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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.


  1. This is amazing…great for the soil…good for the animals…appreciated by the plants and no spent energy! Brilliant…and under two years that is a big achievement. I want one!

  2. Very nice! I have had worm bins and a composting toilet system but not both together. How does the worm farm not get too wet? Does the moisture run through quickly but the solids stay longer somehow?
    Thanks, Susan in Colorado US

  3. Excellent, Chris! I was excited to hear about your system and it does sound like a fine one, indeed. Nice work on the video, as well. It’s fun to hear your voice and see the local wildlife.

    Gravity is a miraculous force, isn’t it? The off-the-grid farm I lived on last year had an above ground source of drinking water (I’m sure I’ve mentioned that on my blog a time or two) and it was all gravity fed, so no need for extra energy. In fact, a bit of water was run down from the small dam in the creek to the bottom of the driveway to power a microhydro generator, so the gravity (and water) gave us multiple uses.

    I’m surprised the worm farm is actually one of the approved sewage systems. That’s great, but it’s always a bit of a pleasant surprise to see something that really is sustainable actually be certified by the powers that be. Do you have any idea how many people opt for a worm compost system? I would assume rare, but any idea how rare? Also, did you install the system yourself or have it installed? How involved were you in building and setting it up?

    Thanks for this article. Very intriguing stuff.

  4. Hi Lumbuck,

    Thanks. It was square metre.

    The quote was from “Organic growing with worms”, by David Murphy (2005), page 23:

    “Under ideal conditions, some commercial varieties will populate as densely as 44,000 worms per square metre, while agricultural worms in a paddock may be crowded with 400 per square metre. Commercial worms achieve sexual maturity in a matter of months or even weeks.”

    The commercial worms referred to are: Tigers; Reds; Blues and African Night Crawlers.

    I reckon that it is measured in square metres because although worms live in a 3 dimensional world, the commercial species are unlike earthworms in that they generally feed only in the top soil so that is where you will generally find them.

    Hi Rosy,

    Thanks. Yeah, I love the interactions with the animals here, the kangaroos are getting more used to me too as time goes on. The top soil here is just getting deeper all the time.

    Hi Susan,

    Good question. At the bottom of the worm farm is a filter which the company who supplied the system is somewhat mysterious about. At a guess, I’d say it was some sort of geofabric which doesn’t compact or break down readily but is also porous. This slows the movement of the water through the mass of organic matter at the bottom of the worm farm, whilst also allowing the finer vermicast (worm poo) to escape (you can see it in the photo of the inspection trap – it looks like a kind of sandy sludge).

    The system itself also has the wind driven aerator, which drives air through the system creating a fast compost pile which also just happens to be well drained.

    If you have a look at the inspection trap on the video, you’ll notice that there were lots of worms inside the trap underwater (worm tea) squirming around doing their worm like thing. However, the photo of the inspection trap in the article was taken the following day and it was relatively dry for the worms.

    A mate of mine does aquaponics systems and he has also remarked about the resiliency of the worms in the grow beds which are regularly flooded and then drained.

    As an additional note, I get droughts and bushfires here too and it is always comforting to note that there is a well fed and constantly watered patch of green plant matter (herbage) for the wildlife to feed on (it also acts as a bit of a fire break too).

    Hi all,

    I welcome all questions and comments about the system.


  5. You haven’t mentioned the dangerous accumulaton of heavy metals in human excreta. As apex consumers we bioaccumulate small amounts of heavy metals which can build up in unmonitored waste systems.

    1. Ned, I am in my 74th year and have been laid up these last twelve weeks and counting. I am in London UK at the moment and will be returning to South Africa.soonest. I have had the time,inclination and free wifi to do research on all thing ecological.
      I too am worried about the uptake of heavy metals, and have found some research about it. I am not an IT fundi at all but this is what I found.URL
      “not least since it is evident that many toxicants are readily transferred from earthworms into biotec components higher in the food chain, thus posing a risk to the terrestrial food chain”
      (Ma 1987,Pankakoski et al 1993. Perhaps there are more scientific papers out there. I will keep on looking.

      1. Hi Mary,
        One of the reasons I no longer write for this website is because of comments like yours. From my perspective you obsess about minor concerns such as heavy metal build up in the soil, without even asking what sort of diet I consume and/or how the system is working on a long term basis. What do you reckon happens to your manure, hows the ocean looking these days? Then in the next breath you’re skiting about flying from London to South Africa! How is that carbon footprint of yours looking? The cognitive dissonance that you display is appalling. It is one thing to be an arm chair theorist, it is another thing completely, to get in the ring and give it a go. Any system can have holes poked in it.

