Sonolysis of Chloro-Organics in Bleach Plant E-1 Effluents

Abstract

Degradation of chloro-organics in bleach plant E-1 effluents by ultrasound sonication was investigated to evaluate the effects of ultrasonic treatment on the dechlorination. On sonolysis, ca. 65mol% of 4-chlorophenol (1) at concentration of 1.0x10 -4 M in aqueous solution was decomposed and 35mol% of chlorine in the substrate was released as chloride ions (Cl) alter 80 min at room temperature under atmospheric pressure. By contrast, under the same reaction conditions, only ca. 11mol% and 3mol% of (1) were decomposed at the concentrations of 1.0x10 -3 M and 1.0x10 -2 M with the release of ca. 5 and 1mol% of Cl - , respectively. Although the kinetics for the disappearance of (1) fits a first-order law, the rate constant decreases with increasing initial concentration of the substrate. This suggests that the disappearance rate of (1) does not follow the first order law and the reaction mechanism involved is rather complex. When hydrogen peroxide was added to the solution in the molar ratio of substrate to hydrogen peroxide 1:10, both the rates of degradation and dechlorination were not affected. However, an addition of a smaller amount of hydrogen peroxide to the solution resulted in a decrease in the rate of the degradation. In the presence of hydrogen peroxide, the kinetics for the decomposition of (1) also follows the same pattern for that without hydrogen peroxide. On sonolysis, polychlorinated oxylignins (PCOLs) isolated from E-1 effluent released chloride ions. The high relative mass PCOL released larger amounts of chloride ions than the low relative mass PCOL. The sonolysis brought about a very small decrease in the relative mass of PCOLs, and no significant degradation of PCOLs except for release of chloride ions. This result suggests that an acoustic cavitation by ultrasonic treatment plays a important role in cleavage of C-Cl bonds, but not C-C bonds.