Defoamers and Antifoams for Water Treatment: 6 Types, Dosage and Selection

Defoamers and antifoams for water treatment are 6 chemistries in 2 classes, silicone and non-silicone, that break foam already on the water or stop new foam from forming in aeration basins, clarifiers, cooling towers, boilers and evaporators. Certified maximum use levels start at 0.1 mg/L (ppm) as product, while general water and wastewater feeds run 5 to 50 ppm (basis not stated in the source), so which chemistry belongs in which system?

The silicone class holds polydimethylsiloxane (PDMS) and silicone polyether; the non-silicone class holds polypropylene glycol, EO/PO block copolymer, mineral oil and fatty alcohols. Defoamers are also written anti-foam, antifoaming agent or anti-foaming agent. They form one of the 16 families of water treatment chemicals.

Doses must name their basis, because a 20 % active emulsion delivers only one fifth of its product dose as active silicone. Two hard rules decide selection: oil and silicone defoamers are never dosed upstream of RO or NF membranes, where oil and grease is capped at 0.1 mg/L, and filamentous foam is rarely controlled by any defoamer. NSF/ANSI/CAN 60 certifies antifoamers at 0.1 to 100 mg/L as product, most of them for evaporative desalination feedwater only, and 21 CFR 173.310 lists polyglycols, not silicones, for steam that contacts food.

Every value on this page is checked against primary sources (NSF listings, eCFR, US EPA, peer-reviewed studies and membrane and treatment handbooks); see our methodology and fact-checking process.

What Is a Defoamer in Water Treatment?#

A defoamer in water treatment is a chemical additive, such as a silicone emulsion, a polyglycol or a mineral-oil blend, that breaks foam already formed on process water; an antifoam is the same kind of chemical dosed beforehand to stop foam from forming. NSF/ANSI/CAN 60 files these products under the product function "Antifoamer".

Is there a difference between a defoamer and an antifoam?#

A defoamer eliminates foam that already exists and an antifoam prevents further foam, but the two terms are used interchangeably for the same chemistries. Fast antifoams destroy standing foam within a minute, while slow antifoams act over minutes and suit continuous prevention. The label on the drum matters less than the chemistry, the dose basis and the feed point.

Where does foam form in water treatment systems?#

Foam forms in 6 places in water treatment: activated-sludge aeration basins, anaerobic digesters, high-solids clarifiers, cooling towers, boilers and evaporative desalination units. The 6 foam sources are listed below with their main cause.

• Aeration basins: white billowing foam at start-up, low sludge age and shock loads.
• Anaerobic digesters: foaming potential, classified by an aeration test in a study of 16 full-scale Danish digesters.
• High-solids clarifiers: foam in gas-cleaning systems.
• Cooling towers: tertiary-treated wastewater makeup, oil and organics, microbiological growth and concentrated dissolved solids.
• Boilers: high alkalinity and solids, and fatty acids saponified into a crude soap.
• Evaporative desalination units: foam in thermal desalination feedwater.

Each foam source decides which chemistry is safe to feed.

How Do Defoamers Work?#

Defoamers work in 3 steps: an insoluble, low-surface-tension droplet enters the foam film, spreads or bridges across it, and thins the film until it ruptures, with hydrophobic particles helping the droplet break in. Denkov's 2004 review of antifoam mechanisms sets out the conditions for each step.

Film entry, bridging and rupture#

An antifoam works only when its droplets can enter the foam film: the bridging coefficient must be positive (B > 0) and the entry barrier low, and an oil loaded with hydrophobic particles outperforms either the oil or the particles alone (Denkov, 2004). The entry barrier is the decisive criterion, because the magnitudes of the entry, spreading and bridging coefficients do not directly predict how well an antifoam performs. Hydrophobic silica is the classic particle: it pierces the film and lowers the entry barrier for the oil phase, and its use in light oil antifoams was patented in 1963.

