BACKGROUND: In this study, the effects of additives (manganese (III) oxide (Mn3O4), Cu+2, Fe0 and potassium iodate (KIO3)) and radical scavengers (sodium carbonate (Na2CO3), perfluorohexane (C6F14) and t-buthyl alcohol (C4H10O)) on the dephenolization, decolorization, dearomatization and detoxification of olive mill wastewater (OMW) by sonication were investigated because wastewaters from this industry are not removed effectively. RESULTS: The maximum COD, color, total phenol and total aromatic amines (TAAs) removal efficiencies were 63, 82, 78 and 71%, respectively, at 60 degrees C with sonication only. The TAAs and phenol yields were increased to 96 and 97% with 6 mg L-1 KIO3 and 3 mg L-1 Fe0 while color removal reached 97% with 6 mg L-1 C6F14. The total annual cost with sonication only was 665 epsilon m-3 year-1 while the cost slightly increased (666 epsilon m3 year-1) with C6F14. The maximum acute toxicity removals were 97-98% in Daphnia magna and Vibrio fischeri The Microtox acute toxicity test was more sensitive than the Daphnia magna to the OMW samples. CONCLUSION: COD, color, total phenol, TAAs and toxicity in an OMW were removed efficiently and cost-effectively by sonication. (c) 2012 Society of Chemical Industry