Photo-oxygenation to support nitrification in an algal–bacterial consortium treating artificial wastewater

► Algae photo-oxygenation can be used to support nitrification in a photo-bioreactor. ► Ammonium conversion (7.7mg/Lh) was higher than reported for high rate algae ponds. ► Nitrification (81–85%) rather than algae uptake caused efficient ammonium removal. Oxygenation by photosynthesis in a mixed culture of algae and nitrifiers was investigated for its potential to support nitrification. An open photo-bioreactor (1L fermentor; 30°C) was inoculated with an enriched culture of nitrifiers obtained from activated sludge and a pure culture of Scenedesmus sp. The reactor was illuminated (60μmol/m2s) and operated as a sequencing batch reactor with 50% discharge per cycle and sludge retention time of 15 or 30days. Full nitrification of synthetic wastewater (50mgNH4+-N/L) without mechanical aeration was achieved after less than 14 cycles (18.5h React per 24h cycle) and the biomass steadily increased until a concentration of 1.9g VSS/L with 29mg chl-a/L. The maximum observed nitrification rate was 7.7mgNH4+-N/Lh. A mass balance showed that ammonium removal was primarily by nitrification (81–85%) rather than by ammonium uptake by algae.