Vermicomposting of a lignocellulosic waste from olive oil industry: a pilot scale study

The vermicomposting with Eisenia andrei of dry olive cake, a lignocellulosic waste produced during the extraction of olive oil, either alone or mixed with municipal biosolids, was studied in a nine-month pilot scale experiment. Number and biomass of earthworms and enzyme activities were periodically monitored and relevant properties of the final products were determined. In the assayed substrates, the total biomass of earthworms increased at the end of the experimental period between 9 and 12-fold respectively in comparison with the earthworm biomass initially inoculated. The increase in hydrolytic enzymes and overall microbial activity during the vermicomposting process indicated the biodegradation of the olive cake and resulted in the disappearance of the initial phytotoxicity of the substrate. However, the recalcitrant lignocellulosic nature of the dry olive cake prevented suitable humification during the vermicomposting process. For this reason, in addition to organic amendments, other management procedures should be considered.