The biofilm of SSBR Raw sequence reads

Although silver nanoparticles (Ag-NPs) were found to be responsible for N2O generation, the mechanism of Ag-NPs induced N2O production has remained controversial and needs to be confirmed. In this study, chronic Ag-NPs exposure experiments were conducted in five independent sequencing batch biofilm reactors to systematically assess the effects of Ag-NPs on N2O emissions. The results indicated that a low dose of Ag-NPs (< 1 mg/L) could slightly suppress N2O generation. In contrast, a high dose (5 mg/L) of Ag-NPs would stimulate N2O emissions by 67.54%. ICP-MS and SEM-EDS together revealed that high Ag-NPs content would accumulate on the biofilm surface when exposed with 5 mg/L Ag-NPs. Microelectrode and stable isotope analyses further demonstrated that the accumulated Ag-NPs would construct the anaerobic zone in biofilm, which may be responsible for the stimulation of the nitrite reduction pathway to release N2O. A metagenomic analysis further attributed the higher N2O emissions under high dose of Ag-NPs exposure to the higher activity of ferredoxin-nitrate reductase and nitrite reductase (NO-forming) (i.e., 1.52- and 1.29-fold higher, respectively). These findings collectively suggest that chronic high dose Ag-NPs exposure could enhance the N2O emissions by forming anaerobic micro-environment in biofilm.