Assessment of the influence of inoculum substrate ratio on biochemical methane potential test of biodegradable plastics and on the active microbial community.

The inoculum-substrate ratio (ISR) is a critical parameter for performing reproducible biochemical methane potential test. The influence of ISR on the mesophilic and thermophilic biochemical methane potential test of two biodegradable plastics was evaluated. Poly(lactic acid) (PLA) and Polyhydroxybutyrate (PHB) were selected for this study, the first for being recalcitrant to mesophilic anaerobic digestion (AD) and the second by contrast for being readily biodegradable under AD. Several ISR were tested: 1, 2.85, 10 g(VS).g(VS)-1. An increasing ISR was associated with an enhanced biodegradation kinetic. However, the biodegradation yield was not changed. ISR of 1 on PHB resulted in an inhibition of the methane production due to accumulation of volatil fatty acids and acidification of the reactors.