        1. Hi Chris,
          I just put in a worm sewerage system. Would you mind if I spoke with you about yours re growing food between dispersal pipes?

  6. Hi Ned,

    There are small trace amounts of heavy metals in human excrement (in fact you’ll find them in most manures). However if you read back over the article you will see that the worm tea and vermicast is utilised for the production of herbage. The wildlife here distributes this around the surrounding area through their scats (they also eat from a wide variety of areas so are not at any risk). In addition to this, the area is cut, collected and distributed a few times per year and this also dissipates any possible build up. In addition to this a good compost system binds metals of all sorts into more stable compounds.

    You may want to explain to readers what an unmonitored waste system is as it is unclear from your comment? The worm farm here is inspected by the company that installed it twice per year as per the EPA regulations.

    Because I add a lot food scraps to the worm farm here the worm farm is monitored every day. I know more about my wastes than most people would about theirs in developed countries.

    Incidentally, if you are concerned about this matter, what happens to your wastes?

    Most centralised waste systems simply dump this particular problem into the ocean, where it finds its’ way into the food chain along with the dioxins, phosphates, pesticides (the list goes on)…


  7. Great article Chris. Here we have a composting toilet (Clivus Multrum), worm farm, and the chooks, so there are always decisions to be made about which scraps go where! In the buckets today I have pumpkin seeds for the chooks, onion and orange skin into the loo, and egg shells, crushed finely, and some celery to the worms.
    We use barley straw from just down the road for extra Carbon in the loo and worm farm.

    The accumulation of heavy metals (and other toxic stuff) in waste is a problem in centralised waste treatment works for large population centres, Mercury from fillings is a significant one. For consumers of organic produce, that has not been grown in superphosphated soils, which suffer from heavy metal such as Cadmium accumulations, I do not think there is likely to be any problem at all.

  8. Wow! That’s impressive! Did you mention anywhere how much it cost? (either relatively, compared to your solar energy system, or a general dollar amount). I have never heard of this kind of system, so I wonder if the US doesn’t allow it… It seems like a wonderful system for rural areas. I know my septic eventually feeds back into the ground but ithe sludge has to be pumped, and I’d rather the worms got it. :-)

  9. Hi Ned,

    It finally dawned on me this afternoon that you are applying reductionist thinking to a complex system (ie. The environment).

    The term heavy metals does not just refer to music, but also to any unspecified metals. However, if you re-read part 3 of the series which specifically looks at soil, you’ll note that most plants require all sorts of metals in order to grow (just like animals do). As a hint, look at the “Diversity” section for a few examples.

    Where you are wrong is that you look at human excrement as a waste product and consider that it may accumulate in a single point within the environment. Whereas, with a diverse ecosystem, where those human outputs are being utilised by other plants and animals as an input, there is little chance of a build-up.

    I reckon you may benefit from reading a basic ecology text book.

    Also, it is worthwhile quoting Bill Mollison, “Though the problems of the world are increasingly complex, the solutions remain embarrassingly simple.”


  10. Hi Chris
    I just came by from the Archdruid’s blog.
    Nice to see this integrated stuff in action.
    And to read other comments.

    You have a nice site – downhill – and I like the productive little meadow you have grown, and the way your soil nutrients get spread around, including your meadow cuttings. I also like your integrated use of worms. Our worms (though only in a simple bin) like yours need a bit of roughage to supplement throw-away veg and such.

    Our system (in GB) is an old digestion system in a buried brick tank, but they got the gradients slightly wrong and the final waste water distribution is very inadequate – the whole system backs up. (The other tanks in the area have similar problems that go back to when ‘mains’ water was put in a number of decades ago. Before that there was not enough water for flush toilets or piped plumbing.)

    Unfortunately where we are is a flattish site and would need pumping. Wind driven aeration though ought to be possible. It puts the cost up. I think we could take cae of heavy metals. I am curious though about possible pathogen or even parasite control. Your system does not deliver direct to the vegetables and if any soil nutrients from these finally end up among the vegetables via the mowing/cuttings they have effectively been ‘laundered’ by the meadow. I am guessing your local authorities are very relaxed about such a system?

    Do you think you are supplying a net input over the longterm of phosphate or potassium into your system? I guess you import some food from outside? Re-cycling what you use inside the system has to be an important first step in any case.

    Congrats and best wishes


  11. Not sure if I missed this, but what happens when the tank fills with organic matter? I understand their will be some reduction in inputs through the varying processes but at some point the holding tank must fill?

    How do you remove the solids when that point is reached?

