Worked design example: Birm catalytic pre-stage and triple-media pressure filters treating borehole water with elevated iron (2.1 mg/L) and manganese (0.18 mg/L) for food-grade process water. 18 m³/hr continuous duty, cascade aeration, potassium permanganate oxidation, automatic backwash.
Treating a borehole or groundwater supply? See our full approach — aeration and catalytic multimedia filtration for iron and manganese, ultrafiltration for SDI and RO pre-treatment, and disinfection for potable supply — with example arrangements by application.
Borehole TreatmentA baked-goods manufacturer draws process water exclusively from a private borehole at 18 m³/hr. A water analysis commissioned following product quality complaints revealed iron at 2.1 mg/L and manganese at 0.18 mg/L — ten times and three times the EU Drinking Water Directive limits respectively. Raw turbidity is 3.2 NTU. Iron staining is occurring on internal pipe surfaces and product contact equipment; manganese produces a metallic off-taste in product. The site’s trade association technical audit has flagged the raw supply as non-compliant with the food safety plan. A dedicated iron and manganese removal system is required upstream of the production water storage tank, targeting outlet concentrations of < 0.05 mg/L Fe and < 0.02 mg/L Mn.
DWD limits for context: The EU Drinking Water Directive (2020/2184) sets Fe at 0.2 mg/L and Mn at 0.05 mg/L as parametric values. For food production, internal food safety plans typically specify tighter limits at the point of use. This design targets 0.05 mg/L Fe and 0.02 mg/L Mn to provide a working margin against analytical variation and any concentration from dead-legs within the facility distribution system.
Not every borehole requires greensand filtration. The appropriate treatment train depends on iron and manganese concentrations and the outlet quality target:
| Raw Iron | Raw Manganese | Recommended Treatment |
|---|---|---|
| < 0.3 mg/L | < 0.05 mg/L | Multimedia filter alone (in-bed contact oxidation with dissolved oxygen) |
| 0.3–1.0 mg/L | < 0.05 mg/L | Cascade aeration + multimedia filter |
| > 1.0 mg/L | < 0.05 mg/L | Aeration + greensand or Birm pre-stage + multimedia polishing filter |
| Any | 0.05–0.2 mg/L | Chemical oxidation (KMnO₄) + greensand/Birm + multimedia filter |
| > 2.0 mg/L | > 0.1 mg/L | Full iron/Mn plant: cascade aeration, KMnO₄ dosing, greensand, multimedia — this application |
Borehole pump delivers water at 18 m³/hr. At pH 7.1 the iron is predominantly in the soluble Fe²⁺ form — clear and colourless at this point. Manganese is fully dissolved as Mn²⁺. Both are invisible in solution; discolouration only develops after oxidation and precipitation downstream.
Water cascades over a packed aeration tower or tray cascade, introducing atmospheric oxygen. Aeration oxidises Fe²⁺ to Fe³⁺ (rust-coloured Fe(OH)₃ precipitate): 4Fe²⁺ + O₂ + 10H₂O → 4Fe(OH)₃ + 8H⁺. CO₂ stripping during aeration raises pH from 7.1 to approximately 7.4–7.6, improving the kinetics for downstream manganese oxidation. Aeration alone cannot achieve the Mn outlet target at this concentration.
KMnO₄ solution is dosed by a peristaltic pump at approximately 1.9 g per gram of Mn²⁺ (stoichiometric requirement). At pH ≥ 7.0, KMnO₄ rapidly and reliably oxidises Mn²⁺ to MnO₂ precipitate, independent of dissolved oxygen availability. A flow-paced dosing controller maintains the correct dose rate across varying borehole flows; an online manganese analyser on the treated water outlet verifies product quality and triggers a high-level alarm if Mn exceeds 75% of the target limit.
A GRP pressure vessel charged with Birm® catalytic media retains the Fe(OH)₃ and MnO₂ precipitates formed upstream. Birm also catalyses continued in-bed oxidation of residual Mn²⁺ using dissolved oxygen — no chemical regenerant is needed; backwash with clean water restores the bed. Backwash triggered at 0.4 bar differential pressure or a 48-hour timer. Outlet from this stage: Fe < 0.1 mg/L, Mn < 0.05 mg/L.
A second GRP pressure vessel charged with anthracite–sand–garnet removes residual turbidity and any fine Fe/Mn fines that escape the Birm stage. Turbidity is reduced from approximately 1–2 NTU to < 0.5 NTU. The media bed also provides a guard against any KMnO₄ overdose events: residual permanganate adsorbs onto the anthracite, preventing pink colouration in the product water. Outlet: Fe < 0.05 mg/L, Mn < 0.02 mg/L, turbidity < 0.5 NTU.
Treated water enters the existing 50 m³ production water storage tank, compliant with the EU Drinking Water Directive and the site food safety plan. Continuous inline turbidity and iron monitoring on the treated water delivery line provides early warning of any exceedances before water reaches the production process or storage tank.
The choice of iron/manganese filtration media directly affects maintenance demands, chemical storage requirements, achievable flow rates, and long-term running costs:
| Media | Mechanism | Regenerant | Max SLR | Mn Removal | Notes |
|---|---|---|---|---|---|
| Manganese Greensand (glauconite) | Adsorption + catalysis | Dilute KMnO₄ solution (periodic) | 5–8 m/h | Excellent | Traditional choice; requires chemical storage |
| Birm® | Catalysis (DO-dependent) | None | 8–12 m/h | Good (pH ≥ 6.8) | Recommended — simplest operation, no chemical store |
| Pyrolox (MnO₂) | Catalysis | None | 3–5 m/h | Excellent | Very dense; suits low flow rates; highest capacity |
| MTM (Micro-Thane-Media) | Catalysis | None | 10–15 m/h | Excellent | Premium; high capacity; smallest vessel footprint |
| Filox-R (72% MnO₂) | Catalysis | None | 5–7 m/h | Excellent | High MnO₂ content; handles high Fe + Mn simultaneously |
Recommended for this application — Birm®: At pH 7.1–7.5 post-aeration and with substantial dissolved oxygen available from the cascade aeration stage, Birm provides reliable Mn oxidation without any chemical regeneration. Designed conservative SLR of 8 m/h gives a required vessel area of 2.25 m² (approximately 1,700 mm vessel diameter). No KMnO₄ chemical storage or periodic regeneration is required; only clean backwash water. If a future analysis reveals Mn spiking above 0.3 mg/L, upstream KMnO₄ dosing can be added without replacing the Birm media.
| Stage | Media | SLR | Required Area | Vessel Diameter | S/S Height |
|---|---|---|---|---|---|
| Stage 1 — Iron & Manganese Removal | Birm® catalytic media | 8 m/h | 2.25 m² | 1,700 mm | ~2,200 mm |
| Stage 2 — Multimedia Polishing | Anthracite / Sand / Garnet | 12 m/h | 1.5 m² | 1,400 mm | ~2,000 mm |
Footprint estimate: Both GRP vessels side by side require approximately 3.5 m width × 1.75 m depth, plus service access. The cascade aeration tower (typically 0.8–1.2 m diameter × 2.5–3.0 m height) can be sited outdoors adjacent to the filtration building or inside if headroom permits. The KMnO₄ dosing skid (including day tank, dosing pump, and containment bund) adds approximately 0.8 m × 0.8 m. Total installation footprint including pipework, dosing skid, and service clearances: approximately 5.5 m × 2.5 m.
Our process engineers will review your borehole water analysis, flow rate targets, and product quality requirements to size the aeration stage, select the optimum catalytic media, and design the polishing multimedia filter and backwash sequence.
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