Coagulants for Water Treatment: 13 Types, How They Work, Dosage and Selection

Coagulants for water treatment are 13 chemicals in 4 classes, from aluminum and iron salts to cationic polymers, that destabilize turbidity, color and organic matter at the rapid-mix point so they can be settled and filtered out. Their doses run from 0.2 mg/L (ppm) of a cationic polymer to 200 mg/L of alum in drinking water, so which coagulant fits which water?

The 13 coagulants fall into 7 inorganic metal salts (alum, ferric chloride, ferric sulfate, aluminum chloride, sodium aluminate, ferrous chloride and ferrous sulfate), 2 prehydrolyzed aluminum coagulants (PAC and ACH), 2 organic polymer coagulants (polyDADMAC and polyamine), 1 natural coagulant (tannin) and 1 coagulant aid (bentonite). Aluminum sulfate and polyaluminum chloride are also spelled aluminium sulphate and polyaluminium chloride. Together they form the first of the 16 families of water treatment chemicals.

Coagulants work by charge neutralization, sweep floc or polymer patches, and every metal salt except sodium aluminate consumes alkalinity: 0.50 mg/L as CaCO3 per mg/L of dry alum and 0.92 mg/L per mg/L of ferric chloride. Turbidity, alkalinity, temperature and the application decide the choice, a jar test confirms it, and 66 % of US surface-water plants also dose a polymer, mostly cationic. NSF/ANSI/CAN 60 caps each certified product at its own maximum use level, from 1.2 mg/L for tannin products to 795 mg/L for some ferric chloride products, while residual aluminum and polymer monomers carry their own limits.

Every value on this page is checked against primary sources (NSF listings, eCFR, AWWA, CEN, Health Canada, WHO); see our methodology and fact-checking process.

What Is a Coagulant in Water Treatment?#

A coagulant in water treatment is a positively charged chemical, such as alum, ferric chloride or polyDADMAC, that neutralizes the negative charge on colloidal and suspended particles so they agglomerate into flocs. US federal rules define coagulation as a process using coagulant chemicals and mixing by which colloidal and suspended materials are destabilized and agglomerated into flocs (40 CFR 141.2).

Coagulation destabilizes particles within seconds at rapid mix; flocculation then grows them into settleable floc by gentle stirring (40 CFR 141.2), often helped by a high-molecular-weight polymer flocculant. The sequence and the differences are explained on coagulation and flocculation in water treatment.

What does a coagulant remove from water?#

A coagulant removes 5 groups of contaminants: turbidity and suspended solids, color, natural organic matter (the precursor of disinfection byproducts), phosphorus in wastewater and, with iron salts, dissolved sulfide in sewers. The 5 removal targets carry these reference numbers.

• Turbidity: combined filter effluent at or below 0.3 NTU in at least 95 % of monthly measurements (40 CFR 141.173).
• Color: metal-salt coagulation for color reduction runs at pH 4.5 to 5.5 (Veolia Water Technologies Handbook, chapter 5).
• Natural organic matter: surface-water systems remove 15 to 50 % of TOC by enhanced coagulation (40 CFR 141.135).
• Phosphorus: 0.87 mg of aluminum or 1.80 mg of iron per mg of phosphorus, stoichiometric.
• Sulfide: 1.16 mg of iron(III) or 1.74 mg of iron(II) per mg of sulfide sulfur, stoichiometric.

Each removal goal sets where the coagulant is dosed.

Where is a coagulant dosed in a treatment plant?#

A coagulant is dosed at the rapid-mix point, the zone of highest turbulence ahead of flocculation, because charge neutralization happens within seconds. Conventional filtration follows it with flocculation, sedimentation and filtration, while direct filtration skips sedimentation (40 CFR 141.2). Wastewater plants feed phosphorus precipitants at 3 points: primary, simultaneous or tertiary.

