What actually happens when you poop in a composting toilet?

Tuesday June 2nd 2015

Poop, kaka, number two, the black banana, the bondi cigar, colon cobras, doo-doo, the monkey's tail, mud bunnies, mr ploppy, or the simple turd… no matter what you call it (and trust us we’ve heard all the names!) we all do it. But not all of us have gotten over our ‘poo-a-phobia’ to realise this is actually a resource that can be utilised, and utilised effectively.

To help you overcome your social conditioning of looking at poop as a waste product (LOL - it’s even labeled as a waste product) we’ve put together an article all about the science of a composting toilet and what actually happens to your poop once it heads down that chute and into the dark recesses of a composting toilet!

Composting 101

We’ve all seen our grandparents’ composting bin out in the back garden. You might even have one yourself. They come in many different shapes, sizes and styles from a bin to a barrel through to a simple mound on the ground. We’ve all seen them and know that we get beautiful, dark and nutrient rich soil at the end of it but what actually happens in that pile to make kitchen scraps go from peelings and cores to dirt?

Well, there are four things you need for composting to work:-

  • organic material
  • carbon
  • microorganisms (usually in the dirt)
  • air, and
  • water

The good thing about your garden variety composting heap is that a composting toilet works pretty much the same way. Humans tend to make a lot more liquid than kitchen scraps and that needs to be taken into account when manufacturers design a composting toilet, but other than that the concept is the same.

The technical term for what happens in a compost heap is aerobic respiration, which you can read all about here but basically the process goes like this.

  • Organic material goes into the compost system
  • Microorganisms start breaking down the organic material
  • Air and water help to sustain this process until materials are fully broken down
  • You now have compost!

What type of organic material can go into a composting toilet?

There’s a lot of debate over what can and can’t go into a composting toilet and we have some general guidelines for you to follow so if you’ve asked yourself “what can you put in a composting toilet?” here’s a guide:-

  • Poo (obviously)
  • Wee (again, this one is pretty obvious)
  • Chuck (yup you can add that too)
  • Wood shavings
  • Food scraps
  • Garden clippings
  • Lawn clippings
  • Animal manures
  • Leaves and weeds
  • Hay
  • Coffee grinds
  • Straw
  • Also leftovers from beer brewing or cider making (which may add to point number 3)
  • Shredded junk mail or newspaper
  • Rice hulls
  • Sugar cane bagasse
  • Peat moss

 What are these “Microorganisms” that you talk about?

Ok, here’s where the biology lesson starts to kick in a little. There’s a few main microorganisms that can be found in a composting toilet and they are:-

Bacteria
These are by far the most abundant critters that you will find in a composting pile be it your average garden compost bin or a composting toilet. The types of microorganisms you will find are usually mesophilic or thermophilic bacteria.

Mesophilic organisms like a moderate temperature between 20 and 45°C and are the same organisms you will find in cheese, yogurt and are also used in beer and wine making (we even have them on our skin, in our mucus and gastrointestinal tracts).

Thermophilic bacteria or thermophiles are very similar to mesophilic bacteria except they thrive in higher temperatures than their mild weather loving cousins ( between 41 and 122°C).
They can be found in some of the more extreme environments on earth (like hot springs and deep sea hydrothermal vents) and are thought to be some of the earliest organisms to appear on earth.

Both these types of bacteria help break down the organic matter in your compost and will raise the temperature. So it’s usually the Mesophilic bacteria that kick things off, then when things start to heat up, the Thermophiles take over!

Actinobacteria
These little guys help with the process of decomposition of organic matter and help to regulate the overall health of your compost pile. It’s no wonder that they’re also used in the creation of antibiotics.

They are particularly helpful in breaking down the tough cellulose and lignin elements found in wood and paper, so if you’re adding garden matter and shredded paper to your composting toilet, you’ll want some of these little guys in your pile!

Fungi and Moulds
Fungus and moulds in your compost pile take things to the next level. They’re great at helping break down larger and more complex organic molecules like fats, carbs and proteins and break them down to their simplest parts. They’re like the mushroomy Hulk of the compost pile – smashing everything down to it’s simplest form except they’re not as angry or as green.

How it all comes together

When you first install a composting toilet usually your system will come with some ready made humus and a microbe mix that will kick-start your composting process. When you start adding organic matter like human waste, toilet paper, sawdust, etc this creates an environment where the Mesophilic organisms will start doing their work.

When the heap heats up (thanks to the Mesophilic organisms) the Thermophiles start taking over and breaking down the organic matter. As you add other elements into the pile (newspaper, garden waste, leaves, etc) this will introduce other organisms into the composting process. All up there can be millions of different organisms ranging from the tiny (Mesophilic, Thermophilic organisms and Actinobacteria) through to your helpful fungi, moulds and even macroorganisms that have been introduced through garden waste like some insects and bugs.

Making sure you have a regulated temperature to increase the ability of all these microorganisms to do their thing is essential. This is where the Clivus system in particular is great as you have a series of fans, chambers and vents to ensure the correct airflow, water distribution and temperature is achieved to get you wonderfully rich and useful humus for your garden in the shortest amount of time.

The four stages of the composting process

In all there are four major stages that your organic matter goes through when it passes through a composting toilet:-

Stage 1 - The Mesophilic Phase
We know from before that our friendly little Mesophiles are organisms that like moderate temperatures. As the pile is going through this phase it combines carbon with oxygen to create energy that in turn creates heat and food for the Mesophiles to start reproduction. As more and more of them proliferate in your compost heap the temperature rises even more which takes us to...

Stage 2 - The Thermophilic Phase
This is where things really start to heat up. As we have learnt, Thermophiles like things a little hotter. In this phase much of the human organic material will break down but the larger more complex elements that come from garden waste or newspaper, etc will not have broken down as much. This happens in the next phase.

Stage 3 - The Cooling Phase
This is where all the little critters that were chased away by the high temperatures and Thermophiles start making their way back to the pile to make a start decomposing the larger, more complex elements in the pile. This is where your Actinobacteria (remember the Hulks of the compost pile) and perhaps fungus and moulds come into play to break everything down further.

Stage 4 - The Curing Phase
This is what we like to call the ‘good wine’ or ‘good cheese’ phase. This is where you sit back and let the compost mature and kill off any of the nasties that can be found in the organic material that you’re adding into it.

The curing phase reduces the risk of substances like phytotoxins appearing in your compost. These toxins can be harmful to both plants and animals (remember humans are animals!) so it’s imperative that you use a composting toilet safely and follow the manufacturer's instructions carefully and allow your compost to reach full maturity before use.

That’s it - you’re in the know about number two

So that’s it – our article all about the science of a composting toilet and what actually happens to your poop once it heads down that chute and into the dark recesses of a composting toilet!

Now that the mystique and unknown has been washed away, it doesn’t seem so icky anymore, does it?

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