Retention of anthropogenic microparticles in a wastewater treatment and reclamation plant combining membrane bioreactor and reverse electrodialysis treatments

Anthropogenic microparticles, including natural and semisynthetic cellulosic textile fibres and microplastics, are generated globally as by-products of human activities and enter the environment mainly via wastewater. Wastewater treatment plants (WWTPs) play a crucial role in reducing these pollutants, thereby improving water quality and supporting planetary health. This study evaluates the concentration, variability, and characteristics of such particles across different stages of an urban WWTP in Tenerife (Canary Islands, Spain) equipped with a membrane bioreactor (MBR) and reverse electrodialysis (RED), and further examines their correlations with physicochemical water parameters and environmental factors. Monthly fieldwork in 2023 involved triplicate sampling at six WWTP points and reclaimed water supplied at a banana farm for crops irrigation. A total of 252 samples were generally submitted to an oxidative digestion, filtered, and the resulting anthropogenic particles (n = 12,847 items) were analysed using stereomicroscopy and Fourier transform infrared microspectroscopy (n = 1124 items). Particles ranged from 50 to 6607 μm and were categorised into fibres, fragments, films, and microbeads, with fibres accounting for over 60 % at all stages. Average concentrations were 926 ± 438, 2342 ± 658, and 43 ± 43 items/L in the influent, biological reactor, and final effluent, respectively. Composition analyses revealed 21 polymers in the influent but only 4 in the final effluent, with cellulosic fibres always being the predominant type. Time-dependent analyses showed higher particle loads in warmer months, yet an average retention of 95 % highlighted the efficacy of the system in reducing harmful microplastics pollution.