Plant-Derived Bio-Carriers in MBBRs Enhancing Heterotrophic Nitrification-Aerobic Denitrification for Sustainable...

Sustainable wastewater treatment in recirculating aquaculture systems (RAS) requires efficient nitrogen removal, yet conventional plastic-based biocarriers pose environmental concerns. This study evaluates Luffa cylindrica-based bio-carriers, particularly modified luffa sponge (MLS), as an eco-friendly alternative for enhancing nitrogen removal in HNAD-MBBRs while simultaneously examining system performance under sequential C/N variation representative of RAS wastewater conditions. Three laboratory-scale HNAD-MBBRs were compared, each using a distinct bio-carrier: MLS, unmodified luffa sponge (ULS), and plastic K3 Kaldnes carriers (PKC). The systems operated for 56 days under varying carbon-to-nitrogen (C/N) ratios (10.5, 7, and 5). Microbial community analysis (16S rRNA sequencing) and biofilm morphology (SEM imaging) were conducted. The MLS outperformed other carriers, achieving 99.93% ammonium, 99.49% nitrite, and 99.19% nitrate removal at a C/N ratio of 7. Microbial analysis revealed a richer population of nitrogen-cycling bacteria such as Thauera and Hydrogenophaga on MLS, while SEM confirmed dense biofilm colonization with rod-shaped bacteria and extracellular polymeric substances (EPS). The MLS-based wastewater treatment system demonstrates superior nitrogen removal efficiency and microbial support, offering a sustainable alternative to plastic biocarriers in MBBRs. This aligns with global efforts to reduce plastic waste in aquaculture while maintaining high treatment performance.