Removing nitrogen from wastewater with side stream anammox: What are the trade-offs between environmental impacts?

Anaerobic ammonium oxidation (anammox) is a novel way to reduce nitrogen in ammonium rich wastewater. Although aquatic eutrophication will certainly be reduced, it is unknown how other environmental impacts may change by including anammox in the treatment of wastewater. Here, life cycle assessment (LCA) was used to assess the environmental profile of a full scale wastewater treatment plant over its complete life cycle. Changes in the environmental profile by introducing a two-step anammox system in the side stream were assessed based on monitoring data from the full scale Dokhaven wastewater treatment plant (Rotterdam, The Netherlands). Our results confirmed that the two-step anammox technique further reduced life cycle nitrogen emissions compared to the regular treatment of nitrogen in wastewater. This led to a decrease in marine eutrophication potential of 16% for the total wastewater treatment plant. However, our LCA results showed that these ammonium reductions came at the cost of increasing climate change and other environmental impacts. Climate change impacts increased with 9% going from a traditional wastewater plant to the one including two-step anammox, due to increased direct emissions next to electricity use. Our LCA highlights trade-offs when adding two-step anammox for nitrogen removal in wastewater treatment systems. This has significant implications for other WWTPs as these trade-offs should not neglected when implementation of anammox is considered.