Continuous treatment of clofibric acid by Trametes versicolor in a fluidized bed bioreactor: Identification of transformation products and toxicity assessment

Abstract

The aerobic degradation of the blood lipid regulator clofibric acid (CLOF) was studied in a continuous bioreactor treatment using the white-rot fungus Trametes versicolor. Experiments in Erlenmeyer flasks with the compound at 30μgL−1 showed that CLOF can be completely degraded at near environmentally relevant concentration after 4 days. The degradation process was scaled-up in an air-pulsed fluidized bioreactor operated in continuous mode with a hydraulic retention time of 4 days. The results show that 80% of the fed concentration (160μgL−1) was reduced at the steady state (from day 12 to the end). Here, CLOF removal rate was 12.5μgg−1 dry weight biomassd−1. The 2-(4-chlorophenoxy)-2-(hydroxymethyl)propanoic acid (hydroxy-CLOF) was identified as major metabolite, confirming the degradation of CLOF, but its concentration remained constant in the medium. In addition, in a batch bioreactor treatment the undegradability of hydroxy-CLOF was demonstrated. Finally, acute toxicity tests (Microtox) performed with the bacterium Vibrio fischeri showed that the final culture broth in both batch (15min EC50 of 55%) and continuous (11%) experiments were more toxic than the beginning (61%).