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

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 (60 μmol/m2 s) and operated as a sequencing batch reactor with 50% discharge per cycle and sludge retention time of 15 or 30 days. Full nitrification of synthetic wastewater (50 mgNH4+-N/L) without mechanical aeration was achieved after less than 14 cycles (18.5 h React per 24h cycle) and the biomass steadily increased until a concentration of 1.9 g VSS/L with 29 mg chl-a/L. The maximum observed nitrification rate was 7.7 mgNH4+-N/Lh. A mass balance showed that ammonium removal was primarily by nitrification (81-85%) rather than by ammonium uptake by algae.