Meaning
Biological digestion occurring at moderate temperatures represents the initial stage of the industrial composting process where bio-polymers begin their physical breakdown. During the mesophilic phase, which occurs between twenty and forty-five degrees Celsius, specialized fungi and bacteria colonize the compost pile and consume easily degradable sugars. This activity generates the initial heat that transitions the pile into the high-temperature stage required for polymer chain cleavage.
Polymer Response
Thermoplastic starch and other highly amorphous biodegradable resins begin to absorb moisture and soften during this low-temperature stage. Although the main chain-scission of polylactic acid occurs at higher temperatures, the preliminary hydrolysis that starts during the mesophilic phase is essential to prepare the polymer structure for subsequent microbial attack. The rate of water absorption at this stage determines the overall speed of the disintegration process.
Microbial Transition
As the temperature rises past forty-five degrees, the mesophilic microbial population declines and is replaced by heat-tolerant species. This transition must occur smoothly to ensure that the decomposition of organic matter is uninterrupted. If the compost cools prematurely, the system returns to the mesophilic phase and prolongs the total time needed to degrade the plastics.
Process Duration
Maintaining this phase for a short duration prevents the excessive consumption of nutrients before the high-temperature sterilization begins. Most industrial operators aim to transition the compost pile rapidly to maximize throughput.
