Accelerated transformation and deactivation of erythromycin in superheated water. 1. Temperature effects, transformation rates, and the impacts of dissolved organic matter

The presence of antibiotics and other pharmaceuticals in the environment is of increasing concern. The stringent treatment of point discharges of antibiotic wastes holds promise as an approach for curtailing growing trends of microbial resistance. The work described in this two-part series explores the use of superheated water as a medium for the accelerated transformation and deactivation of a specific target antibiotic, erythromycin. Part 1 of the series focuses on parent compound conversion, and Part 2 examines transformation mechanisms and reaction products. This paper, Part 1, highlights the results of reactor studies performed in both batch and flow-through modes. The data presented confirm that accelerated conversion of erythromycin, based on parent compound disappearance as measured by high-pressure liquid chromatography, occurs in water under superheated conditions. Given an initial erythromycin concentration of 50 mg/L, greater than 85% apparent conversion was achieved within 30 min in the batch system at all temperatures investigated in the range from 125 to 200 degrees C. The presence of dissolved organic matter extracted from two natural soil materials, at concentrations of 2.5-20 mg/L, was shown to have little effect on the overall extent of transformation of erythromycin in the batch system. The rates of decomposition observed were found to be best described by a psuedo-first-order expression, one in which the rate coefficient increased linearly with increasing initial concentration of the antibiotic. First-order rate behavior was verified in subsequent flow reactor experiments. The temperature dependence of rate was also examined, and an activation energy of 68.8 U/mol was determined.