The core of this biological regeneration is how to effectively simultaneous reduce Fe(III)EDTA and Fe(II)EDTA-NO, two mainly products in the ferrous chelate absorption solution. reaction: Fe(II)EDTA+NOFe(II)EDTA-NO One significant drawback of this additive is usually that Fe(II)EDTA can be easily oxidized by oxygen in the flue gas and be formed Fe(III)EDTA. The oxidation of ferrous EDTA has been described to proceed via a complex multi-step mechanism summarized by the following equation: 2Fe(II)EDTA+1/2O2+2H+2Fe(III)EDTA+H2O Fe(III)EDTA, which is not capable of binding NO, would decrease scrubber answer capacity. Consequently, the Fe(III)EDTA reduction rate affects NOremoval efficiency. To circumvent this problem, reducing agents such as sulfite/bisulfite, dithionate, sulfide, ascorbic acid, glyoxal, iron metal, etc. and electrochemical method have been researched to regenerate ferrous chelates (Shi et al., 1996b; 1996c). However, none of these approaches have produced promising results because of the high costs, the production of unwanted by-products, or the low reduction rate. Recently, a new approach to reduce Fe(III)EDTA using cultivated active sludge made up of iron-reducing bacteria (Li et al., 2003), is now being researched. The biological process can be expressed by the equation: In our previous studies, a bacterial strain identified as sp. isolated from mixed cultures could be employed effectively to reduce Fe(III)EDTA (Jing et al., 2004a). The ferric ion, serving as a terminal electron acceptor, is usually reduced to ferrous ion, so that Fe(II)EDTA can be regenerated. In the metal chelate absorption process, the main complex, Fe(II)EDTA-NO, which can also serve as a terminal electron acceptor, may have some effects around the biological reduction of Fe(III)EDTA. However, to the best of our knowledge, there are no reports around the inhibition of sp. cell growth and biological reduction of Fe(III)EDTA by Fe(II)EDTA-NO. In order to get better insight into the biological reduction of Fe(III)EDTA, a competitive inhibition study would be conducted in this work. MATERIALS AND METHODS Chemicals Disodium ethylenediaminetetraacetate (Na2EDTA, 99.95%), FeCl36H2O (99.5%), D-glucose (99.5%, cell culture tested) were from Shanghai Chemical Reagent Co., China. All other chemicals were analytical CPUY074020 grade reagents. Bacterial strains Bacterial strains were isolated from mixed culture with terminal electron acceptors of Fe(III)EDTA. The strain CPUY074020 is usually rod-form and Gram unfavorable, DNAJC15 1.0 m in diameter and 3.0 m in length, mono, binary or short catenarin-arrange, nonmotile and without gemma, and was identified as sp. Detailed physiological properties can be found in our previous paper (Jing et al., 2004a). Enrichment of bacterial strains was done in 250 ml conical flasks made up of 100 ml basal medium at 40 C and shaked at 140 r/min in a rotary shaker. Cells in the medium were harvested by centrifugation at 5000 r/min for 15 min and washed twice with 0.1 mol/L phosphate buffer (pH 7.0), and then suspended in the phosphate CPUY074020 buffer at certain concentration for use. Details of the process can be found in Jing et al.(2004b). Analytical methods The concentration of ferrous irons and total irons in answer was determined by the 1,10-phenanthroline colorimetric method at 510 nm. The concentration of Fe(II)EDTA-NO was measured by a model 723A spectrophotometer at 420 nm. The concentration of cells was decided from the linear relationship between the optical density at 610 nm (OD610) and dry cell weight. Experiments The complex of Fe(III)EDTA was prepared with equal mol FeCl36H2O and Na2EDTA. Preparation of Fe(II)EDTA-NO answer: NO was bubbled through a solution of ferrous EDTA until full breakthrough of NO was observed in the sparging vessel effluent. The prepared answer was stored in a glass serum vials under N2 positive pressure to avoid oxidation of ferrous EDTA in answer. Details of the process can be found in Jing et al.(2004c). The inhibition experiment was conducted in 50 ml conical flasks sealed with teflon-coated rubber septa in a gyrating shaker at 140 r/min and heat of 40 C. The anaerobic condition.