Résumé
Compostable materials represent an innovative solution to reduce the environmental impact of plastic materials, by providing an alternative route for end-of-life treatment. With the mandatory separation of bio-waste at source, some of these materials could be treated in industrial composting plants in combination with food waste, and thereby contribute to the circular bioeconomy by creating valuable compost, which serves as a beneficial organic soil amendment for agriculture. However, while lab-scale measurement methods exist to certify the biodegradability of a material under industrial composting conditions, they cannot perfectly replicate the real processing conditions. The presence of biodegradable food packaging therefore represents a challenge for organic waste management processes, and it is crucial to assess their biodegradation performance under real conditions. A large-scale experiment was carried out on 40 tons of biowaste directly collected from households at an industrial composting station using open-air windrow technology. After manual cleaning, two batches of 20 tons containing the same initial biowaste mixture were studied, one as “Control” and the other as “Materials” in which 1.28 wt% (323 kg) of certified compostable plastics have been introduced. The composting process of the two batches was monitored for 4 months, during which time representative samples were taken to analyze the degradation mechanism of each major family of compostable materials (e.g., starch blends, PLA, polyhydroxyalkanoates (PHAs)). The data generated by this experiment were used for assessing the environmental impacts of composting process versus incineration of the plastics.Results indicated that no effect of the incorporation of these compostable materials on the composting process was observed. An analysis of the safety and quality of the final compost, carried out by an independent accredited laboratory, certifies that the "Materials" compost complies with the requirements of standard NF U44-051 relating to compost and organic soil improvers, as well as with organic farming criteria. No ecotoxicity has been demonstrated on plants, earthworms or daphnia. Agronomic fertilizing and amending quality were high, the "Materials" compost even enhancing barley growth. The compostable materials showed rapid biodegradation after 4 months with around 2 wt% of very small residual fragments consisting mainly of PHA, which disintegrated more slowly due to geometric factors. The evolution of the morphology of the materials revealed specific degradation mechanisms depending on the polymers introduced. The environmental assessment demonstrated an advantage for composting over incineration for seven of the eight indicators considered.This large-scale composting study evidenced the successful integration of compostable materials with biowaste upholding product safety and quality. The compostable materials lost 98% of their mass in less than 4 months, which is the usual composting time. The environmental assessment indicated that composting biodegradable plastics with biowaste had less impact than incineration. In short, compostable materials can be part of sustainable waste management strategies.