Metabolic products comparison in autotrophic and heterotrophic nitrogen removal: Insights into membrane fouling

Metabolic products play a significant role in membrane fouling during biological wastewater treatment. However, the differences in metabolic product composition and membrane fouling potentials between autotrophic (anammox, AN) and heterotrophic (denitrification, DN) nitrogen removal systems are not well understood. This study cultivated autotrophic and heterotrophic nitrogen removal systems and analyzed the compositions of their metabolic products. The analysis methods included fluorescence excitation-emission matrix-parallel factor analysis (EEM-PARAFAC), Fourier transform infrared spectroscopy (FTIR), size exclusion chromatography coupled with organic carbon and nitrogen detection (SEC-OCD-OND), and Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Subsequently, the membrane fouling potential of these metabolic products was evaluated by dead-end membrane filtration experiments with microfiltration (MF) and ultrafiltration (UF) membranes. Significant differences in metabolic product composition existed between AN and DN nitrogen removal systems, which led to a distinct impact on membrane fouling. In the AN nitrogen removal system, membrane fouling was relatively mild despite the high abundance of polysaccharides (with C-O-C ring vibrations) and tannin-like substances in metabolic products. Its fouling was primarily caused by the rejection of humic substances. Conversely, in the DN nitrogen removal system, the high rejection of proteins and polysaccharides in SMP (52 % and 62 %) and EPS (18 % and 59 %) caused a pronounced flux decline, greatly increasing membrane fouling potential. These findings enhance understanding of membrane fouling mechanisms in autotrophic and heterotrophic nitrogen removal systems, providing actionable strategies to mitigate membrane fouling in biological nitrogen removal coupled with MBR process.