Biotic and abiotic factors of biodegradable plastic degradation in biowaste valorisation systems: understanding as a first step to eco-design – BioCyPlast
How to make biodegradable plastics truly biodegradable?
Most so-called “biodegradable” plastics do not completely degrade in biowaste management channels nor in the natural environment. In order to develop materials without any risk for the environment, we need to better understand their degradation mechanisms and integrate these criteria right from their design.
Understanding today to better design tomorrow
Plastics have become a major source of environmental pollution and health concern. This pollution arises from direct discharge in the environment (agricultural films, wastewater) and from leaks out of waste management systems. Among them, plastic bags, films and food packaging are difficult to sort out and recycle in household waste management systems. Soiled and damaged, they end up “at best'' in incineration, “at worst” in landfills or in the environment where they generate micro- and nanoplastics (MNPs) and represent a major threat to the environment and health. In Europe, 23 million tons of plastic packaging are wasted every year, generally after a single and very short use. About 32% leak out from collecting and sorting systems and end up in the soil and oceans. <br />To limit this pollution, biodegradable plastics have been developed. They can be discarded with organic waste and treated in biowaste management systems such as composting facilities. Well-known examples are the starch-based compostable plastic bags used for the selective collection of food waste. However, two drawbacks remain: 1st, some of these plastics are not completely biodegradable; 2nd, others are not biodegradable at all during anaerobic digestion process. This leads waste managers to report incomplete degradation of so called «biodegradable plastics« during anaerobic digestion and even sometimes during composting.<br /> To improve biowaste and plastics valorisation, we must develop materials that degrade completely during biowaste management, regardless of the system. However, the rules linking material formulation and its biodegradation are still poorly understood, particularly for anaerobic degradation. We hypothesise that designing such material requires: i) to determine the key parameters (physical, chemical and microbiological) responsible for their degradation in biowaste management conditions; ii) to implement these parameters in eco-design models that include the material end-of-life as an intrinsic property, acknowledging that this may also require the adaptation of waste management systems.<br />In this context, the BioCyPlast project sets up an integrative strategy based on: <br />• Selecting commercially available biodegradable materials and producing tailored made ones (with different formulation, structure, size, crystallinity...) dedicated to the study of their biodegradation (WP1),<br />• Monitoring experimentally their fragmentation and assimilation under controlled conditions of composting and anaerobic digestion using specific analytical methods (WP2 & WP3),<br />• Developing innovative tools to better monitor and understand the mechanisms of plastic colonisation and disintegration up to the generation of nanoplastics (WP3),<br />• Integrating all these data into predictive modelling approaches to anticipate the ecological footprint of biodegradable plastics, from material conception to biowaste management systems (WP4).
This 48 months project has four technical work packages (Figure):
WP1 – Provision of pristine and treated materials through abiotic pre-treatments
This WP will supply the entire project with commercial or tailor made materials, and test the impact of various pretreatments likely to change their intrinsic properties and affect their biodegradability (grinding, UV irradiation, oxidation, thermal treatment). Three types of materials will be studied as film or grinded film:
• positive and negative controls of biodegradation, respectively a cellulosic (e.g. Kraft) and a polyethylene material
• commercially biodegradable and/or compostable materials such as starch-PBAT (Polybutylene adipate terephthalate, e.g. Mater-Bi) bags and Polylactic acid (PLA) food ware.
• tailored made biodegradable composites with perfectly controlled formulation and properties, made of PolyHydroxyButyrate-Valerate (PHBV) with various percentages of cellulosic filler.
The properties of all these materials will be determined in WP3, while their biodegradability during simulated composting and anaerobic digestion will be assessed in WP2.
