Which Composting System Do I Prefer?
Which Composting System Do I Prefer?
Article by Piet Kruger of Convertech Biological Conversion Technology
“Which Composting System Do I Prefer?” is one of the most frequently asked questions that I encounter when dealing with organic waste management alternatives.
Potential clients tend to look at composting from a different perspective than compost makers, and often are somewhat taken aback when presented with the intricacies and technical requirements of establishing and managing a compost facility. I find that more often that not the client’s expectations tend to lean towards a simplified process with minimal inputs required during the process. Whilst this is by no means unrealistic, and indeed any organic waste disposal alternative worth it’s salt should attempt to conform to this, the reality is often quite different when dealing with composting on a day to day basis.
Making compost is not cheap or easy. It requires the equipment enabling the compost maker to mechanically manipulate vast quantities of raw material that is seldom homogenous. A compost pile is a complex living organism in its own right, and as such requires the same, if not more, care than any other living creature.
I remember way back when I attended my first formal composting training course, the utter incredulity that I experienced when first presented with C:N Ratios, moisture content, pH, porosity, NH4, NH3, ash content, carbon, lignin, cellulose, hemi-cellulose, Malliard reactions and so on. I honestly felt afterwards that the entire composting process was turned into something a lot more scientific and intentionally made more difficult than it ought to be. After all, I successfully made several batches of garden compost without even knowing any of this!
As time went by I grudgingly had to admit the error of my initial impressions. The experts were right. Making a few small batches of compost without having a verifiable end result or time constraints is easy and certainly does not require the compost maker to entertain all those science bits. However, producing high quality compost cost-effectively while consistently meeting quality, environmental and safety standards is a different proposition altogether.
Compost systems are primarily grouped around the aeration and turning methods used. Active requires equipment, passive requires time. Active achieves a more homogenous end product whilst passive achieves a cheaper but less homogenous end product.
To use the wise words of one of my mentors, “you can correct just about any mistake you made by incorporating additional turns in a compost pile…” This is very true, as turning compost – by whatever means you have at your disposal – will create an opportunity to inspect and correct the three primary components necessary for proper composting. These three are a) Carbon to Nitrogen Ratio; b) Moisture content of the compost substrates and c) pH and structure of the compost substrate.
The general rule of thumb is to achieve a 30:1 carbon to nitrogen ratio with a moisture content of around 66% at make-up (when you mix everything together to start the composting process)
Less nitrogen and your compost pile will have difficulty in heating properly and too much will produce large quantities of ammonia (NH3) that just blows off into the atmosphere. Typically compost piles will have a higher than 8 pH during the first few weeks of composting and then gradually reduce to somewhere around neutral as the compost process draw to a close. The high pH in the early stages is as a result of NH3 and NH4 which is highly alkaline.
As organic material decomposes, it produces organic acids and also forms new “chemical” type acids such as the gypsum (Calcium Sulfate) added to compost will assist in formation of Sulfuric acid (H2SO4) and reduce the pH that way. Anaerobic conditions also have a pH reducing effect. The reduction of pH in an anaerobic compost pile is dramatic, but fortunately this is not entirely irreversible.
It is important to know that anaerobic conditions are not desirable in a compost pile, and prolonged anaerobic periods will reduce the quality of your compost. The main reasons why you should avoid anaerobic conditions are that these conditions are primarily responsible for bad smells and may also produce flammable methane in extreme circumstances.
Moisture content is as important as the two other points mentioned above. Without proper moisture levels available inside the compost, microbes cannot convert the organic material and composting can come to a standstill if the moisture content drops too low. Also important is that too much moisture will reduce the quantity of available oxygen inside the substrate and facilitate anaerobic conditions and leaching of compost liquor.
So how does all of this relate to my favorite composting system. The composting system of choice must be able to :
- Facilitate easy and thorough mixing of raw materials
- Require minimum movement of compost
- Provide proper aeration and drainage
- Provide an easy and reliable method of turning the compost.
 I have made compost with just about every system available on the market today, and for me the system of choice is an aerated channel system. This system combines the benefits of an aerated bunker with the ease of turning a windrow. Compost moves down the channel every time it is turned with the channel turner, and eventually is disgorged at the other end as a beautiful and homogenous dark brown compost. Please visit Transform Compost Systems for more information on this brilliant composting system. The photo on the right is one of their systems in action, and is published here with their permission. (Thank you to Dr.John Paul, president of Transform Compost Systems)
Not at any point is it required that you bring in the front-end loaders and conveyor trains and overhead mixing gantries or the blending lines that so often are essential in making the high tech indoor systems functional. The structure of the final compost is excellent due to more aggressive turning and substrates of any density can be mixed together and the aerated channel system will still be able to effectively deal with it. The secret is that the system relies on both artificial aeration and mechanical turning to achieve an end product. Neither one of the two systems can produce compost of similar quality on its own.
Systems which I do not personally like are the compost-in-a-bag type systems. They just do not provide any practical means of handling compost and tend to be more of a pain in the long run.
There is also much to say for a proper windrow system that is turned daily. The problem with windrows is just that they are too smelly, and for that reason I am hard pressed to recommend them. The aerated channel provides the simplicity of a windrow without the drawbacks.
Any composting system requires a turning mechanism. Compost turners come in all shapes and sizes, and building a channel turner is not more costly than building a normal compost turner. The only difference is that a channel turner is accessible when it breaks down in the middle of a pile, a standard compost turner is not. The channel turner is certainly much cheaper than any of the other indoor compost handling equipment.
Composting channels are fitted with exactly the same pipe and spigot system that are used in bunkers and these aeration pipes also act as drainage systems, allowing the compost maker to re-use the leachate, again saving water and at the same time providing nitrate and nitrite protection for the environment.
Finally, aerated channels can be contained inside plastic greenhouses or can be covered with more permanent structures, turning the aerated channel system in a fully fledged indoor system – at half the cost and 100% of the efficiency.
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