Heavy oil, due to its complex hydrocarbon structure and resistance to degradation, poses significant environmental challenges. There is a lack of knowledge about the biodegradability of heavy oil in the natural environment under aerobic and anaerobic conditions. In this study, we used microbial communities of water and soil samples to investigate the biodegradation of heavy oil. Gas chromatography (GC) analysis was used to measure residual oil. Under aerobic conditions, soil-derived microorganisms demonstrated significantly higher degradation efficiency—achieving up to 80.3% removal—compared to water-derived samples, which showed a maximum degradation of 52.1%. Anaerobic conditions, on the other hand, clearly slowed down degradation; the maximum degradation rates in water and soil samples were 43.7% and 11.1%, respectively. Although no clear linear relationship was found, the correlation between initial microbial populations and degradation performance revealed that higher counts of heterotrophic and oil-degrading bacteria generally enhanced biodegradation. Under anaerobic conditions, especially, persistent hydrocarbon peaks in both environments suggest the presence of recalcitrant heavy oil fractions such as polycyclic aromatic hydrocarbons. In conclusion, this study emphasizes the crucial roles microbial sources and oxygen availability play in maximizing bioremediation techniques for environments contaminated with heavy oil.

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.

Polyhydroxybutyrate (PHB) composites represent a promising sustainable solution to address the environmental challenges posed by conventional polymers across multiple sectors. This comprehensive review synthesizes current knowledge on PHB-based composites, examining their development, performance, and biodegradation characteristics in diverse applications such as packaging, biomedical devices, agriculture, aerospace, and environmental remediation. Various composite fabrication methods, including melt blending, solution casting, electrospinning, and in situ polymerization, are evaluated for their impact on functional properties. Natural fiber- and nanomaterial-reinforced PHB composites are critically analyzed for their mechanical integrity, thermal stability, surface chemistry, biodegradability, and environmental compatibility. Practical challenges, including manufacturing scalability, cost-effectiveness, and long-term stability in complex environments, are discussed within circular economy and regulatory frameworks to situate PHB composites for realistic industrial and environmental deployment. This review provides timely insights for researchers and practitioners aiming to develop environmentally compatible, scalable biopolymer-based solutions across multiple domains.

Low temperatures increase the viscosity of heavy oil and limit the solubility of short-chain alkanes, which increases their toxicity to microorganisms and delays biodegradation. This study aimed to isolate efficient heavy oil-degrading bacteria from contaminated soil and sewage sludge to evaluate their potential for bioremediation under cold climate conditions. Using enrichment culture with heavy oil as the sole carbon source, two potent strains (designated C1 and C2) were isolated from the Japanese soil, and a third strain (C3) was isolated from the Korean sludge. All three strains were identified as Pseudomonas aeruginosa via 16S rDNA sequencing. Residual oil was estimated using Gas chromatography analysis. At 30°C, C1, C2, and C3 showed 57%, 51%, and 33% after 7 days, respectively. At 15°C, degradation was delayed by a lag phase, suggesting a temperature-dependent metabolic activation. At 10°C, C3 displayed negligible activity, whereas C1 and C2 degraded 49% and 12% in two weeks. Notably, at 5°C, no activity was observed in 7 days. However, 35% degradation was observed by C1 and C2 after 98 days. The strains C1 and C2 also showed 60% and 70% heavy oil biodegradation in artificially contaminated soil at 5°C. In conclusion, these Pseudomonas strains, especially C1 and C2 demonstrated the ability to degrade heavy oil in low-temperature environments and can contribute to environmental sustainability.

The removal of heavy oil under low-temperature conditions is a significant global challenge. This study aimed to assess the long-term whole-cell biocatalytic degradation of heavy oil in water and soil by bacteria isolated from contaminated soil in Muroran, Japan, under cold conditions. Enrichment cultures using heavy oil as the sole carbon source yielded 15 potent heavy oil-degrading isolates. However, only the C1 strain retained its activity under low-temperature conditions and was identified as Pseudomonas aeruginosa C1 using 16S rDNA sequencing. Gas chromatography analysis revealed that at 30 °C (water medium), strain C1 degraded 57% of heavy oil within 7 days. At 15 °C, the degradation efficiency of C1 declined due to a temperature-dependent metabolic lag phase (1 day); however, at 15 °C, 70% degradation was observed in seven days. In long-term experiments at 5 °C and 10 °C, 35% and 40% degradation were recorded for C1 after 98 days. In artificially contaminated soil at 5 °C, C1 achieved 60% biodegradation. These results demonstrate cold-adapted whole-cell activity against heavy oil and motivate the design of controlled, contained ex situ reactors (e.g., enzyme-based or cell-free systems) for safe remediation in cold climates.