Investigation of the Effects of Waste Olive Pomace on Vermicompost

The effects of olive pomace on the degradation of organic matter were investigated via vermicomposting. Biomass consisting of eggshell, cabbage, banana peel, napkin, nutshell, cattle manure, and soil was amended with varying amounts of olive pomace (0, 15, 30, 37.5%). These four mixtures, with a total of 2000g, were fed to 170 Eisenia fetida earthworms per mixture. Nitrogen adsorption-desorption, FT-IR, and elemental analyses analyzed samples collected from biomass at the end of 45 days. Results were evaluated to determine the effect of olive pomace on organic matter degradation and earthworm vitality. Nitrogen adsorption-desorption isotherms of feedstock revealed a decrease in void volumes, implying the formation of a compact structure with olive pomace addition. Vermicomposting of biomass enhanced biomass’s compactness, further validated by decreases in BET surface areas, pore sizes, and pore volumes. The 31% increase of earthworm biomass in the presence of 37.5% olive pomace implied an affinity of Eisenia fetida towards olive pomace. This finding was further validated by FT-IR peaks obtained at 2850 and 2923 cm-1, showing increased biomass aromaticity due to the degradation of readily biodegradable aliphatic structure introduced by olive pomace. Ongoing organic matter degradation could be observed with the decrease of C/N ratios in the presence of olive pomace as high as 15%. However, a further increase in olive pomace increased the C/N ratio, which was explained by the increase in total nitrogen values during vermicomposting. Elemental analyses evaluated regarding C/N, O/C, and H/C ratios also indicated increased earthworm mobility with increasing olive pomace in the feedstock. The results obtained in the study were interpreted to introduce olive pomace as a preferable nutrition source for earthworms, which was the highlight of the present study