How Do Coagulants Work?#

Coagulants work in 3 ways: their cations neutralize the negative surface charge of particles, their metal hydroxide precipitates sweep particles out of the water, and cationic polymers bind particles in electrostatic patches. Metal salts use the first 2, with dose and pH deciding which dominates.

Charge neutralization#

Charge neutralization is the main mechanism of every coagulant: trivalent aluminum and iron ions are about 700 times more effective than sodium ions at collapsing the negative charge of particles in drinking water. Schulze-Hardy theory puts the relative effectiveness of mono-, di- and trivalent ions at 1 : 100 : 1,000; measured drinking-water practice gives 1 : 60 : 700 for Na+ : Ca2+ : Al3+ (Hach).

What happens when the dose overshoots neutral charge? Particles take on a positive charge and re-disperse, so turbidity rises again. Zero zeta potential is the theoretical ideal, most utilities run slightly negative after coagulation, and a positive zeta potential indicates likely coagulant overfeed.

Sweep floc and hydroxide precipitation#

Sweep floc forms when the coagulant dose exceeds the solubility of its metal hydroxide, so aluminum or ferric hydroxide precipitates and enmeshes particles as it settles. Alum shows both regimes: a low dose at slightly acidic pH neutralizes charge, while a higher dose near neutral pH produces sweep floc. The alum reaction with natural alkalinity reads Al2(SO4)3·14H2O + 3 Ca(HCO3)2 → 2 Al(OH)3 + 3 CaSO4 + 6 CO2 + 14 H2O.

Aluminum hydroxide reaches its minimum solubility at about pH 6.2 at 20 °C (68 °F) and about pH 6.7 at 5 °C (41 °F) (Health Canada, 2021). Ferric hydroxide is less soluble than aluminum hydroxide, which gives iron salts their wider working pH range.

Why do coagulants consume alkalinity?#

Metal coagulants consume alkalinity because their hydrolysis releases acid: each mg/L of dry alum consumes 0.50 mg/L of alkalinity as CaCO3, and each mg/L of ferric chloride consumes 0.92 mg/L. Each mg/L of dry alum (as Al2(SO4)3·14H2O) also produces 0.44 mg/L of carbon dioxide. Ferric sulfate consumes 0.75 mg/L as CaCO3 per mg/L of anhydrous Fe2(SO4)3 (calculated). Sodium aluminate works the other way: 1 mg/L of Na2Al2O4 (88 %) raises alkalinity by 0.54 mg/L and lowers carbon dioxide by 0.47 mg/L (NHMRC, Australian Drinking Water Guidelines).

Health Canada (2021) ranks coagulants from the least to the most alkalinity consumed as follows.

1. ACH, about equal to polyaluminum silicate sulfate
2. Polyaluminum chloride (PAC)
3. Polyaluminum sulfate
4. Alum, about equal to ferric sulfate
5. Ferric chloride

Basicity explains the order: a prehydrolyzed coagulant arrives partly neutralized and releases less acid.

13 Types of Coagulants in 4 Classes#

The 13 coagulants used in water treatment fall into 4 classes plus coagulant aids: 7 inorganic metal salts, 2 prehydrolyzed aluminum coagulants, 2 organic polymer coagulants, 1 natural coagulant and 1 coagulant aid.

Table 1 compares the 4 coagulant classes and the coagulant aids by members, charge carrier, basicity and role.

1. Inorganic metal salt coagulants (7)#

Inorganic metal salt coagulants are monomeric aluminum and iron salts that hydrolyze to cationic hydroxo species and metal hydroxide; this class has 7 coagulants: aluminum sulfate, ferric chloride, ferric sulfate, aluminum chloride, sodium aluminate, ferrous chloride and ferrous sulfate. All 7 have 0 % basicity, and all but sodium aluminate consume alkalinity.

Aluminum sulfate (alum)#

Aluminum sulfate (alum) is the reference metal-salt coagulant: liquid alum carries 48.5 % dry alum equivalent (8.0 to 8.4 % Al2O3), and drinking-water doses run 5 to 200 mg/L (ppm) as Al2(SO4)3·14H2O. Very dirty water can need up to about 500 mg/L. Dry alum (lump, granular or powder) contains about 17 % Al2O3.