WP2 – Materials biodegradability
This WP will carry out experimental trials at lab and pilot scales to determine the biodegradation mechanisms of pristine and pre-treated materials from WP1 in simulated biowaste composting, anaerobic digestion reactors and natural environment (Ecotron). Several process parameters will be tested for composting and anaerobic digestion such as the inoculum origin, the inoculum/substrate ratio, temperature (mesophilic or thermophilic), etc. Processes parameters and microbial community’s dynamics will be monitored while properties of the deteriorated materials will be analyzed over time in WP3. The results will provide data to WP4 for designing new materials that better fit the biodegradation criteria required for composting and anaerobic digestion.
WP3 – Material properties
This WP is dedicated to the analysis of pristine, pre-treated and biodegraded materials by classical methods such as SEM, FT-IR, pyrolysis-GC-MS, DRX, DSC, EA-IRMS etc. and to develop new methods for NMR monitoring of biodegradation and MNPs extraction and characterization. A biofilm culture reactor will also be developed to characterize the attached microbial populations.
WP4– From understanding to eco-design
The WP4 will integrate all the knowledge acquired along the project in the eco-design approach of partners such as such as the ongoing STR (Structure-Transfer-Reaction) approach. Additional criteria related to biowaste management chains such as collection, sorting, treatment conditions, etc. will be considered for integration into the Decision Support System of partners in close collaboration with the key partners of the materials life chain. This will allow adjusting the material formulation and elaborating suggestions for key stakeholders such as materials producers, policy makers, waste managers and citizens.
The expected results are:
• the determination of the abiotic and biotic factors involved in materials biodegradation,
• the definition of the specifications required for the end-of-life of biodegradable plastic packaging materials in biowaste management chains,
• the development of new tools to better monitor plastic colonization and disintegration up to the generation of nanoplastics,
• the identification and characterisation of microbial strains and enzymes involved in the disintegration and assimilation of plastic polymers, and
• the production of recommendations for biowaste collection and management in waste valorisation systems.
Being at the beginning of the project, our perspectives are:
1. To acquire knowledge on the mechanisms of disintegration and degradation of the studied materials under the conditions of composting and anaerobic digestion of bio-waste.
2. To identify pre-treatments and/or key microorganisms that will improve the biodegradation of materials.
3. To develop a material based on PHBV and cellulose that is:
• Totally biosourced, with polymers of non-food origin,
• Completely biodegradable in the shortest possible time, whatever its environment and without releasing MNPs
• Usable for the design of food packaging if possible.
Members of the consortium have been accepted for a session keynote at the 9th International Conference on Engineering for Waste and Biomass Valorisation WasteEng2022, to be held in Copenhagen (Denmark), June 27-30, 2022 to present a literature review on biodegradable plastics degradation in anaerobic digestion.
Managing the end-of-life of plastic materials is the key challenge to fight plastic pollution. Besides plastic recycling, biodegradable plastics have been developed that can be discarded with organic waste to be valorised through biowaste management systems. However, the ability of these materials to completely biodegrade within these systems is highly controversial and poorly understood, particularly under anaerobic digestion conditions.
In this context, the BioCyPlast project aims to lay the foundations for a better understanding of the biotic and abiotic mechanisms of degradation of biodegradable plastics during composting and anaerobic digestion. The research strategy is based on the study of material degradation dynamics as function of the biopolymer type, formulation, structure, and physicochemical and biological conditions. New analytical methods will also be developed to monitor material colonisation by microorganisms and material degradation up to nanoplastics and beyond. The gained knowledge will be integrated into predictive modelling approaches to support the specifications of future biobased biodegradable plastics and anticipate their ecological footprint, from material conception to biowaste management systems. Recommendations will also be made to improve biowaste valorisation systems.
Project coordination
Patrick DABERT (Optimisation des procédés en agriculture, agroalimentaire et environnement)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
Partnership
UMR 6118 GEOSCIENCES RENNES
OPAALE Optimisation des procédés en agriculture, agroalimentaire et environnement
IATE Ingénierie des Agropolymères et Technologies Emergentes
Help of the ANR 503,906 euros
Beginning and duration of the scientific project:
December 2021
- 48 Months
