Liquid PAC or PAC powder: how to choose

Yes. Both are polyaluminium chloride; they differ in strength and in how they are handled. IS 15573:2018, the Indian Standard for polyaluminium chloride, covers it as a liquid or a powder, each in medium- and high-basicity types, as a coagulant for drinking-water treatment. The US EPA notes that PAC is supplied mainly as a solution but also as a solid, with its strength stated as percent aluminium oxide (Al2O3).

Source: Bureau of Indian Standards, 2018; US Environmental Protection Agency, 2022

Al2O3 says how much aluminium a kilogram carries. Basicity, the ratio of hydroxide to aluminium, affects how that aluminium behaves: the UK Pool Water Treatment Advisory Group (PWTAG), writing about swimming pools, says higher basicity generally means more polymer, higher cationic charge density and higher efficiency. A jar test shows what that means for your water.

Source: US Environmental Protection Agency, 2022; Pool Water Treatment Advisory Group (PWTAG), 2014

Source: Bureau of Indian Standards, 2018; CPHEEO, Ministry of Housing and Urban Affairs, Government of India, 2024; Institut für Arbeitsschutz der DGUV (IFA), GESTIS Substance Database, 2023; Nexchem Ltd, 6 Mar 2023; Solenis LLC (SDS hosted by Pennsylvania Department of Environmental Protection), 14 Jan 2020; Aditya Birla Chemicals (India) Ltd, 2013; Henan Xunyu Chemical Co., Ltd, 2021

Table 1 of IS 15573:2018 sets minimum Al2O3 at 9.5% (medium basicity) and 10.2% (high basicity) for liquid and 28.0% for both powder types, and minimum relative basicity at 35% and 64% in either form. Annex B defines relative basicity as moles of OH per three moles of aluminium. Other documents express basicity differently (the Australian Drinking Water Guidelines give about 50% w/w), so ask how a supplier measured it.

Source: Bureau of Indian Standards, 2018; National Health and Medical Research Council (Australia), 2005

• Liquid: specific gravity at 25 °C at least 1.18 (medium) or 1.20 (high), viscosity 3-10 mPa.s at 20 °C. Powder: bulk density at least 0.65 g/ml.
• Maximum chloride as Cl: 12.5% and 10.5% for liquid, 37.5% and 31.0% for powder (medium, high). Insolubles: 0.5% liquid, 1.50% powder. TOC: 80 ppm liquid, 240 ppm powder.
• Toxic substances, ppm maximum (liquid / powder): mercury 0.2 / 0.6, arsenic 5 / 15, iron 80 / 240, manganese 20 / 60, chromium 15 / 45, selenium 8 / 24. Amendment No. 1 (June 2020) cut cadmium to 2 / 6 and lead to 8 / 24.

Source: Bureau of Indian Standards, 2018; Bureau of Indian Standards, 2020

One kg of 28–32% powder holds 280–320 g of Al2O3, the same as 2.8–3.2 kg of 10% liquid. For any other pair, divide the Al2O3 you need by each product's Al2O3 fraction: 100 kg of Al2O3 is 100 ÷ 0.10 = 1,000 kg of 10% liquid, or between 100 ÷ 0.32 = 312.5 kg and 100 ÷ 0.28 = 357.1 kg of powder.

Source: Bureau of Indian Standards, 2018

Only 100 kg of a tonne of 10% liquid is Al2O3, yet you haul and store the whole tonne. It fills 820–847 litres at the 1.18–1.22 specific gravity (20 °C) in the Australian guidelines. Grade names are not a reliable guide to strength. Gujarat Alkalies and Chemicals sells liquid PAC-10, PAC-14 and PAC-18 and powder PAC-30 without defining the numbers in its announcement, and Grasim's SAB18/KANPAC18 data sheet gives a minimum of 16.5% Al2O3 for the liquid and 29% for the powder. Recalculate from the Al2O3 on the certificate of analysis (CoA) whenever the grade changes.

Source: National Health and Medical Research Council (Australia), 2005; Gujarat Alkalies and Chemicals Limited, 7 Feb 2025; Grasim Industries Limited, Chemical Division (copy uploaded by a seller to IndiaMART), 2018

Convert through Al2O3: work out how much Al2O3 the current dose delivers, then how much of the new product delivers the same. Ireland's EPA manual warns that aluminium sulphate is sold by % Al2O3, which is not the same as % of the salt. PAC is also sold by % Al2O3, so check which of the two a dose or a price refers to. The Australian guidelines quote typical doses of 5–100 mg/L as product with 10% Al2O3 (more for very dirty water). The US EPA's 1999 coagulation manual reports doses as active chemical and shows the scaling with one example: 9.1 mg/L of active ferric chloride is 21.7 mg/L of a 42% solution.

