Uptake pathway and continuous removal of nitric oxide from flue gas using microalgae

Nitric oxide (NO), a major constituent of NO_x in fossil fuel flue gas, can be removed by the microalga, Dunaliella tertiolecta, in a bubble-column-type bioreactor. The uptake pathway of NO was investigated, and it was found that little NO was oxidized in the medium before its uptake by algal cells and that NO mostly permeated directly into the cells by diffusion based on the mass balance of nitrogen and the change in nitrate and nitrite concentration in the medium in batch culture. For further application of this system, it is necessary to remove NO over a long duration, and the stability of NO removal is important. NO removal rate of about 50–60% could be maintained stably for 15 days in continuous culture under the light condition. Because the consumption of nitrate was reduced by the amount of taken NO, NO rather than nitrate is preferentially utilized as a nitrogen source for cell growth. Therefore, this algal system is useful for continuous NO removal and production of algal biomass using NO as a nitrogen source.