Humanure
The best book I’ve read on composting is The Humanure Handbook - A Guide to Composting Human Manure by Joseph Jenkins. It’s an essential read for anyone interested in gardening, composting, or sustainable living. Jenkins masterfully addresses the potential concerns of composting human waste, making the case for its value in an entertaining and authoritative way. Backed by research and practical experience, his book challenges composting myths and presents a simple, effective approach to turning human waste into valuable compost.
Inspired by Jenkins’ approach, I decided to try a compost toilet when faced with the challenge of installing a toilet in a small shower room. Instead of dealing with the hassle of traditional plumbing, I opted for a compost toilet. It was a simple solution: a bucket, sawdust, and some basic ventilation. This setup has served us well for 15 years, turning 'waste' into valuable compost for our garden.
I’d never considered composting our own sewage. Why bother? It’s not something most people think about. We use the toilet, pull the handle or push the button, and it’s gone. Out of sight, out of mind. Only in our case, in South Devon, it goes to a badly maintained sewage works with broken filters (I know the man commissioned to replace them) and a system that allows sewage into the rivers when the sewage works can’t cope with it, like, when it rains. So out of sight, out of mind, till you go for a walk by the river.
Dealing with your own sewage seems an absurd proposition though when for most of us, the instant disposal solution is available. The first thing that struck me when I considered trying it was the strange irony of going to do all the work I’d need to do to have our poop taken away, when I was in the habit every year of collecting farm yard manure – taking a trailer to the farm, loading the trailer with a fork, driving home with my pile, unloading it into a wheelbarrow and taking it down the steep hill which is my garden. I was sending my own manure away, with the installation work involved and the ongoing costs for water to flush it and then doing all that work to collect animal manure. We ARE animals!
So now I’ve been using a compost toilet for 15 years. The work I have to do at home is collect a large sack of coarse sawdust from a nearby joinery workshop. A sack will keep us going for 2-3 months. We do our business on a little commode covering a bucket. Business done, we put a little shovel of damp sawdust on it. There’s no more smell than with a flushing toilet, and that is soon dealt with by the automatic fan with a timer. When the bucket is full, I empty it onto the compost heap. In summer, I cover that with weeds. In winter, I might add another thin layer of sawdust. If it’s really cold, it doesn’t matter.
When the compost bin is full, I start filling a new one and leave the first to sit, the material decomposing. After a few months, I shovel the finished compost onto raised beds, amongst the fruit trees and bushes, or into an enclosure in one of my greenhouses for use in potting plants. I have a sideline in selling fruit and nut trees that I propagate, and this is the only compost I use for the pots. The trees grow well, and people are pleased with their purchases. It amuses me that really, they’re buying my poop, sawdust, and weeds with added tree seeds or cuttings. After a year or two, those ingredients turn into nice little trees!
Anyway, I won’t make the case for composting your toilet matter here. If you’re really interested, just buy the Humanure book (I’m not on commission). Mr. Jenkins makes the case. I have a degree in microbiology. You’d think I’d know the ins and outs of it all, but Mr. Jenkins had a lot to teach me.
But there are two issues I have with the guidance in the Humanure book. The first is the way that the compost heap just sits on the ground – all that precious nitrogen and other nutrients seeping away into the soil and eventually making it to the groundwater where it does no good at all. This point is addressed in the designs of the concrete and the IBC tank designs.
The other point is that humanure is presented as all or nothing. I am currently building an off-grid house with a good-sized garden. A compost toilet (bucket/sawdust) dumped into an IBC composting bin is ideal for the situation. But the vast majority of people have the usual flushing toilets. Removing them to make way for a compost toilet would be a lot of work and probably devalue your house. And there are times, perhaps when you are ill, you can’t be bothered with the work of collecting sawdust and emptying buckets of poop. But there is a useful compromise which doesn’t necessitate a compost toilet.
A Practical Compromise
Most of the plant food that comes from the humanure bucket is actually contained in the urine. 70-90% of the nitrogen excreted by the human body is excreted in the urine. Your poop has more phosphorus than your urine, but only by volume, and the phosphorus in the poop is in a less soluble form than that found in urine. It’s a similar situation with potassium too. So while the poop has some valuable nutrients for plants, it has little that isn’t also in urine. But the main thing growing plants need is nitrogen, and the great majority of that is in urine.
So without going to the trouble of building a compost toilet, you can get most of the benefit of a compost toilet simply by adding urine to your compost. Urine is considered a compost ‘accelerator,’ which means even if your heap is just a pile of plants on the ground, pouring urine onto the heap will add nitrogen and the rest to the heap, which is what your bacteria need to get the composting process really going. But look at the chemistry page and see what happens to urine when it is poured onto a compost heap.
A compost heap is teeming with bacteria. Plants are just covered in them. You don’t have to add any. All you have to do is provide the right conditions and the bacteria multiply very quickly indeed (some bacteria can double every 20 minutes!). The right conditions are a mix of high carbon material (e.g., dead vegetation, sawdust) and high nitrogen material (e.g., fresh grass cuttings, coffee grounds, urine), moisture, and air. Very many of those bacteria have an enzyme called urease, which breaks down the urea in urine and begins its transformation into more stable and less smelly nitrate.
So when you pour urine onto a heap, the heap gets all the moisture it needs (it needs to drain out the bottom to prevent it from becoming water-logged, which can turn the heap anaerobic and smelly), it gets all the nitrogen it needs (some is adsorbed into the compost material, making the compost contain more immediately available plant nutrients) and the liquid you can collect from the bottom of the heap is high in nitrates, and contains some potassium, phosphorus, and small quantities of other minerals.
Rather than switching to having a compost toilet, you can get most of the benefit and less of the work simply by putting a bucket in your garage or shed and peeing into that and emptying it into your compost bin daily.
I’d recommend rinsing and scrubbing the bucket daily though. We used to have a ‘compost’ toilet on a boat, and collected the urine using a separating seat. The urine went down a pipe into a 5-litre bottle which was emptied daily. No matter how much I rinsed those bottles, they’d build up a layer of stuff on the inside which was impossible to remove and started to smell. Rinsing wasn’t enough, even with sea-water. We just had to start a new bottle every week.
So, I’d recommend a compost toilet along the lines Mr. Jenkins recommends – just using a bucket and collecting all the urine and poop and adding a covering of sawdust after each use – if you want an off-grid system, or you want to maximize what you add to your compost heap, or you don’t want to send your sewage down the river. But most of the benefits of having a compost toilet can be won simply by adding your urine to the heap.