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 vermicomposting 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 the wastewater organics by enzymatic action (enzymes work as biological catalysts bringing pace and rapidity in biochemical reactions).

How a vermicomposting ecosystem system works

Section through the vermicomposting ecosystem within the toilet tank showing function

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 organic material is consumed by the ecosystem in the process of neutralising the nitrogen passing through the tank. The speed at which the material decomposes will depend on several variables – the prevailing temperature and humidity in the tank, the number of people using the toilet, the age of the vermicomposting ecosystem (it improves with age), and the type of organic material you are adding. For a family of 4, the tank should need topping up roughly once every 4-6 months.

The tank should never need emptying, but periodically some of the vermicompost and worms can be removed and added to growing beds to increase fertility and soil biota.


System maintenance

Tank maintenance

Maintenance of the vermicomposting ecosystem is very simple. Provided you have followed the construction guidelines in this website and understood the biology of the system, your toilet should need only occasional topping up of the organic material contained in the IBC tank.

Biofilter material for vermicomposting toilet ecosystem. This is sawmill waste consisting of pine bark and wood chippings and shavings with a C:N ratio of between 200-1300:1 (Image © Beach Davies)

Human waste is high in nitrogen (N) and the vermicomposting ecosystem requires a large amount of carbon (C) in order to process it. The C:N ratio should be roughly 30:1. Mixing slow-release carbon-rich materials such as wood chips and shavings with more bioavailable carbon stores like leaf litter, dead bracken and straw ensures a good balance which will provide the ecosystem with enough carbon reserves for several months.

  C:N ratio
High Nitrogen materials
Human faeces 6-10:1
Human urine 0.8:1
High Carbon materials suitable for use in the system
Compost 15-20:1
Biochar 19-442:1
Dry leaves 40-80:1
Straw 50-150:1
Corn stalks 60-120:1
Pine needles 80:1
Rice hulls 110-130:1
Mixed paper 100-200:1
Corrugated cardboard 600:1
Bark – hardwood 100-400:1
Bark – softwood 100-1200:1
Wood chips and shavings – hardwood 450-800:1
Wood chips and shavings – softwood 200-1300:1

The C:N ratios in this chart are average and may vary according to source. The majority were obtained from Cornell University’s publication, Composting in the Classroom which also contains guidelines for calculating the C:N ratio of your mix of materials

Check the tank frequently during the settling-in stage. For the first couple of weeks of use, there may be a very slight odour from the tank as the worms adjust to their new environment and the ecosystem starts to establish itself. Thereafter, any smell should disappear.

The first sign of a problem is usually odour. Check that water is draining satisfactorily from the tank after flushing. If you have used organic material which is too fine, such as sawdust, blockages are possible and the tank will fill with water, eventually drowning the worms.

Don’t allow the level of organic material in the tank to fall too low before refilling as the C:N ratio will fall below optimum and the ecosystem’s health will suffer. About one third full is the minimum level you should let it get to, but half full is a safer minimum.


Flush toilet maintenance

One of the most common questions asked about this system is whether it’s possible to use household cleaning chemicals in toilet maintenance. Yes it is. Worms have a very high tolerance for chemical pollution and in her original experiments with her own and other vermicomposting sanitation systems, Anna Edey subjected her worms to all manner of cleaning chemicals without discernible effect. Further, cleaning chemical residues could not be detected in the vermifiltered water exiting the system.

That said, I personally prefer not to use these products and have found I’ve never needed more than a regular brushing with water to keep the toilet clean.


‘Greenfilter’ maintenance

Monitor your greenfilter. Plant at least one indicator plant so you can see if water leaving the tank has been cleaned to a sufficient degree. Use plants which are heavy feeders and will speedily show nitrogen deficiency if they are lacking. Citrus trees are good for this if you are able to grow them in your climate. Roses are more suited to colder climates.

Nitrogen shortages can cause slow growth, smaller leaves, yellowing, short branches, premature autumn colour and leaf drop, and can increase the likelihood of some diseases. Watch particularly for the older leaves yellowing more than the newer ones, and an even yellowing as opposed to yellowing between the veins of the leaves. If you start to see these signs in your indicator plants after a couple of years of operation, you know your tank is functioning well because next to no bioavailable nitrates are making it through the system.

You can then manure the suffering plants. They should respond within reasonable time with leaves greening up again and growth becoming more vigorous. Be aware though that if the tree or shrub is under stress due to low light or extreme temperatures, it may develop nutrient deficiency problems even though adequate nutrients are available. Diseased or damaged roots, unsuitable soil pH (citrus trees don’t like alkaline soils), waterlogged sites, and plantings that are too deep can result in inefficient nutrient absorption. Adding manure under these conditions will not enhance growth.

Also be sure to check your greenfilter(s) during extreme rainfall events to make sure the additional water loading isn’t causing problems.

The ‘greenfilter’ will eventually break down into rich compost. Unlike the worm tank, it doesn’t need refilling, but a periodic topping with a woody mulch material will ensure the ecosystem has enough carbon for its needs.


What happens if I go away?

This is another common question, particularly for people planning to install the system for tourist or seasonal accommodation. Clearly the worms need to have a supply of food if the toilet is unused for any period of time.

We recommend adding a quantity of horse manure to the tank. How much depends on how many worms inhabit the tank and how long the toilet is going to be unused, but as a guide, for a 4-person tank started with 1kg of worms we would recommend adding 20kg for every month the toilet will be unused. This amount provides a comfortable margin of error to maintain the vermicomposting ecosystem at the optimal density of worms for an average household.


Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License