Fast and slow antifoams#

Fast antifoams rupture foam films by bridging and destroy foam in under a minute, while slow antifoams act from the Plateau borders, the thicker channels between bubbles, over minutes to tens of minutes and leave some residual foam (Denkov, 2004). Knockdown of standing foam on a clarifier or basin surface calls for a fast type. Continuous prevention in a recirculating system tolerates a slow one.

Cloud-point antifoams: how polyglycols switch on#

Polyglycol antifoams are cloud-point antifoams: they stay dissolved below their cloud point and separate into active droplets above it, so their cloud point has to sit below the process temperature but not below the storage and feed-line temperature. Polypropylene glycol and EO/PO block copolymers both work this way.

6 Types of Defoamers in 2 Classes#

The 6 defoamer chemistries used in water treatment fall into 2 classes: 2 silicone types, polydimethylsiloxane and silicone polyether, and 4 non-silicone types, polypropylene glycol, EO/PO block copolymer, mineral oil and fatty alcohols. Co-active particles, such as hydrophobic silica and ethylene bis-stearamide wax, are carried inside these products and never dosed alone.

Table 1 compares the 2 classes by chemistry, active phase, co-active, form and key rule.

1. Silicone defoamers (2)#

Polydimethylsiloxane (PDMS)#

Polydimethylsiloxane (PDMS, CAS 63148-62-9) is the reference silicone antifoam active, sold as a 100 % active compound with hydrophobic silica or as a water-dilutable emulsion of 10 to 50 % active, 20 % being common. "Silicone oil" and "dimethylpolysiloxane" name the same chemistry, and PubChem also lists the alternative polymer CAS 9016-00-6.

Silicone polyether#

Silicone polyether (CAS 71965-38-3) is polydimethylsiloxane grafted with EO/PO polyether chains, which makes the antifoam self-emulsifying in water. It is still a silicone, so the exclusion from RO and NF feed applies to it as well.

2. Non-silicone defoamers (4)#

Non-silicone defoamers are silicone-free antifoams built on polyglycols, hydrocarbon oils or fatty alcohols; this class has 4 chemistries: polypropylene glycol, EO/PO block copolymer, mineral oil and fatty alcohols. The 2 polyglycols are the cloud-point types, which switch on above their cloud point. Mineral oil types depend on a dispersed particle, ethylene bis-stearamide wax (developed in the early 1970s) or hydrophobic silica, to pierce the film.

Polypropylene glycol (PPG)#

Polypropylene glycol (PPG, CAS 25322-69-4) is the polyglycol antifoam of boiler programs, listed in 21 CFR 173.310 as polyoxypropylene glycol with a minimum molecular weight of 1,000. It is also used in water-based form against wastewater foam.

EO/PO block copolymer#

EO/PO block copolymer (CAS 9003-11-6) is a non-ionic polyether antifoam with good dispersing properties, useful where deposits are a problem. The block copolymer itself is not listed in 21 CFR 173.310, although the butanol-started monobutyl ethers of polyethylene-polypropylene glycol (random 1:1 EO:PO by weight, minimum molecular weight 1,500) are.

Mineral oil defoamers#

Mineral oil defoamers (white mineral oil, CAS 8042-47-5) carry ethylene bis-stearamide wax (CAS 110-30-5) or hydrophobic silica and are heavy-duty agents for knocking down surface foam. Hydrocarbon types are never used on filamentous foam and never fed ahead of RO or NF membranes.

Fatty alcohol defoamers#

Fatty alcohol defoamers are C7 to C22 alcohols and 2-ethylhexanol (CAS 104-76-7), used as water-based emulsions; they were among the first effective defoamers but are expensive. 1-Octanol (CAS 111-87-5) shares the formula C8H18O (130.23 g/mol).

Commercial forms: compounds, emulsions and concentrates#

Defoamers are supplied in 2 main forms, so every defoamer dose must state whether it is as product or as active. The 2 forms are listed below.

• Silicone compounds: concentrates of PDMS and hydrophobic silica at 100 % active, used neat or emulsified for water systems; one supplier instructs stirring them under low shear before use.
• Emulsions: water-dilutable liquid defoamers of 10 to 50 % active, with 20 % active the common strength.

