Plouviez M, Shilton A, Packer MA, Guieysse B 2017a. N2O emissions during microalgae outdoor cultivation in 50 L column photobioreactors. Algal Research 26: 348-353.

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ABSTRACT

This study investigated the potential environmental significance of nitrous oxide (N2O) emissions from outdoor microalgal cultivation. Chlorella vulgaris, Neochloris sp., and Arthrospira platensis were cultivated in 50 L pilot scale photobioreactors (PBRs) operated in fed batch mode and fed with either nitrate (NO₃⁻) or ammonium (NH₄⁺) as the nitrogen (N) source. When NO₃⁻was supplied as N-source, Neochloris sp., and C. vulgaris cultures emitted 50.0–14,200 nmol·N₂O·m^− 2·h^− 1 (36 days of cultivation, n = 136, median = 2220 nmol·N₂O·m^− 2·h^− 1) and 9.60–38,000 nmol·N₂O·m^− 2·h^− 1(90 days of cultivation, n = 332, median = 4050 nmol·N₂O·m^− 2·h^− 1), respectively. Based on the emissions representing 25–75% of the data recorded from C. vulgaris fed NO₃⁻ (1500–8000 nmol·N₂O·m^− 2·h^− 1), N₂O emissions factors were estimated as 0.1–0.4% of the N input load of 25 g·N·d− 1. Further monitoring of C. vulgaris cultures showed that N₂O emissions were positively correlated to biomass concentration (R² = 0.77) and light intensity (R² = 0.57). Nitrous oxide emissions were not detected when C. vulgaris was cultivated using ammonium as N-source (32 days of cultivation, n = 84), or when A. platensis cultures were cultivated with NO₃⁻ as N-source (36 days of cultivation, n = 90). The use of ammonium as N-source or the selection of appropriate algae species could therefore provide simple N₂O mitigation strategies.