The promotion and inhibition effect of graphene oxide on the process of microbial denitrification at low temperature

This study found that graphene oxide (GO) improved microbial denitrification at low temperatures (similar to 12 degrees C), and the optimal concentration was 10 mg/L as the removal rate of NO3-N increased by 17%. At the optimal concentration, GO improved the electron transport system activity of the microbes and enhanced the activity of nitrate reductase and nitrite reductase while exhibited low microbial toxicity. The addition of GO increased the content of tightly bound extracellular polymeric substances (EPS). The results of fluorescence spectrometer indicated that GO accelerated the renewal of bound EPS (B-EPS). Fourier Transform infrared spectroscopy (FTIR) results showed that GO affected the secondary structure of the protein in B-EPS, making B-EPS more hydrophobic and promoting microbial aggregation. B-EPS affected by GO can promote the electron transfer process of microorganisms. However, high concentration (>25 mg/L) of GO may inhibit denitrification by competing for electrons, which was not conducive to denitrification thermodynamically.

Automated summary

Graphene oxide (GO) was found to enhance microbial denitrification at low temperatures, with the optimal concentration being 10 mg/L. However, high concentrations of GO may inhibit denitrification by competing for electrons. GO can improve electron transport system activity, increase nitrate reductase and nitrite reductase activity, and enhance microbial aggregation.