Evaluation of vermicomposting of 2- phase olive mill waste (OMW) to produce a soil amendment

Abstract

This study investigates the potential utilization of Olive Mill Waste (OMW) vermicompost as a soil amendment. With the continuous production of OMW as a byproduct of olive oil extraction, it is an imperative need to find sustainable solutions to utilize it, in order to mitigate the contamination of agricultural land and the disposal in natural water streams. Without a common European legislation, the problem of waste disposal is becoming increasingly challenging. In response, this study aims to explore potential solutions by investigating vermicomposting of four different OMW treatments (OMW 0, OMW 25, OMW 50, and OMW 75). All treatments consisted of mixtures of OMW, raw manure, and composted manure in different proportions. The experiment spanned two months and the findings confirmed the potential use of OMW vermicompost as a soil amendment. Initially, it was found that OWM is not harmful for earthworm consumption, as the earthworms from all treatments significantly increased their biomass up to 50%. Furthermore, after measuring the physical properties of the mixture, it was found that vermicomposted OMW can stabilize the pH at around 7 to 8 and the EC at around 0.6 0.8 mS/cm. In the germination phase of lettuce seeds, all treatments exhibited good responses, with the low OMW treatments experiencing a greater germination rate. However, there were no statistically significant differences observed, and no toxicity issues occurred in the young seedling. After creating three different extracts of the four OMW treatments with 25%, 50%, and 75% OMW content it was found that in 25% extract no statistically significant differences were observed in stem length across all treatments. On the other hand, in root length it was observed that as the quantity of OMW increases in the 25% extract, root length experienced higher increase. In the same pattern, in the 75% extract, no differences were observed between all OMW treatments and control in stem length. Additionally, in root length measurements, all OMW treatments in the 75% extract exhibit larger root compared to control. In the OMW 25 and OMW 75 treatments, a slight increase was observed in higher OMW concentrations in stem length compared to control, without statistically significant differences. Tremendous differences were observed in root length as in both treatments, as the concentration increased, the root length values were significantly increased compared to control. Overall, the potential use of OMW vermicompost as a soil amendment seems to be a viable and sustainable management practice.