Evaluation of the maturity of organic waste composts

Olive-mill wastes represent a significant environmental problem in Mediterranean areas due to their significant production during a short period of time. Their high polyphenol, lipid and organic acid concentrations make them phytotoxic wastes. Composting is one of the technologies used for the valorization of those wastes, producing a fertilizer useful for poor soils. The present study is an attempt to elaborate upon organic matter transformations and define the parameters for product maturity by adapting chemical and spectroscopic methods during composting. The aim of this work was to study the changes involved in the composting process of four piles during 200 days, and follow up the maturity of the final product during composting. Fourier transform infrared (FTIR) spectroscopy has been proven to be an appropriate analytical method for the qualitative assessment of compost stability. FTIR spectroscopy results revealed enrichment in aromatic structures and a degradation of the aliphatic and alcoholic structures indicating stabilization of the final compost. The results showed that stability of the final product was reached after 7 months of composting. The phytotoxic effects of olive mill wastes and animal manures was assessed by germination index. Indeed, the germination indices of piles 1, 2, 3 and 4 reached 131.31%, 72%, 90.56%, and 105.37%, respectively, at the end of the process. This demonstrated the absence of phytotoxicity in the majority of mature composts.