Influence mechanisms of textile-dyeing sludge characteristics on degradation of anilines by integrated ultrasound-permanganate treatment

In order to support the use of integrated ultrasound-Mn(VII) for the removal of anilines, this study investigated for the first time the influence of the sludge characteristics on the reaction kinetics of target anilines including o-toluidine, p-chloroaniline, 2-methoxy-5-methylaniline, and 2,4,5-trimethylaniline. The results indicated that with a KMnO4 dosage of 1 mM and an ultrasound power density of 0.90 W cm−3, 68.85%, 85.53%, and 78.50% of anilines can be removed from textile sludge plant 1, 2, and 3. Higher removal efficiency of anilines was achieved at a lower pH value, smaller particle size, and more negative ζ-potential. The target anilines exhibited substantial reactivity toward Mn(VII) with the maxima of second-order rate constants at a pH value near their pKa values for o-toluidine (0.80 M−1s−1 at pH 4), p-chloroaniline (0.65 M−1s−1 at pH 4), 2-methoxy-5-methylaniline (0.45 M−1s−1 at pH 4), and 2,4,5-trimethylaniline (0.34 M−1s−1 at pH 5). Moreover, the biodegradability of textile-dyeing sludge was greatly enhanced by integrated ultrasound-Mn(VII) treatment. This integrated treatment was proposed as an effective method for the disposal of anilines in textile-dyeing sludge.