How it works
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Vermifilters purify wastewater. The "filter" is a media substrate such as sawdust, bark or woodchips which is maintained by earthworms to remain aerobic and porous. Vermifilters are not just a filter, they are also an incredibly diverse living system made up of macro- and micro-organisms living in balance. Microorganisms attach to the surface of the media substrate and consume pathogens and dissolved organics from the water as it passes through. The worms, as caretakers of the system, maintain the population of microorganisms by grazing their surplus growth, producing castings (humus), the perfect media additive. All this while also aerating the media with their burrowing.
The process requires virtually no maintenance and being aerobic, is rapid and generates no smell.
Vermifilters can be used for:
- primary treatment, intercepting and digesting the solids at source rather than conventional mix-and-treat sewage treatment;
- secondary treatment following a primary treatment septic tank (or vermifilter).
Vermifiltration is therefore well suited to both household treatment and also community-based treatment using simplified sewers.
Stage 1: the Vermidigester (primary treatment vermifilter)
The first stage removes solids from the wastewater flow at source.
Household wastewater enters the vermidigester and solids accumulate on the surface while the liquid component filters through and exits the digester. Almost all of the solids in the wastewater are retained and digested into stabilised earthy humus by earthworms, while the filtered wastewater either enters the second stage to be further treated, or enters a properly constructed subsurface soakage field to infiltrate into the surrounding soil.
Stage 2: Secondary vermifiltration
Secondary vermifilters remove oxygen demand and pathogens, to produce clean, nutrient rich water suitable for crop irrigation.
The second stage involves a slightly different reactor, again utilising an aerobic substrate. The wastewater trickles through the media, filtering out fine suspended solids and organic substances. The aerobic conditions encourage microroganisms that attach to the substrate and form a "biofilm", which in turn offer a food source for worms and other macro-organisms, all living in balance within the "living" digester, consuming pathogens and degrading organic compounds present in the water. At the same time oxygen dissolves into the water from the oxygen-rich environment in the reactor. Respiration and oxidation takes place without depleting dissolved oxygen, purifying the wastewater by removing biological oxygen demand (BOD). from the "living" digester.
The result is clean, nutrient rich water suitable for irrigating pasture, trees or crops. Nitrogen, phosphate and potassium are retained and the water is best described as liquid plant food, suitable for irrigating crops and completing the nutrient cycle.
The worms are best described as "caretakers" of the system. They burrow in the substrate and ensure this remains aerobic and well drained. Worms consume and digest surplus biofilm and generate humus. This humus forms additional substrate, an aerobic home for the biofilm to attach to and a comfortable residence for the worms.