Reverse osmosis chemicals are the 9 groups of chemicals that an RO, nanofiltration or ultrafiltration plant doses into its feedwater or uses on its membranes, from intake chlorine and the bisulfite that removes it to antiscalants, biocides, cleaners and preservatives, so that the polyamide membrane sees less than 0.1 mg/L (ppm) of free chlorine and no scale, colloids or biofilm. A brackish-water RO train concentrates its feed about tenfold at 90 % recovery, so which chemical goes in where, at what dose, and how is it proven?
Online chemicals, such as chlorine, bisulfite, acid and antiscalant, enter the running feed; offline chemicals, such as cleaners and preservatives, act on stopped membranes. Each belongs to a family of water treatment chemicals that RO plants use with their own limits and dose bases.
The dosing order runs oxidant, coagulant, bisulfite, acid, then antiscalant at 2 to 5 mg/L as product. Feedwater limits and cleaning triggers define control, ORP, SDI and normalized data prove it, and NSF/ANSI/CAN 60 governs potable use.
Every value on this page is checked against primary sources (membrane manufacturer manuals, NSF listings, eCFR, AWWA, CEN, EPA); see our methodology and fact-checking process.
What Are Reverse Osmosis Chemicals?#
Reverse osmosis chemicals are pretreatment, conditioning, cleaning and storage chemicals that keep an RO, NF or UF membrane rejecting 95 to more than 99 % of dissolved salts without scaling, fouling or oxidizing it. The membrane removes the salts; the chemicals protect the membrane, and cleaners are flushed out before service.
What goes wrong in an RO system without chemical treatment?#
An untreated RO system fails in 5 ways: scaling by calcium carbonate, sulfates, fluoride or silica, colloidal fouling, organic fouling, biological fouling and oxidation of the polyamide layer by chlorine. The 5 failure modes, as the DuPont FilmTec RO and NF Technical Manual (Form 45-D01504) describes them, are listed below.
- Scaling: tail elements, where the concentrate is strongest.
- Colloidal fouling: lead elements, measured as SDI.
- Organic fouling: pretreatment needed above 3 mg/L TOC.
- Biofouling: biofilm within 3 to 5 days, lead-end pressure drop.
- Oxidation: polyamide degraded after about 200 to 1,000 ppm-h.
Diagnosis by location and autopsy is covered under membrane fouling.
Online and offline chemicals: the dosing order in an RO plant#
An RO plant doses its online chemicals in a fixed order, oxidant, coagulant and flocculant, sodium bisulfite, acid and antiscalant, ahead of a 5 µm cartridge filter, while cleaners and preservatives are used offline. The same manual lists the online chemical sequence of an RO plant in 8 steps.
- Oxidant at the intake.
- Coagulant and flocculant.
- Filtration.
- Sodium bisulfite (SBS).
- Acid.
- Antiscalant.
- Cartridge filter, 5 µm.
- High-pressure pump.
Acid and antiscalant pumps are interlocked with the feed pump, and high-pH and ORP alarms shut the train down. Pump types are described under chemical dosing pumps.
9 Types of Reverse Osmosis Chemicals in a Membrane Program#
The 9 types of reverse osmosis chemicals are oxidants, coagulants and flocculants, dechlorination chemicals, acids and pH adjusters, antiscalants, biocides and sanitizers, cleaning chemicals, preservatives and UF/MF backwash chemicals, and the first 5 are dosed online in that order. Table 1 compares each function by chemicals, dosing point, dose basis and constraint.
