Degradation of widespread pharmaceuticals by activated sludge: kinetic study, toxicity assessment, and comparison with adsorption processes

Abstract

The growing presence of pharmaceutical compounds in aqueous systems leads to the search for new efficient and eco-friendly solutions to this problem. Although pharmaceutical products are widely found in the aqueous environments, there is limited understanding of their ecological effects. To augment the removal of pharmaceuticals, a bench reactor was inoculated with activated sludge and fed with a synthetic medium. Two pharmaceuticals of widespread usage, ibuprofen (IBU) and paracetamol (PARA) in the range 0.4 to 1 mg L-1 were used. The uptake values increased from 0.192 to 0.660 mg g-1 for IBU and from 0.104 to 0.341 mg g-1 for PARA. The removal efficiency reached values from 99.1 to 99.5% and is independent of the initial IBU concentration. For PARA the removal percentage ranged from 93.3 to 98.8 decreasing with the increase on the initial concentration. The removal mechanism is well described by pseudo-first order and pseudo-second order kinetic models for all concentrations tested. At same time, batch assays were performed in order to assess the toxicity of both pharmaceuticals into the activated sludge using quantitative image analysis (QIA). For IBU experiments, QIA studies showed that this compound favors the growth of aggregated biomass rather than filamentous bacteria. A comparison between this biological technology and adsorption by a commercial porous ceramic material and Pinus bark was also performed. The results showed that the biological technology allowed better results (99.5% against 19.4 and 9.3 %, respectively for the ceramic material and Pinus bark) for IBU. The results obtained for PARA showed comparable results for the biological technology and for adsorption by the ceramic material. The activated sludge system presented here appears to be a promising treatment for pharmaceutical contaminated effluents and the biomass present in the activated sludge seems do not be negatively affected by the presence of high concentrations of both pharmaceuticals.