Microplastic removal and fouling mitigation in a pilot-scale Living Membrane bioreactor for urban wastewater treatment

Membrane bioreactors (MBR) have emerged as one of the most effective technologies for microplastic (MP) removal from wastewater. However, their wider application is limited by membrane fouling, which increases energy demand and operational costs. This study presents the living membrane bioreactor (LMBR), an innovative MBR configuration employing a modified self-forming dynamic membrane, in which an external cake and an encapsulated biofilm act in series as biological membrane filters. The LMBR technology has been previously shown to produce high-quality permeate and to operate with lower membrane fouling rates than conventional MBR. However, its performance has so far only been assessed at laboratory scale and using synthetic wastewater. In this study, the start-up performance of a 100 L pilot-scale LMBR was investigated for the treatment of actual urban wastewater. The LMBR showed high retention efficiencies for polyethylene (94.5 ± 13.6%) and polydimethylsiloxane (84.4 ± 14.4%) MPs, as well as high removal efficiencies for COD (98.9 ± 1.1%) and NH₄-N (97.0 ± 4.0%). Low permeate turbidity values (1.5 ± 0.8 NTU) throughout the operating period indicated the formation of a stable Living Membrane filter. The LMBR operated at low transmembrane pressures (2.6 ± 0.6 kPa) and low fouling rates (0.012 ± 0.70 kPa·day⁻¹), enabling continuous operation and preventing the need for external cleaning of the membrane module. The study demonstrated that the pilot-scale LMBR achieved high MP removal efficiencies, while maintaining low membrane fouling rates during the 60-day operation period. However, the highly variable NO₃-N and PO₄-P removals require further investigations and optimization of the LMBR system to fully meet the demands of urban wastewater treatment.