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)?, 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 FeAsO?; As(III) must first be oxidized to As(V) before fixation:

• Fe(OH)? + H?AsO? → FeAsO?↓ + 3H?O

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?, SO?2?, HCO?? cause no interference; control PO?3?<0.5 mg P/L and Si<10 mg SiO?/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.