Ferric chloride#

Ferric chloride (FeCl3) is the iron coagulant with the widest working pH, about 4 to 11, and is sold as a 38 to 42 % FeCl3 solution. A 42 % solution contains 14.5 % iron. Drinking-water doses run 2 to 100 mg/L (ppm) as FeCl3·6H2O. Beyond coagulation, ferric chloride precipitates phosphorus, controls sewer sulfide and conditions sludge for dewatering.

Ferric sulfate#

Ferric sulfate (Fe2(SO4)3) is the sulfate-based iron coagulant, less corrosive than ferric chloride and able to run in existing alum dosing systems. The liquid grade carries 39 to 45 % w/w Fe2(SO4)3 (11 to 12.5 % Fe), and the granular grade 18.5 to 20 % Fe. Drinking-water doses run 2 to 100 mg/L (ppm) as Fe2(SO4)3, at a coagulation pH of 4 to 11.

Aluminum chloride#

Aluminum chloride (AlCl3) solution is the chloride analog of alum: a monomeric aluminum salt with 0 % basicity, supplied as a 28 to 35 % AlCl3 solution. It hydrolyzes like alum and consumes alkalinity, but adds chloride instead of sulfate.

Sodium aluminate#

Sodium aluminate (NaAlO2) is the alkaline aluminum coagulant: it adds alkalinity instead of consuming it, which suits soft, low-alkalinity water and lime softening. Liquid grades carry 29 to 35 % Na2Al2O4, and drinking-water doses run 2 to 60 mg/L (ppm) as Na2Al2O4, often paired with alum. One mg/L of Na2Al2O4 equals about 3.5 mg/L of dry alum. In cold-process lime softening, sodium aluminate improves magnesium and silica reduction.

Ferrous chloride#

Ferrous chloride (FeCl2) is an iron(II) salt made from steel-pickling liquor and used mainly for sulfide control in sewers, with coagulation, sludge dewatering and chlorite reduction as further roles. Sulfide precipitation takes 1.74 mg of iron(II) per mg of sulfide sulfur (stoichiometric). After chlorine dioxide pre-oxidation, 3.31 mg of Fe2+ reduces 1 mg of chlorite (calculated).

Ferrous sulfate#

Ferrous sulfate (FeSO4·7H2O, copperas) coagulates only after oxidation to iron(III), and its use in public water supply has largely stopped because the excess chlorine it needs forms trihalomethanes. The heptahydrate contains 20.1 % iron. Oxidation takes 0.635 mg of chlorine per mg of Fe2+ (calculated).

2. Prehydrolyzed aluminum coagulants (2)#

Prehydrolyzed aluminum coagulants are basic aluminum chlorides in which part of the acid is already neutralized; this class has 2 coagulants, PAC and ACH, plus sulfated and silicated variants. Basicity equals OH/(3 Al) x 100 on a molar basis. Polyaluminum chlorosulfate (PACS), polyaluminum silicate sulfate (PASS) and polyaluminum hydroxychlorosulfate are minor variants of the same chemistry.

Polyaluminum chloride (PAC)#

Polyaluminum chloride (PAC) is a prehydrolyzed aluminum coagulant with about 50 % basicity in its medium grades, so it needs less alkali than alum and forms larger, faster floc. Liquid PAC usually contains at least 10 % Al2O3, and powder at least 30 % Al2O3. Drinking-water doses run 5 to 100 mg/L (ppm) as product (10 % Al2O3).

Aluminum chlorohydrate (ACH)#

Aluminum chlorohydrate (ACH) is the highest-basicity member of the PAC family, about 83 % basic, and works from pH 6 to 9 usually without any alkalinity adjustment. The "50 % solution" label is a strength label, not the basicity; the liquid carries 12.2 to 12.7 % Al (23 to 24 % Al2O3). Drinking-water doses run 3 to 100 mg/L (ppm) as product. Ahead of microfiltration and ultrafiltration membranes, ACH appears to reduce fouling (NHMRC).

