A composting flush toilet

When I first started planning the infrastructure here, I intended throughout to use Joe Jenkins‘ dry composting toilet system. Beautifully simple and easy to construct and maintain, convenient and portable, no requirement to separate urine from fæces, and an efficient composting system designed for optimum thermophilic decomposition. It’s no wonder Jenkins’ toilets have been dubbed ‘Loveable Loos’. What’s not to like?

Many people though are surprisingly squeamish about dry toilets. When I came across Anna Edey’s experiments with vermicomposting in Massachusetts 18 years ago for processing sewerage out of a conventional flush toilet, described on the website promoting her book, I was intrigued. The fact that it coincided with us beginning renovations on an outhouse toilet for the wee house (designed to be guest accommodation) seemed fortuitous. The outhouse was ideally situated for it and putting in a composting flush toilet for the guest accommodation seemed like an excellent idea. When we then discovered a nice old ceramic flush toilet bowl still in one piece at the local dump, it seemed to be signalling the perfect opportunity to give this method a try. Edey’s website didn’t give full details, but there was enough information for me to work the rest out for myself.

While some would argue that any flush toilet is an unnecessary use of fresh water, this side of the quinta badly needs water in summer and the series of green filters Edey uses to process the liquid component of the flushings will help green up this area. Also this land is pretty short on worms – it gets too dry in summer for them to survive – and compost including worm castings is demonstrably more nutritious than compost without castings, so by installing both Jenkins’ and Edey’s systems, I hope to get the best of both as well as to be able to experiment with and demonstrate the use of two sewerage processing systems that improve, rather than pollute the environment.

This is how it works. The toilet flushings drain through a normal waste pipe into an insulated plastic container which contains a large quantity of worms who inhabit the surface layers of a large quantity of carbon-rich organic filter material (wood shavings, partially composted leaf litter, etc). The container is insulated to prevent the worms either freezing or cooking. When the flushings enter the container, the solids remain in the container to be processed by the worms and the liquids drain through the filter material and exit the container in another waste pipe to be carried to a bed (or series of beds) where they are taken up by growing plants or processed by soil bacteria.

So this is how we built it …

Another 1,000-litre plastic IBC tank forms the basis of our worm composting toilet system. We first made an access hatch by cutting half of the top off. It slots back in place very neatly – you can only just make out the cut in this photograph – held in place by the screw-top lid to the central opening (through which the waste pipe empties into the tank) and supported by an aluminium bar which clips onto the rest of the frame each side

Having put the tank in place, we then connected 110mm plastic waste pipe to the outlet and dug it into a trench leading to where the first of the green filters would be dug

The tank is sited immediately below the toilet. We decided to use schist to make an insulated container for it, rather than sawn timber. It’s longer lasting, we had lots of schist on hand for free, it would blend into its environment much better in stone and Martin reckoned he could build a dry-stone walled container in about the same time as it would take to make one out of wood.

The tank with the toilet waste pipe connected

As the walls were built, insulation was added to keep the worms within optimum temperature range, 13-27°C both winter and summer. Closest to the tank, we used sheets of polystyrene insulation, and filled the gap between insulation and stone wall with Leca (lightweight expanded clay aggregate)

The dry-stone walls grow

Access to the pipework draining the tank will be possible if necessary

A large stone slab on the front wall of the container makes it easier to access and empty the tank

Container complete, slate wall covering in place, and wooden framework ready for the galvanised corrugated roof. We opted for this roof covering because it makes a lightweight roof easily moved to gain access to the tank. More insulation will be fixed to the underside of the roof and the top of the tank

Toilet, tank and pipework into the green filter bed, dug ready for filling and laying of pipework

The first green filter bed

Once we’ve got water piped and stored on this side of the quinta to allow for flushing, the tank will be half-filled with wood shavings and partially-composted leaves, bracken, etc, and then horse manure containing lots of worms – Eisenia fetida or tiger worms commonly found wherever piles of manure have been left to age for a while. The horse manure, besides being a good source of the worms, also provides the starter material for the worms to get working on.

The first green filter, about 1.5m³ in volume, will also contain a lot of organic matter – wood shavings, leaf mould, dead bracken, compost – to act as an organic sponge and carbon reserve which, when mixed with soil, will soak up and hold the liquids for the plants that will be grown in the bed and balance out the high nitrogen content of the urine-rich water. Rather than an open pipe at one end of the bed, the liquid will flow through a number of smaller perforated pipes to distribute it more evenly. With the comparatively small volume of liquid likely to be generated by the toilet (grey water goes elsewhere), I am thinking at the moment that this one bed will likely be sufficient to deal with it, but will build in the option to create a further filter bed if it appears necessary. There is no possibility of contamination of groundwater or neighbouring properties, so we have flexibility to experiment.

UPDATE: June 2014 The toilet is now working. See the next post about it here.

UPDATE: November 2016 The toilet has been working for 2 years now. It’s generated a lot of interest. My local municipality are now planning to install vermicomposting units based on this system in local villages. The first was commissioned in July 2016. You can now legally use this method of sewage processing in this region. I have also created a new website with full details of the system, it’s design, construction, maintenance, and more besides, including a forum. The aim is for the site to become a repository of community-sourced experience with installing and operating this system.