Anaerobic Composting

municipal composting facility

Anaerobic composting or composting without the presence of oxygen has been practiced for centuries.
Records indicate that the Chinese are the oldest known civilization to practice this form of composting to fertilize their rice paddies.

In more technical terms, anaerobic composting is composting organic materials, using living anaerobic organisms such as bacteria in an environment that has no oxygen present.
This is the same process you will find occurring in nature as peat bogs and marshes.

Unless you happen to have access to a large field of water you are going to have to find another way to create your anaerobic compost pile.

While most composting experts will talk about not letting your compost piles get too wet or they will rot, anaerobic composting requires approximately 70% moisture levels in order for it to work properly.

The Standard Compost Pile

You can turn your current compost pile into an anaerobic one quite simply and effectively by adding plenty of water.
Yes I know we have spent hours telling you how important it is to maintain moderate to low moisture levels, but with this type of composting you need to remove the oxygen from your compost pile.

The water will drive out the oxygen and keep it out if you keep the water level high enough.

By covering the pile to help keep in the moisture, you will end up with a slimy mess, which indicates that it is working properly.

You should however, be prepared for a very odoriferous (don’t you love this word – I can almost smell it) compost pile. This is really more suitable to households with larger tracts of land where the aforementioned odoriferous pile can be placed away from the house or the neighbors.

This is not really a household practise but keep reading because there is an easy way to compost anaerobically at home. Just skip down to Bokashi Composting if this is what you want to read about.

The Submerged Pile

This method of creating anaerobic compost is very similar to that which is has been in use by the Chinese for centuries and involves keeping your compost under water.

For this you will need a large tank, plastic pool or tank that is big enough to hold your compost and then be filled with water.

As your compost pile decomposes the odors are trapped in the water. While slightly more involved than a standard anaerobic compost pile, your neighbors will certainly appreciate it. But … this is really for the experts.

anaerobic composting in a fieldThe Big Bag Theory

You have probably seen this method in use in the local farmers’ fields, this would be the long white bags that lay in the fields over the winter.

This could be for you and is simple.

You need a large heavy duty plastic garbage bag. You first layer the bottom of the bag with soil, then add your compostable materials and add enough water to make everything moist.

Seal the bag so that no air can get in and roll it to get things started and then leave it alone for 6-8 weeks.

 No Hole in My Bucket

Off all the different forms of anaerobic composting, the bucket method is perhaps the easiest and least offensive.

This is a long term project and will take up to a year (yes, commitment is required but then again, a year goes so fast these days) to create the compost you are looking for.

You simple cut the bottom from a five gallon bucket and plant it a few inches into the ground.

You then fill it with your scraps and organic waste, place the lid on it and forget it for a year.

Do not open until the year has passed or you will let in more oxygen and ruin the process.

As you can see a fair amount of patience is required for this method. At the end of the year you will have perfectly usable humus. All of these forms of anaerobic composting work well, some will produce more compost than others, while at the same time creating a rather smelly situation.

Bokashi Composting

BokashiYou may have heard of Bokashi composting.

It is an anaerobic form of composting using a bucket but easier to manage than the hole in the ground method and with much faster results.

The good thing about Bokashi composting is that meat and dairy which are banned from traditional composting are fine to use in the Bokashi system which composts anaerobically.

The scraps are put into a bucket and then covered with some inoculated bran (see picture).

When the bucket is full the lid is sealed shut to  ensure no oxygen enters the bucket. It is left for approximately 10 days.

The commercially made systems have a spigot  (look at the picture) at the bottom of the bucket and every few days the leachate needs to be drained from the bucket.

This is a link to an experiment with Bokashi that may interest you if you want to see more about how it actually works.

It is also well worth reading the comments at the end of the post.

Alert! You will notice that it is a post from 2008 which seems light years backwards in the world of the internet considering it is now 2015, however remember Bokashi composting is hundreds of years old and there hasn’t been any dramatic changes since 2008.

Click here for reviews on Amazon from people who have used the Bokashi system.

Comments

  1. G’day Jenny,
    Great advice. When I made my 1st huge compost heap years ago I was blown away by the heat generated. Ended up with great compost, but the local possums beat me to the vegies !!! Next attempt will feature a 2 metre fence !
    Cheers
    Harry

  2. Compost King says:

    Happy Possums Harry. Fence sounds like a good idea.

  3. Sounds like there’s a lot of science behind composting. I had never heard of anaerobic composting before. And yes I’d always thought that you had to keep water away from composting. Anaerobic composting sounds like a longer term form of composting, as it takes about a year of uninterrupted peace to come to fruition. That means you’d probably use this composting technique in addition to others that you could add more compost to as you go.

  4. Hi,Compost King.
    I love this site so many great tips some I have never heard of before and will now be using as I am not allowed to have a bin here now he wont even know I am composting :-)

  5. Hello Composting Tips,

    Sounds like a great way for composting with water and keep it moist. Never knew there was so many different ways to compost scraps and use in the garden. So love coming here to read what tips/hints you have about composting.

    Cheers
    Lisa

  6. Compost King says:

    Thanks Lisa, glad you are finding the information interesting.

