The WOMW used in this work was characterized by a slightly acid pH of 5.5 and a conductivity of 6.5 mS/cm (Table 1). The solid amount was particularly high, with a TS value around to 215 g/L and a volatile fraction of about 88%. The chemical oxygen demand resulted of about 243.5 gO2/L. The free ammonium nitrogen was negligible if compared to TKN, resulting averagely equal to 2.5 gN/L. The polyphenols amount, almost 5 g/L, underlines the high phytotoxic power of WOMW. These values confirmed the much higher pollution load of WOMW if compared with the olive mill wastewater produced by three continuous decanter