Biodegradable Plastic Reduces Ammonia Odor Emission during Thermophilic Composting

Abstract

One of the biodegradable plastics, poly- -caprolactone (PCL), was mixed with the composting material, and the quantity of CO₂ that evolved in association with the decomposition of the plastic during thermophilic composting was determined from the difference between the quantity of CO₂ evolution in the presence and the absence of the plastic. Ultimate degradability, defined as a molar ratio of carbon loss as CO₂ to the carbon contained in the plastic that have been added to the composting material, began to elevate about 72 h after the initiation of the composting, indicating that the PCL decomposition occurred vigorously after the middle stages of composting. The ultimate degradability of PCL reached approximately 43.4 % at the end of 7 days composting. The pH value for the composting with PCL was lower than that without PCL throughout the composting period except at the earliest stage of composting. In the composting with PCL, the concentration of NH₃, the greatest nuisance odor compound among the exhaust gases that evolve during the composting process, was half or smaller than that observed for the composting without PCL at the middle stage of composting, and NH₃ was not detected at the later stage of composting. It was thus found out that the PCL degradation causes the decrease in pH value of the composting material and the reduction of NH₃ evolution into exhaust gas.