PAC is not automatically better than alum. The correct choice is the coagulant that produces specification-compliant water at the lowest total cost under the same water and process conditions. Compare as-supplied product dose, CoA active content, pH and alkalinity change, polymer demand, sludge, filterability, and the volume of water actually accepted.
The Importance of Clean Water and the Role of Water Treatment Chemistry
Coagulation destabilises colloidal particles so floc can form and then be separated by sedimentation, dissolved air flotation, or filtration. PAC (poly aluminium chloride) and alum (aluminium sulfate) are both aluminium coagulants, but their speciation, basicity, active content, acidity, supply form, and response to actual water can differ materially.
Price per kilogram is therefore not a complete comparison. A lower-priced product can require more coagulant, alkalinity correction, polymer, and sludge handling. Conversely, a lower product dose does not necessarily mean a lower active dose. PT Beta Pramesti Asia evaluates the options through jar testing and process data before matching them to industrial PAC and ACH coagulants.
What Are PAC and Alum?
PAC is a family of pre-polymerised aluminium coagulants; “PAC” alone does not define grade, basicity, or active content. Alum is aluminium sulfate and also comes in different forms and strengths. Use the correct lot TDS and CoA rather than assumptions based on the common name.
| Buyer or operator question | PAC | Alum | Evidence that must be held constant |
|---|---|---|---|
| What is the dose basis? | mg/L as-supplied product plus CoA active content | mg/L as-supplied product plus CoA active content | Water batch, jar volume, stock strength, density, and product lot |
| What happens to pH? | Depends on basicity, dose, and water alkalinity | Commonly consumes alkalinity; actual movement must be measured | Initial and final pH/alkalinity at the same elapsed time |
| How is floc separated? | Can suit sedimentation, DAF, or filtration when mixing is right | Can also work in all three processes | Rapid mix, slow mix, settling/flotation, temperature, and a filter test that simulates the plant |
| Does a lower dose mean lower cost? | Not necessarily | Not necessarily | Whole-program cost per volume of accepted water |
The US EPA jar-test guidance describes jar testing as a way to determine chemical type and amount for optimum floc formation. It also says the test should simulate the plant’s mixing rates and detention times and be documented so it can be repeated.
History and Evolution of PAC and Alum
Alum has a long operating record as a conventional coagulant, while PAC was developed as a pre-polymerised family whose properties vary by grade. That development widened the operator’s choices but did not remove the need for testing. An EPA technical memorandum on conversion from alum to PAC records potential PAC advantages while still framing the change as a utility-specific research and evaluation programme.
Technology age is not a selection criterion. Compare supply consistency, lot documentation, availability, handling risk, and performance on both normal and genuinely adverse raw-water conditions.
How to Normalise PAC and Alum Active Dose
The first normalisation separates product dose from the active content stated on the CoA. Use the same basis—such as mass percent as Al₂O₃—only when both certificates report it comparably.
Delivered product (kg/day) = product dose (mg/L) × flow (m³/day) ÷ 1,000.
Declared active (kg/day) = delivered product × CoA active mass fraction.
Illustrative example, not a dosage recommendation: a plant treats 5,000 m³/day. Jar tests use PAC powder at 35 mg/L with a CoA of 30% as Al₂O₃ and alum at 55 mg/L with a CoA of 17% as Al₂O₃.
| Calculation | PAC | Alum |
|---|---|---|
| Delivered product | 35 × 5,000 ÷ 1,000 = 175 kg/day | 55 × 5,000 ÷ 1,000 = 275 kg/day |
| Declared active | 175 × 0.30 = 52.50 kg/day | 275 × 0.17 = 46.75 kg/day |
| Active per m³ | 10.50 g/m³ | 9.35 g/m³ |
Here PAC uses less delivered product but slightly more declared active. Active content does not predict performance because basicity and speciation differ; water quality and process performance decide the outcome. Substitute the actual CoA values rather than treating 30% and 17% as defaults.
Benefits and Limitations of PAC
PAC may produce a more favourable floc, final pH, or response at a particular temperature or water condition. The result depends on PAC grade and basicity, actual water, mixing, and the separation process. Claims of “lower dose” or “less sludge” are valid only when product basis, active content, sludge solids, and accepted-water output are all equivalent.
