Integrated hybrid system for hydroponic wastewater treatment with a membrane bioreactor, microbial peroxide producing cell, and UVC-LED

This study presents an innovative hybrid water treatment system integrating a microbial peroxide-producing cell (MPPC), a membrane bioreactor (MBR), and an ultraviolet C light-emitting diode (UVC-LED) for long-term (293-day) operation, focusing on process control and performance optimization for hydroponic wastewater treatment. The MPPC unit was electrochemically optimized based on voltage output, electrode potential, and polarization behavior, achieving in situ hydrogen peroxide (H₂O₂) generation of 69μMh^-1 (equivalent to 2.3mgL^-1 h^-1) over 12h, with pH rising from 3.3 to 7.9. MBR performance was evaluated in terms of flux, transmembrane pressure (TMP), and key water quality parameters, achieving removal efficiencies of 95% for COD, 82% for NH₄⁺-N, 81% for T-N, and 18% for T-P. Despite effective filtration, culturable microbial contaminants persisted (exceeding 10⁶ CFU/mL) in the MBR permeate (MBR-P), necessitating UVC-LED disinfection. Based on inactivation kinetics, optimal UV fluence ranges were determined as 7-35 mJ/cm² for bacteria (including spores), 62 mJ/cm² for viruses, and 170 mJ/cm² for DNA fragments, achieving >4-log (99.99%) significant elimination. Additionally, UVC-LED/H₂O₂ advanced oxidation effectively degraded atrazine in both model (phosphate buffer solution) and real (filtered MBR-P) matrices, utilizing H₂O₂ sourced from MPPC. This study demonstrates the feasibility of an integrated MPPC/MBR/UVC-LED system for treating hydroponic wastewater, addressing both microbial disinfection and organic pollutant removal. These findings lay the groundwork for future system optimization and practical deployment in the sustainable treatment of hydroponic wastewater within smart farming applications.