| # | Function | Typical chemicals | Where dosed | Dose and basis | Main RO constraint | Source |
|---|---|---|---|---|---|---|
| 1 | Oxidants and oxidizing biocides | Sodium hypochlorite | Intake, 20 to 30 min reaction | 0.5 to 1.0 mg/L (ppm) free residual as Cl2 through pretreatment | Removed before the membrane (< 0.1 mg/L) | DuPont FilmTec manual 45-D01504 |
| 2 | Coagulants for water treatment | Ferric sulfate, ferric chloride; ACH before MF/UF; anionic or nonionic flocculants | In line ahead of filtration | Ferric 10 to 30 mg/L | No aluminum; no cationic carryover | DuPont FilmTec manual 45-D01504 |
| 3 | Dechlorination chemicals | Sodium bisulfite, sodium metabisulfite | Upstream of cartridge, static mixer | SMBS 1.34 (theory) / 3.0 (practice); SBS 1.47 / 1.8 to 3.0 mg per mg Cl2; at least 20 s | ORP verified before membrane | DuPont 45-D01504; Hydranautics TAB-111 |
| 4 | pH adjustment chemicals | Sulfuric, hydrochloric acid; caustic soda (boron pass) | After SBS, before antiscalant | Seawater about 10 mg/L H2SO4 to pH about 7; acid-only target LSIc -0.2 | Sulfate adds CaSO4 risk | DuPont 45-D01504; Hydranautics TAB-111 |
| 5 | RO antiscalants | Phosphonates (ATMP, HEDP), polymers | After acid, before 5 µm cartridge | 2 to 5 mg/L (ppm) of feed as product | No cationic polymer, Fe or Al | Hydranautics TAB-111 |
| 6 | Membrane biofouling control | DBNPA (slug), hydrogen peroxide (offline) | RO feed or CIP skid | H2O2 0.1 wt % below 25 °C (77 °F), pH 3 to 4, 20 min | Chlorine-type agents excluded | DuPont FilmTec manual 45-D01504 |
| 7 | RO membrane cleaning chemicals | Caustic + SLS or Na4EDTA; HCl; citric acid; sodium hydrosulfite | Offline, CIP tank | 0.1 wt % NaOH (pH 12); 0.2 wt % HCl (pH 1 to 2); 2.0 wt % citric | pH/temperature envelope | DuPont Form 45-D01696 Rev 13; Hydranautics TSB107 |
| 8 | RO membrane preservation | Sodium metabisulfite | Offline, in vessels | 1 to 1.5 % SMBS solution | Replace at pH 3 or lower | DuPont FilmTec manual 45-D01504 |
| 9 | UF and MBR membrane cleaning chemicals | NaOCl + NaOH; HCl; citric or oxalic acid | Backwash water (CEB) | 0.1 % NaOCl + 0.05 % NaOH; 0.1 % HCl; 2 % citric or oxalic | Alkaline CEB then acid CEB | DOW UF manual (2011); DuPont inge design manual Rev 9 (2026) |
Manufacturer figures; a plant's own values come from its projection or supplier. Cleaning and CEB concentrations are wt % of the cleaning solution, not feedwater doses.
1. Oxidants for intake chlorination#
Oxidants such as sodium hypochlorite are dosed at the intake to hold 0.5 to 1.0 mg/L of free chlorine through pretreatment after 20 to 30 minutes of reaction, and they must be removed before the membrane (DuPont FilmTec manual). The same manual does not recommend chloramine, chlorine dioxide, iodine, quaternary ammonium compounds or copper sulfate on polyamide.
2. Coagulants and flocculants for RO pretreatment#
Coagulants for RO pretreatment are iron salts, ferric sulfate or ferric chloride at 10 to 30 mg/L in line, because the manual does not recommend aluminum coagulants ahead of polyamide membranes. Flocculants are anionic or nonionic, because cationic polymer, iron or aluminum meeting an anionic antiscalant forms a gum-like gel. Aluminum chlorohydrate appears to reduce fouling before MF/UF (Australian Drinking Water Guidelines, NHMRC).
Coagulation, dechlorination and pH are planned together under RO pretreatment chemistry.
3. Dechlorination chemicals: sodium bisulfite and SMBS#
Dechlorination chemicals remove free chlorine before the cartridge filter: sodium metabisulfite needs 1.34 mg per mg of chlorine in theory and 3.0 mg in practice (technical manual), sodium bisulfite 1.47 mg in theory and 1.8 to 3.0 mg by design with at least 20 seconds of reaction (Hydranautics TAB-111). SMBS for RO is food grade and not cobalt-activated.
This worked example is calculated from the manual's practice ratio, with every input labelled.
- Feed flow: 100 m³/h (440 gpm).
- Free chlorine: 1.0 mg/L as Cl2.
- Dose: 3.0 mg per mg Cl2 = 3.0 mg/L as 100 % SMBS.
