Researchers and engineers are committed to finding effective
approaches
to reduce dissolved organic nitrogen (DON) to meet more stringent
effluent total nitrogen limits and minimize effluent eutrophication
potential. Here, we provided a promising approach by adding specific
doses of 2-hydroxy-1,4-naphthoquinone (HNQ) to postdenitrification
bioreactors. This approach of adding a small dosage of 0.03–0.1
mM HNQ effectively reduced the concentrations of DON in the effluent
(ANOVA, p < 0.05) by up to 63% reduction of effluent
DON with a dosing of 0.1 mM HNQ when compared to the control bioreactors.
Notably, an algal bioassay indicated that DON played a dominant role
in stimulating phytoplankton growth, thus effluent eutrophication
potential in bioreactors using 0.1 mM HNQ dramatically decreased compared
to that in control bioreactors. The microbe-DON correlation analysis
showed that HNQ dosing modified the microbial community composition
to both weaken the production and promote the uptake of labile DON,
thus minimizing the effluent DON concentration. The toxic assessment
demonstrated the ecological safety of the effluent from the bioreactors
using the strategy of HNQ addition. Overall, HNQ is a promising redox
mediator to reduce the effluent DON concentration with the purpose
of meeting low effluent total nitrogen levels and remarkably minimizing
effluent eutrophication effects.