Yesterday was World Toilet Day (yes, really). This is actually an admirable campaign by WaterAid to raise awareness of the fact that one in three people around the world don’t have access to a safe and private toilet. This, of course, leads to unsanitary conditions which results in the spread of infection and disease. You’ve probably never given it a second thought, but loos literally save lives.

Has the TARDIS’ replicator function gone funny?

So, with the topic of toilets in mind, I started thinking about chemical loos. If you live in the UK, the name Portaloo ® will probably spring to mind. This has practically become a generic word for a portable toilet, but it is (like Hoover, Sellotape and others) actually a brand name. I’m told that in America they call them porta-pottys or honey-buckets, which I rather like. In any case, all the chemicals and plastic make them seem like modern inventions, surely?

Actually, not at all. The idea of a self-contained, moveable toilet that you can pick up and take from place to place may be newer, but people have been using chemical toilets for hundreds of years. For example after, ahem, ‘business’ had been completed in an an old-fashioned wooden outhouse – basically a tall box built over a hole in the ground – the user would sprinkle a little lye or lime down the hole to help with the smell.

Don’t get sodium hydroxide on the toilet seat.

Both of these are strongly basic chemicals. Lye is either sodium hydroxide or potassium hydroxide, and lime is calcium oxide. Both mix with water to form extremely corrosive, alkaline solutions and, incidentally, give out a lot of heat in the process. Both are very damaging to skin. These were the days before health and safety; whatever you did, you had to try not to spill it on the seat.

Urea, a key chemical in urine, reacts with strong alkalis in a process known as alkaline hydrolysis. This produces ammonia, which is pretty stinky (if rather tough on the lungs), so if nothing else that helped to cover up other smells. Ammonia also kills some types of bacteria (which is one reason it’s popular in cleaning products). Flies generally don’t like high concentrations of it either, so that’s another plus.

Alkalis also have another effect in that decomposition of human waste is pH dependent; it works better in acidic conditions. Adding lye or lime raises the pH and slows down this decomposition. On top of this (literally) both lime and lye are hygroscopic: they absorb water. This keeps moisture down and allows a solid ‘crust’ to form on the surface of the waste, making it difficult for any volatile, smelly chemicals to escape. Lovely.

Bleach and ammonia could result in a rocket up your…

One word of caution: it’s very, very important you don’t try to clean such an outhouse with any kind of bleach. Bleach, which contains sodium hypochlorite, reacts with ammonia to form hydrogen chloride, chlorine gas and chloramine. None of which are good for your health. Even more dramatically (if this is more dramatic than death – you decide) if there’s lots of ammonia you might get liquid hydrazine, which is used in rocket fuels because it’s explosive. Who knew that toilet chemistry could also be rocket science?

But you don’t find buckets of lye in modern chemical toilets (although, apparently, there are still some people out there using it). So what’s in there? At one time, formaldehyde, otherwise known as methanal, was common. You probably recognise it as embalming fluid; the stuff that Damien Hirst floated that shark in. It’s an extremely effective preservative. Firstly, it kills most bacteria and fungi and destroys viruses, and secondly it causes primary amino groups in proteins to cross-link with other nearby nitrogen atoms, denaturing the proteins and preventing them from breaking down.

Don’t worry, this won’t appear in your chemical toilet.

Interestingly, whilst definitely toxic in high concentrations, formaldehyde is a naturally-occuring chemical. It’s found in the bloodstream of animals, including humans, because it’s involved in normal metabolism. It also appears in fruits and vegetables, notably pears, grapes and shiitake mushrooms. The dose, as they say, makes the poison. I mention this because there are certain campaigners out there who insist it must be completely eliminated from everything, something which is entirely unecessary not to mention probably impossible (just for the hell of it, I’m also going to point out here that an average pear contains considerably more formaldehyde than a dose of vaccine).

All that said, because formaldehyde is extremely toxic in high concentrations, and because it can interfere with the breakdown processes in sewage plants (because it destroys bacteria), formaldehyde isn’t used in toilets so much anymore. In fact, many of the mixtures on sale are explicitly labelled “formaldehyde-free”. Modern formulations are enzyme-based and break down waste by biological activity. They are usually still dyed blue (if you work your way though the colour spectrum, it’s probably the least offensive colour), but usually using food-grade dye. As a result, what’s left afterwards is classed as sewage rather than chemical waste, making it easier to deal with.

So, this has been brief tour around the fascinating world of toilet chemistry. You’d never have guessed there was so much to it, would you? Now, have you considered twinning your toilet?