Enhanced aquaculture wastewater treatment in a biofilm reactor filled with sponge/ferrous oxalate/biochar composite (Sponge-C2FeO4@NBC) biocarriers: Performance and mechanism

Fabricating low-cost and efficient biofilm carriers for moving bed biofilm reactors in wastewater treatment is crucial for achieving environmental sustainability. Herein, a novel sponge biocarrier doped with NaOH-loaded biochar and nano ferrous oxalate (sponge-C2FeO4@NBC) was prepared and evaluated for nitrogenous compounds removal from recirculating aquaculture systems (RAS) wastewater by stepwise increasing ammonium nitrogen (NH4+-N) loading rates. The prepared NBC, sponge-C2FeO4@NBC, and matured biofilms were characterized using SEM, FTIR, BET, and N2 adsorption-desorption techniques. The results reveal that the highest removal rates of NH4+-N reached 99.28 ± 1.3% was yielded by the bioreactor filled with sponge-C2FeO4@NBC, with no obvious nitrite (NO2--N) accumulation in the final phase. The reactor packed with sponge-C2FeO4@NBC biocarrier had the highest relative abundance of functional microorganisms responsible for nitrogen metabolism than in the control reactor, confirmed from 16S rRNA gene sequencing analysis. Our study provides new insights into the newly developed biocarriers for enhancing RAS biofilters treatment performance in keeping water quality within the acceptable level for the rearing of aquatic species.