  12. Hi Joel,

    Thanks mate. The wildlife treat the place here like a supermarket!

    It’s great design to have systems perform multiple functions and that one with the micro-hydro sounds awesome.

    The company has been around for about a decade and a half, and they would have had to do some hard yards to get the EPA approval. They even do large systems for commercial places too. The system was at the more expensive end of things (it cost about 3 x what a septic tank would have cost me). But, you end up spending more upfront, with very little ongoing costs plus you get the benefit of all of the nutrients. Septic tanks have a lot more ongoing costs (as they need to be regularly de-sludged), so it probably works out cheaper in the long run.

    You see worm farm installations all over the place in rural areas, but they are in the minority. Installation is done by the company and it usually takes about 1 to 2 days. Although they cleaned up after themselves (80m / 262ft of trenching), I didn’t have any involvement other than spreading compost, a bit of smoothing and encouraging the plant growth. On the other hand, I watched the whole system being installed and could reproduce it if I had to.

    Hi Gordon,

    Thank you. I hear you about the scrap hierarchy that’s why you have such good chickens! Clivus Multrum have been around for years too and are a really good system. I’ve wondered what you used for carbon in your system and that is a good local solution. It really does help speed up the composting process to have a balanced compost pile. Here, I use composted woody mulch and throw it in with the food scraps which does pretty much the same thing. Interesting stuff.

    Yeah, you’re correct about produce grown in those soils. I wonder about food too as the quality has gone down in recent times. As an example, a few mates at different locations source imported garlic from the same chain and it just tastes odd to me, although they don’t seem to notice. I understand that it is being sprayed with methyl bromide as an anti-fungal agent. Oh well.

    Hi CathyM,

    This is one of my favourite systems here. As I commented to Joel above, it costs about 3 times what a septic tank installation would cost here (but I’m unsure what that would be in US terms).

    Yeah, with your septic, the liquids may be returned to the soil via a leach field (or by evaporation as some do here), but the solids accumulate and are eventually required to be pumped out. It is a pretty anaerobic environment and a bit nasty too. Still even that lot could be composted back to usefulness if properly aerated and fed a fair amount of carbon materials (about 20x I think may just do it, plus lots and lots of aeration) and leave for 6 months.

    They do retrofits of existing septic systems with these worm farm systems too. A basic composting system with worms may be the way to go, if you want to get access to those nutrients. PS: I hope the drought isn’t affecting your garden too much.


  13. Hi Phil,

    Thanks. Yeah, you are spot on about the worms also needing a bit of carbon roughage in addition to all of those intense nitrogen inputs. I add composted woody mulch here and the worms love it!

    Yikes, a backed up system is pretty unpleasant. I’ve read that a lot of people where you live utilise reed bed systems and the local councils are sympathetic to the idea. The reeds traditionally were used in roofing repairs too.

    Piped water is sort of like the electricity system here as its’ only been up this way for a few decades too (no piped water here though, and electricity is cut off on hot windy days because of the bush fire risk, yikes).

    Incidentally, night soil disposal was one of the main historical uses of a cottage garden. I laughed when I saw Hugh Fearnly Whittingstall on television digging around in his first incarnation of river cottage exclaiming about the fertility of the cottage garden (do love his work though, much respect)!

    On flat sites here they utilise a small submersible pump in the worm farm which only triggers when the worm tea reaches a certain level in the bottom of the poly tank. Still pumps are an additional layer of complexity. Have you thought about a composting system – they are very easy to install?

    I wouldn’t grow root vegetables with this system, just in case. Leaf vegetables are quite acceptable though. It was recommended to plant fruit trees over the leach fields, but there are enough fruit trees here already and I’ve displaced the local wildlife, which is why I give them the herbage and they love it. However with the pump you could potentially send the worm tea anywhere and they allow for this arrangement with the system.

    Yeah, I still purchase food stuffs and am a long way from self-sufficient, although every year the amount of food purchased does get less (this year has seen a huge increase in citrus output). I’m a net importer of nutrients (a random collection of nutrients, really) though as nothing organic leaves the property – there is no garbage service in any case (just a recycling depot for glass, plastics and metals). As you quite rightly say, using what you have access to is the first important step.

    Hi sopalop,

    Really loved the photos on your website, thanks for the link. Nice work.

    Haha! Good question. The system never fills with organic matter and never has to be de-sludged (unlike septic tanks). The reason for this is that although the worms primarily eat bacteria, fungi etc, they also ingest a large component of organic matter. This gets broken down inside the worm into vermicast which due to its small size exits the worm farm with the worm tea. It’s kind of like a sandy material and you can see it in the photo of the inspection trap in the article.

