New directions in biological nitrogen removal and recovery from wastewater.

This review summarizes strategies for biological nitrogen removal (BNR) and recovery from wastewater. The most commonly used BNR technology nitrification/denitrification is also the most energy intensive, even though there are lower energy options, including nitritation/denitritation and more efficient partial nitritation/Anammox; the latter is well demonstrated for side-stream treatment and progressing toward mainstream applications. Nitrogen recovery can be done through cell assimilation with phototrophs, but bottlenecks with solids separation and space requirements limit applications to tertiary treatment. Whereas, microbial electrochemical cells are energy efficient at recovering nitrogen from side streams, but not capable of achieving low effluent levels. The combined strengths of these emerging approaches will improve wastewater nitrogen removal by reducing energy consumption, minimizing effluent nitrogen, and maximizing nitrogen recovery.