The effect of applying treatment sludge and vermicompost to soil on the biodegradability of poly(lactic acid) and poly(3-hydroxybutyrate)

Abstract

In this study, the biodegradability of poly(lactic acid) (PLA), the most widely produced bioplastic, and poly(3-hydroxybutyrate) (PHB), known for its very biodegradability, was investigated in soil and soil amended with nitrogen sources, such as treatment sludge and vermicompost. Biodegradability was evaluated over 180 days by measuring the amount of carbon dioxide (CO2) and analyzing samples with scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). PLA showed a low biodegradation (6%) in soil, but this increased to 40% in soil amended with treatment sludge and 45% in soil amended with vermicompost. PHB completely degraded within 90 days in soil; however, this process extended to 120 days in soil amended with vermicompost and 150 days in soil amended with treatment sludge. The organic and microbial content of the amendments enhanced PLA biodegradation, while PHB degradation slowed after 50 days as microorganisms prioritized other organic matter. SEM and FTIR analyses after 60 days showed more intense degradation of both bioplastics in soil amended with vermicompost. These findings highlight the potential of treatment sludge and vermicompost for improving bioplastic degradation, contributing to sustainable waste management and soil enhancement.