- Result: 3.0 x 100 x 0.024 = 7.2 kg/d (15.9 lb/day) as 100 % SMBS.
- Product: 7.2 / 0.30 = 24 kg/d (52.9 lb/day) of 30 % solution.
Other flows run in the chemical dosage calculator converts mg/L into kg/d, lb/day and pump settings.
4. Acids and pH adjusters for RO feedwater#
Acids lower the feed pH to turn alkalinity into carbon dioxide and keep calcium carbonate dissolved in the concentrate: the bulletin recommends a concentrate LSI of -0.2 with acid alone, and seawater plants typically dose about 10 mg/L of sulfuric acid to a feed pH near 7 (technical manual). Caustic soda raises the pH of a second pass for boron rejection.
5. RO antiscalants#
RO antiscalants are threshold scale inhibitors, mainly phosphonates and polymers, dosed continuously at 2 to 5 mg/L (ppm) of feed as product upstream of the cartridge filter and downstream of acid injection (TAB-111). The manual recommends antiscalant on seawater RO above 35 % recovery.
Chemistries and dose arithmetic sit on the RO antiscalant page. The same molecules serve boilers and cooling towers as scale inhibitors.
6. Membrane biocides and sanitizers#
Membrane biocides and sanitizers control biofilm, which forms within 3 to 5 days in biologically active feedwater, so the technical manual sanitizes every 3 to 5 days in summer and about every 7 days in winter. DBNPA raises ORP to about 400 mV at 0.5 to 3 mg/L, so the ORP setpoint is bypassed during dosing. Hydrogen peroxide sanitization runs at 0.1 wt % below 25 °C (77 °F), pH 3 to 4, for 20 minutes, at most twice a week.
Oxidizing and non-oxidizing biocides for water treatment are compared across systems on the family hub.
7. RO membrane cleaning chemicals (CIP)#
RO membrane cleaning chemicals are alkaline cleaners for organics and biofilm and acid cleaners for scale and metal oxides, and the maker's cleaning procedures (Form 45-D01696, Rev 13, February 2026) clean alkaline first unless the foulant is only calcium carbonate or iron oxide. Sulfuric acid and cationic surfactants are never used, and no cleaning runs below 20 °C (68 °F).
Five cleaning solutions cover most RO foulants.
| Cleaner type | Example solution | Removes | Note | Source |
|---|---|---|---|---|
| Alkaline + surfactant | 0.1 wt % NaOH + 0.025 wt % SLS, pH 12 | Organics, biofilm | Not below 20 °C (68 °F) | DuPont Form 45-D01696 |
| Alkaline + chelant | 0.1 wt % NaOH + 1.0 wt % Na4EDTA, pH 12, max 35 °C (95 °F) | Organics, sulfates, antiscalant gel | Repeated for gels | DuPont Form 45-D01696 |
| Mineral acid | 0.2 wt % HCl, pH 1 to 2, 25 °C (77 °F) | Calcium carbonate, metal oxides | Never sulfuric acid | DuPont Form 45-D01696 |
| Organic acid | 2.0 wt % citric acid = 17.0 lb (7.7 kg) per 100 US gal (379 L) | Carbonate and sulfate scales, metal oxides | NSF "Membrane Cleaner", MUL "NA" | Hydranautics TSB107.30 |
| Reducing cleaner | 1.0 wt % sodium hydrosulfite, pH 5 | Iron fouling | Not sodium bisulfite or hydrosulfide | DuPont Form 45-D01696 |
Acids, chelants and inhibitors for other equipment are grouped under descaling and chemical cleaning agents.
8. Membrane preservatives for shutdown and storage#
Membrane preservatives protect elements during shutdowns longer than 48 hours: the technical manual fills the vessels with 1 to 1.5 % SMBS, checks the pH weekly and replaces the solution when the pH falls to 3 or lower, at least monthly.
9. UF and MF backwash and CEB chemicals#
UF and MF membranes are cleaned by chemically enhanced backwash (CEB) with 0.1 % hydrochloric acid, 2 % citric or oxalic acid, or 0.1 % sodium hypochlorite with 0.05 % caustic soda dosed into the backwash water, (Table 1 sources). Every alkaline CEB is followed by an acid CEB, which alone removes iron-coagulant residue, and seawater caustic CEB stays at or below 2 mmol/L NaOH (pH 9.5 to 9.7).
