Hacking biofilm developed in a structured-bed reactor (SBRRIA) with integrated processes of nitrogen and organic matter removal.

Biomass samples from a structured-bed reactor subjected to recirculation and intermittent aeration (SBRRIA) were analyzed to investigate the bacterial community shift along with the changes in the C/N ratio. The C/N ratios tested were 7.6 ± 1.0 (LNC) and 2.9 ± 0.4 (HNC). The massive sequencing analyses revealed that the microbial community adjusted itself to different organic and nitrogenous applied loads, with no harm to reactor performance regarding COD and Total-N removal. Under LNC, conventional nitrification and heterotrophic denitrification steered the process, as indicated by the detection of microorganisms affiliated with Nitrosomonadaceae, Nitrospiraceae, and Rhodocyclaceae families. However, under HNC, the C/N ratio strongly affected the microbial community, resulting in the prevalence of members of Saprospiraceae, Chitinophagaceae, Xanthomonadaceae, Comamonadaceae, Bacillaceae, and Planctomycetaceae. These families include bacteria capable of using organic matter derived from cell lysis, ammonia-oxidizers under low DO, heterotrophic nitrifiers-aerobic denitrifiers, and non-isolated strains of Anammox. The DO profile confirmed that the stratification in aerobic, anoxic, and anaerobic zones enabled the establishment of different nitrogen degradation pathways, including the Anammox.

Effect of operating conditions on N2O production in an anammox sequencing batch reactor containing granular sludge.

Nitrous oxide (N2O) is one of the gases with the greatest impact in the atmosphere due to its persistence and significant contribution to the greenhouse effect. This study provides an insight into the dynamics of N2O production in wastewater nitrogen removal systems. A 10 L sequencing batch reactor containing enriched anammox biomass was subjected to different operational conditions, i.e., temperature, feed time, NO2 -/NH4 + ratio and the initial concentrations of NH4 + and NO2 -. Tests showed no significant differences in maximum N2O production when the system was operated with a shorter feed time and no increase in the operating temperature. A higher N2O production was observed when the initial NO2 -/NH4 + ratio increased from 1.3 to 1.7 and 1.9. The highest initial concentration of NO2 - was linked to an increase in residual N2O at the end of the batch cycle, probably due to heterotrophic denitrifying metabolism.