Inhibition of ferrous iron (Fe2+) to sulfur-driven autotrophic denitrification: Insight into microbial community and functional genes

The effect of Fe2+ on the performance of sulfur-driven autotrophic denitrification (SDAD) using S-0 as electron donor was evaluated. The experimental results showed that as initial Fe2+ concentration increased, nitrate (NO3-) removal rate significantly decreased. Fe2+ ion (0.1 mM and 1 Mm) inhibited SDAD rate (approximately 10% and 50%) and resulted in an accumulation of nitrite (NO2-) and nitrous oxide (N2O). The relative abundance of Thiobacillus was positively correlated with NO3- removal rate, whereas negatively correlated with Fe2+ concentration, suggesting that Fe2+ inhibited the sulfur-oxidizing denitrifying bacteria. Moreover, the abundance of bacterial 16S rRNA, denitrifying genes (narG, nirS, nirK and nosZ) and sulfur-oxidizing genes (soxB and dsrA) decreased with the increase of Fe2+ concentration, among them nosZ and soxB were the most sensitive genes to Fe2+, and nosZ/narG, soxB/(bacterial 16S rRNA) and soxB/nirK had influence on NO3- removal rate, while nosZ/ (bacterial 16S rRNA) affected N2O accumulation rate.