Changes in the nutrient dynamics and microbiological properties of grape marc in a continuous-feeding vermicomposting...

Finding strategies to reuse and treat organic wastes is of utmost need. Biological processes offer the possibility to transform them into safer end products with benefits for both agriculture and the environment. Moreover, it represents an ecologically-sound and economically attractive alternative to landfill disposal and incineration. In this work, we evaluated the feasibility of vermicomposting to treat and process grape marc, the main solid by-product of the wine industry. The long-term changes in grape marc derived from both white and red winemaking processes were assessed throughout the process of vermicomposting from a physico-chemical and microbiological perspective. New layers of fresh marc were added sequentially in the presence and absence of earthworms (Eisenia andrei) forming an age gradient during a 42-week period. An optimal moisture level of 70% was maintained over the course of the process. The pH fell within weak-alkaline levels through the layerś profile and the electrical conductivity was between 200 and 300 µS cm^-1, providing optimum conditions for earthworm growth. The mass loss caused by earthworm activity led to an increased content of macro- and micronutrients at the end of the trial. An overall decrease in microbial biomass and its activity, indicative of a stabilised material, was also recorded with depth of layer. Altogether, this points to vermicomposting as a suitable management system for processing grape marc with a dual purpose, that is fertilizer production and environment protection. This is especially relevant in the current attempts to reach a fully circular economy.