Vermicomposting of Grape Marc Waste

Vermicomposting was performed in a rectangular metal pilot-scale vermireactor (4 m long × 1.5 m wide × 1 m high). The vermireactor was housed in a greenhouse with no temperature control. A 12 cm layer of vermicompost was used as a bed for the earthworms (Eisenia andrei) before adding the grape marc. The initial earthworm population density in the vermireactor was 297 ± 20 individuals m⁻², including 19 ± 3 mature earthworms m⁻², 215 ± 37 immatures m⁻² and 63 ± 18 cocoons m⁻², with a mean biomass of 58.4 ± 15 g m⁻². Fresh grape marc (158 kg fresh weight) was added to the bed in a 12 cm layer. A plastic mesh (5 mm mesh size) was used to divide the vermicompost bedding from the fresh grape, allowing for earthworm migration and facilitating sampling of the grape marc, but preventing the mixing of processed grape marc and vermicompost bedding. The density and biomass of the earthworm population were determined every 14 days during the trial (91 days) by collecting 10 samples (five from above and five from below the plastic mesh) of the material in the vermireactor. The samples were collected with a core sampler (7.5 cm diameter and 12 cm height).
For sampling of microbial activity and composition, the grape marc layer was divided into 5 sections, and two samples (10 g) were taken at random from each section at the beginning of the experiment and after 7, 14, 28, 42 and 91 days of vermicomposting. The two samples from each section were combined and stored in plastic bags at −80 °C until analysis.