baseline.
How to Switch from Alum to PAC: Dosing Conversion Guide
Don’t substitute PAC at the same dosage rate as alum. The two aren’t equivalent on a 1:1 basis.
- Baseline your current alum dosage. Record turbidity removal, floc characteristics, and sludge volume at your current rate.
- Run a jar test with PAC. Start at roughly 30 to 50% of your current alum dosage by weight, then adjust based on floc formation.
- Check pH. PAC’s wider range may reduce or remove the need for separate pH correction. Test without it first.
- Evaluate floc quality and settling time. PAC flocs typically form and settle faster, which may allow reduced clarifier retention time.
- Confirm grade match. Drinking water, industrial, and wastewater streams need different PAC grades and basicity levels.
- Scale up gradually, from jar test to pilot to full dosing, monitoring turbidity, residual aluminium, and sludge output at each step.
- Re-baseline your cost model. Savings usually show up more in reduced sludge handling than in the chemical line item alone.
Actual optimum dosage depends on grade, basicity, raw water quality, and temperature, so confirm with a trial before scaling.
When to Choose PAC vs When to Choose Alum
Choose PAC if: raw water is cold, low turbidity, or seasonally variable; sludge disposal cost is significant; you’re treating drinking water and need lower residual aluminium; or you’re capacity constrained.
Choose alum if: budget is tightly constrained on a per-kg basis; existing infrastructure and staff training are built around alum; raw water is consistently warm and easy to coagulate; and sludge handling isn’t a bottleneck.
Neither is universally better. The right choice depends on your water source, plant infrastructure, and total cost model, not unit price alone.
Whichever coagulant you land on, don’t skip documentation. Request the COA, TDS, and SDS for the specific grade before you order, and if you’re treating drinking water, confirm your PAC carries relevant certification (such as NSF/ANSI/CAN 60, REACH registration, or the equivalent local standard) before it goes anywhere near a potable supply. A supplier who can’t produce this paperwork on request isn’t one to build a switch-over plan around.
Ready to make the switch? Request a quote for certified PAC grades, or request a sample to run your own comparison first.
Conclusion
PAC and alum both clarify water by neutralizing suspended particles, but they get there differently, and that difference shows up in dosage, sludge volume, and total treatment cost. Alum still has a place where budgets are tight and raw water is easy to treat.
For most plants dealing with variable water quality or rising sludge disposal costs, PAC’s efficiency gains typically outweigh its higher unit price. If you’re evaluating a switch, start with a jar test against your own water, then talk to a supplier who can back the numbers with documentation.
Ready to compare grades for your application? Request a quote or request a sample to test against your water source.
Have questions on grade selection or dosing for your specific plant? Contact us and we’ll walk through the specs with you.
