Clockwise from top left: Wheelie-bin compost toilets in situ; Composting toilet diagram; A very normal looking throne above a composting toilet system; Composting toilet diagram.
Composting toilets are natural, self-regulating waste treatment systems. They use no water, no chemicals and produce no polluting discharge. The design of a composting toilet allows for a simple and odourless decomposition, resulting in nutrient-rich compost.
Composting toilets look like any regular toilet and are increasingly replacing the typical flush toilet in homes. By using a composting toilet, homeowners save on water consumption (on average 35,000 litres a year!), return valuable nutrients to their soil, keep waste management on-site, reduce dependency on services and increase self-sufficiency.
First things first: check with your local health authority to find out whether owner-built composting toilets are permitted in your area.
A composting toilet’s design ensures the correct levels of moisture, oxygen, carbon and nitrogen are achieved to allow for a naturally occurring composting process. We’ve provided guidance to help you create a wheelie-bin compost loo, but you can apply these principles to make a composting toilet to suit your situation with whatever resources you have available.
The components of a compost loo are:
- The chamber. The composting toilet chamber is simply the receptacle that is used to contain the contents of your compost pile. It can be a wheelie bin, a 44-gallon drum or anything else you can think of that will fit this purpose. Second-hand wheelie bins are easy to come across; alternatively, you can buy them from hardware stores for around $60 to $100.
- The throne (aka the pedestal). The place you sit to ponder life and reflect on how, by sitting on the throne of your composting loo, you’re saving the planet. It’s a place that everyone spends time every day (some more than others!), so it’s worth making it a good one. In the wheelie-bin model, the chamber sits below the floor, so any type of pedestal can be used. There are a range of composting toilet pedestals for sale or you can build your own and mount a toilet seat to it.
- Drainage. Much of the liquid that enters your compost chamber will be either absorbed by the compost pile or evaporated via the composting process. Any excess liquid will move down to the bottom of the chamber and needs to be able to freely drain away. You can create a ‘false floor’ in the bottom of your wheelie bin by covering an old bread crate or some form of mesh in shade cloth. This false floor should allow liquids to drain through, but be sturdy enough to retain the solids above. The false floor is held above the bottom of the chamber to create a space for liquids to drain into and, ultimately, away from. The liquid draining away from your chamber typically runs into a small absorption trench consisting of a coarse aggregate and distribution drain pipe. This absorption trench is backfilled and buried below the ground. The components for your false-floor drainage shouldn’t cost more than $50. A hose fitting at the base of the wheelie bin can connect to a drain pipe leading to an absorption trench.
- Ventilation. Providing good ventilation to your compost chamber is essential for creating healthy composting conditions and eliminating odours. If you’re planning to install a composting toilet inside your home, it is strongly recommended that you use a small 12-volt fan. The fan will provide a good, steady oxygen supply to your compost and ensure 24/7 smell-free operation. The fan is mounted inside PVC pipework to pull air through the chamber and push it up through a ventilation stack. The ventilation stack needs to rise above your roofline to ensure any odours are dissipated into the atmosphere. 12-volt ‘computer fans’ are relatively cheap to buy; choose a heavy-duty model, as these are better equipped to withstand the moist environment that they will be operating in. Quality fans that will give you a good few years of service cost about $80. Passive forms of ventilation include using a wind-driven whirlybird or painting your PVC ventilation pipe black: the sun heats it up, sets up a convection current and pulls the air upwards!
Composted humanure is typically given a minimum of six months to fully decompose to ensure it’s ready to empty from your compost chamber. The amount of time it takes to fill a chamber is dependent on the usage it gets and the size of the chamber. You’ll need a minimum of two chambers to allow one chamber the time to compost while the other is ‘in service’. Depending on usage, you may need more than two chambers in your rotation to allow for the minimum six-month composting period. And the end result – safe, clean, fertile compost!
Making A Wheelie-Bin Compost Toilet
The wheelie-bin model is an example of what’s known as a ‘batch cycle system’. Another popular composting toilet design is the ‘continuous cycle system’ (e.g. Clivus Multrum), which can also be owner-built, but requires more resources to do so.
- Step 1: Chambers Source at least two wheelie bins; second-hand ones are fine. Bigger wheelie bins will have a greater capacity, but will require greater underfloor space. The standard kerbside 240 litre wheelie bin will have plenty of capacity to suit full-time use by four to five people.
- Step 2: Throne Source your throne. Composting toilet pedestals are available for purchase and start at around $300. Alternatively, you can build your own – be creative! Anything that you can fix a toilet seat to …
- Step 3: Drainage Drill a drainage hole at the bottom of (not underneath) the wheelie bin. The drill-hole size will depend on what irrigation fittings you have available. Using standard irrigation fittings (usually 25 mm), fix a valve and hose nozzle to the outside of the bin, in through the hole. Once the wheelie-bin toilet is in place, the hose nozzle is connected to a hose fitting and hose to allow excess liquids to drain away, typically into an absorption trench.
- Step 4: Drainage The false floor of the chamber can be made using an old bread crate, a piece of steel reinforcement mesh or any other similar material that will hold its shape. This will need to be cut to size and shape (using a jigsaw or grinding cutter) to fit into the bottom of the wheelie bin. Once cut to size, wrap your false floor in shade cloth. Using a spacer, your false floor needs to sit about 100 m above the bottom of the bin. This spacer can be achieved by putting some old bricks in the bottom of the bin or using rebar chairs. Place your spacers in the bottom of the wheelie bin and your false floor on top of them. The hole (from step 3) should now be below your false floor in the bin.
- Step 5: Ventilation Cut a hole near the top of the bin to allow a 100 mm PVC pipe to protrude into the bin by about 100 mm. Using the required fittings (fittings required will differ depending on your installation requirements), run the PVC pipe away from the bin and up the external wall of the toilet building. Inside this ventilation pipework, mount your ventilation fan. Fan housings are available from composting toilet suppliers or you can DIY by packing the fan directly inside the PVC using a spongy, packing foam to hold it in place.
- Step 6: Connection Cut a hole in the lid of your wheelie bin to allow the chute (or pipe) that extends below your throne into the bin. A suitable chute can be sourced when you purchase your toilet pedestal or you can make your own chute from a length of 250 mm diameter PVC (or similar).
- Step 7: Preparation Place a 50 mm deep layer of bulking agent in the bottom of your bin, covering the false floor. Feed the chute from the throne through the lid of the wheelie bin, connect your fan to a suitable power source, connect your drain nozzle to your drainage hose and you’re ready to go!
Installing a composting toilet not only reduces water waste, it also transforms a waste product into a valuable resource: compost! There are many different systems and models, so do some research to find the best one for you. Then start reaping the benefits of on-site waste management, reduced bills and increased self-sufficiency!