Evaluating membrane bioreactor treatment for the elimination of emerging contaminants using different analytical methods
Naroa Lopez-Herguedas, Mireia Irazola, Iker Alvarez-Mora, Leire Mijangos, D. Bilbao, Néstor Etxebarría, Olatz Zuloaga, Maitane Olivares, Ailette Prieto
Abstract
Since wastewater treatment plants (WWTPs) were not originally designed to eliminate contaminants of emerging concern (CECs), alternative strategies like membrane bioreactor (MBR) technology are gaining importance in achieving effective CEC removal and minimising their environmental impact. In this study, composite wastewater samples were collected from the biggest WWTP in the Basque Country (Galindo, Biscay) and the performance of two secondary treatments (i.e. conventional activated sludge treatment, CAS, and MBR) was assessed. The combination of a suspect screening approach using liquid chromatography tandem high-resolution mass spectrometry (LC-HRMS) and multitarget analysis by gas chromatography-mass spectrometry (GC-MS) allowed the detection of approximately 200 compounds in the WWTP effluents. The estimated removal efficiencies (REs) revealed that only 16 micropollutants exhibited enhanced removal by MBR treatment (RE > 70% or 40 – 60%). The environmental risk posed by the non-eliminated compounds after both treatments remained similar, being anthracene, clarithromycin, bis(2-ethylhexyl) phthalate (DEHP) and dilantin the most concerning pollutants (RQ > 1). The Microtox® bioassay confirmed the MBR’s efficiency in removing baseline toxicity, while suggesting a similar performance of CAS treatment. These minimal differences between treatments call into question the worthiness of MBR treatment and emphasise the need to seek more efficient alternative treatment methods. Contaminants of emerging concern (CECs) primarily enter the environment via wastewater treatment plants, since conventional treatments struggle to remove them completely. Thereby, the development of more effective methods is essential. Among the different emerging treatments, membrane bioreactors (MBR) have gathered special attention as promising alternatives for mitigating the environmental impact of CECs. However, this multidisciplinary approach revealed that MBR performs similarly to conventional treatments. Considering the substantial economic and energy expenses of MBR technology, it may not represent an efficient enough solution for widespread implementation and further research is required to find more effective alternatives.