Improvement of the anaerobic biodegradation of olive mill wastewaters by prior ozonation pretreatment

The purification of olive mill wastewaters (OMW) is investigated by a single anaerobic digestion in a batch reactor containing immobilized microorganisms, and by the combination of an ozonation pretreatment followed by an anaerobic digestion. In the single anaerobic digestion the removal of the COD is determined and the methane yield coefficient, which is the best measure of the extent of transformation of the biodegradable substrate, is also obtained, its value being 194 ml CH4/g COD. A kinetic study is performed by using the Monod model combined with the Levenspiel model, due to the presence of inhibition effects. Both models lead to the determination of the kinetic parameters of this anaerobic treatment: kinetic constants, critical substrate concentration of inhibition and inhibitory parameter. In the combined process, the ozonation pretreatment of OMW achieves a great reduction in the phenolic compounds, leading to a significant increase in the methane yield coefficient in the following anaerobic digestion, its value being 266 ml CH4/g COD.