Removal of nitrogen from anaerobically digested swine manure was investigated using a sequencing batch photobioreactor (SBPR) with alternating light and dark periods. The reactor was seeded with an algal-bacterial consortium consisting primarily of Chlorella spp., which was originally collected from a wastewater treatment plant. The SBPR was operated in two different phases: Phase 1(Day 0-80) without additional carbon source and phase 2 (Day 90-163) with sodium acetate addition. Profiles of nitrogen during Phase 1 (no external carbon addition) are shown in Figure 1. During Phase 1a, overall NH4+ removal was relatively low, with approximately 9.5% assimilated into biomass and 51.3% removed by nitritation. Increasing the light intensity on day 50 improved the nitritation efficiency to 76.3%. The high NH4+ in the influent and the low DO (Figure 1b) favored the growth of ammonia oxidizing bacteria (AOB). Denitritation efficiency was low due to the low bioavailability of COD in the centrate feed. During Phase 2, sodium acetate addition resulted in improved denitritation rates (Figure 2). When acetate was provided with the centrate feed at the beginning of the dark period (Phase 2a), some nitrite remained in the effluent. However, effluent nitrite could be eliminated by shifting the operating cycle so that centrate was fed at the beginning of the light period and acetate was provided at the beginning of the dark period (Phase 2b). With carbon source addition during the dark period, the reactor completely removed ammonium without aeration; 80% of this removal was through nitritation/denitritation. The high temperature, high concentrations of ammonium and nitrite and low DO effectively inhibited nitrite oxidizing bacteria, resulting in stable nitritation in the SBPR. The hybrid microalgal photosynthesis and nitritation-denitritation process has the potential to save up to 85% of aeration requirements and 40% of external carbon source demand.

Novel shortcut nitrogen removal process by algal-bacterial consortia in a sequencing batch photobioreactor (SBPR)

249th National Meeting (2015)

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