Analysis of the ozonation of 2-mercaptobenzothiazole in water and tannery wastewater using sum parameters, liquid- and gas chromatography and capillary electrophoresis

Abstract

2-Mercaptobenzothiazole (MBT) is known as a widespread, toxic and poorly biodegradable pollutant. In this study, MBT has been ozonated in pure water and in spiked tannery wastewater at various pH-values to investigate its oxidative destruction. All oxidation tests performed similarly concerning the sequence of occurrence of the main transformation products. MBT and its breakdown products showed a high affinity towards ozone as indicated by the rates for partial oxidation and mineralization. Using HPLC–DAD, benzothiazole was identified as the first ozonation product, reaching up to 60 mol% of the original MBT-concentration, followed by low concentrations of 2(3H)-benzothiazolone. Only small amounts of additional hydroxybenzothiazoles have been found by GC/MS. In all tests, a compound with the sum formula of benzothiazol-2-sulfonate (BTSO 3) proved to be a main transformation product. IR-, NMR-, UV- and MS-spectra were highly similar to pure BTSO 3. However, benzothiazole-2-sulfite is proposed as the correct structure since a slow hydrolysis reaction occurred and HPLC-retention times were different by comparison with BTSO 3. By further ozonation, 7 organic and 3 inorganic anions have been identified using capillary electrophoresis with indirect UV detection. In conclusion, MBT is readily transformed by ozonation and, thus, wastewaters containing high amounts of MBT should easily be detoxified using ozone.