Response surface methodology for the optimization of the ultrasonic-assisted rhamnolipid treatment of oily sludge

This study investigates the recovery of oily sludge using ultrasound-assisted rhamno-lipids and uses oil recovery yield as an evaluation index. The Box-Behnken response surface method was employed to investigate the individual and interactive effects of four different operating factors: frequency, dosage, liquid-solid ratio, and stirring speed. The model optimization results showed that the order of degree of influence of these four factors is frequency > liquid-solid ratio > dosage > stirring speed. The mathematical model predicted the highest oil recovery yield as 92.27%, which was highly accurate (in the 95% confidence interval) as from the experimental results, the highest oil recovery yield was 89.95% under optimal reaction conditions (frequency = 25.58 kHz, dosage = 150.45 mg/L, liquid-solid ratio = 4.1:1 mL/g, and stirring speed = 407 rpm). Thus, the deviation from the prediction model was only 2.32%, indicating that this method provides a theoretical basis for the treatment of oily sludge and can be implemented for practical application in Huaidong in the Xinjiang Province. (C) 2021 The Authors. Published by Elsevier B.V. on behalf of King Saud University.