Food Forests, Part 4: Humanure (black water)

Poo. We all do it. Even the smallest microbes do it. However, when you are connected to a centralised sewerage system, unless it stops working – which is not much fun – you don’t have to think about it much at all. A quick flush and off it goes, somewhere else, to be processed at some distant location, somehow or another. It’s all very mysterious really and for most of us it is someone else’s problem. However, when you are not connected to a centralised sewerage system, it is inevitable that you’ll become more acquainted with the stuff sooner or later.

I live in an area that has no connections to a centralised sewerage system, so each property has to have a system that caters to the needs of its inhabitants in this matter. But, it is no wild west either, where you can do as you please. The state government here in Victoria, Australia, has the Environment Protection Authority which regulates and certifies the various commercially available sewage systems. As a householder, you are only able to install a system that has been certified by the EPA.

Centralised sewerage systems aren’t perfect. They have been outstanding in virtually eliminating water borne diseases such as cholera and typhoid, which were historically major killers. At the same time though, they use vast quantities of water and energy. Mostly though, the processed (and sometimes unprocessed) end products of this centralised system end up dumped in the ocean. Wouldn’t it be better if these end products ended up back in the soil where they could be used to fertilise the next crop of vegetables, grains, fruit, or whatever?

There’s also one dirty little secret that centralised sewerage systems have and it is that when it rains heavily or floods, often untreated sewage spills into local creeks and rivers and eventually finds its way into the ocean.

Why did I choose the worm farm system?

If you spend a bit of time observing nature, you’ll quickly notice that animal manure is often used as a fertiliser and also as a food source by all sorts of creatures. Here, kangaroo, wallaby and wombat manure is often sifted through by the native birds. Dung beetles have been released around here and they can often be seen over summer scurrying away with a present to their holes. Insects such as millipedes breed in the stuff. Sometimes the rain disperses the manure so that it quickly gets broken up and absorbed into the topsoil where it is consumed by the soil flora and fauna. In essence, nature has systems for dealing with manure which really involves a long chain of progressively smaller animals until it becomes soil food for plants.

Humans, on the other hand, love engineering solutions when it comes to humanure — and the more complex and energy intensive, the better! Some of the other approved systems that I could have chosen use ultra violet radiation to sterilise the humanure, others add complex chemicals such as chlorine, whilst others accumulate the solids and when the unit is full (and completely anaerobic too!), they are required to be pumped out, transported and treated elsewhere. Some of the units were so complex they required alarms and telephone lines so that computers could alert the supplying companies if the system failed. Yet, despite these engineering marvels, it should be remembered that nature provides this service for free!

So, after careful consideration, I chose to work with nature and install an approved worm farm to process all the humanure and grey water from my household.

Do worms eat poo?

A common misconception about worms is that they eat the organic matter in the compost pile. This is not the case and according to David Murphy, the author of the book, Organic Growing with Worms, whilst worms do ingest 50% of all matter that they encounter, their preferred diet is micro-organisms such as algae, bacteria, fungi, micro-arthropods and protozoa. Compost worms, as distinct from other types of worms such as earthworms, like a nutrient rich diet, so that a biologically active compost pile is their preferred place of abode. Another fun and fascinating fact about compost worms is that, under ideal conditions, they can achieve a population density of 44,000 per square metre. Honestly, with all those worms in the worm farm, I’m scared to put my hand in it!

Most permaculturalists will be aware of the benefits of compost piles and how various bacteria, fungi etc. quickly convert organic matter into usable soil. The worm farm system works exactly the same as a large compost pile, except that it is both aerated and has compost worms (sometimes also called manure worms) to accelerate the process.

What are the components of the worm farm system?

A schematic of the worm farm is shown below:

A schematic of the worm farm

My house is plumbed as per a normal house with flushing toilets, so the system is invisible to visitors. As the worm farm is located downhill of my house, the grey and black water flows through normal plumbing pipes to the worm farm system using gravity. No additional energy is required, which was a strong consideration in system selection as we are reliant on solar power.

A further benefit of this system is that any compostable matter not consumed by our chooks or dogs can also be thrown into the compost bin located at the top of the worm farm. This also allows regular inspection of the system.

Compost bin over worm farm

The outputs of the worm farm are worm tea which is a mix of water, bacteria, fungi, vermicast (worm poo) and compost worm eggs which is then distributed over 80 metres of trenches. The trenches are on contour (just like a swale) and have plastic reln drains covered in geo fabric. The trenches are covered over with soil and herbage is grown above this. My understanding is that the system I have which is in a 3,000 litre poly tank, has the capacity to process up to 1,800 litres of water per day (although we use about 150 litres per day on average).

The final point about the system is that aeration is provided by a wind driven aerator which draws air into the worm farm with even the mildest of breezes.

Inspection trap

Benefits of the system

  • Nutrient capture: Whenever I eat food or drink beverages that have been grown elsewhere, I know that the nutrients in these food items will eventually be captured in my soil.
  • Any good permaculture system will have multiple uses and the worm farm fits this description.
  • As mentioned previously, the top of the worm farm has a compost bin lid which you can use to throw in food scraps or other organic matter. As the worm farm is quite large, you can even throw in organic matter that smaller worm farms would struggle with, for example citrus peel, onions and (unfortunately) road-kill. It will even process small quantities of antibiotics without any noticeable effect on the worm population.
  • The worm farm returns nutrient rich worm tea to the herbage all year regardless of the weather. The lush herbage in turn stays moist and mineral rich.
  • Another undocumented feature of the herbage is as a bribe to the local wildlife. I could easily have planted fruit trees or non root vegetables over the trenches, but my house and food forest takes up space within the forest environment which may have pushed out other animals. The herbage is more nutrient rich than most other areas within the immediate area, so a variety of birds and animals are consistently in that area and they spread their scats (and hence fertility) in amongst the surrounding forest and also right throughout the food forest here. Nature does this job for free!

A wallaby enjoys the benefits of the worm farm


There are a few limitations to the worm farm system:

  • It is important to use garden friendly soaps to avoid a build-up of sodium (ie. salts) in the topsoil, but mostly I’ve just used whatever products I’d normally use and I monitor the herbage that is growing above the trenches for any changes.
  • Plastics and synthetic materials can’t be disposed of in the worm farm even if they state that they are bio-degradable. This can include nappies and sanitary napkins.
  • Whilst the worm farm can process a small amount of paper and cardboard, too much of these materials can form an impermeable layer and reduce the efficiency of the processing.


I really like the worm farm system and find it easy to live with. I also like that it is kind to the environment. The surprising thing for most people is that the worm farm has only a very mild earthy smell, exactly like a well aerated fast compost pile. I take particular delight in scaring visitors by daring them to have a look into the worm farm and for the truly adventurous sorts I dare them further to take a deep breath. It is disappointingly mild for some thrill seekers!

Also it is worth noting that the waste products that enter the worm farm tend to be low in carbon. So, to speed up the composting process and also provide fungi to the compost pile, I regularly add small amounts of woody mulch materials. The materials at the bottom of the worm farm have never built up and I understand that the system itself never requires to be emptied.