Enhancing biological conversion of NO to N₂O by utilizing thermophiles instead of mesophiles

The production of nitrous oxide (N₂O) through the biological denitrification of nitric oxide (NO) from flue gases has recently been achieved. Although the temperature of flue gas after desulphurization is usually 45-70 °C, all previous studies conducted microbial denitrification of NO under mesophilic conditions (22-35 °C). This study investigated the biological conversion of NO to N₂O in both mesophilic (35-45 °C) and thermophilic conditions (45-50 °C). The results showed that temperature has a great impact on N₂O production, with a maximum conversion efficiency (from NO to N₂O) of 82% achieved at 45 °C, which is obviously higher than the reported conversion efficiencies (24-71%) under mesophilic conditions. Additionally, high-throughput sequencing result showed that the genera Enterococcus, Clostridium, Romboutsia, and Streptococcus were closely related to NO denitrification and N₂O production. Microbial communities at 40 and 45 °C had greater metabolizing capacities for polymeric carbon sources. This study suggests that thermophilic condition (45 °C) is more suitable for biological production of N₂O from NO.