3. Organic polymer coagulants (2)#

Organic polymer coagulants are low- to medium-molecular-weight cationic polymers with high charge density, used as the primary coagulant or alongside a metal salt; this class has 2 coagulants: polyDADMAC and polyamine. Melamine-formaldehyde resin, a low-molecular-weight cationic resin for paint detackification, belongs to the same class.

High-molecular-weight polyacrylamides bridge floc rather than neutralize charge and belong to a separate family. Their polymer types, charge and molecular weight are compared on flocculants for water treatment.

PolyDADMAC#

PolyDADMAC is a high-charge-density quaternary ammonium polymer dosed at 0.2 to 6 mg/L (ppm) as 100 % polymer when it is the primary coagulant. Alongside a metal salt the dose drops to 0.2 to 1 mg/L. Its molecular weight runs 10^5 to 10^6 g/mol, and it is chlorine resistant and not pH sensitive. Overdosing re-disperses particles.

Polyamine (epi-DMA)#

Polyamine (epi-DMA) is a cationic epichlorohydrin-dimethylamine copolymer sold at 49 to 56 % solids and usually fed alongside ACH or alum. Viscosity runs from 100 to 9,000 cP and tracks molecular weight. Under chloramination, polyamines show a higher NDMA formation potential than polyDADMAC.

4. Natural coagulants (1)#

Natural coagulants are plant- and shell-derived polymers, such as tannins, chitosan and moringa seed protein; 1 of them, tannin, has an entity page and an NSF/ANSI/CAN 60 listing.

Tannin#

Tannin is a polyphenolic plant extract, chemically modified for coagulation, whose NSF/ANSI/CAN 60 listings cap drinking-water use at 1.2 to 1.5 mg/L as product. Water-treatment tannins are quebracho or wattle (mimosa) extracts or cationic tannin polymers, so no single CAS number applies.

5. Coagulant aids (1)#

Coagulant aids are materials that strengthen or weight floc without being the primary coagulant; this site covers 1 of them, bentonite.

Bentonite#

Bentonite is a montmorillonite clay added to low-turbidity water so that metal-hydroxide floc forms around dense clay nuclei and settles faster. It is fed at rapid mix, ahead of or with the primary coagulant.

Which Coagulant for Which Water? Selection by Application and Water Quality#

Coagulant selection depends on 4 factors: raw-water turbidity, alkalinity and pH, water temperature and the application, and a jar test on the actual water confirms the choice. Bench-scale jar tests simulate full-scale coagulation, flocculation and sedimentation.

By raw-water turbidity#

Raw-water turbidity sets the coagulant approach: above 60 NTU a cationic polymer alone normally clarifies, while below 60 NTU a metal salt is paired with a cationic polymer (Veolia Water Technologies Handbook, chapter 5). The 3 turbidity bands work as follows.

• Below 10 NTU: an inorganic salt plus a cationic polymer, because a polymer alone usually cannot clarify; bentonite can add weight to the floc.
• 10 to 60 NTU: an inorganic salt plus a cationic polymer.
• Above 60 NTU: a polymeric primary coagulant alone is normally sufficient.

By alkalinity and pH#

Alkalinity and pH decide between aluminum and iron: aluminum coagulants work best at pH 6.5 to 7.5 in lowland surface water, while iron coagulants handle soft colored water at pH 4.0 to 5.0 and hard water coagulated at pH 8.0 or above. Highly colored upland water coagulates best with aluminum at pH 5.5 to 6.5 (Irish EPA, Advice Note 15, 2014). For low residual metal, Health Canada (2021) gives pH 4.5 to 6 for iron coagulants.

What if the water lacks the alkalinity a metal salt consumes? Coagulation pH should be adjusted with an acid or an alkali (lime, caustic soda or soda ash), never by overdosing the coagulant, which raises dissolved residual metal. ACH and sodium aluminate need little or no alkali. Lime, caustic soda and soda ash are compared on pH adjustment chemicals.