RO Control Limits: Feedwater, Operating and Cleaning Limits#
An RO chemical program works to 3 sets of limits: feedwater limits that pretreatment chemicals must meet, operating limits of the membrane element, and cleaning triggers and pH limits for offline chemistry. Table 3 collects them.
| Parameter | Limit | Note | Source |
|---|---|---|---|
| Free chlorine in feed | < 0.1 mg/L as Cl2 | Degradation after about 200 to 1,000 ppm-h | DuPont 45-D01504 |
| SDI15 / MFI-0.45 | ≤ 5 (< 3 recommended) / limit 4, target < 1 | ASTM D4189-23 / D8002-24 | DuPont 45-D01504 |
| Turbidity | < 1 NTU | Minimum requirement | DuPont 45-D01504 |
| Fe3+ / Al / Mn | 0.05 mg/L each | Feed | DuPont 45-D01504 |
| Fe2+ | Up to 4 mg/L at pH < 6, O2 < 0.5 mg/L | Anoxic wells | DuPont 45-D01504 |
| TOC / COD | Pretreat above 3 mg/L / 10 mg/L | Organic fouling | DuPont 45-D01504 |
| Oil (hydrocarbon or silicone) | 0.1 mg/L | No defoamer upstream | DuPont 45-D01504 |
| AOC / BFR | 10 µg/L acetate-C / 5 pg/cm² ATP | Biofouling potential | DuPont 45-D01504 |
| H2S | 0.1 mg/L affects RO | Keep anaerobic | DuPont 45-D01504 |
| Cartridge filter | 5 µm (< 10 µm absolute); replace at least every 3 months | Before HP pump | DuPont 45-D01504 |
| pH / temperature (operation) | 2 to 11 / max 45 °C (113 °F) | Standard polyamide | DuPont 45-D01504 |
| Operating pressure | BW 41 bar (600 psi); SW 69 to 84 bar (1,000 to 1,200 psi) | As printed | DuPont 45-D01504 |
| Pressure drop | 3.5 bar (50 psi) per vessel; 1 bar (15 psi) per element | Maximum | DuPont 45-D01504 |
| Recovery | Brackish about 90 %; seawater about 50 % | Design maximum | DuPont 45-D01504 |
| Cleaning trigger | Flow -10 %; salt passage +5 to 10 %; ΔP +10 to 15 % | Normalized | DuPont Form 45-D01696 |
| Cleaning pH | 1 to 13 (25 °C / 77 °F); 1 to 12 (35 °C / 95 °F); 1 to 10.5 (45 °C / 113 °F) | BWRO/SWRO elements, Rev 13 | DuPont Form 45-D01696 |
| ORP shutdown | DuPont 175 to 200 mV; Hydranautics warn > 300, shut down 350 mV | After SBS mixing | DuPont 45-D01504; TAB-111 |
Feedwater limits for polyamide RO membranes#
Polyamide RO feedwater must carry less than 0.1 mg/L of free chlorine, an SDI15 of at most 5 (below 3 recommended), less than 0.05 mg/L each of ferric iron, aluminum and manganese, and less than 0.1 mg/L of oil (DuPont FilmTec manual). Turbidity stays below 1 NTU, and 0.1 mg/L of hydrogen sulfide already affects RO. No oil or silicone defoamer goes upstream.
Operating limits: pH, temperature, pressure and recovery#
Standard polyamide elements operate at pH 2 to 11 and at most 45 °C (113 °F), at up to 41 bar (600 psi) for brackish-water and 69 to 84 bar (1,000 to 1,200 psi) for seawater elements (same manual). Recovery reaches about 90 % on brackish and about 50 % on seawater; CF = 1/(1 - Y) gives a concentration factor of 4 at 75 %.
