Mechanistic insights into nitrification by microalgae-bacterial consortia in a photo-sequencing batch reactor under different light intensities

Abstract

NH4+ removal by a consortium of microalgae, ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) was examined in a photo-sequencing batch reactor (PSBR) under various light intensities (150, 500, 1500 and 2000 μmol m−2 s−1). Nitrification performance revealed that the light stress tolerance of the consortium was up to 1500 μmol m−2 s−1 during the 12 h study. NH4+ removal efficiencies due to nitrification and microalgae uptake at 150, 500, 1500 and 2000 μmol m−2 s−1 light intensities are 100, 100, 6.2 and −2.2%, respectively. The nitrogen mass balance revealed that the microalgal-nitrifying (AOB and NOB) bacterial consortium utilized 19.89% of supplied ammonium for the growth and maintenance of microalgae, whereas 79.29% was eliminated through bacterial nitrification process at 150 μmol m−2 s−1. Ammonium uptake and bacterial nitrification were affected at light intensity ≥1500 μmol m−2 s−1, thus revealing that ammonium removal mechanism is strongly governed by the daily average light intensity (DALI). Based on the empirical equations to calculate the oxygen balance in PSBR the effect of DALI on nitrification performance was deduced as follows: (1) below 40 μmol m−2 s−1: insufficient O2 for nitrification; (2) at 40 μmol m−2 s−1: sufficient oxygen for nitrification with less than saturated dissolved oxygen; (3) 40–160 μmol m−2 s−1: sufficient oxygen for nitrification with significant dissolved oxygen; (4) above 160 μmol m−2 s−1: failure of nitrification, owing to inhibition of microalgal-bacterial consortia.