Remembered to take a photo:
The heap on the left is turned every month or two and is about 6 months old. The one on the right is our active bin and will keep adding to it until we use all the left one up around the garden. The left bin was also filled, but over the past 6 months it was reduced in volume by about ⅓.
The front of the bin is open to allow access for turning and also for the wheelbarrow (dropping off materials or taking our completed compost).
When I was involved in a commercial composting operation, the heaps were about 40-50 long, 8m at the base and about 3-4m high. When freshly made, they held around 1200m3 of materials. Over the 8-12 week composting period, the volume reduced by about ¼ to ⅓. The loss of volume wasn’t a concern as the materials had a positive product value (the business was paid to accept materials from a range of difference sources and the loss in volume effectively increased its stock value). Heaps were turned when the temperature reaches 70°C and weren’t allowed to go past 80°C. Past 80°C can cause a range of problems such as the death of the compost (all active microbes are killed stopping the composting process) or lead to spontaneous combustion (if temperature keep rising and the moisture content is right for such conditions). The base mix, turning etc was done to reduce composting times. Regular testing was also carried to ensure that the compost process was completed and that the mixes met relevant statutory and quality requirements.
If you want a good text on composting, it is worth spending the money and getting this book.
