Next-Generation Rotating Biological Contactors for Wastewater Management: Bioelectrochemical Integration, Biofilm Monitoring, and Process Intensification

Rotating biological contactors (RBCs) represent one of the most energy-efficient and robust attached-growth technologies for wastewater treatment. Over the past two decades, significant advancements have been achieved in RBC reactor design, disc materials, operational optimization, biofilm monitoring, and hybrid integrations with emerging treatment technologies. This review presents a comprehensive overview of the evolution of RBC systems, ranging from conventional disc-based aerobic reactors to advanced configurations integrated with bioelectrochemical systems such as microbial fuel cells (MFCs), microbial electrolysis cells, and rotating disc bioelectrochemical reactors. The review also discusses emerging RBC–microalgae systems for nutrient recovery, biomass valorization, and circular bioeconomy applications. Key operational and performance parameters, including chemical oxygen demand/biochemical oxygen demand removal, nitrification–denitrification, biofilm dynamics, energy consumption, hydrodynamic effects, and long-term process stability, are critically evaluated. Particular emphasis is placed on extracellular electron transfer mechanisms, electrode configurations, rotational hydrodynamics, and energy recovery in RBC–MFC hybrid systems. Recent developments in smart monitoring approaches, including optical coherence tomography, microscopy-based biofilm analysis, sensor-assisted monitoring, and intelligent process control strategies, are also reviewed for their potential to improve operational reliability and predictive maintenance. Furthermore, major operational challenges, such as biofilm sloughing, seasonal variability, mechanical stress, odor generation, corrosion, and scale-up limitations, are critically discussed. Future perspectives highlight the potential of advanced disc materials, conductive biofilm supports, smart monitoring systems, digital process optimization, and hybrid resource-recovery platforms for next-generation sustainable wastewater treatment. Overall, this review provides researchers and engineers with an updated understanding of modern RBC technologies and their growing role in energy-efficient, decentralized, and environmentally sustainable wastewater management.