Assessment of nitrification process in a sequencing batch reactor: Modelling and genomic approach

Nitrification of ammoniacal nitrogen (N-NH₄⁺) to nitrate (N-NO₃^-) was investigated in a lab-scale sequencing batch reactor (SBR) to evaluate its efficiency. During the nitrification process the removal of N-NH₄⁺ reached 96%, resulting in 73% formation of N-NO₃^-. A lineal correlation (r² = 0.9978) was obtained between the concentration of volatile suspended solids (VSS) and the maximal N-NO₃^- concentration at the end of each batch cycle under stationary state. The bacterial taxons in the initial inoculum were identified, revealing a complex diverse community mainly in the two major bacterial phyla Proteobacteria and Actinobacteria. The FAPROTAX algorithm predicted the presence in the inoculum of taxa involved in relevant processes of the nitrogen metabolism, highlighting the bacterial genera Nitrospira and Nitrosomonas that are both involved in the nitrification process. A kinetic model was formulated for predicting and validating the transformation of N-NH₄⁺, N-NO₂^- and N-NO₃^- and the removal of organic and inorganic carbon (TOC and IC, respectively). The results showed how the increase in biomass concentration slowed down the transformation to oxidised forms of nitrogen and increased denitrification in the settling and filling stages under free aeration conditions.