A larger outdoor mycofiltration bed is a contained growing medium that uses fungal activity, together with the physical structure of the bed, to help manage selected water or damp materials. The word mycofiltration combines “myco”, meaning fungi, with filtration. In practice, the bed may slow and hold water, trap some solids, and provide conditions in which fungi and other organisms can interact with organic material.
These systems are best treated as one possible part of a broader remediation plan, not as a guaranteed clean-up method. The right design depends on what is being treated, how much is present, where it comes from and what must happen to the treated water or material afterwards.
What a larger mycofiltration bed is intended to do
A bed generally contains a porous, carbon-rich material such as suitable wood-based material, mixed with fungal-inoculated material where appropriate. Water or damp material is directed through or across the bed at a controlled rate. The physical bed can help retain particles, while fungal growth may contribute to the breakdown or transformation of some organic compounds.
Fungal performance is not universal. Different fungi behave differently, and a species or growing medium that performs well in one situation may not be suitable in another. Temperature, moisture, oxygen, acidity, competing organisms and the nature of the contaminant can all affect results. Without testing, it is not possible to assume that a bed will remove a particular contaminant or make water safe.
On a lifestyle block, a larger bed might be considered for a defined, manageable source such as runoff from a composting or organic-material handling area, drainage associated with a non-hazardous workshop process, or water that has already been assessed and is suitable for this type of trial. It may also be used as a polishing or holding step alongside other controls.
It should not automatically be used for sewage, septic discharge, animal effluent, pesticide residues, fuel or oil contamination, heavy metals, unknown chemicals, or water that could carry disease-causing organisms. These situations may require specialist treatment, testing, permissions or disposal arrangements.
Start with the source, not the bed
Before choosing a design, write down what the bed is expected to receive. Useful questions include:
- Where does the water or material come from?
- Is the source consistent, seasonal or affected by heavy rain?
- What substances might be present, and are they known or only suspected?
- How much water or material arrives in a typical period and during a storm?
- Could the flow contain pathogens, chemicals, sharp objects or other hazards?
- What will happen to the outlet water, used growing medium and trapped solids?
If the source is unknown, testing and professional advice should come before construction. A simple visual inspection is not enough to confirm that water is safe for discharge, irrigation, livestock or contact with people.
Choose the site carefully
A larger outdoor bed needs enough space for the bed itself, inlet and outlet controls, safe access and future maintenance. Select a location where untreated flow cannot accidentally reach a stream, drain, bore, well, garden, grazing area or neighbouring property.
Consider the natural slope, soil permeability, flood risk and distance from surface water. A bed should not rely on unknown ground conditions to contain contamination. Where there is any risk of seepage, an appropriate liner or other engineered containment may be needed. The suitability of that containment depends on the material being handled, so it should not be selected solely on price.
Plan for weather. Heavy rain can overwhelm a bed, disturb the growing medium or send untreated water around the system. Include a way to divert clean stormwater away from the bed and a safe overflow or shut-off arrangement for unusual flows. The site should also be reachable for loading, inspection, replacement and removal of spent material.
General design and construction considerations
There is no single correct size, depth, fungal species or treatment rate for every project. Those details should be based on the source, expected flow, climate, available materials and any evidence from testing or a qualified adviser.
A practical layout commonly needs:
- Source control: Keep unnecessary clean water out and reduce the amount of contamination entering the system.
- Pre-treatment: Use settling, screening or another suitable step where solids could block the bed. This does not make hazardous material safe, but it can reduce physical loading.
- Contained bed area: Build a stable structure that can hold the selected growing medium without slumping or washing away.
- Even distribution: Spread incoming water across the bed rather than allowing it to form one fast channel.
- Controlled outlet: Make the outlet visible and accessible so flow can be checked and redirected if necessary.
- Weather protection where needed: Use covers, bunding or other measures if wind, drought, frost or intense rainfall could disrupt the system.
Locally available materials may reduce transport and replacement costs, but “natural” does not automatically mean suitable. Avoid materials that may contain preservatives, glues, dyes, unknown residues or other substances that could add to the problem. Ask for information about the source and treatment history of purchased wood products and other inputs. Do not introduce a fungus or material into the environment simply because it is easy to obtain; choose organisms and substrates appropriate to the intended use and local rules.
Establishing the bed
Prepare the structure before adding the growing medium. Check that the base is stable, the liner or containment is intact, and the inlet and outlet can be isolated. Keep animals and unauthorised people away while the system is being built and tested.
Fungal establishment may take time and may be affected by competing organisms and changing weather. Follow the requirements of the selected inoculum or supplier where one is used, but do not assume that visible fungal growth proves treatment is occurring. A bed can look healthy while allowing water to bypass the active zone, or it can support fungi without addressing the target contaminant.
Begin with a manageable flow if possible. Inspect the first wetting events for ponding, leaks, short-circuiting, erosion, odour, unusual colour and overflow. Keep a basic record of dates, weather, flow conditions, maintenance and any testing. Records make it easier to identify changes and support decisions about replacement or professional review.
Operating and maintaining the system
Outdoor beds are working treatment systems, not install-and-forget landscaping. Routine checks should include:
- inlet pipes, screens and distribution areas for blockage;
- the bed surface for channels, pooling, drying, settlement or erosion;
- containment edges, liners and outlets for leaks or damage;
- signs that water is bypassing the intended treatment area;
- unexpected smells, discolouration or changes in flow; and
- animal access, windblown material and weed or plant growth that interferes with inspection.
Growing medium can settle, clog or become depleted. Fungal activity can decline, and material can accumulate substances that should not be spread elsewhere. Replacement or replenishment intervals cannot be set responsibly without knowing the loading and performance of the particular system. Used material may need to be handled as potentially contaminated waste rather than composted, burned, spread on land or fed to animals.
Arrange testing when it is important to demonstrate that a contaminant has reduced, or before allowing outlet water to enter a sensitive area. If results worsen, the bed floods, the outlet changes unexpectedly or containment fails, stop the inflow where possible and prevent discharge until the cause is understood.
Protect people, animals and the wider site
Clearly mark the bed and restrict access by children, pets and livestock. Use suitable protective equipment when handling suspect material, wet growing medium or accumulated solids, and wash hands after maintenance. Keep tools and equipment used for the bed separate from those used around food, animal feed and gardens.
Most importantly, do not allow untreated material or contaminated runoff to reach soil, waterways, crops, wells, animals or people. A bed should have a clear plan for leaks, extreme rainfall, power or pump failure, and safe removal of spent material.
When to seek advice
Get professional advice, testing or regulatory guidance before proceeding where contamination is unknown, hazardous or likely to affect groundwater or surface water; where sewage, effluent, pesticides, fuels, solvents, metals or animal waste are involved; where the bed will be large or receive continuous flow; or where discharge could leave your property.
Ask an appropriately qualified environmental, water-management or remediation professional to review the source, containment, monitoring plan and disposal arrangements. Local requirements may apply even if the project is on private land.
Keep expectations realistic
Mycofiltration is an emerging and site-dependent approach. It may be useful in a carefully selected role, but it is not a substitute for preventing pollution, reducing the source, testing, conventional treatment or compliance with relevant requirements. A responsible project balances affordable, locally practical materials with proper containment, monitoring and a plan for failure. Spending less on construction is not a saving if the result is uncontrolled runoff, repeated replacement or harm to the surrounding site.