    Also worms are one of the few creatures on the planet that suffer from very few diseases and also interestingly supply their own anti biotic compounds. They punch well above their weight!



  14. A great article!

    Many thanks for writing this up, I was completely unaware such systems existed.

    Please could you clarify what if any constraints apply regards the inputs, for instance:

    is it alright to use normal detergents, here I am thinking of things like liquid hand/body soaps, shampoos, washing up liquid, dishwasher tablets, soap powders, etc for washing machines?

    do you have to use special toilet paper, I know that they are necessary in septic tanks?

    is the input from the toilet macerated?


  15. Hi ChrisR,

    Thanks. Most of the soaps that I use are plant based. However, even these have sodium in them and over time this may accumulate in the soil. The developers of the system don’t seem to think this is too much of a problem, so I’ll just observe the system and environment see how it goes. There is a constant herbage cover over the trenches so it should be OK. Most likely it is not enough to ever worry about.

    The system is pretty resilient to all sorts of chemicals (including antibiotics), but you don’t want to overdo it and that goes for any system (including the centralised urban systems). I inspect the system most days because I throw in the scraps that the chooks and dogs don’t want and it always seems to look and smell the same.

    I’m aware that systems that rely only on bacteria alone can be wiped out through excessive usage of cleaning chemicals (bleach etc.). Not good. You can restart the bacterial culture in these systems by chucking in some dynamic lifter (or compost).

    As to toilet paper, I use toilet paper manufactured from 100% recycled paper. There are no special requirements though with this system and the toilet paper counts towards carbon materials in the compost pile. You can add paper and cardboard to the system if you want, but I generally add composted woody mulch to keep the whole system operating on a very fast cycle.

    The input is not macerated and I’ve chucked in dead chooks, leather riggers gloves, roadkill you name it. If it was once alive, you can chuck it in.

    The photo above tells the story, as it looks just like a crumbly soil and has only a very mild earthy smell.



  16. hey chris, love this article, i was wondering if you would be able to tell me about setting up one of these in an urban setting, we are starting an eco-aware community in miami florida and i would love your input!

    thanks samuel

  17. The best method of disposal of human waste that I have seen was in a Lahu mountain village in Thailand, where the houses were built on stilts, and the pigs lived below. The pigs preference was for the warm variety!
    But this system would be the one I would choose, because its simple, neat and tidy – thank you


  18. Hi,

    Great System!

    But i have a question about the wandering off of the worms: You write that worm eggs are washed away, but do you see adult worms wandering off?
    This could make a great feeding system in Aquaponic, or any kind of pond…


  19. Hi Chris,

    We are off the grid, western NSW and looking to upgrade our very poor working septic system, which backs up with little use, mostly due to limited gravity in pipe work.

    Could you please advise who installed your system.

    Many thanks,

  20. Hi Steven,

    The herbage that grows above the infiltration trenches is constantly cropped by the wombats, wallabies and kangaroos that live here. About once a year (just before Christmas) when the growth exceeds their ability to eat it, I have to chop and drop all of the herbage (for fire prevention reasons). The combination of these two actions means that the plant roots also shed material within the soil. Add on a lot of manure from the animals + the activities of dung beetles and there is plenty for composting worms to eat. So they do get away from the system and if you dig (I really try not to dig anywhere if I can help it) you’ll find lots of worms. I had to dig a hole for a free standing solar panel mount recently and found that in only a few years since installation, the top soil is about 150mm deep at a location nearby the infiltration trenches.

    We bring so much organic matter onto our properties in all sorts of ways (eg. Food) that it is a shame to send it elsewhere. Much better to get that organic matter into the soil.

    Hi Donna,

    The system was supplied and installed by A&A Worm Farms. They have been around for years. Septic systems can be retrofitted. You’ll notice the difference pretty quickly as the worm farm is aerobic and has only a minor earthy smell. Septics on the other hand are anaerobic and you wouldn’t to take a deep breath from that lot!

    You should always comply with government regulations in relation to these matters, but having said that, there is no technical reason why you couldn’t build your own worm farm?



  21. Hi Chris,
    thanks for such a a well written article. I a planning to set up an off-grid house in northern Philippines and have been researching options for the blackwater. I think this is very a neat and functional system, although I have seen some negative comments about a similar system, biolytix (?).
    As the article has been written in 2012, would you mind giving us an update as to how the system is going please? Is it still functioning as well as it was in the beginning and is there any other/ major maintenance you have to do since?
    thank you so much for sharing.

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