By water temperature#

Cold water favors prehydrolyzed or iron coagulants: below 5 °C (41 °F) alum loses more efficiency than iron, and the optimum pH of aluminum coagulants shifts by about 0.4 units between 2 and 20 °C (35.6 and 68 °F). Iron coagulants show no such shift (Irish EPA, Advice Note 15). Health Canada (2021) puts the optimum pH for alum at 6.5 to 7.0 in cold water below 10 °C (50 °F) and 6.0 to 6.5 in warm water; for PAC the values are 6.8 to 7.3 and 6.3 to 6.8.

Water at 0 °C (32 °F) is twice as viscous as water at 25 °C (77 °F), so floc settles more slowly in winter. As a single-utility example, one Canadian utility switches to PAC below 12 °C (54 °F) and uses alum above it.

By application: drinking water, wastewater and industrial systems#

Each application has a default coagulant family: aluminum and iron salts with a cationic polymer in drinking water, iron or aluminum salts for phosphorus removal, iron salts for sewer sulfide and ACH or polyDADMAC ahead of membranes. Drinking water adds a regulatory layer on organic matter.

Surface-water systems under the Stage 1 DBPR must remove 15 to 50 % of TOC by enhanced coagulation, depending on source TOC and alkalinity (40 CFR 141.135). Step 2 jar testing ends where an extra 10 mg/L of alum removes 0.3 mg/L of TOC or less, and Step 2 is explained under enhanced coagulation and TOC removal.

Wastewater and industrial programs set the dose by stoichiometry or jar test instead of a TOC rule.

Table 2 lists the default coagulants, the reason and the key number for each application.

Iron salts dominate sewer and phosphorus duty, while aluminum salts and polymers dominate potable clarification; all wastewater programs are compared on wastewater treatment chemicals.

Coagulant Dosage Ranges by Chemical#

Coagulant doses in drinking water range from 0.2 mg/L (ppm) of polyDADMAC as active polymer to 200 mg/L of alum as dry alum, and every range is tied to its own basis: as product, as active polymer or as a defined hydrate. Drinking-water ranges follow the NHMRC Australian Drinking Water Guidelines.

Table 3 gives the typical dose, basis and coagulation pH for each coagulant and system (mg/L = ppm).

A dose without its basis is meaningless: a PAC dose of 30 mg/L as product (10 % Al2O3) delivers 3 mg/L as Al2O3, not 30 mg/L. In potable water, the product dose is also capped by the product's NSF/ANSI/CAN 60 maximum use level. Generic polymer doses from Hach run 0.1 to 2 mg/L as a primary coagulant, 0.1 to 0.5 mg/L as a coagulant aid and below 0.1 mg/L as a filter aid.

How do coagulant doses convert between chemicals?#

A 10 mg/L alum dose (as Al2(SO4)3·14H2O) equals 5.5 mg/L of anhydrous ferric chloride or 9.1 mg/L of ferric chloride hexahydrate in metal equivalents (US EPA Enhanced Coagulation Guidance Manual, 1999, Table 3-1). The equivalence is chemical, not performance: the jar test still decides.

Table 4 lists the dose of each form that equals 10 mg/L of alum (Al2(SO4)3·14H2O).

Each mg/L of dry alum delivers 0.091 mg/L of aluminum. On the alkaline side, 1 mg/L of Na2Al2O4 equals about 3.5 mg/L of dry alum (NHMRC).

How is a coagulant dose turned into a feed rate?#

A coagulant feed rate equals dose times flow times 8.34 divided by purity: 30 mg/L of dry alum at 10 MGD (37,854 m³/d) needs 2,502 lb/day (1,136 kg/d), or about 1,760 L/d (465 gal/d) of commercial liquid alum. The US formula is lb/day = mg/L x MGD x 8.34 / purity (Florida DEP, 2014); the metric form is kg/d = mg/L x m³/d / 1,000 / purity.

