Vermicomposting Toilets: low tech and open source approach for ecofriendly human waste disposal
How it Works
The solid wastes from the toilet drop into the centre of the tank and fall on the surface of the organic material where they’re consumed by the worms. The flush water passes through the organic material which, after the ecosystem has had a chance to develop, is colonised by billions of bacteria as well as the worms. Bacteria remove nitrates from the waste water and use them to break down the carbon locked up in the organic material. Worms degrade thewastewater organics by enzymatic action (enzymes work as biological catalysts bringing pace and rapidity in biochemical reactions).
The reduction in the 5-day Biological/Biochemical Oxygen Demand(BOD5), one of the principle measures used in the assessment of successful sewage treatment, is typically over 90% in as short a throughput time as 10 minutes. In 1-2 hours, 98-100% can be removed. Chemical Oxygen Demand (COD) is reduced by 80–90%, total dissolved solids (TDS) by 90–92%, and the total suspended solids (TSS) by 90–95%.
There is no sludge and no clogging. All wastes are consumed within the tank, including toilet paper.
The vermifiltered water leaving the worm tank can be cleaned further in any of, or a series of, greenfilter beds, on-contour percolation trenches (swales) or mulch pits, sized according to the volume of water passing through the tank. If grey water is being processed through the tank as well as black water, this part of the system needs to be several times larger than it would be for black water alone.
Since the water has already been cleaned in its passage through the worm tank, pipe length calculations and soil depth requirements based on hydraulic loading rates for domestic septic tank percolation trenches and leach fields are far in excess of what’s required.
Greenfilter beds, percolation trenches and mulch pits fed by a vermicomposting system are filled to a depth of 0.5m with the same organic material as is used in the worm tank. This encourages the development of the same ecosystem within a loose-textured, well-aerated matrix, so similar rapid percolation rates can be expected within the organic layer of the greenfilter as are seen in the worm tank.
Worm eggs will pass out of the tank in thevermifiltered water to colonise thegreenfilter areas. While permitting rapid percolation, the organic material will also act as a sponge to hold water for uptake by plants and will serve to improve the texture, fertility and water retention capacity of the surrounding soil as well as forming the principal substrate for a massive increase in the soil biota present. This results in cleaner water with fertility, moisture and fungal communication pathways for the vegetation. It will also improve the percolation rates through the surrounding soil as it too is colonised by worms, improving texture and aeration. Earthworms are able to increase the hydraulic conductivity and natural aeration of soil not just through the physical action of burrowing, but by granulating the clay particles which pass through their bodies.
This is a whole different equation to working with an essentially inorganic filtration concept. As with the worm tank, it’s a self-regulating living system.
The minimum recommended soil depth for a conventional septic system to operate effectively is 1 to 1.5m. This is not the case with a vermicomposting system. The ‘greenfilter’ areas need a minimum soil depth of only 0.5m.
Hydraulic loading rates for conventional septic systems are generally based on infiltration rates though clogged soil surfaces for domestic septic tank effluent. Current practice has been to simply apply these rates, 0.07 to 0.42 litres per day per m2 or 0.20 to 1.2 gallons per day/ft2, to the infiltrative surface bottom area with the site-specific rate based upon the soil textural properties. Often soil textural properties are assessed with reference only to the mineralogical properties of the soil itself, not the amount of organic material and soil biota present. Yet it’s the latter which primarily determine how well the waste water is cleaned and purified.
Since every individual installation will be unique to its particular context, as a guide, the area of greenfilter required can be calculated by reference to soil percolation tests for grey water discharge. Since these are also calculated without taking into account the level of soil biota present, it’s likely to provide a comfortable margin of error.
Run pipework from the worm tank to a distribution box in the greenfilter area(s) in the same diameter as the supply. From the distribution box, run smaller diameter perforated pipe through the uppermost 20cm of the organic material. Wrap the perforated pipes in geotextile filter fabric or horticultural fleece to prevent blocking by the organic material.
For on-contour percolation trenches or swales, the perforated pipework should also be laid on contour.
Mulch pits don’t require perforated pipework. Small diameter waste pipes fed from the distribution box are sufficient.
Greenfilter areas serve best to irrigate trees and shrubs, and can include edible species.