Recovery of Nitrous Oxide from Wastewater Treatment: Current Status and Perspectives

Abstract

Nitrous oxide (N<inf>2</inf>O) has been studied intensively in wastewater treatment as a detrimental greenhouse gas. However, increasingly more studies have adopted a contrasting objective, recovering N<inf>2</inf>O from wastewater as an energy resource. This article critically reviewed and analyzed the current status of N<inf>2</inf>O recovery research in wastewater treatment, to identify knowledge gaps and guide future research. Overall, N<inf>2</inf>O recovery is a promising research direction while still in active development. At present, unstable nitritation, the low energy potential, and potential environmental risks of N<inf>2</inf>O harvesting render the recovery of N<inf>2</inf>O from mainstream wastewater technically and economically challenging. High-strength wastewater treatment is more favorable for N<inf>2</inf>O recovery due to the high energy potential, established nitritation approaches, and significant carbon/aeration savings. The coupled aerobic-anoxic nitrous decomposition operation (CANDO) process is currently the most investigated and promising N<inf>2</inf>O recovery process. Nevertheless, more research is needed for its implementation on a large scale. Research opportunities for the CANDO process have been identified in this paper. Meanwhile, N<inf>2</inf>O recovery via autotrophic denitritation is a more recent concept, with limited studies hitherto. More experiments are needed to investigate its technological feasibility. Furthermore, other novel N<inf>2</inf>O recovery processes, e.g., truncated denitrification and chemical oxidation, should also be explored to facilitate the recovery of N<inf>2</inf>O from wastewater.