Cleaning triggers and cleaning pH limits#
An RO train is cleaned when normalized permeate flow falls 10 %, normalized salt passage rises 5 to 10 % or normalized pressure drop rises 10 to 15 %, because a 30 to 50 % loss may not be fully recoverable (cleaning procedures Form 45-D01696; Hydranautics TSB107). Allowed cleaning pH narrows with temperature, from 1 to 13 at 25 °C (77 °F) to 1 to 10.5 at 45 °C (113 °F).
How Is an RO Chemical Program Monitored and Tested?#
An RO chemical program is proven by 3 kinds of measurement: online ORP and chlorine readings that protect the membrane, SDI and MFI tests that rate the pretreatment, and normalized performance data that reveal scaling and fouling. Table 4 lists the tests and methods.
| Test | Method | Where / how often | Target |
|---|---|---|---|
| ORP | Online probe | After dechlorination mixing | Below the manufacturer threshold |
| SDI | ASTM D4189-23, 0.45 µm, 47 mm, 207 kPa (30 psi) | RO feed; 3 times a day on surface water | SDI15 ≤ 5, < 3 recommended |
| MFI-0.45 | ASTM D8002-24 | RO feed | < 1 (about SDI < 3) |
| Normalized flow, salt passage, ΔP | ASTM D4516-19a | Daily trend | Table 3 triggers |
| LSI / Stiff-Davis (concentrate) | ASTM D3739-19 (≤ 10,000 mg/L TDS) / D4582-23 (> 10,000) | Projection, feed analysis | LSIc < 0 without antiscalant |
| ATP (biofilm formation rate) | ASTM D4012-23a | Biofouling studies | < 1 pg/cm² stable, > 100 severe |
ORP and chlorine monitoring before the membranes#
ORP after the dechlorination mixing line is the shutdown signal of an RO plant: DuPont uses a 175 to 200 mV threshold, while Hydranautics warns above 300 mV and shuts down at 350 mV (TAB-111). No single setpoint is universal, and DBNPA dosing raises the reading.
Units and electrode care are explained under oxidation-reduction potential (ORP).
SDI and MFI testing of RO feedwater#
SDI testing rates the colloidal fouling potential of RO feed by filtering it through a 47 mm, 0.45 µm membrane at 207 kPa (30 psi) under ASTM D4189-23, and RO feed needs an SDI15 of at most 5, below 3 recommended. Surface-water plants test 3 times a day; media filtration reaches SDI15 below 5, MF/UF below 1.
The full silt density index (SDI) procedure sits on the SDI page.
Normalized performance data and concentrate LSI#
Normalized performance data, standardized under ASTM D4516-19a, separate fouling from changes in temperature and pressure: scaling shows first as rising pressure drop in the tail elements, biofouling at the lead end. Concentrate scaling is predicted with the LSI up to 10,000 mg/L TDS and the Stiff-Davis index above it.
Index arithmetic and worked examples sit on the Langelier saturation index (LSI) page.
Which Standards and Regulations Apply to Membrane Chemicals?#
Membrane chemicals are governed in 3 layers: NSF/ANSI/CAN 60 certification when the permeate becomes drinking water, AWWA and EN standards plus pesticide registration for biocides, and discharge rules for concentrate and spent cleaning solutions.
NSF/ANSI/CAN 60 functions for membrane chemicals#
NSF/ANSI/CAN 60 certifies membrane chemicals under 3 product functions, each with product-specific maximum use levels (MULs) as product (NSF listings, 2026-10-21). The 3 functions are listed below.
- Reverse Osmosis Antiscalant: 202 companies, 1,582 products, 2,139 product-function rows; most common MUL 10 mg/L.
- Membrane Cleaner: 104 companies, 768 products, 982 product-function rows; MUL "NA" (offline, flushed out) on 969.
- Reverse Osmosis Membrane Biocide: 42 companies, 186 products, 242 product-function rows; MUL "NA" on 179.
48 of 50 US states require NSF/ANSI/CAN 60 (NSF 2019). How MULs are set and read is explained on NSF/ANSI/CAN 60.
AWWA and EN standards and biocide registration#
Three AWWA standards cover membrane systems, ANSI/AWWA B114-22 for RO and NF, B112-25 for MF/UF and B130-23 for membrane bioreactors, while in Europe phosphonate antiscalants for drinking water follow EN 15040:2014 under Directive (EU) 2020/2184, Article 12. One US DBNPA label limits use to "non-potable reverse osmosis systems" (EPA Reg. No. 88714-2).
