Cocomposting of olive oil mill by-products: chemical and microbiological evaluations

An experiment was performed to evaluate the possibility of cocomposting wet husk and wastewater, the two main olive oil mill by-products. The pH, E.C., total C and N, humic substances, phenolics, volatile acids, lipids, P and K plus yeast, fungi, heterotrophic-, cellulolytic- and nitrifying bacteria and phyto toxicological parameters were monitored during a 120-day stabilization process. Performances of the composting system adopted, together with physicochemical characteristics of starting material and final product, are reported. Composting was found to induce a high level of organic matter change, with decrease of organic carbon, total nitrogen and C/N ratio, as well as of the easily biodegradable lipids. Good metabolic activity of the microbiological population, with the exception of the nitrifying bacteria, and a complete detoxification of starting material were also observed. The results obtained suggested that composting might be an adequate low-cost strategy for the recycling of olive oil by-products.