Quasi science or Quackery? Tech experiment for compost.

    Composting may be Earth-friendly, money saving, and good for your garden too. However, even in ideal circumstances, it can chew up a bit of time that many people can't do on a routine basis. I get it, life gets in the way!

    The best way to ensure everything is breaking down rapidly is get the right mix of carbon/nitrogen/air and water into the bins and provide regularly "turning" your compost pile. A lot of people think turning their pile over only allows oxygen to get where it's needed, but it goes beyond that. Not only does turning provide aeration, it also assists by loosening up the compost (which further assists aeration and moisture penetration), it also distributes moisture more evenly, and mixes the microbes, bugs, and worms around into relatively "untouched" sections of the pile.

    Despite the numerous benefits, turning the pile over on a regular basis is one of the first things to be skipped by your average composter. I freely admit I am guilty of this myself.

    Ironically, most commercial compost bins (think most of those plastic ones found in your average hardware store) make turning them over harder. Compost tumblers do bring benefits, but require regular (as in hourly) rotations and be heavily insulated (which most aren't) to be most effective. Even if all that is done, the insulated tumblers are often very limited in compost capacity, despite their high cost.

    Making the most of what you have....

    If you're like me, then you might already have a plastic compost bin (or four) and want to see if you can help things along a little bit without too much effort. Yes, I'm lazy. So I want to find an easy way to add air and water to my compost bins.

    This idea has been done on a variety of scales, using 100mm (4") and 50mm (2") pipes riddled with holes and industrial air pumps, leaf blower/vacuums, air compressors and many alternatives as well. However, none of the web sites I have found seem to indicate what quantifiable benefit is gained by going to this much trouble.

    Another issue is that almost none of these solutions are really practical for people who are living far closer to their neighbours. All of these systems generate a tremendous amount of noise, have high running costs, and are quite expensive to implement.

    Speaking of cost....

    If you spend $300 on equipment, then you could have bought yourself over 5 cubic metres (5,000L) of delivered compost for that. That far exceeds the combined capacity of my compost bins, which comes in at only 1470L. You might think that I'd need to do 3.4x (5000/1470L) to break even, but you're forgetting that compost takes up less space as it breaks down. To get 5000L of finished product. I'd actually need to do 6-7 complete batches of compost to match that. I might only get 3 or 4 per year.

    Having done those depressing calculations... the good side to that, is that my current setup is saving me $150 per year already. These bins have been in place for 5 years, so they've probably generated savings of $750, and the bins cost me just under $250. So they've paid themselves off already.

    Noise issues...

    So what can one do when their neighbour complains when a tree branch rubs against the gutters and that makes too much noise? A blower vac, air compressor, or industrial air pump is going to be orders of magnitude more irritating. Thus a little bit of idle thought and consideration went into my "crazy scheme to convert your everyday compost bin into a marginally-more-effective bioreactor".

    As a tech head, Permaculture-trained, compost nutter/enthusiast, I decided to do a little experiment. For those of you who have read or written science articles/lab reports before, you'll find the format quite familiar. However, my conditions are very limiting. They include (in no particular order):

    • It must be very quiet.
    • It mustn't be frightfully expensive (I've limited it to $300).
    • It must work with a minimum of intervention, preferably automatically.
    • It only needs to accelerate a 440L pile of compost. I'm negotiable on the amount, but if it accelerates the decomposition by even 10% that would be a win.
    • It must have low running costs.

    Sound impossible... well as my grandfather used to say:

    "You don't have to use a 10lb fishing line to catch a 10lb fish, if you do it in a slow and steady way".

    This is going to be a very small scale project... but it'll still add thousands of litres of air over the coming months, and hundreds of litres of water. So without further ado:

    Analysing the Effects of Adding Airflow & Irrigation to Commercial Compost Bins.


    To evaluate the effectiveness of adding a small scale forced airflow and irrigation setup to a typical 400L bottomless compost bin in accelerating decomposition.


    While active turning and gentle mixing is likely to produce a faster breakdown of compost materials. Adding a regular, small scale supply of both air and water into the compost pile will hopefully accelerate the process to some degree without manual intervention. By using a long-term, low flow method with both water and air, this should avoid problems such excessive temperature loss, as well as flooding, or excessive dehydration. All of which slow decomposition rates.


    Three identical 440L compost bins, side by side, are modified to varying degrees.

    • Left bin: No modification, just used as purchased. (Control sample)
    • Middle bin: Augmented airflow added.
    • Right bin: Augmented airflow and irrigation added.

    Airflow modification:

    Augmenting the airflow, involved connecting a small 5W solar powered aquarium/pond air pump to a standard 4mm irrigation line. That line was piped into a small 5.5mm hole in the side of the compost bin, then into 4mm "weeping" hose 2m long, coiled inside a layer of pea straw within the compost pile. I have found that I don't like weeping line for watering purposes, but for aeration, I think it'll be ideally suited.

    I filled the compost bin with straw to bring this closer to the light for the photo. This is not the final position. It will be buried further into the pile to aerate the parts least likely to receive air, and to force the air through as much of the compost as possible. Also, I'd recommend spiralling outwards instead of inwards so the greatest air pressure is in the centre.


    The air pump controllers have speed/flow rate control. I have set it to the lowest setting on both pumps. Also, the pumps have a timer function that run for 10 minutes every hour. (I have only just noticed that the pumps I ordered have batteries so they will continue to operate like this during the night, despite the lack of light. Personally, I'd recommend not getting one with a battery, as this will ensure quiet during the night, and perhaps stop cold air from being pumped into the bin... which will slow decomposition). As a stop-gap measure I have enabled the timer function to reduce the potential impact of noise on the neighbours.

    Irrigation modification:

    I have simply added a single brass 4mm irrigation spray head by drilling into the exact centre of my circular compost bin, and poking the head through. This spray head has a standard 4mm in-line tap control on it should I want to adjust the flow rate, or turn it off completely. It is then tied into the front garden zone on my automatic irrigation system.

    Water line poked through the lid, with a spray head inverted on the other side.
    Water line poked through the lid, with a spray head inverted on the other side.

     I will have to rely on temperature readings and visual observations in order assess the effects of this approach. While I don't think I'll get a great deal of effect during winter, I'll check once per month to what (if any) changes have occurred. As things warm up, I might check as frequently as weekly. Given that Canberra really doesn't warm up until September, sometimes October, I'd recommend patience.

    Notes and concerns with experimental methods:

    My irrigation system is a fully automatic model which uses Internet-based weather forecasts to deliver an appropriate amount of watering.

    First concern: Particularly dry/hot times may cause problems for this experiment as it might flood the compost, and/or quench compost temperatures so much that it'll impede efficient decomposition.

    Second concern: There might not be enough room in the compost bin for even water distribution. The spray head requires some empty air space in the top for the water to disperse evenly. I don't always have space at the top.

    Third concern: The water pressure may be insufficient for wide dispersal from a spray head. Perhaps several lines with separate drippers/sprays may be more effective. However, I'm trying to drill as few holes as possible at this stage.


    This experiment was started on ANZAC Day (25th April, 2020). Since we're in late Autumn, we can expect that the compost bins will slow down considerably over winter. However, it will be interesting to see how they go by spring.


    To be announced when we have more data. Stay tuned.

    © 2022 WaywardHam.net. All Rights Reserved.