Biodegradability properties of sulfonamides in activated sludge

Twelve different sulfonamides were selected for a biodegradation study using a respirometric screening test and an activated sludge simulation test. A simple bacterial growth inhibition test was applied to show that the sulfonamides did not affect the bacteria at the concentration levels used. None of the compounds were degraded in the screening rest, leading to the conclusion that sulfonamides cannot be classified as readily biodegradable. In the simulation test, primary degradation of mixtures of four compounds at concentration levels of 250 to 500 mu g/L were tested and analyzed using high-performance liquid chromatography. Biodegradarion occurred after lag phases of 7 to 10 d at 20 degrees C when nonadapted sludge was applied. Test compounds were degraded within a few days. At 6 degrees C, degradation lag phases and degradation rates were three to four rimes longer. Degradation curves fit well to the logistic growth model, indicating growth of specific degraders in the test system. Sulfonamide adapted bacterial cultures were able to degrade either the same compounds as previously added or four other sulfonamides in a rapid and uniform way (t(1/2) from 0.2 to 3 d). This finding shows that if capable of degrading one sulfonamide substance, these bacteria may also degrade many other sulfonamides. In practice, this implies that because the biodegradation rate is found to be identical for several sulfonamides in the sludge, the compounds may be assessed as a group by studying only a few compounds in applications such as environmental fate assessments. The mechanism for inducement of sulfonamide adaptation to the bacteria was not revealed in this study.