Treatment of slaughterhouse wastewater using high-frequency ultrasound: optimization of operating conditions by RSM

Slaughterhouse processes produce substantial amounts of high organic strength wastewater due to high COD level. A fundamental work had been carried out to explore the removal of COD from actual poultry slaughterhouse wastewater by ultrasound irradiation. The effect of applied frequency, power density, irradiation time, pH, and adding H₂O₂ on COD removal was investigated. The COD removal reached ultimate levels after irradiation time of 180 min. The COD removal percentage increased from 2% to 43% and from 2% to 49% when the power density increased from 160 to 1200 W/L at working frequencies of 1142 and 578 kHz, respectively. Increasing the pH from 7 to 9 reduced the COD removal from 51% to 13%. At low power densities, the high frequency (1142 kHz) was more efficient in COD removal than low frequency (578 kHz) and vice versa at high power densities. A combined system of US and H₂O₂ was more effective in removing COD than US standalone system. Finally, the kinetics of the COD decay using sonication was found to obey the first-order model. In conclusion, the US can be used efficiently at least to pretreat slaughterhouse wastewater with a COD removal of about 50%.