Limits of the anammox process in granular systems to remove nitrogen at low temperature and nitrogen concentration

Achieving robust and highly efficient nitrogen removal in a mainstream anammox reactor by introducing low concentrations of readily biodegradable organics

“…In phase I, the reactor was operated without rbCOD input. Relatively high nitrification activity results in an increase in nitrate production and a deterioration in nitrogen removal performance (Figures 2, 3), as demonstrated in the literature (Díaz et al, 2020;Li W. et al, 2020). The DO (0.06-0.08 mg/L) supporting nitrification transferred from influent and air at the top of the reactor during mechanical mixing (Figure 3A).…”

“…In this study, an effective and applicable strategy was employed to solve nitrate accumulation caused by undesired NOB activity in mainstream anammox reactors. Other strategies have been reported to reduce nitrate yield, including purging the oxygen in the influent with nitrogen gas, minimizing the surface area of the reactor in contact with the atmosphere by adopting a high height/ diameter ratio, and providing protective covers in the anammox reactor (Díaz et al, 2020). However, these measures may not be economical or applicable in some cases, especially for upgrading existing WWTPs because they require major retrofitting of the reactor configuration.…”

“…Whereas the secondstage anammox reactor became a major source of nitrate generation. Excessive nitrate production in anammox reactors due to undesired NOB activity has been reported in different reactor configurations, including sequencing batch reactors (SBR), completely stirred tank reactors, and expanded granular sludge blanket reactors (Sánchez Guillén et al, 2016;Liu et al, 2018;Zhang et al, 2019;Díaz et al, 2020;Li W. et al, 2020). Most of the NOB suppression methods developed in first-stage PN reactors are not applicable to second-stage anammox reactors because they may inhibit anammox activity.…”