Microbial Degradation of Chromium‐Tanned Leather During Thermophilic Composting: A Multi‐Scale Analysis of Community Dynamics and Structural Disruption

Chromium-tanned leather waste presents a significant environmental challenge due to its resistance to microbial degradation and potential to release toxic chromium compounds. This study aimed to evaluate the biodegradability of wet blue leather through thermo-philic composting without the addition of exogenous microorganisms, and to characterise the associated microbial communities. Composting trials were conducted in 2 L and 40 L Dewar vessels under controlled thermophilic conditions. Gravimetric analysis, scanning electron microscopy (SEM), high-throughput sequencing, and microbial culturing were applied. The small-scale system achieved a 38.94% mass loss, whereas the large-scale composting resulted in the complete disintegration of leather into fragments smaller than 1 cm after approximately 40 days. Metagenomic analysis revealed distinct microbial communities in leather compost, enriched with genera such as Sinibacillus, Bdellovibrio, and Thermomyces, which are known for their thermotolerant enzymatic activity. SEM images confirmed bacterial colonisation and biofilm formation on the leather surface. Cultivable strains with metal tolerance and proteolytic potential were also isolated. These findings demonstrate that composting under thermophilic conditions can effectively degrade chromium-tanned leather. The study also provides a basis for the development of targeted microbial treatments or biotechnological strategies to reduce the environmental impact of the leather industry and support circular bioeconomy approaches in waste management.