Optimization of In-Vessel Food Waste Composting: Enzyme Activity and Microbial Dynamics

A series of greenhouse-based, rotary-drum bioreactor experiments was designed to study microbial dynamics and enzyme activity during optimization of food waste composting. This work aims to optimize food waste composting by defining the best food waste-to-bulking agent proportion controlling conditions and by evaluating the food waste composting process when inoculated by a bacterial inoculant product compared to uninoculated compost. Three experiments were run in total. The two first experiments were conducted for 48 days with sampling at each step of composting, while the third experiment last 50 days and included one extra sampling date. In the first experiment, 50:50, 65:35 and 80:20 (mass:mass) food waste-to-woodchips proportions were evaluated and proportions of 65:35 and 80:20 were retained and evaluated again in experiment 2. The last experiment evaluated the effect of a commercial Bacillus sp. inoculant product on food waste composting and utilized the 80:20 proportion. Proportions of food waste-to-bulking agent in the first two experiments affected water content and enzyme activity. Generally, water content decreased over composting and enzyme activity was greater in the 80:20 compared to 65:35 food waste–to-woodchips proportion compost. The Bacillus treatment increased thermophilic bacteria, but not enzyme activity and enzyme activity increased throughout composting such that it was greatest in the curing stage. Observationally, 80:20 compared to 65:35 food waste–to-woodchips proportion retained composting in the thermophilic and higher temperatures and enzyme activity into the curing stage, which may facilitate decomposition. Inoculation facilitated faster increase into and prolonged retention within thermophilic stage. These effects should be investigated more thoroughly in future research