Study on the Fate of Pharmaceuticals in Aqueous Media: Synthesis Characterization and Detection of Biotic and Abiotic Transformation Products using Electrochemical Advanced Oxidation Processes and Bioconversions
The present study contributes with valuable data for a better fundamental understanding on the fate of pharmaceutical residues in the environment, dealing with the main challenges concerning this increasingly worrying environmental issue.
The used Electrochemical Advanced Oxidation Processes (EAOPs), electro-Fenton (EF) and anodic oxidation (AO), showed to be a very efficient alternative for the oxidative degradation and or mineralization of acidic solutions of the pharmaceuticals ranitidine (RNTD) and furosemide (FRSM), attaining almost complete mineralization of the drugs after 6 h of electrolysis. A comparative study on the mineralization of RNTD solutions by EF and SPEF processes in a 2.5 L capacity pre-pilot flow plant demonstrated the higher oxidation capacity of SPEF, achieving very good mineralization rates, thus evidencing the potentiality of this technology at greater scale for the treatment of wastewaters containing pharmaceutical pollutants. The application of an EF pre-treatment coupled with a biological process for the degradation of both drugs was also conducted. EF pre-pretreatment was capable of enhancing the solution biodegradability envisaging a biological treatment, which efficiently removed the short-chain carboxylic acids that had been formerly generated during the pre-applied electrolysis. In this way, the combination of both processes was confirmed as a very promising technology for the treatment of pharmaceuticals-containing wastewater.
Several transformation products (TPs) were detected and identified during the electrochemical oxidation of the studied drugs. Toxicity tests, based on the inhibition of bioluminescence of the marine bacteria V. fischeri, evidenced that some of these oxidation by-products were more toxic than starting molecule, since the global toxicity of the solution increased on the first stages of the electrolysis. However, the abatement of the toxicity in the final stages of the electrochemical treatments, demonstrated the effectiveness of these technologies for both the mineralization and detoxification of the RNTD and FRSM solutions. The use of the fungi Cunninghanella echinulate for the bioconversion of FRSM led to the formation of three main bio-transofrmation products: the previously identified saluamide and pyridinium, and the new detected keto-alcohol derivate. These TPs were generated by both, biological and electrochemical approches, evidencing their high probability to be found in environmental compartments as the most likely TPs of FRSM by different oxidation conditions. This study is thus presented as a very useful alternative for the assessment of the fate of pharmaceutical residues in the environment.