Is a biochar filter right for your water?
Biochar filters are powerful — but only for the right types of water. This gateway step helps land managers, farmers, contractors, consultants, and regulators decide whether a biochar biofilter is appropriate, or whether another technology (engineered activated carbon, specialist media, or settlement-only systems) is the correct choice.
This page is the single decision guide for BiocharFilters.co.uk.
Use this page before reading the technical resource pillars.
Decision step 1 — are you within water‑quality scope?
Scope boundary (go / no‑go)
On farms, estates, and landholdings, rainfall that exceeds field capacity will move off‑site.
You are within water‑quality scope if water leaving your land connects — directly or indirectly — to a ditch, stream, pond, drain, wetland, or other receiving water during rainfall events.
This applies whether the connection is:
- permanent or occasional,
- visible or seasonal,
- historic or inherited.
If no connected pathway exists → no filtration decision is required.
If a connected pathway exists → continue to Step 2.
Decision step 2 — what type of water are you dealing with?
Use‑case boundary (context setting)
Different water sources carry different risks, pollutants, and regulatory expectations. Identify the category that best matches your situation.
A. Agricultural runoff
Water moving off fields, tracks, yards, or livestock areas containing:
- soil and fine sediment,
- nutrients (P, N),
- organic matter,
- manure‑associated bacteria,
- trace/background metals only.
Biochar suitability: ✔ Excellent
This is the core use case for biochar biofilters.
B. Surface water / SuDS / landscape runoff
Roof drainage, estate roads, paths, car parks, and low‑duty commercial areas containing:
- sediment and tyre dust,
- moderate nutrients and organics,
- moderate bacteria,
- low–moderate metals.
Biochar suitability: ✔ Strong
Works well in swales, vegetated basins, pre‑treatment cells, and low‑duty filter beds.
C. Highway runoff with strict metals limits
Water from major roads where dissolved copper and zinc must be removed to defined numeric discharge targets.
Biochar suitability: ✖ Not suitable
These applications require engineered activated carbon or specialist media with certified performance.
D. Industrial runoff
Runoff from manufacturing, plating, vehicle washing, airports, scrap, or heavy industrial yards.
Biochar suitability: ✖ Not recommended
High dissolved metals, solvents, or hydrocarbons require engineered media with known breakthrough curves.
E. Combined sewer overflow (CSO)
Storm events that overwhelm sewer systems, releasing untreated sewage mixed with stormwater.
Biochar suitability: ✖ Impossible
High solids, fats, wipes, and hydraulic surges make filtration impractical.
If your water falls under A or B → continue to Step 3.
If your water falls under C, D, or E → biochar is not the correct technology.
Decision step 3 — what is the dominant pollutant challenge?
Suitability boundary (what biochar can and cannot do)
Biochar biofilters are well suited where the objective is:
- reducing sediment and turbidity,
- reducing phosphorus or nutrient losses,
- moderating dissolved organic carbon,
- supporting passive biofilm association under controlled conditions,
- physically retaining bacteria associated with particulates and biofilms.
Biochar biofilters are not suitable where the objective is:
- removing dissolved copper, zinc, nickel, or similar metals to strict numeric limits,
- demonstrating guaranteed, certified removal efficiencies,
- meeting fixed discharge concentrations independent of flow conditions.
If your priority matches the first list → continue to Step 4.
If your priority matches the second list → use engineered activated carbon or specialist media.
Decision step 4 — what happens to the media at end‑of‑life?
Outcome boundary (reuse vs disposal)
Biochar biofilters are uniquely valuable because they can be designed for soil reuse when used on soil‑compatible waters.
Where operating conditions, feedstock choice, and inflow water quality are suitable, spent biochar filter media may:
- align with PTE limits following assessment,
- contribute to soil structure and aggregation,
- add stable carbon consistent with soil‑fit biochar definitions,
- help close nutrient and carbon loops.
Where soil reuse is not required or not permitted (e.g. industrial or metals‑compliance sites):
- predictable removal performance takes priority,
- disposal routes are fixed,
- reuse value is irrelevant.
If soil reuse is part of the objective → biochar biofilters are strongly favoured.
If soil reuse is not required → engineered media is usually the better choice.
Decision step 5 — where should intervention occur?
Placement boundary (practical realism)
Where water is already moving, intervention is only realistic at points where flow can be accessed, slowed, or treated without re‑engineering the land.
In practice, this limits intervention to:
- field edges where runoff leaves managed ground,
- ditches or swales where water is already concentrated,
- pond or wetland inlets protecting receiving waters,
- final polishing points before discharge.
This choice defines the type, scale, and maintenance needs of any system.
The consolidated decision rule
Biochar biofilters are appropriate for soil‑compatible, low‑to‑moderate duty water flows that support passive surface interactions — not for metals‑compliance systems or sewer overflows.
| Water type | Biochar suitability |
|---|---|
| Agricultural runoff | ✔ Yes |
| Surface water / SuDS | ✔ Yes |
| Highway metals | ✖ No |
| Industrial pollutants | ✖ No |
| CSOs | ✖ No |
Where to go next
If biochar is suitable for your site:
- Part 1: Water quality & regulations — understand the drivers and compliance context
- Part 2: Filtration system design — understand how systems are configured
- Part 3: Soil reuse & carbon compliance — understand safe and compliant end use
If biochar is not suitable, this decision guide has already saved you time, cost, and regulatory risk.