How to Remove Arsenic from Drinking Water: As(III) Oxidation, Adsorption Media, and RO
Posted by ForeverPure Engineering Team on May 4th 2026
Arsenic in groundwater is a public-health crisis on three continents. The EPA MCL is 10 µg/L (0.010 mg/L); WHO matches that. Removing arsenic is straightforward chemistry once you understand speciation — get that wrong and you'll buy expensive media that strips half the arsenic. This guide walks the full treatment design from raw-water speciation to spent-media disposal.
1. Test for Total Arsenic and Speciate As(III) vs As(V)
Collect samples per EPA Method 200.8 (ICP-MS) for total arsenic. For speciation, use field-stable cartridges (Metalsoft AsXP, OnGuard A/S) that capture As(V) on column and let As(III) pass; lab analyzes both fractions. Speciation drives every downstream choice. Without it, you'll over- or under-design pretreatment. See our arsenic treatment overview.
2. Test pH, Iron, Manganese, Silica, Phosphate, and Sulfate
These compete with arsenic for adsorption sites. Phosphate is the worst competitor — > 0.5 mg/L slashes GFH capacity by half. Silica > 30 mg/L reduces GFH bed life. Iron > 0.3 mg/L oxidizes and coats media. Get a full anion panel before specifying any media.
3. Oxidize As(III) to As(V) Before Treatment
Free chlorine 1.0 mg/L with 10 minutes contact time converts > 95% of As(III) to As(V). Permanganate (KMnO4) 0.5–2.0 mg/L is faster and works at any pH. Ozone is excellent but expensive at small scale. UV alone does NOT oxidize arsenic — common misconception. After oxidation, dechlorinate with activated carbon if downstream RO membranes are sensitive.
4. Choose the Treatment Strategy by Arsenic Concentration and Flow
POU/POE for residential (≤ 1 GPM): NSF/ANSI 53-certified RO under sink, or NSF/ANSI 58 for the As(V) claim. Small commercial (1–50 GPM): adsorption media (GFH or activated alumina) in pressure vessel. Large municipal/industrial (> 50 GPM): coagulation-filtration with ferric chloride, or RO + brine management. Review the cost-per-1000-gallons comparison before specifying.
5. Size a GFH Adsorption System
Empty Bed Contact Time (EBCT) target: 3–5 minutes. For 25 GPM design flow at 5 min EBCT: 25 × 5 = 125 gallons of media (≈ 17 ft³ at 50 lb/ft³ wet density). Vessel: 24" diameter × 65" sidewall typically holds 22 ft³ — gives 30% expansion headroom. Throughput depends on As load: at 50 µg/L raw and EPA target 10 µg/L, expect 30,000–60,000 bed volumes before breakthrough.
6. Engineer the Pretreatment
Particulate filtration to 5 µm protects the bed from fouling. If iron > 0.3 mg/L, add greensand or birm pretreatment. If pH > 8.5, consider acid injection to 7.0–7.5 to extend GFH capacity. Phosphate and silica usually have to be lived with — adjust media volume upward to compensate.
7. Plan for Breakthrough Monitoring
Monitor effluent arsenic monthly with field test strips (Hach EZ Arsenic, range 0–500 µg/L) and quarterly via lab ICP-MS. Set the breakthrough action level at 8 µg/L (80% of MCL) — this gives time to schedule media replacement before regulatory exceedance. Track total gallons treated and bed volumes to predict next changeout.
8. Handle Spent Media Disposal Compliantly
Test spent media via EPA TCLP 1311 before disposal. Most exhausted GFH passes the 5.0 mg/L TCLP arsenic threshold and can go to non-hazardous landfill. Some loaded media fails TCLP and is RCRA hazardous (D004) — requires a licensed hazardous waste hauler. Document chain-of-custody. The supplier often takes spent media back for stabilization at lower cost than landfill.
9. Document, Report, and Re-Verify
Maintain a treatment log: feed/effluent arsenic by date, gallons treated, EBCT, bed volumes, pretreatment performance. State drinking-water programs require quarterly compliance sampling at minimum. Re-validate the design after every 10,000 bed volumes — feedwater shifts and competing-anion levels change real-world capacity.
Frequently Asked Questions
What's the EPA MCL for arsenic?
10 µg/L (0.010 mg/L). California's Public Health Goal is 4 µg/L. WHO provisional guideline is 10 µg/L. The most-affected regions globally include Bangladesh, India (West Bengal), Vietnam, and parts of the southwestern US (Arizona, Nevada, New Mexico).
Why does As(III) vs As(V) matter?
As(V) (arsenate) carries a negative charge at typical groundwater pH and adsorbs readily on iron oxides and activated alumina. As(III) (arsenite) is uncharged and barely adsorbs. Oxidizing As(III) to As(V) before any media is what separates a working system from a failure.
Does standard RO remove arsenic?
RO removes ~95% of As(V) but only 50–70% of As(III). For source water with > 50 µg/L total arsenic and unknown speciation, oxidize first (e.g., free chlorine 1.0 mg/L for 10 min) then RO.
Is granular ferric hydroxide (GFH) the best media?
GFH (Bayoxide E33, GEH 102) leads on capacity per gram for As(V) at pH 6.5–8.5. Granular ferric oxide (GFO) and titanium dioxide (Metsorb) are alternatives. Activated alumina works but needs aggressive pH adjustment to ~5.5–6.0 for full capacity.
Talk to a ForeverPure Engineer
Contaminant removal performance is feedwater-specific — the same media that strips arsenic at one site fouls in three months at another. Our application engineers will size and quote a tested treatment train for your exact source water and discharge target.
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