The worked example uses these inputs: dose 30 mg/L as dry alum (Al2(SO4)3·14H2O), flow 10 MGD (37,854 m³/d), purity 1.0 on the dry-alum basis, and liquid alum at 48.5 % dry alum equivalent with a specific gravity of about 1.33, which carries about 0.645 kg of dry alum per liter (5.3 to 5.5 lb per US gallon). Dividing 1,136 kg/d by 0.645 kg/L gives about 1,760 L/d. The chemical dosage calculator converts mg/L into kg/d, lb/day and pump settings.

How Is Coagulant Dose Controlled and Tested?#

Coagulant dose is controlled in 3 layers: jar tests set the chemical and dose, online signals such as streaming current track it, and settled and filtered turbidity plus residual metal prove it.

Jar testing for coagulant selection and dose#

A coagulant jar test runs 1 or 2 L of raw water per jar through 1 minute of rapid mix at 100 rpm, 30 minutes of flocculation at 30 rpm and 60 minutes of settling (US EPA, 1999). The alum stock should be no more than 7 days old, with a pH below 3.0. The jar test runs in 5 steps.

1. Prepare a fresh 20 g/L alum stock, so that 1 mL in a 2 L jar gives 10 mg/L.
2. Dose a series of jars in 10 mg/L steps.
3. Mix, flocculate and settle at the set speeds and times.
4. Measure settled turbidity, pH and color in each jar.
5. Repeat in 2 to 3 mg/L steps around the best jar (Irish EPA).

The largest floc is not necessarily the best. Interpretation and dose calculation are covered in the jar test procedure.

Online control: streaming current, zeta potential and feed-forward#

Online coagulant control uses 3 signals: streaming current, which reads zero at neutralized charge, zeta potential measured on grab samples, and feed-forward dose models built on raw-water turbidity, color or UV254. The 3 signals compare as follows.

• Streaming current: a reading of 0 indicates neutralized charge, but salinity, conductivity and pH swings disturb the signal, and sensor siting is the main difficulty.
• Zeta potential: most utilities hold it slightly negative after coagulation; a positive value points to overfeed.
• Feed-forward model: dose = p1 + p2 m1 + p3 m2, with raw turbidity, color or UV254 as inputs and an alarm at about 20 % mismatch with the metered dose (Irish EPA, Advice Note 15).

Performance targets: turbidity and residual metal#

Coagulation performs when combined filter effluent stays at or below 0.3 NTU in at least 95 % of monthly measurements and never exceeds 1 NTU (40 CFR 141.173), and when residual aluminum or iron stays low. Combined filter effluent is measured in NTU, and NTU and FNU readings are explained under turbidity in water.

EPA's optimization goals go further: settled water below 1 NTU 95 % of the time when raw water is at or below 10 NTU (below 2 NTU when raw water is at or below 20 NTU), and filtered water below 0.1 NTU 95 % of the time (EPA 815-R-20-004, June 2020). Health Canada (2021) recommends monitoring total and dissolved aluminum daily or more often at plants that use aluminum coagulants.

Seasonal pH control matters: in Health Canada case studies, residual aluminum rose from below 0.05 to about 0.3 to 0.4 mg/L without seasonal pH adjustment and stayed below 0.06 mg/L with it.

Turbidity targets also earn treatment credit, and filter-performance credits sit in the Surface Water Treatment Rules.

Which Standards and Regulations Apply to Coagulants?#

Coagulants for drinking water are governed in 4 layers: NSF/ANSI/CAN 60 product certification, AWWA and EN product standards, limits on residual aluminum and iron, and treatment techniques for polymer monomers. NSF/ANSI/CAN 60 is required in the regulations of 48 of 50 US states (NSF, 2019). Only sodium aluminate and tannin appear in 21 CFR 173.310, as boiler water additives; the other 11 coagulants are not listed in 21 CFR 173.310.

