NOx removal from flue gas by an integrated physicochemical absorption and biological denitrification process.
An integrated physicochemical and biological technique for NO(x) removal from flue gas, the so-called BioDeNO(x) process, combines the principles of wet absorption of NO in an aqueous Fe(II)EDTA(2-) solution with biological reduction of the sorbed NO in a bioreactor. The biological reduction of NO to di-nitrogen gas (N(2)) takes place under thermophilic conditions (55 degrees C). This study demonstrates the technical feasibility of this BioDeNO(x) concept in a bench-scale installation with a continuous flue gas flow of 650 l.h(-1) (70-500 ppm NO; 0.8-3.3% O(2)). Stable NO removal with an efficiency of at least 70% was obtained in case the artificial flue gas contained 300 ppm NO and 1% O(2) when the bioreactor was inoculated with a denitrifying sludge. An increase of the O(2) concentration of only 0.3% resulted in a rapid elevation of the redox potential (ORP) in the bioreactor, accompanied by a drastic decline of the NO removal efficiency. This was not due to a limitation or inhibition of the NO reduction, but to a limited biological iron reduction capacity. The latter leads to a depletion of the NO absorption capacity of the scrubber liquor, and thus to a poor NO removal efficiency. Bio-augmentation of the reactor mixed liquor with an anaerobic granular sludge with a high Fe(III) reduction capacity successfully improved the bioreactor efficiency and enabled to treat a flue gas containing at least 3.3% O(2) and 500 ppm NO with an NO removal efficiency of over 80%. The ORP in the bioreactor was found to be a proper parameter for the control of the ethanol supply, needed as electron donor for the biological regeneration process. The NO removal efficiency as well as the Fe(III)EDTA(-) reduction rate were found to decline at ORP values higher than -140 mV (pH 7.0). For stable BioDeNO(x) operation, the supply of electron donor (ethanol) can be used to control the ORP below that critical value.
van der Maas
Peter
P
Sub-Department of Environmental Technology, Wageningen University, Bomenweg 2, P.O. Box 8129, 6700 EV Wageningen, The Netherlands.
van den Bosch
Pim
P
Klapwijk
Bram
B
Lens
Piet
P
D000042:Absorption; D000393:Air Pollutants / Q000302:isolation & purification*; D019149:Bioreactors; D007501:Iron / Q000737:chemistry; D009584:Nitrogen / Q000737:chemistry; D009589:Nitrogen Oxides / Q000302:isolation & purification*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry
D000393:Air Pollutants; D009589:Nitrogen Oxides; D007501:Iron; D009584:Nitrogen; D010100:Oxygen