Enhanced biological removal of NOx from flue gas in a biofilter by Fe(II)Cit/Fe(II)EDTA absorption

► The mole ratio of the mixed absorbent of Fe(II)Cit to Fe(II)EDTA is selected to be 3. ► The biofilm was formed well on the packings after long-term adaptation. ► The system could achieve a high efficiency and flexibility in the sudden changes. ► High NO concentration and relative short EBRT had negative effect on NO removal. ► The new system can reduce operating costs with lower EDTA supplement.