Many researchers have attempted in the past to look at the possibility of using ultrasonic irradiation or sonication in degrading organic compounds in aqueous wastewater. Ultrasonic irradiation was found to be a safe, clean and effective method for deterioration of specific organic compounds. Ultrasonic irradiation can be used as a stand-alone process, or can be integrated with other treatment methods. However, very limited study focuses on the application of ultrasonic irradiation for treating industrial wastewater; therefore, it is considered as a new research. When water is exposed to ultrasonic irradiation,⁺H and ^-OH radicals are produced; the latter is a strong oxidizing agent which can degrade organic pollutants. This study uses raw Palm Oil Mill Effluent (POME) as a test media to investigate the effectiveness of ultrasonic irradiation in reducing organic compounds based on the Chemical Oxygen Demand (COD) concentration at selected operating conditions, namely power density of ultrasonic probe and addition of catalysts. Results showed percentage reduction of COD was highest at power density 29W/L than power density 55W/L. Power density 29W/L of ultrasonic probe chose to combine with catalysts. Application of ultrasonic irradiation with presence of the catalysts CuSO₄ and FeSO₄, increased the percentage of COD reduction, but FeSO₄ gave a better result. The highest percentage reduction of COD of raw POME is around 30% after ultrasonic irradiation process combined with the catalyst FeSO₄.

Palm oil production is a major agricultural industry in Malaysia. In 2006, there were more than 4.2 million ha. of palm oil plantations which produced 16 million tons of oil (Chou, 2007). In total, about 110 million tons of renewable non-oil biomass (trunk, fronds, shells, palm press fiber and the empty fruit bunches) are produced each year. Furthermore, approximately 0.65 tons of raw Palm Oil Mill Effluent (POME) is produced for every ton of fresh fruit bunches. In 2006, palm oil mills in Malaysia produced more than 58 million tons of POME (Chou, 2007). POME is an acidic, brownish, colloidal suspension, characterized by high content of organics and solids and is discharged at a temperature of 80-90 °C (Table 1). Wastewater treatment facility is one of the most important components in the palm oil industry. This facility is normally used to treat a large volume of POME generated during the production of Crude Palm Oil (CPO) before the effluent is safely discharged to the surrounding environment through water canal or river (Saifuddin and Fazlili, 2009). Specifically, the amount of POME generated is approximately 3.8 m³ for each ton of CPO produced (Ma and Ong, 1988). The problems associated with aerobic treatment of POME using a pond system are long retention time (90-120 days), large area requirement and high demand for maintenance, loss of nutrition and high emission of methane. It is important to develop an alternative concept for POME treatment (Ma, 2000).

Ultrasonication has been widely used to degrade organic compounds from wastewater for many years; many reports were published about the sonochemical degradation of individual organic compounds (Songlin Wang et al., 2008). However, very little was reported about the effect of ultrasonic irradiation to real wastewater like POME. Sonochemical decomposition of organic pollutants in aqueous solution is a consequence of the formation and collapse of high-energy cavitation bubbles. Upon collapse, the solvent vapor is subjected to an enormous increase in temperature and pressure (Vicenzo Naddeo et al., 2007). Under such extreme conditions, the solvent molecules undergo hemolytic bond breakage to generate radicals. When water is sonicated, ⁺H and ^-OH radicals are produced; the latter is a strong oxidizing agent and can react with organic pollutants (Chu et al., 2001).

Environmental Sciences Journal, Ultrasonic Irradiation, Palm Oil Mill Effluent, POME, Agricultural Industry, Palm Oil Production, Ultrasonication, Sonochemical Applications, Sonochemistry Theory, Palm Oil Plantations, Sonochemical Decomposition, Organic Pollutants.