Bioremediation of olive mill wastewaters by composting.

Olive-mill wastewaters (O.M.W.) containing about 7% solids were composted with wheat straw in a forced aeration static pile. Two percent urea was added to ensure a C/N ratio of about 35. To avoid overdosing with water, a fraction of the O.M.W. equal to the weight of the straw was added initially. When composting had reached the thermophilic phase, additional doses of O.M.W. were added every 3 days as water evaporated. The ratio of O.M.W. solids:straw approached 1:1 and the thermophilic phase was extended to 35 days. Temperature, oxygen consumption, pH, C/N, total organic carbon, total extractable carbon, humic and fulvic acids and lignin degradation were followed during the process. The humification was assayed following the degree of humification, the humification rate and the humification index which respectively reached the values of 78%, 37.8% and 0.28 after 2 months. Humic acids were characterized by their elemental composition and molecular weight. A lignin degradation of about 70% was assayed at the end of the thermophilic phase. No phytotoxicity was recorded on the end product, the chemical and physical properties of which suggest its possible use as fertilizer.