Composting in Hong Kong: Thermal & Aerobic

Composting in Hong Kong: Thermal & Aerobic

Composting is not a new concept to many people. Farmers used to put all farm and animal wastes together, leaving the pile for some months and then put the materials back into the soil. In some cases, the ‘compost’ works well with crops, while sometimes it may not work at all or even cause problems in soil and crops.

Composting is a common practice. Yet, people seldom look into the science behind composting. It is crucial to understand the microbiology of decomposition, so as to guarantee high quality compost for real benefits in farming. Only through understanding the scientific mechanisms of composting can we revive the ecology in soil and enhance the sustainability of our food production system.

What is COMPOST?
– It is a process of decomposition of different materials originated from living things and their bioactivity in solid form with the aid of “microbiome” in an aerated environment.

Why aerobic?

  • to ensure there is enough oxygen for microorganisms to reproduce and decompose materials in the compost
  • turning the compost at the beginning stage aerates a compost pile

Why thermal?

  • a properly made compost pile with the correct ratio of materials could reach at least 55°C, but not exceeding 65°C at all time
  • the heat of a compost pile could kill weed seeds and plant pathogens, as well as denature antibiotics

 

Recipe for Compost[1]

Mainly three types of raw materials in respective proportion:
(C: N=Carbon to Nitrogen Ratio)

  1. High Nitrogen (N) = FRESH manure, legumes, germ of seeds; C:N around 10.
    In Hong Kong context, we have been using soy bean dreg collected from soy bean product shops. As GMO soy bean is common in the market, we need to test before using.
  2. Green = anything cut when it was green and still contains the sugars, proteins, and carbohydrates; must be dried in order to store; C:N between 30 and 60.
    In our experience, we can use fruit waste, vegetables waste from central kitchen or wet market, or chinese medicine waste
  3. Woody = wood (chips are better than sawdust), stalks, paper, cardboard… anything high in cellulose and lignin; Enhance beneficial fungi during storage. C:N above 60.
    This is the most difficult materials to find in Hong Kong, and easiest to be contaminated by heavy metal. This is why we need to test for heavy metal level in mature compost.

Fungal and Bacterial Balanced Small-scaled Compost Recipe:
Ratio of materials: 10% High Nitrogen, 40% Green Plant Materials, 50% Woody Materials
Volume: at least 1 cubic meter
Generally takes 6 to 8 months to be mature.

Sources and References

[1] Environment Celebration Institute, retrieved from: https://environmentcelebration.com/research/10-steps-to-making-thermal-compost/

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