Response of a three dimensional bioelectrochemical denitrification system to the long-term presence of graphene oxide

• Increasing GO decreased denitrification efficiency and altered community abundance.
• Denitrifying genes abundances were decreased under high GO stress.
• Long-term presence of GO caused chronic impacts onto the microorganisms.

In this study, a three dimensional bioelectrochemical denitrification system (3D-BEDS) was operated under long-term graphene oxide (GO) condition to treat high nitrate polluted water. When GO concentration increased from 0 to 100 mg L−1, nitrate removal efficiency slightly decreased from 99.52% to 94.81%. However, when GO concentration was further increased to 150 mg L−1, the denitrification efficiency dramatically decreased to 74.95%. Increasing GO concentration in this BEDS resulted in decreased community richness, and the abundances of the dominant bacterial communities presented obvious shift. The abundances of denitrifying genes napA, nirS, and nirK showed no obvious changes with GO concentration lower than 50 mg L−1. However, the abundances of the three genes decreased when GO concentration was further increased to higher than 100 mg L−1. The increased lactate dehydrogenase (LDH) release and reactive oxygen species (ROS) production demonstrated that long-term presence of GO caused chronic impacts onto microorganisms in this BEDS.