How it works

Low cost wastewater treatment for the world

The revolution in domestic wastewater treatment...

Vermifilters purify wastewater. The "filter" is a media substrate such as sawdust, bark or woodchips, 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 worms and microorganisms living in balance, consuming pathogens and organic substances from the water as it passes through the filter. The worms, as caretakers of the system, aerate the media with their burrowing, maintaining the porosity and producing castings (humus), the perfect media additive.

The process requires virtually no maintenance and being aerobic, is rapid and generates no smell. The purified, odour-free, nutrient rich water is suitable for surface irrigation of crops or pasture. Nutrients are recycled and household water is reused for growing crops or trees. Learn more about the nutrient cycle.

Vermifiltration is therefore well suited to both household treatment and also community-based treatment using simplified sewers.

Vermifiltration offers on-site wastewater treatment to a high level and at low cost.

Primary treatment of domestic wastewater - the vermidigester

The first stage removes solids from the wastewater and digests these.

Wastewater enters the vermidigester vault at the top. Solid waste (poo, toilet paper, kitchen waste, hair etc) is retained in the vermidigester and accumulates on the media surface, where worms reduce this to humus. The liquid filters through the substrate and exits the vermidigester at the bottom.

A spreading "wet" compost heap accumulates solids in the digester vault. Worms consume this heap from underneath in a continual process as more waste is added.

Twin digesters

Twin digesters offer a resting period each side before humus is removed. One digester is active while the other rests. This means when the contents are dug out from one side, these will be fully decomposed.

The inlet is rotated after several years to allow the humus in each side to age and become pathogen free. Helminth (e.g. roundworm) eggs are completely destroyed in two to three years.

Domestic vermidigester with twin vaults. The cladding material is fibre cement board

The filtered wastewater either enters the secondary vermifilter stage to be further treated, or enters a properly constructed subsurface soakage field to infiltrate into the soil.

Design a primary vermidigester »

Secondary treatment of domestic wastewater - the vermifilter

Secondary vermifilters remove oxygen demand and pathogens, to produce clean, nutrient rich water suitable for surface irrigation of crops.

Wastewater exiting the primary vermidigester has most of the solids removed. This "primary treated" effluent then enters the secondary treatment reactor or vermifilter.

The wastewater trickles through the media, filtering out fine suspended solids and organic substances. These are rapidly digested by microorganisms and worms in the reactor's aerobic environment, purifying the wastewater to be suitable for surface irrigating pasture, trees or crops. Nutrients (nitrogen, phosphate and potassium NPK) are retained and the water is best described as liquid plant food, completing the nutrient cycle.

Vermifilters can be set up in series depending on treatment level required (secondary or tertiary). Usually one or two in series are sufficient for treatment of domestic wastewater for surface crop irrigation.

The illustration below shows two gravity flow vermifilters in series.

Note the ventilation cavity between the external wall of the reactor and the media basket

The water trickles downwards through the media, filtering out suspended solids, which are rapidly digested by worms and microorganisms in the aerobic environment. Earthworms and microorganisms attached to the media also remove pathogens, nutrients and dissolved organic substances from the wastewater, reducing biological oxygen demand (BOD).

Importantly, the worms also maintain the porosity of the media by borrowing through it and depositing their castings. The worm castings mix with the media, eventually forming a homogenous, porous humus-like substrate that requires no maintenance.

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, which becomes part of the substrate, an aerobic home for the biofilm to attach to and a comfortable residence for the worms.

Design a secondary treatment vermifilter »

Domestic vermifilter reactors are easily made from 250 litre plastic drums.

40 gallon plastic drum secondary treatment reactor. The ventilated basket is made with windbreak cloth, plastic netting, polythene pipe and cable ties.

Oxygen demand and vermifilters

Because the vermifilter reactor provides an oxygen rich media or substrate, microorganisms attach to this substrate and proliferate to form a "biofilm", which in turn provides a food source for the worms. The worms graze the biofilm which maintains the health of the fauna, a bit like grazing cattle maintains the health of pasture. The fauna proliferates 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.

Learn more about Oxygen and wastewater »