DIY Composting toilets
Composting toilets are an extremely good idea. In future they may prove essential. Here's how to make one, cheaply.
If you search the web for information about composting toilets, you will be told that composting toilets are hugely expensive things, with fans, heaters, rotating drums and all sorts of whistles and bells. Also, like so many things on the web, only available to people with zip codes. Even information about them comes at a cost. There are good books on the subject, but here is what I know, from making and using compost toilets.
What is a compost toilet?
A compost toilet is a toilet that allows your "effluent" "poo" "shit" or more politely "humanure" (I will be mainly using the technical terms "poo" and "wee", but you can substitute for these the words "faeces" and "urine" if you prefer) to rot down into a form that can be used safely to feed the soil of your farm or garden.
Why not a just a hole in the ground?
A hole in the ground is OK, so long as it isn't immediately above your drinking water supply or someone elses. Trouble is that most of your precious effluent will soak away deep underground. You pollute quite a large area, without actually feeding the soil effectively.
The simplest designs that we know of is a oil drum, plastic dustbin or wheelie bin, with a platform or seat above it. If you live in a hot place, it is a good idea to make sure that the seat is well above the bin, and if possible put an air tight, or at least fly proof "poo chute" between the seat and the bin, and have an air-tight loo seat to keep flies at bay (a sandbag, on the underside of a board works well). You could even make the whole structure fly proof, with screens on the door, and windows, if you live somewhere very hot. You will need some way to remove the barrel when it is full, and replace it with an empty one. Barrels full of poo are heavy, and anything you can do to make this easier will help (e.g putting the barrel on wheels, lifting it with a pulley system, or at the very least, ensuring that there is a nice level path for people to stagger along carrying the barrel). If you have space, you could avoid this problem, by having several compost toilets, use each one until it is full, put a lid on the barrel or bin, and then start on the next. In which case, you might decide that rather than using barrels, you could use brick or concrete lined pits. A general rule with all composting is that if the "heap" is too small, it will not heat up, and if too large it will not get oxygen to the centre. In the case of compost toilets, oil drums seem to be a good size, but we have seen pits a metre or two wide. As the poo drops from a single point, it will tend to form a cone, which some lucky person will have to level with a stick. Some people empty their containers onto a separate manure heap or pit, and then reuse the containers. If you worry about flies spreading disease, and you cannot make the heap far away from your home, it is probably best to have several containers and seal them when full. This system allows you to have minimal contact with your own poo once it has left your body, and allows the poo to compost without it polluting groundwater.
What do you put in a compost toilet?
Poo (obviously). There are compost toilets that can handle poo and wee, and those that only handle poo. Sometimes there is a separate funnel for weeing into, so that wee can be collected in a separate container and sometimes excess liquid is allowed to drain out the bottom of the toilet. I dislike the latter solution, because human wee itself carries no diseases that I know of, and diluted can be used to feed plants. Wee, mixed with poo however, carries diseases, and if it simply drains into the soil under the toilet the nutrients in it will mainly go into the nearest watercourse. I think it is best to poo in the compost toilet and urinate elsewhere as far as possible(see section on urine below). A small amount of urine will not do any harm as long as the rules of good composting are followed (see below), and the poo heap is not allowed to become waterlogged. People on antibiotics should not use compost toilets (so we are told).
A good compost heap requires a mix of "green" (high nitrogen, low carbon), and brown (low nitrogen, high carbon) materials. The terms "green" and "brown" are more appropriate for garden compost heaps than compost toilets, but we will use them anyway. A compost heap also needs water and air. In the case of compost toilets the "green" material is poo and innevitably some wee (unless you have very good bladder control), and the "brown" should be straw, autumn leaves, pine needles, sawdust, or other dead materials (dead flowering stalks of weeds such as rosebay willowherb, thistles, docks etc. cut in winter are good). Some people add fire ash to get rid of the smell, but this is not good for the composting process, as it tends to soak up water, and exclude air, while providing no "brown" material to fuel the composting. Also if ash from treated wood, coal, coloured paper, plastic, cigarettes or other rubbish is included, you may well be adding toxic heavy metals to the mix. I would not recommend ash for these reasons. Sawdust or wood shavings will do a good job of removing smells (the main smell is ammonia, a nitrogen compound, "brown", carbon rich materials will react with the ammonia as they decay). Straw is without a doubt the best material to mix with your poo, it contains a lot of air, is "brown" and has been used to compost animal poo for centuries. If you don't have any of your own, it is well worth buying it in. Hay is NOT the same thing as straw, it really belongs in the "green" category, and contains little air.
A simple composting urinal can be made by wrapping a straw bale in chicken wire and weeing on it, until the straw rots down to compost. The straw should immobilise most of the nitrogen in your wee, but I would recommend putting the urinal on a patch of grass, to soak up any leakage, and mowing the grass regularly. I'm told that comfrey thrives when fed with wee. Some people reserve their compost toilets for poo, and wee anywhere. This is good if you have a reasonably large lawn which you mow regularly, but remember that human wee is a very concentrated fertiliser, and if you wee too often in the same spot, the grass could get scorched, and the excess nutrients wash away in the rain. Salt accumulation is also supposed to be a problem with human urine, but I have never had any problems in this respect, If you eat a lot of salt laden junk food....well, you probably wouldn't be growing your own vegetables and reading this far :-).
Where to put a compost toilet
It is often tempting to hide a compost toilet out of sight, but I find it is best in a sunny spot, with vegetation around it, grass, trees etc. This stops it getting too smelly, because the ammonia will get absorbed by the growing plants. I prefer compost toilets to be outside, but with good planning, you could make a very nice composting toilet on the side of a building, accessible from indoors. Like I said earlier, think about the problem of moving and storing barrels of poo. Digging the compost toilet into a slope, allows the seat to be a good distance above the barrel. If you live in a flat place, you could improvise a very basic compost toilet with a step ladder and a barrel (and maybe a screen around it if you are a modest type, or have neighbours close at hand). Otherwise, you could have a compost toilet incorporated into a tree house, with the barrel at the foot of the tree. If there is a stone wall across your land, you could put steps on one side, and a hut on stilts at the top of the wall, with a barrel at the other side. Digging deep pits is very hard work, and I prefer not to do it if there is an easier alternative.
Are composting toilets safe?
It is best to leave human manure for a year or two before using it on land. I'm told that the really nasty diseases carried in poo (Salmonella etc.) will die within a year of being composted. Threadworms can live for up to 18 months, but they are hardly life threatening. It is usually fairly obvious from the smell and appearance of the compost, whether it is properly composted or not. If in doubt, either leave the composted poo a while longer, or use it to feed fruit trees or some other crop that will not be in direct contact with the soil (i.e. not root vegetables).