Groundwater Arsenic Removal Process Using Iron Hydroxide Arsenic Removal Filter Media

Groundwater Arsenic Removal: Granular Ferric Hydroxide Adsorbent Process

I. Product Definition and Core Specifications

• Name: BKsorb Granular Ferric Hydroxide Arsenic Removal Filter Media

• Active Components: β-FeOOH + Fe(OH)₃, Iron Content ≥ 600 g/kg

• Particle Size: 0.2–2.0 mm; Bulk Density 1150 kg/m³

• Particle Size: Specific Surface Area ≈ 300 m²/g

II. Arsenic Removal Mechanism (Two-Step Reaction)

1. Surface Adsorption: High specific surface area provides abundant ≡Fe–OH active sites.

2. Chemical Bonding: As(V) replaces surface hydroxyl groups to form stable FeAsO₄; As(III) must first be oxidized to As(V) before fixation:

• Fe(OH)₃ + H₃AsO₄ → FeAsO₄↓ + 3H₂O

III. Advantages Summary

1. High Selectivity: Effective for both As(III) and As(V), achieving 0.01 mg/L compliance in a single filtration.

2. Simple Operation: No additional chemicals or regeneration systems required, low maintenance.

3. Environmentally Friendly: No arsenic-containing sludge or regeneration waste liquid; saturated media can be disposed as general solid waste (brick-making, landfill).

4. Economical: 30–50% reduction in investment and energy consumption compared to reverse osmosis/ion exchange.

IV. Process Unit Flow (Applicable to Groundwater)

1. Pretreatment: 10 μm safety filtration to remove suspended solids; if As(III) proportion is high, optionally add 0.5–1 mg/L NaClO or aeration oxidation (pre-oxidation is optional; effluent still meets standards, but adsorption capacity may be reduced).

2. Adsorption Filtration
   ‑ Packing Height: 0.8–1.6 m (recommended ≥1.0 m)
   ‑ Empty Bed Contact Time (EBCT): 3–5 min
   ‑ Filtration Rate: 10–20 m/h (≤20 m/h ensures effluent As<10 µg/L)
   ‑ Optimal Adsorption pH: 6.5–7.5 (operating range 5–9)
   ‑ Allowable Pressure Drop: ≤0.5 bar

3. Backwashing
   ‑ Trigger Differential Pressure: 0.5 bar; backwash intensity 25–30 m/h; duration 5–10 min, required only 1–2 times per month.

4. Effluent Monitoring
   ‑ Online or weekly manual testing to confirm effluent As<0.01 mg/L.

V. Applicable Water Quality Boundaries

• Arsenic Concentration: 0.03–0.5 mg/L

• Temperature: 5–60 °C

• Coexisting Ions: Cl⁻, SO₄²⁻, HCO₃⁻ cause no interference; control PO₄³⁻<0.5 mg P/L and Si<10 mg SiO₂/L to extend lifespan.

VI. Typical Process Layout

• Small Integrated Units: 1–50 m³/h skid-mounted pressure vessels, upflow or downflow.

• Large Water Plants: Multiple parallel fixed beds, single bed area 5–20 m², total treatment capacity up to 50,000–100,000 m³/d.

VII. Domestically Verified Cases

• Shaanxi 200 m³/h Groundwater Arsenic Removal Project: BKsorb filter effluent As<5 µg/L, in 4th year of operation.

• Gansu 500 m³/d Rural Multi-Village Project: Low temperature 8–12 °C, no media replacement for 2 years, stable effluent.

• Inner Mongolia 80 m³/h Integrated Unit: High hardness water, backwash cycle 10–14 days.