Characterization and Optimization of Mixed Microbial Consortia for Metformin and Guanylurea Bioremediation of River Erpe

Active pharmaceutical ingredients are emerging contaminants increasingly detected in aquatic systems and metformin (MET) and its transformation product guanylurea (GUA) are among the most prevalent worldwide. Bioremediation represents a sustainable strategy to mitigate their impacts while preserving ecosystems and drinking water quality. This study addresses MET and GUA contamination in the River Erpe by optimizing and characterizing two microbial consortia for future in situ application. Optimization focused on identifying suitable temperature and pH conditions, testing biofilm carriers, and evaluating the addition of external carbon sources. Aerobic batch cultures were used to assess degradation performance, expressed as maximum xenobiotic degradation rate. HPLC, colorimetric assays, and quantitative PCR were employed to monitor xenobiotic removal, nitrogen species, and microbial growth. Although temperature and pH conditions boosting degradation were not identified, this study provided valuable insight into nitrogen transformations and consortium responses to environmental parameters, enabling preliminary predictions of their behaviour under Erpe conditions. An effective biofilm carrier was identified for GUA degradation, potentially improving stability and resistance to wash-out. Additional carbon sources also showed promising effects on GUA removal. At the same time, the study highlighted aspects of the current guanylurea consortium that require further optimization and suggested possible solutions: future strategies should improve degradation with further evaluation of carbon amendments and carry out serial transfers to reduce the number of nitrifiers. Furthermore, new enrichment approaches starting from natural samples could be explored to identify potentially more efficient biodegraders.