Ammonia assimilation: A double-edged sword influencing denitrification of Rhodobacter azotoformans and for nitrogen removal of aquaculture wastewater.

ABSTRACT

NO3--N and NH4+-N are two prevalent nitrogenous pollutants in aquaculture wastewater posing a significant health risk to aquatic animals. R. azotoformans ATCC17025 can rapidly denitrify to remove NO3--N, assimilating NH4+-N. The study investigated the influence of ammonia assimilation on bacterial denitrification. Results revealed that low concentration of NH4+-N (≤0.3 mM) accelerated denitrification, whereas high concentration inhibited it. RT-qPCR indicated that the inhibition of NO reduction under high concentration of NH4+-N was the primary cause of denitrification depression, whereas low concentration of NH4+-N enhanced the synthesis of practically all enzymes involved in denitrification. Finally, nitrogen-rich aquaculture effluent was effectively treated in lab-scale using a semi-continuous operation that provided an appropriate NH4+-N concentration for denitrification. This semi-continuous operation treated wastewater 2 times faster than the batch operation and the content of nitrogen decreased to effluent standard. The study can provide guidance for nitrogen removal of aquaculture wastewater with bioaugmentation.