Indoors or outdoors?

Read our introduction to compost toilets, their benefits, and what you can do. Maybe talk to other compost loo owners, read our book or take our online course first to make sure a compost toilet is for you. There aren’t really any situations where you can’t have a compost loo if you’re absolutely determined to – unless you have no way of storing or utilising the composted waste. So maybe if you live in a tower block with no garden it’s not the ideal solution. But even then, if you have an allotment…. After all, there are compost loos you can install in a camper van or a boat, so they will work anywhere as long as you have a way of dealing with the finished products. See below for ideas if you want a compost loo outdoors. If you’re in a rural location, or have enough space, you can build your own indoor, two-chamber compost toilet, with hatches to remove the finished compost. If you’re in an urban location, there are various off-the-shelf models, including very small ones for boats or camper vans.

Outdoors

First, you can buy an off-the-shelf outdoor compost loo in its own structure for an allotment / visitor centre etc. or you can hire compost toilets for a one-off event or festival. See here.

Or you can build your own. You have a few options:

The simplest way to deal with your waste is to compost it directly. Have a bucket with a toilet seat over it, throw in a handful of soak (e.g. sawdust or straw) when you use it, and when it’s full, tip it onto a compost heap, and add straw, hay, garden waste and kitchen waste. The advantage of this system is that it is very cheap and easy, with all the benefits of compost toilets – you keep all your nutrients, and don’t use water to flush them away. The main disadvantage is that you have to handle it before it’s composted, when you are transporting it in the bucket from the toilet to the heap. Most people would not like to do this, although it works well, and if you’re up for it, there’s no reason why not. Well, except that you’d probably have to be well away from other people, as neighbours wouldn’t like it; plus it’s labour intensive, and uncomposted human waste can contain pathogens, and these can be transported back to humans via flies. Also, you wouldn’t want kiddies to play anywhere near the heap, in case they came into contact with pathogens. But this system is fine as long as you understand the points above.

There are simple solutions based on bins – maybe a wheelie bin under a platform, or a plastic container sunk into the ground, or even just a hole in the ground. Throw in a handful of soak (sawdust or straw, for example) each time you use it, and when the container is full, leave it for a year to decompose, while you use another one. The great outdoors can cope with urine easily – it’s a useful fertiliser, in fact. Concentrations of poo can cause local contamination if not contained, so make sure you site your loo well away from watercourses if it’s just a hole in the ground. If it is just a hole in the ground, what you’ve got is a long-drop toilet rather than a compost loo. If however, you add soak (sawdust or straw, for example), and when it’s full you dig another hole, allow the first one to decompose for a year, and then dig it out, you will have useful compost.

Green and Away, an outdoor environmental conference centre in Gloucestershire, built a cabin on stilts over a chamber made of straw bales. It’s used over the course of several conferences or festivals (in the normal way by throwing in a handful of soak – usually sawdust – after use), then the cabin is removed, and the straw bales are pushed in to cover the pile. The floor of the chamber is the earth, which easily absorbs any excess liquid, and the pile is left to compost for one or two years. Grass grows over it and it’s pretty much hidden, and not at all an eyesore. The portable toilet room can then be positioned in a new location over another straw bale chamber. Apparently local Environmental Health inspectors visited and were happy with it. This system is obviously only suitable for rural locations, and only then if you’re sure that children won’t be able to play on the pile. The pile can be dug out and used for compost after it has broken down.

Indoors

There are two very basic considerations, whether your compost loo is DIY or off-the-shelf:

  1. there needs to be a route for a vent pipe to the outside world – so the loo needs to be either near an outside wall or there needs to be a route for the vent through the roof
  2. what are you going to do with the urine?

It’s probably best to deal with the urine issue before going any further, because it can throw a spanner in the works if you don’t get it right. You need to have some way of getting rid of the urine from the solid waste, because if the pile becomes too wet, it will turn anaerobic and smell. Also, urine contains salts that many micro-organisms don’t like. There can be a drain at the bottom of your loo, in which case it’s been polluted by the solid waste, and can’t go into a grey water drain. It has to go into a sewer drain, or into a soakaway, leachfield or reed bed. Alternatively, some off-the-shelf models separate the urine before it gets mixed with the solid matter, and then it could be diverted to a grey water drain, or stored in containers.

Urine can be a useful thing to collect, as it actually contains more nutrients than faeces. It contains much more nitrogen than faeces (up to 90% of the nitrogen we excrete is in urine), three times the potassium, and up to twice the amount of phosphorus. And no pathogens (not in developed countries anyway, although in developing countries it could contain things like liver flukes) – it is sterile, so there are no health worries, just smells. In fact, it’s probably fair to say that if you really want to use human waste as fertiliser, the best thing to concentrate on is urine. You can dilute it and spray it on your garden. You can build your own urine separator too, or install a waterless urinal. You have to come up with a solution that involves i) getting rid of it straight away, or ii) storing it and using it, or getting rid of it later.

If you can rig up a container or a pit with a soakaway, containing sawdust or straw, and divert urine onto it, the combination of nitrogen in the urine and carbon in the sawdust or straw will be perfect to produce excellent compost that you can dig out when ready, and re-fill the container with more sawdust/straw.

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