Investigation of Polyhydroxybutyrate (PHB) Biodegradability in Alkaline Landfill Soil

The increased production of bio-based plastics, such as polyhydroxybutyrate (PHB), raises the need for a thorough understanding of the fate of these materials in natural and controlled disposal environments, such as landfills. However, there is a paucity of knowledge regarding PHB biodegradation at alkaline landfill sites containing incineration ash. This study aimed to investigate the biodegradability of PHB films in alkaline landfill soil (pH 9.7) and campus soil (pH 7). PHB biodegradation was much faster in campus soil (100%) than in alkaline landfill soil (65.2%) after 63 days. Bioaugmentation with Ralstonia insidiosa C1 (Ralstonia sp. C1) enhanced the PHB biodegradability from 13.6% to 35% in landfill soil and from 26.6% to 79.8% in campus soil. Landfill soil had a bacterial CFU of (2.1 × 106) and fungal CFU of (7.3 × 103), which is significantly lower than the bacterial CFU (4.4 × 108) and fungal CFU (1.1 × 107) in campus soil, thereby limiting the biomass required for effective PHB decomposition. Next-generation sequencing revealed that landfill soil lacks key PHB-degrading microbial genera that are normally found in soil, such as Ralstonia, Enterobacter, and Comamonas. In conclusion, PHB biodegradability is strongly affected by alkaline landfill soil, the control of which is the key to ensuring effective in situ bioplastic waste management.