Can bioplastics be treated in conventional anaerobic digesters for food waste treatment?

Abstract

The “European Strategy for plastics” approved by the European Union aims at drastically reducing the use of plastic materials derived from fossil resources, especially single use plastic (SUP). As a consequence, the adoption of biodegradable plastics is forced by different national regulations, especially in France and Italy which banned the usage of single use plastics. Being classified as biodegradable and compostable, the major part of these materials is often collected with the Organic Fraction of Municipal Solid Wastes (OFMSW), basically due by food waste, and sent to biological treatment plants, namely composting and anaerobic digestion for bioenergy recovery or their combination. This study tested the specific methane production and the relative kinetics of the most common single use biodegradable items (carrier bag, cutlery and plates), available on the market. It was demonstrated that sugar cane cellulosic pulp materials have good methane production of 390 L CH4 /kg TVS and a kinetic which is consistent with the anaerobic digestion’s residence time typically applied for OFMSW. On the contrary, starch-based bioplastic and PLA materials remained almost undegraded after 250 days and showed low specific methane production yields in the range 100–200​ L CH4 /kg TVS . The adoption of acidic and basic pretreatments improved the anaerobic digestion performances of starch-based bioplastic and PLA samples. Materials made of poly-hydroxy-alkanoates (PHA) showed higher methane production rates, up to 402 L CH4 /kg TVS in short residence times (around 10 days), which make them adequate to be treated together with food waste in anaerobic digestion plants. • Being labelled as biodegradable, bioplastics are often treated in anaerobic reactors. • Different samples of single use bioplastics were tested for anaerobic degradation. • Starch bioplastic products showed low degradability even at long residential times. • Cellulosic pulp and PHA were consistent with the OFMSW’s anaerobic digestion. • PLA materials had the worst methane production and the lowest hydrolysis rate.