Research Article Received: 20 January 2012 Revised: 2 March 2012 Accepted: 3 March 2012 Published online in Wiley Online Library: (wileyonlinelibrary.com) DOI 10.1002/jctb.3808 Treatment of wastewaters from the olive mill industry by sonication Rukiye Oztekin and Delia Teresa Sponza ∗ Abstract BACKGROUND: In this study, the effects of additives (manganese (III) oxide (Mn 3 O 4 ), Cu +2 , Fe 0 and potassium iodate (KIO 3 )) and radical scavengers (sodium carbonate (Na 2 CO 3 ), perfluorohexane (C 6 F 14 ) and t-buthyl alcohol (C 4 H 10 O)) 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 ◦ C with sonication only. The TAAs and phenol yields were increased to 96 and 97% with 6 mg L −1 KIO 3 and 3 mg L −1 Fe 0 while color removal reached 97% with 6 mg L −1 C 6 F 14. The total annual cost with sonication only was 665 ¤ m −3 year −1 while the cost slightly increased (666¤ m 3 year −1 ) with C 6 F 14 . 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 Keywords: aromatic amines; color; olive mill effluent; phenol; sonication; toxicity INTRODUCTION Agro-industrial wastewaters such as olive-oil mill effluent wastew- aters (OMW) are among the strongest industrial effluents since they cause considerable environmental problems (coloring of nat- ural waters, a serious threat to aquatic life, pollution of surface and ground waters) particularly in the Mediterranean Sea region due to its high organic chemical oxygen demand (COD), polyphenol and aromatic amines concentration. 1 The organic content of the OMW consists mainly of phenols, polyphenols, polyalcohols, sugars, tannins and pectins at concen- trations as high as 200 g COD L −1 . 2 The concentration of phenolic acids in the OMW may vary from as low as 0.05–0.2 g L −1 to as high as 10 g L −1 depending on the type and origin of the effluent. 2 The total aromatic amines (TAAs) in the OMW are known to be carcinogenic and toxic. 3,4 Significant numbers of studies have focused on the efficient treatment of OMWs including various chemical, physical, physic- ochemical and biological treatments or combinations of them. 5 Usually OMW is inappropriate for direct biological treatment and the alternative treatment technologies mentioned above did not give sufficient yields for phenol byproducts (2-phehyl phenol (2- PHE) and 3-phenyl phenol (3-PHE)) and aromatic amines (aniline, 2, 6-dimethylaniline, durene, o-toluidine). 2,4 Even though all of these methods are practicable and effective, they cannot be used ubiquitously with high efficiency and may generate hazardous by-products. 5 Recently, significant interest has been shown in the application of ultrasound for the degradation of OMWs. 6 Sonochemical reactions are induced by directing sound waves into liquids, thereby producing cavitation bubbles. 6 Ultrasonic action produces radicals such as hydrogen, hydroxyl and hydroperoxyl radicals (H • , OH • ,O 2 H • ), respectively, and can be classified as an advanced oxidation process (AOP). 7 The formation of cavitation bubbles and the extent of bubble collapse depend on the sonication frequency, power and sound intensity. Preliminary studies showed that as the sonication frequency and power were increased from 8 kHz to 35 kHz and from 110 W to 640 W the COD yields increased, respectively. 8 As the acoustic power is increased the number of cavitational events and consequently the opportunities for free radicals to be generated increase, enhancing sono-degradation. As the intensity is increased the number of collapsing cavities is also increased, thus leading to enhanced degradation rates, as reported by Psillakis et al. 9 A significant increase in the number of bubbles, close to the emitting surface, was caused by increasing both the sonication power and intensity. An increase in ultrasonic intensity led to greater sonochemical effects in the collapsing bubble. Furthermore, the collapse of bubbles in the reaction cell occurs more rapidly and the number of cavitation bubbles increases thus producing a higher concentration of OH • at optimum ultrasonic intensities. These OH • react with the pollutants and enhance their yields. 10 The research performed for the sono-degradation of the OMW is limited to a few studies and lower removals were obtained for the pollutants: phenolic compounds such as p-coumaric acid ∗ Correspondence to: Delia Teresa Sponza, Dokuz Eyl¨ ul University, Engineering Faculty, Department of Environmental Engineering, Tınaztepe Campus, 35160 Buca/Izmir, Turkey. E-mail: delya.sponza@deu.edu.tr Dokuz Eyl¨ ul University, Tinaztepe Campus, Izmir, Turkey J Chem Technol Biotechnol (2012) www.soci.org c  2012 Society of Chemical Industry