Methods in Compost Manufacture are covered extensively on numerous sites across the net and thus the following is provided not as an alternative to those sites, many of which are extremely good, but as an addition.
Below is an explanation of the environmental conditions that need to be created to encourage the microbiological processes we call Composting. It is provided to give composters a better understanding of the processes they are trying to encourage.
Howards original Indore Method and the New Zealand Box concept
Compost heaps and the containers and methods used to construct them need to conform to certain rules. When Howard originally developed the Indore composting method he did so using shallow pits, which he believed aided moisture preservation. However in most climates composting in pits is both time consuming and more likely to lead to compost becoming waterlogged during wetter periods.
Thus for convenience most composting is now done above ground, and whilst there are various methods and contraptions to accomplish this the most reliable and simple has proved to be the New Zealand Box method.
A simple ‘open box’ construction the New Zealand box is built directly on the ground. With no bottom and with only sides the container both insulates the heap and permits for adequate aeration.
The sides themselves are not built directly on the ground but are often raised 6″ or so to facilitate aeration.
To preserve moisture and heat further the top of a constructed heap is often covered with sacking, old carpet or cardboard. Finally to keep rain out the container is covered by congregated or plastic sheeting. However such covering should not interfere with air flow. Such containers can be constructed singularly, as in the diagram above, or in modular formation as in the moderately sized operation in the photo below.
The materials needed for constructing a New Zealand Box system need only conform to a few practical rules:
- The material must be weather-able and provide insulation
- It must be reasonably resistant to but not chemically treated against the effects of microbial decay and weathering (a usable life of not less than one year)
- easy to handle
- cheap and readily available
Examples include wooden panels and old doors, corrugated sheeting, wooden planks, fencing panels and recycled pallet boards. Containers can even be constructed from old straw bales or compressed cardboard.
Compost Box Dimensions
The last and most important thing to consider with respect to construction of a container is it’s size. In order for the microbial communities to bloom they need a minimum amount of substrate with a sufficient volume to surface area ratio to preserve the environmental conditions. Below this quantity heat and water are lost faster than the microbial action can generate and recycle it. The point at which this is reached depends on many factors but in practice the minimum size for a compost container is 1m x 1m x 1m (a cubic metre).
There is similarly a maximum size too. The heap is dependent on a constant and sufficient air supply that is supplied by natural permeation, usually from the bottom of the container, into the heap. This natural permeation of air decreases towards the centre of the heap and at distances of more than one meter the flow rate is insufficient to maintain the microbial communities. As a rule of thumb a single heap should not exceed 2m x 2m x 2m (eight cubic metres) and ideally be no more than 1.5m in height.
Locating a Compost Bin
Perhaps the only other remaining consideration in construction of containers is location. From an operational perspective ease of access is the priority: composting is heavy work with bulky items and if an operation is sited far from the feed stocks it will greatly increase the effort and time needed to work it. Similarly situating a compost operation on sloping land will greatly increase the amount of energy needed to move material.
Therefore a compost operation should be located on flat land that is easy to access and close to the feed stocks. That said sites which are prone to water logging or are close to surface or drinking water sources should be avoided.
As a rule of thumb composting operations should not be sited within 10 metres of a surface water (river, stream, pond) or 50 metres of a drinking water source (spring, well, bore hole). These though are precautionary distances which assume ‘worst case scenario’ For most small to medium sized operations a ‘worst case scenario’ is highly improbable and so a simple 10 metre rule for all water sources is sufficient.
constructing a thermophillic compost heap (youtube)
next: Compost Architecture
Free Cultural Works (CC-BY-NC-SA) Malcolm McEwen 2011