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Simulation of biowastes and biodegradable plastics co-digestion in semi-continuous reactors: Performances and agronomic evaluation
Summary
This study looked at whether "biodegradable" plastics (like those in compostable food containers) actually break down when mixed with food waste in biogas facilities. The good news: one type (PHB) fully broke down, while the other (PLA) only partially degraded unless pretreated with a chemical bath first, meaning some biodegradable plastics may not fully disappear during typical waste processing, which matters because leftover plastic fragments could end up in the fertilizer made from this waste and spread on farmland. The upside is that adding either plastic didn't harm the quality of that fertilizer, but the findings suggest not all "biodegradable"
The development of selective biowaste collection in most European countries provides new opportunities for the anaerobic digestion sector. In parallel, extensive development of biodegradable plastics like polylactic-acid (PLA) and polyhydroxybutyrate (PHB), which facilitates the replacement of conventional plastics, has taken place in the past decade. This study investigated anaerobic co-digestion in semi-continuous reactors of biowastes (75 % Volatil Solids) and biodegradable plastics (25 % Volatil Solids, PLA and PHB). PHB was estimated to be fully biodegraded in the reactors. By contrast, PLA accumulated in the reactor, and an average biodegradation of 47.6 ± 17.9 % was estimated during the third hydraulic retention time. Pretreatment of PLA, by thermo-alkaline hydrolysis at 70 °C, with 2.5 w/v of Ca(OH)2 for 48 h, improved the biodegradation yield of PLA to 77.5 ± 9.3 %. Finally, it was highlighted that PLA or PHB addition to the feed did not further affect the agronomic properties of the digestate.