Source: Environmental Protection Agency, Ireland, 2002; US Environmental Protection Agency, 2022; National Health and Medical Research Council (Australia), 2005; US Environmental Protection Agency, 1999

1. Dose as Al2O3 (mg/L) = product dose (mg/L) × Al2O3 % ÷ 100.
2. New product dose (mg/L) = dose as Al2O3 ÷ (new product's Al2O3 % ÷ 100).
3. Daily use (kg/day) = dose (mg/L) × flow (m³/day) ÷ 1,000. One MLD is 1,000 m³/day.

Source: US Environmental Protection Agency, 1999; Environmental Protection Agency, Ireland, 2002

Example (illustrative, not a recommended dose): a 10 MLD plant doses 30 mg/L of 10% liquid, or 3.0 mg/L as Al2O3. From powder that is 3.0 ÷ 0.32 = 9.4 mg/L at 32%, or 3.0 ÷ 0.28 = 10.7 mg/L at 28%. Daily use is 300 kg/day of liquid against 94–107 kg/day of powder.

Source: US Environmental Protection Agency, 1999

IS 15573 states Al2O3 by mass, so a litre of 10% liquid at specific gravity 1.20 holds 120 g of Al2O3, and 300 kg/day is 250 L/day, or 10.4 L/h, on the pump. Use the specific gravity on your CoA. Some research states doses as aluminium: a 2023 study by Krupińska used 1 to 5 mg Al per litre. Convert with the IS 15573 factor, Al = Al2O3 × 0.5293, so 3.0 mg/L as Al2O3 is 1.59 mg/L as Al.

Source: Bureau of Indian Standards, 2018; Molecules (MDPI), 4 Jan 2023

IS 15573 wants liquid PAC stored in dark-coloured acid-proof lined tanks under shade. Powder needs a covered dry store instead, because it absorbs moisture from the air.

Source: Bureau of Indian Standards, 2018

The US EPA says to keep PAC indoors or above freezing, Uisce Éireann (Irish Water) specifies 5 °C to 20 °C for stored PAC, and Aditya Birla Chemicals' MSDS warns that PAC may become unstable if stored for long above 40 °C. The US EPA gives a shelf life of approximately 12 months, taken from manufacturers' documents. HydroChemix, a vendor, gives 12–24 months for powder in sealed bags below 70% relative humidity and 6–12 months for sealed 10% liquid at 10–30 °C. We found no standard or regulator that gives a separate figure for powder, so use your supplier's technical data sheet (TDS).

Source: US Environmental Protection Agency, 2022; Uisce Éireann (Irish Water), 30 Nov 2023; Aditya Birla Chemicals (India) Ltd, 2013; HydroChemix (vendor), 6 Aug 2026

Uisce Éireann sizes coagulant storage for 30 to 60 days of use; in the 10 MLD example, 30 days is 7,500 litres of liquid or 2.8–3.2 tonnes of powder bags.

Source: Uisce Éireann (Irish Water), 30 Nov 2023

CPHEEO's 2024 manual says every solid coagulant must be fully dissolved before the solution goes into the raw water, and kept uniform by mechanical agitation; manual mixing is allowed only at plants up to 3.0 MLD. It asks for at least two solution tanks, each holding 12 hours' need at maximum demand.

Source: CPHEEO, Ministry of Housing and Urban Affairs, Government of India, 2024

No standard, regulator or peer-reviewed paper we consulted gives a make-up strength for PAC powder; the figures in use come from suppliers:

• Grasim's data sheet makes 10% and 18% Al2O3 solutions from its 29% (minimum) powder at 1:2 and 1.5:1 powder to water. By weight, those ratios fit a 30% powder; at exactly 29% they give 9.7% and 17.4%.
• Al Burj Chemicals gives 5–10% for solid PAC, says the solution turns viscous above 10% and should be used within about a week; HyChron gives 5–15% w/v. Check whether a percentage means powder or Al2O3.
• Aditya Birla Chemicals warns that PAC kept for long as a solution below about 3% Al2O3 hydrolyses to a white turbid liquid and loses effectiveness.

Source: Grasim Industries Limited, Chemical Division (copy uploaded by a seller to IndiaMART), 2018; Al Burj Chemicals (vendor), 2026; HyChron (vendor), 2026; Aditya Birla Chemicals (India) Ltd, 2013

In lab work, the aluminium species in diluted PAC kept shifting as the solutions aged (Huang et al., 2006). In a jar-test study, letting PAC hydrolyse before it met the test water raised the optimal dose; the authors conclude that making up PAC in deionised rather than tap or effluent water can save coagulant and improve charge-neutralisation coagulation, while tap or effluent water does not affect the performance of sweep coagulation (Zhang et al., 2017). We found no primary source for how long a made-up solution keeps, so batches no bigger than one CPHEEO-sized tank (12 hours' need), made up in the cleanest water available, are the cautious choice. PWTAG, writing about pools, warns that diluting liquid PAC with water forms a gel.

