Bioreactors

Some luck in the garden today.

I have been looking into worm farming as a way of composting larger amounts of garden waste material and kitchen scraps and creating the worm castings that are so valuable to the garden. I’ve more recently come across the Johnson-Su Bioreactor and was impressed by:

1. the large quantity of material it can take
2. not having to turn it once set up
3. how it benefits from the addition of worms
4. breeds worms and mycorrhizal fungi at the same time
5. aerobically fueled, so no nasty anaerobic smells
6. has an initial heating process to destroy seeds and grass runners

Most of the projects I have managed to research on-line have featured woodchips, straw, grass clippings, cardboard and even some additives such as rock minerals or a little manure. After the materials heat up over a period of hours and extend over a couple of days, once the compost begins to cool compost worms can be introduced.

I began to wonder whether such a set-up might also be able to deal with kitchen scraps given that it relies on aerobic activity to break down the materials. It so happens that the Gods of Compost were at play and I came across Diego Footer’s video of a smaller bioreactor in which he puts kitchen scraps.

In a moment of serendipitous glory I located in my garden a bin which I was wanting to use for compost tea, but which had a split in it. This would be perfect. I would riddle it with holes anyway. I also found just the right size length of plumbing pipe left over from the renovation which I would use to put through the middle of the bin. Further to this I also happened to have a length of stainless steel rod which I later placed through the bin and the pipe which would keep the pipe in position whilst we filled it.

Diego’s video was quite thorough and he answered all of the questions I have started to accumulate in my mind. The Johnson-Su Bioreactor method fills the body of the bin in one go to give the initial bulk and heat required to sustain a good temperature. However, Diego adds to his mini-composter as required. If it sinks a little, he adds more until the bin is full. He also has multiple bins active so there is usually a bin to add waste into and he can rotate through as he empties them.

I am hoping that such a technique will also work with a larger bioreactor model. My guess at this point is that there would have to be enough reduction in the materials to accommodate a decent amount of additional material so that the fresher stuff generated enough heat on top of the older material. As yet I have not seen or heard of anyone using the compost bioreactor in such a way, so it may be that it just doesn’t work as well. A fill and leave method seems to be the accepted protocol.

Further to completing this project I also found under the house all the necessary materials for building a large bioreactor. I started that project today also, as a matter of urgency really as there is a lot of green matter and cardboard building up out the back. I managed to finish the outer shell and to locate all the parts I will need so that I can complete it and finish it within the next few days. In anticipation of this I also lopped a few limbs off the wattle tree up the back. It is not doing that well after some storm damage and after a few days of partially drying out it will be easy to mulch and put into the compost mix.

On completion of the kitchen waste bioreactor I placed it over a damaged bucket. I will leave it here for now until we begin to get some waste in it. I figured that it might make for a good experiment to see if the extra air flow from underneath assists the process. It will likely also capture any liquid nutrients that may seep from the bottom. Once I am comfortable with the process I will sit it somewhere out of the way to rest whilst we top it up a little more. At present it has a layer of dried plant stems left over from seed collecting. They are dry, hollow and fibrous so I figured they would make a great base on top of which to put the higher water content scraps and greens.

More soon on the large bioreactor assembly and how this smaller compost bin is doing.