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• Hollow fiber membrane biofilm reactor (HFMBR) was used for nitric oxide removal. • Flexible non-porous polydimethylsiloxane (PDMS) membrane was used in the HFMBR. • Nitric oxide was reduced to N 2 by denitrifying biofilm on membrane outer surface. • Effect of gas supplying mode on the HFMBR performance was evaluated. • The maximum nitric oxide removal efficiency of 91 % was achieved. Nitrogen oxides (NOx) are one of the most important air pollutants, mainly caused by the combustion of fossil fuels and nitric acid production processes. The hollow fiber membrane biofilm reactor (HFMBR) is a suitable candidate for treatment of biodegradable gases such as NO which has a very low water solubility. In this study, NOx removal performance by denitrification process in an HFMBR using a non-porous polydimethylsiloxane (PDMS) based hollow fiber membrane (HFM) under various conditions was evaluated. A bioreactor was operated for 171 days under varying values of NO inlet load (44.6–89.2 mg m−2day-1), nitrate concentration (0−40 mg NO 3 −-N L-1), membrane inner pressure (0−400 mbarg), and different gas supplying modes as flow-through (open-end) or dead-end (closed-end). During this mode NO could be transferred completely from the gas phase to the biofilm, resulting in an increase in the removal efficiency. Over 4 weeks, the effect of gas supplying mode with a periodical switch of open-end/closed-end was evaluated for different on/off durations. 500 ppm NO/N 2 gas was fed through the lumen of the membranes with a flow rate of 10 mL min-1 for 60, 30, and 15 s and gas outlet port was closed by the solenoid valve for an another 60, 30, and 15 s, respectively. The highest removal efficiency was obtained as 91 % when on/off time was 30/30 s. Results showed that overall performance of the reactor can be increased by modifying inner membrane pressure and gas supplying strategy. [ABSTRACT FROM AUTHOR]