Chemical and spectroscopic analyses of organic matter transformations during composting of olive mill wastes

A piled mixture of olive-mill wastes and wheat straw was composted for 1 year and several of its characteristics (total organic carbon and nitrogen, organic matter, lignin, cellulose, hemicellulose, total fats, water-soluble phenols and the germination index of cress, Lepidium sativum L.) were monitored. In addition, the compost was characterized by Fourier transform infrared spectroscopy (FTIR). The results showed the efficiency of composting in reducing olive-mill toxicity. The C/N ratio and organic matter degradation were 160.50 and 560.50 g kg−1, respectively, after 12 months of composting. Lignin, hemicellulose and cellulose amounts were reduced during the process, their depletion rates reaching final values of 44%, 76% and 58%, respectively. In addition, the fat and water-soluble phenol contents decreased by 97% and 66%, respectively. The germination index reached 99% at the end of the process. This demonstrated the absence of phytotoxicity in the mature compost. The FTIR spectra showed that there was an enrichment in the aromatic groups and a degradation of the aliphatic groups.