A "defoamer concentrate" is the compound; a "liquid defoamer" is usually an emulsion.

Which Defoamer for Which System? Selection by Application#

Defoamer selection depends on 3 questions: what is making the foam, what sits downstream of the feed point, such as activated sludge, a membrane or steam that contacts food, and which basis the dose is written on. A bench dose ladder on the actual water should confirm the choice before full-scale feed.

Table 2 compares the 6 main systems by foam source, defoamer approach and key number.

Each system above belongs to a wider treatment program, and every wastewater chemical program is compared on wastewater treatment chemicals.

Activated sludge and wastewater foam#

In activated sludge, a defoamer controls the white billowing foam of start-up, low sludge age (high F:M), organic or shock loads, over-wasting and recovery from toxicity, and antifoam agents may be used against excessive foam (Veolia Water Technologies Handbook, chapter 37).

Filamentous foam from Nocardia or Microthrix is rarely controlled by a defoamer, and US EPA guidance on Nocardia foam records a poor history for antifoams. Hydrocarbon-based defoamers should never be used on filamentous foam; at one winery an oil-based antifoam fed filament growth. Defoamers do not work on denitrification foam either, and the fix there is higher RAS and wasting with ORP monitoring.

Sludge age, foam removal and selective chlorination for filamentous organisms are covered under filamentous bulking and foaming control.

Cooling towers#

Cooling-tower foam comes from 4 sources: tertiary-treated wastewater used as makeup, oil or organic incursion, excessive microbiological growth and concentrated dissolved solids. Quaternary ammonium biocides, such as ADBAC, can also foam in cooling towers (EPA product label).

Increasing blowdown is the first remedy, and foam depressant chemicals are reserved for extreme cases.

Boilers and food-contact steam#

Boiler-water foaming rises with alkalinity and solids, and alkalinity saponifies fatty acids into a crude soap; because 15 to 20 lb of water circulate per lb of steam and 99.97 % or more must be separated, foam turns quickly into carryover (the same handbook, chapter 16). Drum pressure sets the ABMA limits in Table 2, and internal treatment by drum pressure is covered under boiler water treatment.

An antifoam lets a boiler hold higher boiler-water concentrations without losing steam purity, which reduces blowdown. For steam that contacts food, polypropylene glycol and the other polyglycol entries are listed in 21 CFR 173.310, while silicones are not listed in 21 CFR 173.310.

RO and NF membranes: no oil or silicone defoamer upstream#

Oil and silicone defoamers are never dosed upstream of RO or NF membranes, because the feedwater limit for oil and grease, hydrocarbon or silicone, is 0.1 mg/L (ppm) (DuPont FilmTec Reverse Osmosis Technical Manual 45-D01504-en, Rev. 20, 2026).

A fouled membrane is cleanable with alkaline cleaners only if the flux decline is no more than 15 %. The antiscalants, cleaners and biocides that do belong in the feed are compared under reverse osmosis and membrane chemicals.

Evaporators and thermal desalination#

Evaporative desalination is the one drinking-water use with certified antifoams: most NSF/ANSI/CAN 60 antifoamer listings are footnoted "Certified for addition to the feedwater for evaporative desalination units only" (NSF listings, 2026-10-20). MSF, MED and brine-concentrator dosing is covered on the evaporator antifoam page linked in Table 2.

Defoamer Dosage Ranges and Dose Basis#

Defoamer feeds in water and wastewater systems typically run 5 to 50 ppm (mg/L), a range published without a basis, while certified drinking-water antifoams are capped by product maximum use levels of 0.1 to 100 mg/L as product (NSF listings, 2026-10-20). Supplier ranges run wider: one supplier states 10 to 200 ppm for wastewater.

Table 3 compares published defoamer doses by system, basis and source type (mg/L equals ppm at a density of about 1).

Bench ladders of 5, 10, 25 and 50 ppm are a supplier practice; full scale typically settles 10 to 20 % below the bench result (one supplier states).

