Microbial inoculation enhanced the thermophilic phase and improved final maturity-related properties of coffee husk...

Coffee husk composting is constrained by high lignocellulose content, slow decomposition, and residual phytotoxicity. Whether microbial inoculation can accelerate this process while producing a horticultural growing medium remains unclear. We compared coffee husks composted with a commercial microbial agent (a consortium of photosynthetic bacteria, lactic acid bacteria, yeast, filamentous fungi, and actinomycetes) (CHM) versus without (CH) over 180 days. The CHM treatment reached a higher peak temperature (55.6 °C vs. 43.5 °C) and at the end of composting achieved a numerically greater seed germination index (93.2% vs. 71.2%), indicating enhanced maturation and reduced phytotoxicity. High throughput sequencing showed that CHM did not drastically alter overall microbial α diversity but the final compost exhibited a marked reduction in the relative abundance of the genus Fusarium compared to CH. Beneficial bacterial genera such as Pseudomonas, Sphingomonas, and Alcaligenes showed a non-significant but consistent trend toward enrichment in CHM. When the mature CHM compost was blended with vermiculite, perlite, and decomposed cow manure, blends with lower compost inclusion (1:5 or 1:3 volume ratio of CHM compost to other components) supported tomato seedling growth comparable to a conventional peat based medium. These results demonstrate that microbial inoculation promote a more intense thermophilic phase and enhances final maturity in coffee husk composting, yielding a product with potential to partially substitute for peat in horticultural substrates. This approach offers a practical strategy for recycling coffee processing byproducts into a compost-based growing medium component.