3.2.3. Relationships between microb

3.2.3. Relationships between microbial activity and aeration, friction,
collision
Microbial activity occurs in a three-dimensional space; if we
divide the composting pile into countless equal reaction units
and put these tiny units on a flat surface, the composting process
can be understood as a membrane reaction. Fig. 6 illustrates rapid
degradation mechanism of food waste. It can be observed from the
figure that the oxygen microorganisms need to respire was existed
in a gap between two solid particles. The oxygen transfer process
can be divided into three steps: diffusion in the gas phase, dissolution
at phase interface, diffusion in the water phase. All the diffusion
process followed Fick’s law (Sun and Yang, 2008). According
to the law, the driving force was determined by surrounding conditions
and concentration gradient. The concentration of oxygen is
21% at the beginning of the process (volume fraction of oxygen in
the air), which has the maximum driving force. As composting process
proceed, the concentration of dissolved oxygen was continues
to decrease which triggered the diffusion process and a mixed gas