Insights into microalgal-bacterial consortia in sustaining denitrification via algal-derived organic matter in harsh low-C/N wastewater

Conventional nitrate removal processes are often hampered by insufficient carbon sources for remediating low-C/N wastewater. Herein, a microalgal-bacterial (MB) consortia system was constructed to leverage algal-derived organic matter for sustaining denitrification. The system demonstrated superior nitrate removal performance when assisted by algal-derived organic matter, achieving a 168.62 ± 4.17 % enhancement in nitrate removal capacity compared to the sole bacterial system. Furthermore, Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS) analysis of algal-derived organic matter revealed that specific components facilitating nitrate elimination included unsaturated aliphatic compounds, aliphatic/peptide-like/amino sugars, lignin-like, and tannin-like substances. Notably, the consortia showed preferential utilization of unsaturated aliphatic (35.21 %) and aliphatic/amino sugars over aliphatic/peptide-like/amino acids (31.05 %) and aliphatic/peptide-like compounds (31.31 %) within the CHO, CHON, CHON2, and CHON3 classes, respectively. Metagenomic analysis identified notable disparities in microbial community composition between the bacterial and MB consortia systems. Moreover, the MB consortia exhibited higher abundances of genes encoding nitrate removal enzymes, including those involved in denitrification, assimilatory/dissimilatory reduction, and L-glutamate synthesis pathways. Genes associated with lignin degradation were also detected, suggesting potential indirect contributions to nitrate elimination. Besides, the MB symbiotic microspheres were successfully fabricated and achieved efficient nitrate removal. These findings provide novel insights into the development of innovative MB symbiotic systems for nitrate removal under harsh carbon-limited conditions.