Ozonation Combined with Sonolysis for Degradation and Detoxification of m-Nitrotoluene in Aqueous Solution

Sonolytic ozonation (US/O-3 oxidation) is an advanced oxidation process that has become a focus of intense investigation. In this study, the nitroaromatic compound m-nitrotoluene (MNT) was chosen as a model substrate for degradation experiments in which pH, initial concentration of MNT, ozone dose, and US density were varied. At pH 10.0, initial concentration of MNT 400 mg/L, ozone dose 2.4 g/h, and US energy density 88 W/L, the efficiency of MNT removal reached 98% after 120 min. Of the initial degradation rate of MNT abatement, 9.8, 4.1, and 1.1 mg/(L min) were observed with US/O-3, O-3, and US, respectively. The variation of the concentrations of related anions (oxalate, acetate, formate, and nitrate ion) during the reaction process was ascertained by ion chromatography (IC). The major intermediates detected by gas chromatography/mass spectrometry (GC/MS) were 3-nitrobenzaldehyde, 3-nitrobenzoic acid, nitrobenzene, benzene, butene diacid, oxalic acid, and acetic acid. A degradation pathway is proposed on the basis of these findings. The acute toxicity of the reaction solution to zebra fish (Danio rerio) was estimated after US/O-3 treatment. According to the decreasing lethal rate during the US/O-3 process, it could be deduced that US/O-3 is a powerful tool with which to achieve effective reduction of the toxicity of MNT.