Physicochemical, microbial, and microbiome dynamics in winery waste composting

Compared to more extensively studied composting substrates like food waste or animal manure, winery waste presents unique challenges and opportunities. Its high content of lignin, cellulose, and polyphenolic compounds demands specific microbial consortia for efficient degradation and can potentially inhibit microbial activity if not properly balanced. In the present study, analysis of winery waste composting that combines traditional microbial enumeration with high-resolution microbiome profiling, an approach rarely applied to this type of agro-industrial residue, was implemented. Moreover, a practical proof-of-concept study, for using the composted product as a partial substrate replacement in grapevine cultivation, closing the loop in vineyard waste management, was conducted. Key parameters, such as moisture content, pH, temperature, conductivity, and C/N ratio were monitored, over a 60-day period, along with changes in enzymatic activity and shifts in microbial populations, indicating dynamic microbial activity. At the end of the process, a reduction in the carbon-to-nitrogen (C/N) ratio was observed, pH was stabilized to neutral values, and dehydrogenases activity was notably decreased. Microbiome analysis revealed eight bacterial and six fungal phyla. Acidobacteria, Armatimonadetes, Bacteroidetes, Candidatus Saccharibacteria, Chloroflexi, Cyanobacteria, Planctomycetes were identified. The Ascomycota, Basidiomycota, Chytridiomycota, Entomophthoromycota, Glomeromycota, and Mucoromycota fungal phyla were also detected. The compost exhibited no phytotoxicity and supported grapevine growth comparable to commercial substrates. Winery waste microbial composting led to stable biofertilizer production, evidenced by physicochemical stability, lack of phytotoxicity, and effectiveness in promoting grapevine growth suggesting the potential of composting as a sustainable waste management solution in the winemaking industry.