EN 15039 (polycarboxylates) and EN 15041 (polyphosphates) complete the membrane antiscalant standards under EN standards for drinking water treatment chemicals.
Article 12 rules for treatment chemicals are on EU Drinking Water Directive 2020/2184.
Concentrate and spent cleaning solution discharge#
Spent RO cleaning solutions are neutralized, with oxidants quenched, and discharged to surface water or a sanitary sewer under State and local rules, and surfactants can complicate approval (EPA Membrane Filtration Guidance Manual, EPA 815-R-06-009). Direct dischargers disclose additives such as scale inhibitors, biocides and dechlorinators (40 CFR 122).
Disclosure and WET testing work as described under NPDES permits.
Complete List of Reverse Osmosis Chemicals#
The complete list of reverse osmosis chemicals gives 17 chemicals with function, dosing point and NSF/ANSI/CAN 60 status, in the order of the 9 functions.
| # | Chemical | Function in RO/UF | Where | NSF/ANSI/CAN 60 (NSF listings, 2026-10-21) |
|---|---|---|---|---|
| 1 | Sodium hypochlorite | Intake oxidant; UF CEB | Intake; backwash | Product-specific; most common 84 mg/L |
| 2 | Ferric chloride | Coagulant | In line | Product-specific; most common 250 mg/L |
| 3 | Ferric sulfate | Coagulant | In line | Product-specific; most common 600 mg/L |
| 4 | Aluminum chlorohydrate (ACH) | Coagulant before MF/UF | Ahead of MF/UF | Product-specific; most common 250 mg/L |
| 5 | PolyDADMAC | Coagulant; some listings note RO pretreatment | Ahead of filtration | Product-specific |
| 6 | Sodium bisulfite | Dechlorination | Upstream of cartridge | 8 to 160 mg/L, most common 46 (162 of 386 rows) |
| 7 | Sodium metabisulfite (SMBS) | Dechlorination; preservation | Upstream of cartridge; vessels | 10 to 50 mg/L, most common 15 (11 of 19 rows) |
| 8 | Sulfuric acid | Feed pH | After SBS | Product-specific; most common 50 mg/L |
| 9 | Hydrochloric acid | Feed pH; acid cleaning; UF CEB | Feed; CIP; backwash | Product-specific; most common 40 mg/L |
| 10 | Sodium hydroxide (caustic soda) | Alkaline cleaning; boron pass; UF CEB | CIP; second pass; backwash | Product-specific; most common 100 mg/L |
| 11 | ATMP | Phosphonate antiscalant | Before cartridge | Listed in RO antiscalant products |
| 12 | HEDP | Phosphonate antiscalant | Before cartridge | Listed in RO antiscalant products |
| 13 | DBNPA | Non-oxidizing membrane biocide | RO feed (slug) or CIP | RO Membrane Biocide function, by trade name |
| 14 | Hydrogen peroxide | Membrane sanitization (offline) | CIP skid | Product-specific; most common 3 mg/L |
| 15 | EDTA | Alkaline chelant cleaner | CIP | No chemical category (proprietary products only) |
| 16 | Citric acid | Acid cleaner; UF CEB | CIP; backwash | Membrane Cleaner, MUL "NA" (42 companies) |
| 17 | Sulfamic acid | Acid cleaner | CIP | No chemical category |
MULs are product-specific, as product.
Every other chemical is filterable by CAS, function and NSF status in the water treatment chemical database.
How Is a Reverse Osmosis Chemical Program Bought?#
A reverse osmosis chemical program is bought in one of 2 ways: from a program provider who runs projections, dosing, monitoring and cleaning, or as chemical supply against a specification that requires the NSF/ANSI/CAN 60 listing with its MUL, AWWA conformance and a certificate of analysis. One municipal bid (City of Mansfield, Texas, Bid 2023-25-01) asked for exactly those 3 documents.
How to compare water treatment companies and their service models is covered on the provider guide.
