Biofilm stratification and autotrophic-heterotrophic interactions in a structured bed reactor (SBRIA) for carbon and nitrogen removal

The structured-bed reactor with intermittent aeration (SBRIA) is a promising technology for simultaneous carbon and nitrogen removal from wastewater. In-depth understanding of the vast diversity of microbiological phenomena occurring in the reactor are crucial for its progressive development and optimization. In this research, biofilm samples from the aerobic and anoxic/anaerobic zones of a SBRIA were analyzed through 16S rRNA sequencing to evaluate the bacterial community shift and stratification with variations in the airflow and aeration time. The results showed that the control of the airflow and aeration time were essential to guarantee good reactor performances, as it interfered in nitrifying and denitrifying communities. With an aeration time of 1.75 h and airflows of 2.4, 4.5 and 6.6 L.min-1 nitrification and denitrification occured simultaneously, gresulting in efficiencies close to 80%. A balanced distribution of anammox, nitrifiers and denitrifiers species was noted. The SBRIA configuration allowed anammox species to thrive in all studied conditions, which were identified as Planctomyces, Pirellula and Candidatus Brocadia genus. The optimization of airflow and aeration cycles promote the enrichment of Heterotrophic Nitrification-Aerobic Denitrification (HN-AD) bacteria represented mostly by Brevundimonas, Acinetobacter, Paracoccus and Sphingopyxis. The SBRIA configuration allowed the establishing of different nitrogen removal pathways by syntrophic relationships between nitrifiers, denitrifiers and anammox species, that together were responsible for the high efficiencies observed throughout operation.