Kinetic study of reactions between ozone and benzothiazole in water

Abstract

Benzothiazoles are frequently present in wastewater from rubber related applications, and may be found in surface and underground water bodies causing significant environmental impact. Cost effective treatment processes to deal with such contaminants are needed in both small and large-scale applications. These compounds are poorly biodegradable and could be removed by ozone oxidation before discharge to recipient water courses. Unfortunately, there is limited experimental data reported in the literature on such processes involving benzothiazoles. This article presents experimental data on ozone treatment of benzothiazole (BT), with a view to process design. The effects of pH and radical scavengers on process rate and removal efficiency were assessed at bench scale. Experimental results show that BT could be effectively removed using ozonisation, particularly at pH above 4. The presence of free radical scavengers drastically reduced the BT removal rate even at very low concentrations. Both direct and indirect reactions between ozone and BT were adequately described by second order kinetic schemes, with rate constants estimated at 20 degrees C: kD = 2.3 mol l(-1) s(-1) and kI = 6 x 10(9) mol l(-1) s(-1), respectively. The free radical mechanism accounted for 83-96% of BT removal rate within the pH range 2-9, at 20 degrees C.