Effect of thermophilic composting duration on vermiconversion of olive mill wastewater using Eisenia andrei

Abstract

This study aimed to investigate the effect of different durations of thermophilic composting (TC) on the enhancement of vermicomposting of olive mill wastewater (OMWW). Four mixtures consisting of olive cake, horse manure, and wheat straw, soaked with varying ratios of OMWW (0 %, 25 %, 50 %, and 75 %), were subjected to TC. Following TC durations of 15, 30, 45, and 60 days, the mixtures underwent vermicomposting. Overall, each OMWW ratio demonstrated an optimal TC duration that resulted in maximum earthworm performance. As the OMWW ratio increased, the optimal TC duration extended from 30 to 60 days. The combined TC and vermicomposting process exhibited a final C/N ratio of 13.5 and 95 % decrease in phenolic compounds. The germination index confirmed higher phytostimulant effect of the final product. These findings highlight the positive role of the optimal TC duration allowing the vermicomposting of a substantial quantity of OMWW, thus contributing to olive wastes treatment.