NSF/ANSI/CAN 60 maximum use levels for coagulants#

NSF/ANSI/CAN 60 maximum use levels for coagulants are product-specific and stated as product, from 1.2 mg/L for tannin coagulants to 795 mg/L for some ferric chloride products, with 250 mg/L the most common value for PAC, ACH, aluminum chloride and ferric chloride (NSF listings, 2026-10-21). Each maximum use level (MUL) counts the total dose across all application points.

Table 5 lists the MUL distribution per coagulant in mg/L as product (NSF listings, 2026-10-20; most common values re-checked 2026-10-21).

The sulfated and silicated variants carry 200 mg/L (PACS, also 450 and 175), 200 mg/L (PASS) and 250 or 600 mg/L (polyaluminum hydroxychlorosulfate). The [AL] condition limits aluminum in finished water to 2 mg/L, and the [PY] footnote confirms compliance with the federal monomer rule. How MULs are set and checked is explained on NSF/ANSI/CAN 60.

AWWA and EN product standards for coagulants#

Eight AWWA B-standards and nine EN standards specify coagulant purity and impurity limits, from ANSI/AWWA B403-24 for aluminum sulfate to EN 17034:2018, which replaced the withdrawn EN 881:2004 and EN 883:2004 for aluminum chlorides. EN 891:2023 covers iron(III) chloride sulfate, a product without its own entity page.

Table 6 pairs each coagulant with its current AWWA and EN standard.

Every edition is listed under AWWA B-series standards.

Residual aluminum and iron limits in drinking water#

No US enforceable limit exists for aluminum in drinking water: the federal value is a secondary standard of 0.05 to 0.2 mg/L (40 CFR 143.3), while NSF/ANSI/CAN 60 listings cap aluminum added by a certified coagulant at 2 mg/L in finished water. Other jurisdictions set different kinds of values.

The 5 aluminum values below differ in legal status as well as in number.

• United States: secondary standard 0.05 to 0.2 mg/L, non-enforceable (40 CFR 143.3).
• NSF/ANSI/CAN 60: listing condition of 2 mg/L aluminum in finished water.
• European Union: 200 µg/L as an indicator parameter (Directive (EU) 2020/2184, Annex I Part C).
• Canada: maximum acceptable concentration 2.9 mg/L total aluminum and operational guidance value 0.100 mg/L as a locational running annual average (Health Canada, March 2021).
• WHO: no formal guideline value; health-based value 0.9 mg/L and practicable levels of 0.1 mg/L or less for large plants and 0.2 mg/L or less for small facilities (2010).

Iron carries a US secondary standard of 0.3 mg/L and an EU indicator value of 200 µg/L, and chloride and sulfate each carry a 250 mg/L secondary standard (40 CFR 143.3). Article 12 rules for treatment chemicals are on EU Drinking Water Directive 2020/2184.

Monomer limits for organic coagulants#

Epichlorohydrin from polyamine coagulants is controlled by a treatment technique, not an MCL: the polymer may contain at most 0.01 % residual monomer when dosed at 20 ppm, certified to the State each year (40 CFR 141.111). The MCLG for epichlorohydrin is zero, and the EU parametric value is 0.10 µg/L (Directive (EU) 2020/2184, Annex I Part B). In EPA's fourth Six-Year Review (February 2024), every NSF-tested polyamine sample from 2019 to 2021 was non-detect for epichlorohydrin at 20 mg/kg, one fifth of the treatment-technique level. Both organic coagulants are NDMA precursors under chloramination, polyamines more than polyDADMAC, and the Australian guideline for NDMA is 100 ng/L.

Complete List of Coagulants: All 13 Chemicals in One Table#

The complete list of coagulants below gives all 13 chemicals with their CAS number, class, function, systems and most common NSF/ANSI/CAN 60 maximum use level. Table 7 follows the same order as the classes above.

Coagulants are one family among many: every other chemical is filterable by CAS, function and NSF status in the water treatment chemical database.

