Composting toilets don't live in the garden.

We all know how fantastic compost is and we know to throw the kitchen scraps in there and the hedge clippings and mix the whole lot up with some ever so helpful worms. 

There is however a source of compost few of us think about. In fact it’s something most of us, with perhaps the exception of ten year old boys, prefer to not think about at all if we can get away with it. Human waste. 

A composting toilet is any system that converts human waste into an organic compost and usable soil, through the natural breakdown of organic matter into its essential minerals. Micro and macro organisms do this over time, working through various stages of oxidation and sometimes localised pockets of anaerobic breakdown.  In other words what we call ‘waste’ becomes what composting toilet fans call ‘humanure’. 

It is fascinating, in a strange kind of way, to note there are several types of composting toilets. “Self-contained” composting toilets complete the composting “in situ,” while “central unit” ones flush waste to a remote composting unit below the toilet.

Vacuum-flush systems can flush horizontally or upward. Some composting toilets have a large compartment below the toilet and require more  space than a traditional toilet – not to mention an explanation of what is behind that door for the visiting rellies.  

“In situ” and “central unit toilets” are not much bigger than a traditional toilet – but are still bound to need an explanation when Aunt Mildred visits at Christmas.

You don't have to wander down the garden path anymore thanks to composting toilets.

There are also systems that divert urine and use the addition of lime or significant volumes of wood ash to stabilize pathogens in the faeces called “drying toilets.” This is due to the drying and high-alkaline additives that aim to destroy pathogens. A debate in the ecological sanitation field is whether drying or composting is preferable for more thorough pathogen destruction. A study out of Africa suggests that dehydrated faeces can rehydrate with some pathogens intact.

All composting toilets eventually need some end-product removal. Evidently waste dramatically decreases in volume and after around 5 years only 1-2% of the original volume remains in the form of a mineralised soil. 

So, while a  full-size composting toilet technically does not need to have solids removed for several decades if the active tank volume is at least three times the yearly addition – this does somewhat defeat the purpose of having one.  After all who wants to wait half a lifetime before adding compost to the garden?  However smaller systems may need to remove solids a few times a year.

Additionally there are composting toilets which use electricity, some with electrical systems use fans to exhaust air and increase microbial activity, and still others that require the user to rotate a drum or rotate tines within the composting toilet to allow for a predominantly aerobic breakdown of waste. As the ten year old in our house pointed out – not unlike mixing cake ingredients…..He was the only person interested in desert that evening.