Atmospheric nitrous oxide (N₂O), known for its much higher greenhouse gas potential than CO₂, plays a crucial role in climate change [1]. N₂O emissions from wastewater treatment plants (WWTPs), resulting from biological processes within these facilities, are emerging as a relevant concern [2]. This study aims to investigate the use of immobilised N₂O-respiring microorganisms [3] as a potential method to mitigate N₂O emissions from WWTPs.

Pure cultures of several N₂O-respiring microorganisms (isolates belonging to the genera Pseudomonas, Comamonas or Alcaligenes as well as Wolinella succinogenes) were successfully immobilised in Ca²⁺-alginate beads (2 or 4 %, w/v, alginate). Cell proliferation and colonies formation were observed under appropriate anaerobic N₂O respiration conditions with 10 or 100 % N₂O in the culture headspace. At high cell densities, gas bubbles, presumably consisting of N₂ gas, appeared and occasionally even disrupted the integrity of the alginate beads. Microrespirometry was used to investigate the N₂O consumption rates of alginate-immobilised cells as a function of the number of alginate beads.

This study demonstrates the potential of alginate-immobilised bacteria as a method for reducing N₂O emissions in wastewater treatment plants, which holds promise for climate change mitigation strategies.

References

1 Griffis, T.J., Chen, Z., Baker, J.M., Wood, J.D., Millet, D.B., Lee, X., Venterea, R.T. and Turner, P.A. (2017) Nitrous oxide emissions are enhanced in a warmer and wetter world. Proc. Natl. Acad. Sci. USA 114, 12081-12085.

2 Kampschreur, M.J., Temmink, H., Kleerebezem, R., Jetten, M.S.M. and van Loosdrecht, M.C.M. (2009) Nitrous oxide emission during wastewater treatment. Water Res. 43, 4093-4103.

3 Hein, S. and Simon, J. (2019) Bacterial nitrous oxide respiration: electron transport chains and copper transfer reactions. Adv. Microb. Physiol. 75, 137-175.