Who Supplies Coagulants and Coagulation Programs?#

Coagulants and flocculants form the largest product segment of water treatment chemicals, 38.2 % of a USD 35.8 billion market in Grand View Research's 2025 estimate, and US supply rests on a few bulk chemicals such as alum and ferric chloride.

US production in 2019 reached about 796 million kg of alum, about 45 % of it for the water sector, about 322 million kg of ferric chloride and about 266 million kg of ferric sulfate (US EPA supply chain profiles).

Supply risk differs by chemical. EPA rated the disruption risk Low for alum and ferrous sulfate and Moderate-Low for ferric chloride, ferric sulfate and ferrous chloride (2022), after a 2021 ferric chloride shortage caused by shortfalls in hydrochloric acid and steel-pickling liquor. Distributors and manufacturers by region are listed under water treatment chemical suppliers.

Plants buy coagulation in 2 ways. A program provider runs jar tests, sets up dose control and supports compliance reporting, while a chemical supplier delivers product to an NSF/ANSI/CAN 60 and AWWA specification.

Quotes depend on grade, strength, packaging (drum, IBC or bulk) and delivery point.

Public procurement records show what buyers paid at a given date and place; they include delivery and local terms and are not a current price.

Program providers differ in testing, reporting and service scope, and how to compare them is covered under water treatment companies.

Are Coagulants Safe in Drinking Water and at the Plant?#

Certified coagulants meet the NSF/ANSI/CAN 60 health-effects requirements at or below each product's maximum use level, with aluminum capped at 2 mg/L in finished water, while at the plant the concentrated products are corrosive and need eye and skin protection. The hazard labels differ by chemical: alum is notified (ECHA C&L) as H318, ferric chloride as H302 and H314, and sodium aluminate as H314, H290 and H318; for PAC and ACH, see the supplier SDS. NIOSH sets recommended exposure limits of 2 mg/m³ as Al for soluble aluminum salts and 1 mg/m³ as Fe for soluble iron salts, with no OSHA PEL for either.

What is the most common coagulant used in water treatment?#

Aluminum and iron salts are the bulk coagulants of water treatment: US production in 2019 reached about 796 million kg of alum, about 45 % of it for water, and about 322 million kg of ferric chloride, about 80 % for water treatment. Polymers are the common partner: 66 % of US surface-water plants and 13 % of groundwater plants dose a polymer, predominantly cationic (US EPA, Six-Year Review 4, 2024).

What is the best coagulant for water treatment?#

No single coagulant is best for all water: the best choice is the chemical and dose that meet the turbidity, TOC and residual-metal targets in a jar test on the actual water at the lowest cost per volume treated. Cold, low-alkalinity water favors ACH or PAC, and colored soft water favors iron at low pH.

How much sludge do coagulants produce?#

Each mg/L of dry alum produces about 0.26 mg/L of aluminum hydroxide solids, while switching to an organic polymer coagulant reduces sludge by 50 to 90 % (Veolia Water Technologies Handbook). Metal hydroxide sludge grows with the dose.

Are natural coagulants used by utilities?#

Utilities use few natural coagulants: modified tannins are NSF/ANSI/CAN 60 listed at 1.2 to 1.5 mg/L as product, while chitosan and moringa remain research-level options. In a laboratory study, moringa seed extract at 125 to 150 mg/L removed 83.2 to 99.8 % of turbidity, but natural coagulants vary by origin and lack standardized extraction, scale and cost data.

Do chitosan and moringa have an NSF/ANSI/CAN 60 listing?#

No: NSF/ANSI/CAN 60 has no chemical category for chitosan or moringa, so neither can be certified for US drinking water today.

Which chemicals must never be mixed with coagulants?#

Hypochlorite must never meet ferric chloride or alum, because the acidic coagulant releases chlorine gas, and this pair caused 13 % of 72 documented chemical-unloading accidents between 1953 and 2019. Ferric chloride and alum mixed together react exothermically with acid fumes. PolyDADMAC must not share a feed line with anionic polymers, because the two neutralize each other.