Numerical framework for anaerobic digestion and/or composting of bioplastics and organic waste performance evaluation under real-like large scale operating conditions

Bioplastics are newly designed and developed plastic materials to meet the criteria of sustainability and sustainable development that present the following characteristics: biobased, biodegradable or both properties. They include a whole family of materials with different properties and applications. Bioplastics certified as biodegradable and/or compostable, according to the regulatory plan of Italy and other countries around the world, must be collected with organic waste and follow the same end-of-life path, i.e., organic recycling processes in anaerobic digestion and/or industrial composting plants. However, it should be noted that they are certified according to tests carried out under standardized optimal degradation conditions, that is, conditions that are not always the same as those found in the operation of anaerobic digestion and composting plants. Improper management of these materials can become an increasing problem as their continued widespread use will require large volumes of these materials to be treated in facilities that are not designed to biodegrade bioplastics, resulting in potential contamination of large volumes of undegraded bioplastics in digestate and/or compost produced in the treatment of conventional organic waste. The purpose of this work is to investigate the degradation of the most popular bioplastics currently collected with organic waste through separate collection under the actual operating conditions of waste recycling plants operating through biodegradation processes. Specifically, using both studies conducted at the laboratory scale and evidence of biodegradation plant configuration and operation at the real scale, the Aspen Pus V12 program was used to model and simulate an anaerobic digestion process integrated with a composting process. This evaluated the level of biodegradation, expressed as a percentage of degraded mass, as a function of the implemented process conditions such as temperature and hydraulic residence time (HRT). The bioplastics that have been focused on, certified as compostable, are PLA (rigid disposable containers: cups) and starch-based shopping bags (SBS). The results achieved show that through an anaerobic digestion process alone, after 28 days in thermophilic conditions, PLA can degrade by 42%, and SBS by 44%. The integrated anaerobic/aerobic process provides a biodegradation performance allows 85% and 56% for SBS and PLA, respectively, in case the biopolymers are subjected to 28 days of thermophilic anaerobic digestion and 90 days of composting.