Thermal Aerated Composting
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 soil. In some cases, the “compost” works well with crops, while it may not work at all or even cause problems in others.
Composting is a common practice. Yet, people seldom look into the science behind composting. It is crucial to understand the microbiology of decomposition to guarantee high quality compost for consistent benefits in farming. Only through understanding the science 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 and how to aerate it?
To ensure there is enough oxygen for beneficial 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 could kill weed seeds and plant pathogens, as well as unwanted chemical residues.
Recipe for thermal aerated composting
Mainly 3 types of raw materials in respective proportion:
(C: N=Carbon to Nitrogen Ratio)
High-Nitrogen (N) material: fresh manure, legumes, germ of seeds, etc. with 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.
Green material: anything cut when it was still green with 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.
Brown material: anything high in cellulose and lignin like wood (chips are better than sawdust), stalks, paper, cardboard, etc. with 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. It enhances the growth of beneficial fungi.
Fungal and Bacterial Balanced Small-scaled Compost Recipe:
- Ratio of materials:
10% high-N materials in between layers of 40% green and 50% woody materials is good. - Volume:
1 cubic meter is the minimal for the heat to build up. - Temperature:
The pile needs to get to above 55 ºC within 3 to 7 days from starting. Turn the pile when it starts to reach 71-74ºC as the organisms are growing so fast that they are using up all the oxygen in the pile.The pile must maintain temperature above 55ºC for a full 10-15 days. - Finished pile:
Generally takes 6 to 8 months for a pile to be mature when the temperature returns to ambient.