en تخصصي Special مقاله اصیل Original Article <div style="text-align: justify;"><span class="fontstyle0">Background: </span><span class="fontstyle2">Dissolved air floatation (DAF) is one of the methods has been used for the sludge thickening in wastewater treatment plants. This study aimed to investigate the effects of coagulation and sonication processes as additional configurations on the efficiency of a lab-scale DAF process for thickening of the biological sludge of an industrial wastewater treatment plant in Kashan, Iran.</span><br> <span class="fontstyle0">Methods: </span><span class="fontstyle2">The required amounts of sludge samples were collected from a wastewater treatment plant and kept at temperature of 4&deg;C. Variables, such as pressure (3, 5, and 7 atm), flotation time (5 and 10 minutes), ultrasonic irradiation power (0, 75, and 150 W), and presence/absence of Fe-based coagulant were considered on a sequencing batch reactor (SBR) included coagulation, flotation, and sonication processes, respectively.</span><br> <span class="fontstyle0">Results: </span><span class="fontstyle2">The use of ultrasonic waves led to an insignificant increase in the DAF efficiency (</span><span class="fontstyle3">P </span><span class="fontstyle2">> 0.05), however, the application of coagulant significantly increased the thickening efficiency (</span><span class="fontstyle3">P </span><span class="fontstyle2">< 0.05). The maximum efficiency of the process was achieved at flotation time of 5 min, pressure of 3 atm, and sonication power of 75 W.</span><br> <span class="fontstyle0">Conclusion: </span><span class="fontstyle2">According to the results, DAF has a proper efficiency for thickening of biological sludge. Coagulation compared to sonication has a greater effect on the efficiency of the process.</span></div> Ultrasonic waves, Industrial effluent, Dissolved air flotation, Sonication 59 65 http://ehemj.com/browse.php?a_code=A-10-1-162&slc_lang=en&sid=1 Ali Atamaleki Aliatamaleki69@yahoo.com 10031947532846006169 10031947532846006169 No Department of Environmental Health Engineering, School of Public Health, Kashan University of Medical Sciences, Kashan, Iran Mohammad Bagher Miranzadeh miranzadehm@ymail.com 10031947532846006170 10031947532846006170 No Department of Environmental Health Engineering, School of Public Health, Kashan University of Medical Sciences, Kashan, Iran Gholam Reza Mostafaii mostafai_gr@kaums.ac.ir 10031947532846006171 10031947532846006171 Yes Corresponding author:Department of Environmental Health Engineering, School of Public Health, Kashan University of Medical Sciences, Kashan, Iran Hosein Akbari akbari_h@kaums.ac.ir 10031947532846006172 10031947532846006172 No Biostatistics and Public Health Department, Faculty of Health, Kashan University of Medical Sciences, Kashan, Iran Leila Iranshahi Iranshahi-l@kaums.ac.ir 10031947532846006173 10031947532846006173 No Department of Environmental Health Engineering, School of Public Health, Kashan University of Medical Sciences, Kashan, Iran Farshid Ghanbari farshidbeat@yahoo.com 10031947532846006174 10031947532846006174 No Abadan Faculty of Medical Sciences, Abadan, Iran Atieh Salem atiehsalem70@gmail.com 10031947532846006175 10031947532846006175 No Department of Environmental Health Engineering, School of Public Health, Kashan University of Medical Sciences, Kashan, Iran