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Low cost wastewater treatment for the world
Low cost wastewater treatment for the world
The revolution in domestic wastewater treatment...
The revolution in domestic wastewater treatment...
Vermifilters purify wastewater. The "filter" is a substrate such as bark, woodchips or sawdust, maintained by earthworms to remain aerobic and porous. Vermifilters are not just a filter, they are also an incredibly diverse living ecosystem made up of worms and microorganisms living in balance, consuming pathogens and organic substances from the water as it passes through the substrate. 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, generates no smell. The purified, odour-free, nutrient rich water is suitable for surface irrigation to crops or pasture. Nutrients are recycled and the water is reused for growing crops or trees.
Learn more about the nutrient cycle »
Vermifiltration is a low cost, effective solution for both domestic wastewater treatment and also community-based treatment using simplified sewers.
Primary treatment - the vermidigester
Primary treatment - the vermidigester
For surface irrigation of the treated wastewater, vermifilters treat wastewater in stages, "primary" followed by "secondary" and sometimes even "tertiary".
The first stage removes solids from the wastewater and these are digested by earthworms.
Wastewater from toilets, kitchen, bathroom etc 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.
Accumulating solids form a spreading "wet" compost heap in the digester vault. Worms consume this heap from underneath in a continual process as more waste is added.
Twin digesters
Twin digesters
Twin digesters provide a resting period before humus is removed, i.e. one digester is active while the other rests. This means when the contents are dug out from the digester, these will be fully decomposed.
The inlet is rotated from one digester to the other after several years to allow the humus in each side to age and become pathogen free. To be safe for application to food crops the contents should be rested for three years so that any parasites present in the humus die off. Helminth (parasitic worm) eggs are completely destroyed in two to three years of resting. Capacity of twin vaults must therefore be sufficient so that the other side does not fill with solids before that time.
By digesting the solids, the worms significantly reduce their volume. This "wet" composting process is not like traditional composting because there is insufficient air inside the heap for it to undergo aerobic decomposition. However, the worms introduce air into the heap as they burrow from underneath. Because earthworms consume the accumulated solids from underneath, a wider and shallower heap provides a much larger decomposition zone for the worms to digest.
Domestic vermidigester with twin vaults. The cladding material is fibre cement board
Then, the filtered wastewater exits the digester vault and either enters the secondary vermifilter stage to be further treated, or enters a properly constructed subsurface soakage field to infiltrate into the soil.
The following systems treat wastewater to the secondary level suitable for surface irrigation.
Secondary treatment - the vermifilter
Secondary treatment - 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. Rich in plant nutrients (nitrogen, phosphorous and potassium - NPK), 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 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, aerating it and 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 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.
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.
System design
System design
System design requires an understanding of the site, the location of the dwelling, and where the treated effluent will be irrigated.
Three system types are described below:
Gravity-flow vermifilter: This requires no energy to operate and can only irrigate crops below the effluent source (passive treatment).
Single-pass vermifilter: This uses a single pump (active treatment) followed by gravity flow (passive treatment).
Recirculating vermifilter: This uses recirculation pumps to pass wastewater through a vermifilter multiple times (active treatment).
Gravity flow vermifilter
Gravity flow vermifilter
Gravity flow vermifilters offer a simple method for high levels of treatment where there is fall between one reactor and the next reactor and the effluent field being irrigated. Gravity flow vermifilters are simpler to construct and maintain. Pumps are required for recirculating vermifilters but no fall is required between vermifilters.
Note that if soakage trenches or soak pits are used, the primary vermi-digester (below) is all that is required for primary treatment, followed by disposal to a sub-surface soakage field.
The example below shows a gravity flow vermifilter system with primary and secondary treatment:
This is the simplest system, which can gravity feed treated effluent to land or crops, so no pump is required. Multiple secondary vermifilter reactors can be employed in series. This design suits land with fall between the wastewater entry and treated water exit to a bell siphon and irrigation lines. The bell siphon is necessary to get even pressure/flow of treated wastewater to your irrigation nozzles.
An elevated site with sufficient fall is not always available:
where the land is flat; or
the wastewater flow is at (or below) ground level. Where the effluent needs to be raised into the inlet of the vermifilter (or to the soakage field), a pump is required. The wastewater should go through a primary vermi-digester first (see above) to remove the solids from the flow.
One issue with the gravity flow vermifilter is that the wastewater only passes once through each secondary vermifilter (see above). Multiple passes via recirculation is better.
Single pass vermifilter
Single pass vermifilter
This uses a single pump, followed by gravity flow. The example below shows a single-pass vermifilter with primary and secondary treatment:
This system uses a pump to raise the primary-treated wastewater into an elevated vermifilter. The secondary vermifilter outlet should have sufficient head for a bell siphon to generate pressure on the irrigation lines, for even distribution of water through the drippers.
Recirculating vermifilter
Recirculating vermifilter
The recirculating vermifilter produces a higher level of treatment than single-pass vermifilters. A recirculation pump passes wastewater through a vermifilter reactor multiple times. The example below shows a primary vermidigester followed by a secondary recirculating vermifilter:
The primary treated wastewater is pumped from the sump (above) into the top of a secondary vermifilter and returns via gravity back to the sump. The sump overflows via displacement into a tank with a pressure pump and float switch, or alternatively uses a bell siphon with sufficient fall to generate pressure for surface irrigation.
Oxygen demand and vermifilters
Oxygen demand and vermifilters
Because the vermifilter substrate is rich in oxygen, 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, similar to cattle grazing pasture. The fauna consumes pathogens and degrades organic compounds while at the same time oxygen dissolves into the water. Respiration and oxidation takes place without depleting dissolved oxygen, purifying the wastewater by removing biological oxygen demand (BOD).
Learn more about Oxygen and wastewater »
Capacity and sizing
Capacity and sizing
Vermifilter capacity must take into account the volume of wastewater being treated, including peak flows. Sizing of vermifilters is directly proportional to the number of users. As wastewater volume increases, design of vermifilter reactors can be either modular (more reactors) or scaled (larger reactors).
Learn about constructing a domestic vermifilter wastewater treatment system »
Construction
Construction
Vermifilter.com have put together a section focussed on constructing off-grid solar vermifilter systems that treat wastewater to a standard suitable for surface irrigation of crops, pasture or trees:
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