A digest of the microbiology of composting
The biological process of composting basically uses four stages of micro-organism activity which can be identified by the heat produced at different times. Not every technique uses all stages. Home composting, for example, rarely achieves the Thermophillic stage and therefore does not require a cooling stage either.
Mesophilic stage
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At the beginning, the bugs operate at ambient temperature to break down material. These include fungi, bacteria and actinomycetes. At this stage, acarines, millipedes and isopods will eat through the waste. The soft tissue of the decaying plants supports growth of nematodes and enchytraieds.
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As in any food chain, these creatures then attract predators to feed on them – collembolans eat fungi, ptiliids feed on fungal spores. Nematodes, protozoa and rotifers feed on bacteria.
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The energy released during this feeding frenzy causes a rise in temperature to between 45 and 70°c.
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Thermophilic stage
At these higher temperatures a specialised group of bacteria, fungi and actinomycetes take over.
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The organic degradation happens very quickly then and pathogens, fly larvae and weed seeds are destroyed, partly by the heat.
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Cooling stage
As thermophilic activity declines and temperature falls to 30-40° there is another series of organisms capable of growth at normal temperature and these start to develop in the compost.
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Maturation stage
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Finally, if you leave the compost in a heap, the nitrification stage begins and ammonia turns into nitrites and the nitrates. This is the material that makes plants grow.
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