A dose without a basis cannot be compared: 10 mg/L of a 20 % active emulsion is only 2 mg/L as active silicone.

How is a defoamer dose converted from product to active?#

A defoamer dose as product converts to active by the emulsion strength: 10 mg/L (ppm) of a 20 % active silicone emulsion delivers 2 mg/L as active silicone, while 10 mg/L of a 100 % active compound delivers the full 10 mg/L. Table 4 shows the conversion for the 4 common strengths.

The conversion is arithmetic; performance is confirmed in a bench ladder.

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

Worked example: a defoamer feed equals dose times flow times 8.34 divided by purity, so 10 mg/L (ppm) as product at 37,854 m³/d (10 MGD) needs 378.5 kg/d (834 lb/day) of product, which for a 20 % active emulsion is 75.7 kg/d (167 lb/day) as active silicone. The inputs are a dose of 10 mg/L as product, a flow of 10 MGD (1 MGD = 3,785.4 m³/d), a purity of 1.0 because the dose is already stated as product, and an active fraction of 0.20.

In metric units, mg/L times m³/d divided by 1,000 gives kg/d. For other doses and flows, the chemical dosage and feed rate calculator converts mg/L into kg/d, lb/day and pump settings.

How Is Defoamer Dose Controlled and Tested?#

Defoamer dose is controlled in 3 steps: a bench dose ladder picks the chemistry and dose, the feed point and full-scale trim set the plant dose, and effluent, membrane and steam checks prove it does no harm downstream.

Bench dose ladder and shake test#

A defoamer bench test doses a sample of the foaming water at 5, 10, 25 and 50 ppm, shakes or aerates it and reads foam height and knockdown speed, looking for the lowest dose that gives fast, durable knockdown. The ladder values are a supplier practice; the 4 steps below keep the readings comparable.

1. Take a fresh sample from the foaming zone.
2. Dose the ladder as product and record the basis.
3. Shake or aerate each bottle the same way.
4. Read foam height at once and after a set time.

Feed point and full-scale trimming#

Defoamer is fed to the liquid surface just ahead of the foaming zone, and in high-solids clarifiers of gas-cleaning systems to the high-solids stream or just before the settling unit, with water sprays and weir booms as the mechanical alternatives (Veolia Water Technologies Handbook, chapter 38). One supplier states that full-scale doses settle 10 to 20 % below the bench result.

Side effects to monitor: COD, oil and grease, steam purity#

Every defoamer program monitors 3 side effects: added COD and BOD in the effluent, oil and grease ahead of membranes, and steam purity in boilers. The 3 checks are listed below.

• COD and BOD: one antifoam safety data sheet lists BOD 382,000 ppm and COD 2,220,000 ppm of product, so the feed adds organic load to the effluent.
• Oil and grease: at most 0.1 mg/L in RO and NF feed, the limit that excludes oil and silicone types.
• Steam purity: sodium tracer and cation conductivity at ppb level, against ABMA steam TDS of 0.2 to 1.0 ppm at 0 to 300 psig (0 to 20.7 bar(g)).

Which Standards and Regulations Apply to Defoamers?#

Defoamers fall under 2 US instruments, NSF/ANSI/CAN 60 for chemicals added to drinking water and 21 CFR 173.310 for boiler additives in steam that contacts food, and none of the 6 chemistries has a US MCL, a WHO guideline value or an EU DWD parametric value. Table 5 compares the regulatory status of each chemistry.

NSF/ANSI/CAN 60 listings are product-specific (function "Antifoamer", 0.1 to 100 mg/L as product, NSF listings, 2026-10-20), not per chemistry. 21 CFR 173.310 was last amended by 88 FR 17710, 2023-03-24.

NSF/ANSI/CAN 60 antifoamer listings#

NSF/ANSI/CAN 60 lists defoamers under the product function "Antifoamer" among the miscellaneous water supply products of its Section 8, with product-specific maximum use levels from 0.1 to 100 mg/L as product (NSF listings, 2026-10-20). The maximum use level is the total across all application points.

