Photo-oxygenation for nitritation and the effect of dissolved oxygen concentrations on anaerobic ammonium oxidation

Removal of nitrogen from wastewater without using electricity consuming aerators was previously observed in photo-bioreactors with a mixed algal-bacterial biomass. Algammox is the particular process based on algae, ammoniumoxidizing organisms and anammox bacteria. In this research the activity of anammox bacteria in such an oxygen-producing environment was tested, as well as the effect of short- duration increase in dissolved oxygen (DO) to values potentially inhibiting anammox activity. Sequencing batch photo- bioreactors were fed with settled domestic wastewater enriched with ammonium (200 mg NH4+-N/L) and exposed to light within the photosynthetic active range with intensity of about 500 mu mol/m(2).s. Each cycle consisted of 12 h illumination and 12 h darkness. A well- settling biomass (10 days solids retention time) developed that carried out nitritation, nitrification and anammox. Ammoniumremoval rate during the light periodwas 4.5mg N-NH4+/L.h, equal to 858mg NNH4+/m(2).h or 477mg N-NH4+/(mol photons). When the reactorswere aerated for 3 h to temporarily increase the DO, anammoxwas inhibited at bulk DO values larger than 0.4- 1.0mg/L. For almost oxygen saturated conditions, recovery time was about 9 days. Algammox photo-bioreactors are therefore able to overcome short periods of oxygen stress, provided they occur only occasionally. (C) 2018 Elsevier B. V. All rights reserved.