COMBINATION OF COMPOSTING AND VERMICOMPOSTING OF OFMSW: A CASE STUDY IN SICILY

Abstract

Earthworms elaborate huge amounts of plant debris by ingesting it and converting it into vermicast, the final product of the worm digestion process. Vermicast is widely recognized as a suitable organic fertilizer for plants. To date, controlled vermicomposting of organic matrices, different than bovine manure, such as for example the organic fraction derived from biodegradable solid waste (OFMSW), has recorded contradictory results, effectively limiting the extension of laboratory results to in initiatives on a larger scale than vermicomposting. The most "fruitful" organic substrates remain animal manure and/or selected food waste. In order to deepen the topic, in this study a combined process of composting-vermicomposting was analyzed with Eisenia fetida for the treatment of OFMSW, mixed with a more suitable substrate for earthworms consisting of a mixture of litters animals and pre-selected food waste (OM – pre-selected Organic Matter). As far as OFMSW is concerned, three different fractions from a real plant in the municipal waste management sector (Sicily) were analysed: OFMSW as it is, pre-composted (PC, meant as an organic matrix that has completed the thermophilic biodegradation phase) and Compost (C). The laboratory tests involved 5 different applications with different mixing proportions, partly assisted by the addition of pre-selected organic matter (OM). The physicochemical parameters and growth ratio of the worms in the different treatments were measured and compared. The results showed that the combined process increased the quality of the final product, especially for the selected matrices and for the pre-treated OFMSW, with a fertilising product that appeared homogeneous, granular, odorless and rich in nutrients. In particular, the physicochemical analysis showed a significant reduction of the C:N ratio when vermicomposting was applied to the mixed matrices and MO, with a significant increase in total nitrogen (N) and available phosphorus (P). The number of earthworms increased during the process, both in net weight and growth rate, particularly when OFMSW was mixed with selected organic material. On the other hand, there was a significant accumulation of heavy metals in the "Tea of earthworm"(meant as a liquid phase obtained from organic material biodegradation processes and especially from the metabolic activity of earthworms), and a content of the same gradually lower during the process