Source: Journal of Environmental Sciences (China), 2006; Journal of Environmental Sciences (China), Elsevier, 2017; CPHEEO, Ministry of Housing and Urban Affairs, Government of India, 2024; Pool Water Treatment Advisory Group (PWTAG), 2014

• Tanks: FRP, HDPE or polyethylene, polypropylene, rubber-lined, ebonite-coated or polyethylene-lined mild steel, and acid-proof tile-lined concrete.
• Pumps and valves: Uisce Éireann specifies PVC, PTFE and Viton for coagulant pump wetted parts, and thermoplastic valves only on tanks under 1.5 m³, with rubber- or fluoropolymer-lined iron or steel above that.
• Avoid: aluminium, zinc, galvanised metal, copper, brass, iron and unlined carbon steel (Solenis SDS, Aditya Birla MSDS).

Source: Bureau of Indian Standards, 2018; National Health and Medical Research Council (Australia), 2005; Aditya Birla Chemicals (India) Ltd, 2013; Grasim Industries Limited, Chemical Division (copy uploaded by a seller to IndiaMART), 2018; Nexchem Ltd, 6 Mar 2023; Uisce Éireann (Irish Water), 30 Nov 2023; Solenis LLC (SDS hosted by Pennsylvania Department of Environmental Protection), 14 Jan 2020

IS 15573 requires containers to be marked corrosive and irritating to the eyes, with instructions to rinse with plenty of water, remove contaminated clothing, and wear gloves and eye and face protection. GESTIS lists the solution, from the manufacturer's ECHA registration, as H290 (corrosive to metals) and H318 (serious eye damage), signal word Danger, and calls for goggles, natural rubber or FKM gloves, and an eye bath.

Source: Bureau of Indian Standards, 2018; Institut für Arbeitsschutz der DGUV (IFA), GESTIS Substance Database, 2023

• Liquid: GESTIS and the SDS from Nexchem (10% PAC) and Solenis give UN 3264, Class 8, Packing Group III; an Aditya Birla MSDS gives UN 1760, Class 8, Packing Group I. Under the US rule 49 CFR 173.137, which follows the UN criteria, a liquid that corrodes steel or aluminium faster than 6.25 mm a year at 55 °C is Class 8, Packing Group III even if it does not damage skin.
• Powder: one Chinese maker's MSDS for 29–32% powder says it is not regulated by DOT, IMO or IATA. No regulator classification for PAC powder was found.

Source: Institut für Arbeitsschutz der DGUV (IFA), GESTIS Substance Database, 2023; Nexchem Ltd, 6 Mar 2023; Solenis LLC (SDS hosted by Pennsylvania Department of Environmental Protection), 14 Jan 2020; Aditya Birla Chemicals (India) Ltd, 2013; US Government (eCFR), 2026; Henan Xunyu Chemical Co., Ltd, 2021

Follow the SDS for the exact product you buy, and your transporter's rules.

Liquid suits a plant close to its supplier that wants to pump from a bulk tank without dissolving and has room for acid-proof tanks under shade. There, hauling 2.8–3.2 times the mass can cost less than running a dissolving system. Powder suits a plant far from its supplier, or one that imports, because a tonne carries 280–320 kg of Al2O3 against 100 kg for 10% liquid. It needs dry storage for the bags and full dissolving before dosing.

Source: Bureau of Indian Standards, 2018; CPHEEO, Ministry of Housing and Urban Affairs, Government of India, 2024

To compare offers, divide the delivered price per kg by the Al2O3 fraction on the CoA, add the dissolving cost for powder, check basicity and the other IS 15573 limits, and jar test both. The ferric alum vs PAC guide applies the same method across coagulants.

Rise Chemical India (ISO 9001:2015) supplies both forms, and its office in Kirti Nagar, Delhi handles enquiries, quotes and orders. Its liquid PAC is 10% Al2O3, in 35–50 kg carboys, 200–250 kg drums or tankers. Its PAC powder is 28–32% Al2O3 at 70–85% basicity, in 25 kg and 50 kg bags, with a 250 kg minimum order. See the poly aluminium chloride page, or send an enquiry for either form. At its own factory in Bharatpur, Rajasthan, the company makes ferric alum, and the ferric alum vs PAC guide compares the two coagulants.