Efficient control of wastewater-derived dissolved organic nitrogen and its eutrophication potential via redox...

With increasingly stringent nitrogen discharge standards, effluent dissolved organic nitrogen (DON) in wastewater treatment plants has been recognized as a more significant contributor to the eutrophication of receiving waters than inorganic nitrogen. However, reducing wastewater-derived DON and its eutrophication potential under low-temperature conditions remains challenging. Here, we report a strategy to reduce effluent DON concentration and its labile components of post-denitrification bioreactors at low temperatures by adding small amounts (i.e., 0.1 and 0.15 mM) of 2-hydroxy-1,4-naphoquinone (HNQ). The effluent DON concentration from the bioreactors upon HNQ addition was lower than that in control bioreactors, with a maximum reduction of 64 %. Ultrahigh-resolution mass spectrometry results showed that HNQ addition reduced labile DON, including lipids-, proteins/amino sugars-, and carbohydrates-like molecules, thereby controlling the DON eutrophication potential, which was confirmed using a subsequent algal bioassay. Moreover, partial least-squares path modeling analysis showed that HNQ dosing significantly altered the microbial community (β =  - 0.95, p < 0.01) and function (β =  - 0.97, p < 0.01). This in turn influenced the production and consumption of labile DON, ultimately reducing the DON eutrophication potential. This study demonstrates a simple in situ upgrading scheme for existing post-denitrification devices to address DON-related eutrophication crises occurring in cold weather.