Limitations include variation among grades and suppliers, form-specific storage and handling needs, overfeed risk, and misleading decisions when operators optimise settled turbidity without checking pH, alkalinity, relevant residual aluminium, filterability, and sludge.
Benefits and Limitations of Alum
Alum has a widely understood operating basis and can be effective where raw water, alkalinity, pH, and solids-handling facilities suit it. Competitive product price and established supply can be advantages, but only after pH or alkalinity correction, polymer, and sludge costs are included.
Its response may shift with pH, temperature, colour, and natural organic matter. Overfeed can also produce poor floc or an unwanted residual. Alum should not be treated as a simple default that can run without a dose sweep and control limits.
Water Characteristics:
At minimum, record turbidity, pH, alkalinity, temperature, colour, and the process target. For drinking water or sensitive reuse, add TOC/UV254 and residual aluminium where relevant. For wastewater, add TSS, fractionated COD where available, oil, metals, or permit parameters expected to report to the floc.
Run the dose sweep on samples representing normal and credible adverse conditions. A sample stored too long, allowed to settle, or moved to a different temperature may no longer represent the influent.
Budget Considerations:
Compare cost per 1,000 m³ of accepted water, not per 1,000 m³ entering the plant:
Programme cost/1,000 m³ accepted = (coagulant + alkalinity/pH correction + polymer + energy + sludge handling + rework/disposal) ÷ accepted volume × 1,000.
| Cost component | Data to record | Why it is often missed |
|---|---|---|
| Coagulant | kg/day from as-supplied dose and delivered price | Price per kg does not reveal daily demand |
| Alkali/acid and polymer | kg/day in the same run | “Aids” are often excluded from the comparison |
| Sludge | m³/day, % solids, dewatering, haulage/disposal | Wet volume is not dry-solids mass |
| Accepted water | m³ meeting every criterion | Rework and off-spec output shrink the denominator |
| Operations | Mixing, pumping, cleaning, filter run/backwash | Downstream effects can exceed the coagulant price difference |
Process-Specific Requirements:
Jar testing should reproduce the actual process. Rapid mix, slow-mix gradient and time, temperature, pH adjustment, polymer, and settling period must be equal for both candidates. A DAF evaluation should represent air contact and skimming; a filtration process needs a filterability or pilot test because floc appearance alone does not predict headloss.
Acceptance checklist:
- use one water batch and a verified stock-preparation method;
- include a blank and a dose sweep around the candidate optimum;
- measure final pH/alkalinity, turbidity or TSS, target parameters, settling rate, and sludge volume/dewaterability;
- repeat the candidate condition to expose repeatability;
- move to a plant trial with hold points rather than a full immediate change; and
- evaluate treated water, filter run, sludge, consumption, and tank drawdown over the same period.
PT Beta Pramesti Asia supplies industrial coagulants and flocculants for floc formation and separation. If the chemistry passes but pump delivery is unstable, Watermart dosing pumps provide the equipment handoff; solution strength, viscosity, materials, backpressure, and turndown belong in the specification.
Conclusion
The winner in a PAC-versus-alum comparison is the programme that reliably produces accepted water at the lowest total cost, not the product with the lowest nominal price or dose. Normalise delivered product and active content, then let jar tests and a plant trial decide because active content does not represent basicity and speciation.
Quality criteria come from the water’s end use and site obligations. For Indonesian industrial wastewater, check Government Regulation No. 22 of 2021, Environment Minister Regulation No. 5 of 2014, applicable sector amendments, and the plant’s technical approval; these rules do not prescribe a universal PAC or alum dose. Hazardous-product handling should also follow the current SDS and Government Regulation No. 74 of 2001.
Send water analyses, flow, separation process, quality targets, candidate TDS/CoAs, sludge data, and local costs through the Beta Pramesti Asia contact page to build an auditable test matrix.
Technical sources: US EPA Appendix F—Jar Tests; EPA technical memorandum on converting alum to PAC; Indonesia Government Regulation No. 22 of 2021; and Environment Minister Regulation No. 5 of 2014.