What should a membrane chemical program quote contain?#
A membrane chemical program quote should answer the 7 supplier questions that Hydranautics lists in TAB-111: membrane compatibility, references longer than 1,000 hours, reactions with iron, metals and cationic polymers, recommended and maximum dose, solubility limits, discharge and suitability for potable water. The 7 items are listed below.
- Membrane compatibility.
- References above 1,000 hours.
- Reactions with iron, metals and cationic polymers.
- Recommended and maximum dose, as product.
- Solubility limits.
- Discharge implications.
- Potable suitability (NSF/ANSI/CAN 60 function and MUL).
Cleaning more than once a month justifies a pretreatment upgrade (TSB107).
Where Do Membrane Chemicals Fit in Industrial Water Treatment?#
Membrane chemicals form one of the chemical programs of industrial water treatment, next to boiler, cooling-tower and wastewater programs, and they share most of their molecules with drinking-water and wastewater plants.
Every program is compared on industrial water treatment by application.
Flux, rejection and staging are explained under how reverse osmosis works.
Which chemicals do seawater desalination plants add?#
Seawater desalination plants add the same pretreatment chemicals at seawater doses, inorganic coagulants at 5 to 30 mg/L or ferric chloride at 0.3 to 0.7 mg/L ahead of UF, plus caustic soda in a second pass to raise boron rejection, because seawater carries 4.5 to 6.0 mg/L of boron (Valavala et al., Environmental Engineering Research, 2011). Boron is limited to 1.5 mg/L in the EU, 2.4 mg/L where desalinated water predominates (Directive (EU) 2020/2184), and WHO sets 2.4 mg/L.
Intake, boron and post-treatment programs are covered under seawater desalination chemicals.
Permeate is conditioned by remineralization of desalinated water before distribution, and utility treatment of the permeate follows drinking water treatment chemicals rules.
How do wastewater reuse and high-silica feedwaters change the RO program?#
Wastewater reuse adds calcium phosphate to the scaling list, with tertiary effluent at 6.1 to 12.2 mg/L of phosphate in a DuPont example, while high-silica feeds of up to 100 mg/L as SiO2 need dispersant antiscalants and iron and aluminum below 0.05 mg/L.
Reuse plants run upstream of the RO as described under wastewater treatment chemicals. pH, temperature and dispersant limits are covered under silica scale in RO.
Does reverse osmosis remove PFAS and other dissolved chemicals?#
Utility RO and nanofiltration remove PFAS: both are best available technologies for the regulated PFAS under 40 CFR 141.61(d), and EPA reports removals typically above 90 %, short chains included, with about 20 % of the feed leaving as PFAS-bearing concentrate. PFOA and PFOS carry MCLs of 4.0 ng/L each with compliance from 2029-04-26 (89 FR 32532, 2024-04-26); EPA's 2026 proposals are pending, not final.
GAC, ion exchange and RO are compared under PFAS removal in drinking water treatment.
Can RO membranes tolerate chlorine?#
No: polyamide RO membranes tolerate less than 0.1 mg/L of free chlorine, and 1 mg/L degrades them within about 200 to 1,000 hours (technical manual, Table 3).
How often are RO membranes cleaned?#
Most RO trains are cleaned once every 3 to 12 months, and a plant that cleans more than once a month needs better pretreatment (TSB107 service bulletin).
Which chemicals must never meet in a membrane plant?#
Four chemical combinations must never occur in a membrane plant, because each one fouls a membrane or releases a hazard. The 4 combinations are listed below.
- Anionic antiscalant meeting cationic polymer, iron or aluminum: gel foulant.
- Chlorine CEB waste meeting acid waste: chlorine gas.
- Sulfuric acid in an RO cleaning solution: calcium sulfate precipitation.
- Cationic surfactants on RO membranes: irreversible fouling.
Who supplies reverse osmosis chemicals?#
Reverse osmosis chemicals come from specialist membrane-chemical makers and general water-treatment suppliers, with 202 companies holding NSF/ANSI/CAN 60 listings for RO antiscalants alone (NSF listings, 2026-10-21). BWA put the desalination chemical treatment market at about USD 600 million in 2016 (analyst estimate). Manufacturers, blenders and distributors are compared under water treatment chemical suppliers.