Ultrasonic degradation of trichloro acetonitrile, chloropicrin and bromobenzene: design factors and matrix effects

Power ultrasound has been employed to degrade numerous environmental pollutants. Through a series of experiments, the viability of sonication for pollution control in higher complexity systems was investigated. First, a mixture of chloropicrin (CCl3NO2), trichloroacetonitrile (C2Cl3N), and bromobenzene (C6H5Br) was irradiated in a batch system. At a frequency of 20 kHz and a sound intensity of 30.8 W cm(-2), a minimal difference was observed between rate constants during sonication of a mixture and rate constants during sonication of individual compounds. Ultrasonic irradiation at 358 kHz was also viable for treatment of a mixture characterized by a high chemical oxygen demand (COD = 3470 ppm). Sonication in a complex aqueous matrix, river water, demonstrated minimal to moderate decreases in efficiency compared to sonication in reagent grade water. The recovery ratios for chloride, bromide, and inorganic nitrogen (nitrite plus nitrate) were 72 +/- 1, 56 +/- 3 and 91 +/- 2%, demonstrating the extent of mineralization of the parent compounds. A flow-through reactor was also studied. Higher flow rates and appropriate positioning of the ultrasonic probe accelerated the observed reaction rates. For example, increasing the flow rate from 4.4 to 34 ml min(-1) doubled the sonication coefficient for bromobenzene in a mixture, possibly due to better temperature control and mixing. Also, the sonication coefficient was 34% higher for chloropicrin degradation when the probe was positioned 1 cm from the entrance than when the probe was positioned 14.2 cm from the entrance. (C) 2000 Elsevier Science Ltd. All rights reserved.