en تخصصي Special Orginal Article <div style="text-align: justify;"><span style="font-size:14px;">Management of excess sludge generated in wastewater treatment plants, particularly industrial sludge containing heavy metals, is one of the major environmental and public health challenges. In this study, the efficiency of dissolved air flotation (DAF) assisted by ultrasonic waves was investigated for the removal of selected heavy metals, including chromium, lead, nickel, and copper, during the thickening of recycled sludge. Sludge samples were collected from the Amir Kabir Industrial Town wastewater treatment plant in Kashan, Iran, and experiments were conducted at the laboratory scale under batch conditions. To optimize operational parameters, a jar test was performed to determine the optimal pH and ferric chloride coagulant dosage, which were found to be 7.5 and 200 mg/L, respectively. The effects of operating pressure (3, 5, and 7 atm), flotation time (5 and 10 min), ultrasonic power (75 and 150 W), and coagulant addition on heavy metal removal efficiency were evaluated. The results demonstrated that operating pressure had the most significant effect on heavy metal removal. The highest removal efficiencies of copper (81.37%), nickel (67.59%), and chromium (85.86%) were achieved at a pressure of 5 atm, while the maximum removal of lead (72.31%) occurred at 3 atm. Variations in flotation time and ultrasonic power did not result in statistically significant changes in removal efficiency, whereas coagulant application significantly enhanced the removal of copper and chromium. Overall, the findings indicate that the DAF process is an effective method for reducing heavy metal concentrations in industrial sludge, with operating pressure identified as a key parameter for optimizing system performance.</span></div> Dissolved Air Flotation (DAF), Ultrasonic Waves, Heavy Metal Removal, Sludge Thickening, Industrial Wastewater, Coagulation, Ferric Chloride 9 15 http://jrhms.thums.ac.ir/browse.php?a_code=A-10-184-1&slc_lang=en&sid=1 Ali Atamaleki 10031947532846001637 10031947532846001637 No Department of Environmental Health Engineering, North Khorasan University of Medical Sciences, Bojnurd, Iran Edris Bazrafshan 10031947532846001638 10031947532846001638 No Department of Environmental Health Engineering, Torbat Heydariyeh University of Medical Sciences, Torbat Heydariyeh, Iran Abdolmajid Gholizadeh gholizadeh_eng@yahoo.com 10031947532846001639 10031947532846001639 Yes Department of Environmental Health Engineering, Torbat Heydariyeh University of Medical Sciences, Torbat Heydariyeh, Iran