No abstract

As an attractive alternative to the Haber–Bosch process, an electrochemical process for nitrate (NO3 –) reduction to ammonia (NH3) has made great strides in the development of advanced electrocatalysts to suppress the unavoidable H2 evolution reaction (HER) and side production of N2. However, isochronous NH3 separation and recovery from the mother liquor, especially wastewaters, are awfully neglected in state-of-the-art electrochemical systems. Here, we designed electrochemical three-phase interfaces constructed by a CoP cathode and a flat-sheet gas membrane to achieve NO3 – reduction to ammonia and simultaneous NH3 recovery in the form of (NH4)2SO4 from wastewaters. The partial current density for ammonia yield and its recovery rate were 37.3 mA cm–2 and 306 g NH3-N m–2 day–1, respectively, accompanying 100% NO3 – removal and 99.7% NH3 extraction. By favoring the originally unfavored side reaction HER, it served as the driving force for NH3 separation from the wastewater through gas stripping and membrane separation at the three-phase interfaces. Unexpectedly, the timely NH3 separation could also promote the reduction of NO3 – to ammonia due to the release of much more active sites. From these, we envision that the present electrochemical process can be routinely employed as an effective strategy to address energy and environmental issues with NH3 recovery from NO3 – wastewater.

An increase in the number of publications in recent years indicates that besides ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA) may play an important role in nitrogen removal from wastewater, gaining wide attention in the wastewater engineering field. This paper reviews the current knowledge on AOA and AOB involved in wastewater treatment systems and summarises the environmental factors affecting AOA and AOB. Current findings reveal that AOA have stronger environmental adaptability compared with AOB under extreme environmental conditions (such as low temperature and low oxygen level). However, there is still little information on the cooperation and competition relationship between AOA and AOB, and other microbes related to nitrogen removal, which needs further exploration. Furthermore, future studies are proposed to develop novel nitrogen removal processes dominated by AOA by parameter optimization.