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COMPOSTING

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Source Separated
Organics
Reception at Site
Shredder
Mixer
Technology
Option
Windrows
(Low Tech)
Tunnel Composting
(High Tech)
Maturation
Trommel Screen
Compost
Module 1: Pre-Treatment

Size and shape --- Important in determining microbial activity and airflow within the compost pile:

  • Shredding / grinding / mixing of the feedstock is preferable as a pretreatment step
  • Smaller particle size will result in greater surface area and provide microbes with greater access to their substrate
  • However, if particle size is too small, airflow within will be restricted (anaerobic conditions).

Porosity --- Aids in maintaining aerobic conditions, and increases airflow:

  • Particles with uniform and smooth texture can settle and compact, preventing airflow as well as microbial access to substrate
  • Preferable to include coarser material such as wood chips to increase the void fraction.
Module 2: Active Composting
  • Microbially mediated, controlled decomposition process.
  • Degradation of organic matter into a stable, homogeneous humus-like substance, called compost.
  • Compost can be used as a soil conditioner or soil amendment.
  • Salient requirements for achieving a good break down of organic matter are moisture, oxygen, nutrients and a suitable particle size.
  • Mass reductions of up to 50% and volume reductions of up to 80% can be achieved, as volatile solids in the organic matter get destroyed and exit as CO2.
  • 1 tonne of source-separated organics produces approximately 0.5 tonnes of compost.
Module 3: Curing
  • Hot batch compost needs to be cured, finished off, seasoned before use, allowing partly decomposed compost particles to finish the composting process at a low temperature. Earthworms and other invertebrates will assist with this process.
  • Finished compost will no longer heat up, even after mixing.
  • The initial ingredients are no longer recognizable, and what is left is an earthy smelling substance similar to a rich organic soil.

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