Most antifoamer listings carry the footnote "Certified for addition to the feedwater for evaporative desalination units only", so a listing never means general potable-water use. How MULs are set and checked is explained on NSF/ANSI/CAN 60.

21 CFR 173.310: polyglycols listed, silicones not listed#

21 CFR 173.310 lists 3 antifoam-type boiler water additives for steam that contacts food: polyoxypropylene glycol with a minimum molecular weight of 1,000, butanol-started monobutyl ethers of polyethylene-polypropylene glycol (random 1:1 EO:PO by weight) with a minimum of 1,500, and polyethylene glycol. The rule sets no numeric feed cap for them, only the amount required for the functional purpose (eCFR, last amended 88 FR 17710, 2023-03-24).

Silicones, the EO/PO block copolymer itself, mineral oil and fatty alcohols are not listed in 21 CFR 173.310.

The full additive list is explained under 21 CFR 173.310 boiler water additives.

Drinking-water limits and the foaming-agents secondary standard#

No defoamer chemistry has a US MCL, a WHO guideline value or an EU DWD parametric value.

The US secondary standard of 0.5 mg/L for foaming agents (40 CFR 143.3, non-enforceable) concerns foaming agents in finished water, not defoamers.

In the EU, treatment chemicals fall under Article 12 of the EU Drinking Water Directive 2020/2184.

Complete List of Defoamers: All 6 Chemistries in One Table#

The complete list of defoamers below gives all 6 chemistries with their CAS number, class, co-active, main water-treatment use and 21 CFR 173.310 status.

Who Supplies Defoamers and Foam-Control Programs?#

Defoamers are a standard category in water-treatment chemical catalogs, so the buying decision rests on the specification, not on availability. Distributor catalogs list defoamers or antifoams next to coagulants, biocides and antiscalants, and distributors by region are listed under water treatment chemical suppliers.

A defoamer specification names 6 items: the chemistry and form, the % active, the dose basis, the NSF/ANSI/CAN 60 listing and its footnote where water reaches a drinking-water outlet, the 21 CFR 173.310 status where steam contacts food, and the COD the product adds to the effluent.

Buyers choose between 2 routes. A program provider surveys the foam, runs the bench ladder and sets feed control; a chemical supplier delivers product to the specification.

How to compare program providers is covered under water treatment program providers.

Are Defoamers Safe, and What Are Their Drawbacks?#

Defoamer safety is judged at 2 levels: at the plant, hazards follow each product's safety data sheet, and in treated water only NSF/ANSI/CAN 60 certified products at or below their maximum use level belong in drinking water, most of them in evaporative desalination feedwater only.

Is silicone antifoam safe?#

Silicone antifoam safety is product-specific: the hazard classification sits on each product's safety data sheet, and silicones are not listed in 21 CFR 173.310. Check the supplier SDS for the hazard statements of the exact product.

What are the disadvantages of antifoaming agents?#

Antifoaming agents have 4 drawbacks in water treatment, listed below.

• They add COD and BOD to the effluent.
• Oil and silicone types foul RO and NF membranes.
• Hydrocarbon types worsen filamentous foam.
• Silicone types cost more than the other chemistries.

What is the best defoamer for water treatment?#

No single defoamer is best for water treatment: the best choice is the lowest dose of a chemistry that knocks foam down fast and durably in a bench ladder on the actual water without harming the biology, membranes or steam downstream.

Do food and paper defoamer rules apply to water treatment?#

No: 21 CFR 173.340 (defoaming agents in food) and 21 CFR 176.210 (defoamers in paper and paperboard) are food and paper rules, so the 10 ppm limit for dimethylpolysiloxane in food, zero in milk, is never a water-treatment limit.

Can a defoamer be used in drinking water?#

Only a certified one: a defoamer enters drinking water only as an NSF/ANSI/CAN 60 certified antifoamer at or below its product maximum use level, and most such listings are restricted to evaporative desalination feedwater.