Salinity alters the toxicity of copper nanoparticles to anammox consortia through modulating extracellular polymeric substances and membrane permeability

Among numerous engineered nanoparticles (NPs), CuNPs have been identified as a kind of high-risk inhibitor to anammox bacteria; however, the potential effects of salinity on the toxicity of CuNPs to anammox consortia remain unclear. Their short-term and long-term effects on anammox consortia were investigated by batch assays and continuously-fed bioreactors. The addition of 5.0–7.4 g L−1 NaCl immediately shielded the acute inhibition of 2.0–4.6 mg L−1 CuNPs on anammox activity. However, the coexistence of 5.0 g L−1 NaCl significantly aggravated the inhibitory effect of 3.0 mg L−1 CuNPs on anammox activity after exposure of about one month through reducing the content of extracellular polysaccharides. Even, the membrane permeability was significantly increased with the further increase of NaCl to 8.0 g L−1. Although the relative abundance of anammox bacteria at the DNA level was relatively higher, most of the anammox cells may not be able to perform metabolic functions normally due to membrane damage. Thus, appropriate salinity would attenuate the adverse impacts caused by the short-term shock of CuNPs, while pre-treatment is required to avoid the synergistic stress of high CuNPs when treating high salt wastewater.