  7. I have had renewed interest in this topic after reading that anaerobic composting may help hold onto a greater portion of essential nutrients (especially Nitrogen) that are lost during aerobic composting. Do you know if there is any merit to this? It makes sense to me that nitrogen is lost in aerobic – thus the need to keep adding more but I am unsure about anaerobic. I have read that if you smell ammonia from your anaerobic pile, you should add more carbon as you are losing nitrogen (ammonia=NH3)

    • Compost King says:

      Hi Steve
      That is an interesting question you raise. I believe that anaerobic composting does result in fewer nutrients lost. The smell can be a problem, however this can be overcome by keeping the pile submerged under water. If you are thinking of using bottomless bins in a garden for anaerobic composting make sure the contents are kept moist and the smell should not be a problem. I would be hesitant to add carbon rich materials to an anaerobic pile as this could slow down the process. Have you thought about Bokashi composting which is an anaerobic form of composting?

  8. Hi Compost King:

    I am interested in anaerobic composting for a delicate wilderness site. My plan is to use several five-gallon buckets, wet down the material to be composted, and seal the buckets with the standard snap-on lid. My question is whether the gasses produced during composting will generate enough pressure to pop off the lids. I’d rather not vent them for odor control. I have the space to let these buckets sit for up to two years if necessary. Trying to avoid a compost explosion if possible :)

    • Compost King says:

      Hi Karl
      A compost explosion wouldn’t be pleasant. :) I think you would need to make sure that the lids were secured really well otherwise they may pop off and your anaerobic composting would be ruined. It is probably a matter of trial and error. Let us know how you get on. it sounds interesting.

  9. I built a buried compost pit. I got a 60 gallon barrel and drilled he’s in the sides and bottom. I surrounded it with bricks and got a steel lid to keep pests away.

    I have been adding to it all winter (Canada) and it’s almost full.

    In the spring time when it thaws:

    1. Will the level drop?
    2. Will it break down fast enough that I can continually add kitchen scraps?
    3. Will worms and/or other bugs get in and help the process?

    • Hello Ian
      60 gallons is a decent size and it sounds as though it has worked really well for you over winter.
      I must first of all say that I have never experienced composting in such cold weather however the basic composting rules still apply once the pile has thawed. When Spring comes and the compost has some warmth the level will certainly drop as the composting process begins by reacting to the warmer weather. The thawing process also breaks down the cellular structure and aids in the composting process.
      As the container is in the ground it is hard to say exactly how warm it will get or how long it will take. It will be interesting to see if it is frozen in the middle given that it has had good insulation.
      Fork the contents once you are able to to encourage some oxygen to get into the pile. As far as being able to continually add more kitchen scraps, yes for sure. The thing with continually adding more and more is that you can get to a point where the compost is never done. This might not bother you, some people are happy to lift out the “done” compost and put the rest back into the bin.
      Another option would be to buy a cheap black plastic compost bin, Transfer the contents from the ground compost into the new bin. The heat generated will speed up the composting process and in the meantime you can be adding to the bin in the ground. When winter comes around again, just store the above ground bin. Earthworms are different to the worms in a worm farm but they are still highly beneficial in the garden and you may get other small bugs in there too, all of that is fine.
      I am thinking I might need to add some winter composting tips. Please let us know how you get on with your frozen compost. It would be really useful for other readers.

  10. Thank you for your prompt reply! My goal with this project is waste reduction. Not compost production. If I have to shovel it out every now and then that’s fine but never would be great. I thought it would be kind of like a compost digester green cone only bigger.

    I buried it for the worm thing also thinking it would be like a huge worm tower. I googled it and it was kinda neat. Anyway it has been great for getting rid of kitchen scraps. I have a few times got coffee grinds from coffee shops as I heard they attract worms and generate a lot of heat. Both are good

    • That’s great Ian. Who knows why worms would like coffee grounds. A local cafe where I live, leave the coffee grounds out the front of the store for people to take. When everything thaws you will be able to keep on adding to it – sounds great. A home made compost digester, there’s no reason it couldn’t work. Good luck!

  11. Realistically how long do you think I’ll have before it has to be emptied?

  12. Should have said a little more. 2 adults live in my house. We throw ALL kitchen scraps in the barrel as well as cardboard rolls from paper towel, toilet paper, and wrapping paper. To add a little carbon.

  13. Mmmm, that is difficult to estimate Ian, with out seeing the location and the fact that you are not adding garden waste. Given the size of the barrel and the warm weather that is coming it should last a long time. If you remember, come back and let us know. It’s an interesting experiment.

  14. I will certainly do that. Right now our yard is not finished so the only waste is kitchen waste. When we get our grass planted we plan on doing the mulch cutting so that it does not have to be bagged and I’m not sure how big of a garden my wife is going to want so there may not be a ton of garden waste from that. The pit that I dug is in the south side of the yard and there is a fence that blocks it from sun from the east but it gets mid day and afternoon sun until evening. When the weather warm up I’m going to paint the lid black to absorb more heat.

    The main reason that I did this was to reduce waste. Garbage collection in my city is poor so the least there is in the barrel the better. Also it helps keep the garbage can from stinking.

  15. Has anyone done the “digester” thing and had good success with it? If so how fast does the material level drop in the bin and by how much? I thought the idea with this thing is that the water is expelled from the material and because most stuff you put in is approx 80% water you are left with very little residue.

    Sorry I’m new to this and have lots of questions!

  16. Will worms be attracted to it after it thaws?

  17. Will they still help the process of reducing the volume of whatever I throw in?

  18. We have had warm weather for a few weeks now. I bent a hook on a chunk of rebar and have been able to fluff up the contents of the barrel. It seems to be slot hotter in the bin than the outside temp. The level still hasn’t dropped any noticeable amount but I guess it takes time. I’m hoping that now that I have a tool to mix it with it helps the process along.

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