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

Abstract

Nitrous oxide (N 2 O) has been studied intensively in wastewater treatment as a detrimental greenhouse gas. However, increasingly more studies have adopted a contrasting objective, recovering N 2 O from wastewater as an energy resource. This article critically reviewed and analyzed the current status of N 2 O recovery research in wastewater treatment, to identify knowledge gaps and guide future research. Overall, N 2 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 2 O harvesting render the recovery of N 2 O from mainstream wastewater technically and economically challenging. High-strength wastewater treatment is more favorable for N 2 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 2 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 2 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 2 O recovery processes, e.g., truncated denitrification and chemical oxidation, should also be explored to facilitate the recovery of N 2 O from wastewater.

Successful year-round mainstream partial nitritation anammox: Assessment of effluent quality, performance and N2O emissions

“…This knowledge, in turn, will support the design and establishment of new N 2 O mitigation strategies. In addition, investigations into catalytic off-gas treatment of N 2 O are essential ( Duan et al., 2021 ; Scherson et al., 2013 ). Such treatment will further reduce GHG emissions, and is even evaluated for its potential to generate energy, as for example in the coupled aerobic-anoxic nitrous decomposition operation (CANDO) process ( Scherson et al., 2014 ).…”

Harnessing Photoelectrochemistry for Wastewater Nitrate Treatment Coupled with Resource Recovery

“…Compared to the removal of NO 3 – contaminants as N 2 , the transformation to NH 3 /NH 4 + and N 2 O recovers the N-nutrients and upgrades the energetic value of the reactive-nitrogen contaminant species. Aqueous NH 3 /NH 4 + can be reused as a fertilizer and/or oxidized to generate electricity in an ammonia fuel-cell, and gaseous NH 3 can be used as a fuel to generate heat and produce electricity. − Despite being a potent greenhouse gas, N 2 O is also a powerful oxidizer, especially for the combustion of rocket-fuel and biogas and for supercharging applications as it increases the energy released during the combustion of CH 4 by 37% as compared to using O 2 as an oxidizer. ,, In prior work, bioprocesses have demonstrated viable energy and resource recovery during wastewater denitrification through the formation of N 2 O by coupling N-removal to high-rate and high-efficiency N 2 O generation. ,,, …”

“…This study focuses on evaluating the feasibility of a photoelectrochemical approach to recover nitrogen nutrients from NO 3 – contaminants present in ion-exchange brines − and treated wastewater. ,− The state-of-the-art nitrification-denitrification processes for wastewater treatment are biological approaches that utilize microbes to consume and remove the excess nutrients. , However, the conventional two-stage biological nitrification–denitrification process is energy intensive, consuming up to 45 MJ kg N –1 , − not effective in effluent streams that harbor conditions unsuitable for microbial growth, , and has not been optimized for resource recovery . Proof-of-concept bioprocesses, including the Sharon–Anammox and the coupled aerobic–anoxic nitrous decomposition operation (CANDO) have been proposed to lower the energy intensity and to promote energy recovery from N-contaminants but are yet to be adopted for large scale wastewater treatment. , Ion-exchange, ,, electrodialysis, , and reverse osmosis , are used to treat nitrates (and other ions) at an industrial scale for drinking water applications but result in the production of a secondary nitrate-concentrated brine that requires further treatment . Hence, there is an increasing demand to develop wastewater treatment technologies to harness renewable energy, to be effective for a wide range of effluent stream conditions and to facilitate resource recovery in the form of nutrients and energy.…”

“…12 Proof-of-concept bioprocesses, including the Sharon−Anammox and the coupled aerobic−anoxic nitrous decomposition operation (CANDO) have been proposed to lower the energy intensity and to promote energy recovery from N-contaminants but are yet to be adopted for large scale wastewater treatment. 23,26 Ion-exchange, 5,27,28 electrodialysis, 29,30 and reverse osmosis 31,32 nitrates (and other ions) at an industrial scale for drinking water applications but result in the production of a secondary nitrate-concentrated brine that requires further treatment. 33 Hence, there is an increasing demand to develop wastewater treatment technologies to harness renewable energy, to be effective for a wide range of effluent stream conditions and to facilitate resource recovery in the form of nutrients and energy.…”

“…9,70,71 In prior work, bioprocesses have demonstrated viable energy and resource recovery during wastewater denitrification through the formation of N 2 O by coupling N-removal to high-rate and high-efficiency N 2 O generation. 9,10,26,72 While outside the scope of this work, product separation and collection for NH 3 /NH 4 + and N 2 O could pose significant challenges. Therefore, this aspect needs to be considered in the design and evaluation of practical devices.…”