NOx removal in chemical absorption-biological reduction integrated system: process rate and rate-limiting step.

Biological reduction of Fe(III)EDTA is considered as the key step that limits the removal efficiency of the chemical absorption-biological reduction integrated system. In this study, the process rates of each reaction step under typical conditions (T=50°C, C FeII(EDTA)=1-5 mmol/L, CNO=0-500 ppm, CO2=1-10%, pH=7) were determined. Relevant kinetic constants including rate constants of absorption part and Michaelis-Menten kinetic constants of regeneration part were also obtained. On this basis, the theoretical process rates of each reaction step were predicted and compared in a steady state. The results confirmed that the removal rate of NO in this system is limited by the biological reduction of Fe(III)EDTA. Moreover, it indicated that increasing the concentration of total iron appropriately could enhance the bioreduction of Fe(III)EDTA.

Enhanced reduction of Fe(II)EDTA-NO/Fe(III)EDTA in NO(x) scrubber solution using a three-dimensional biofilm-electrode reactor.

A promising technique called chemical absorption-biological reduction (CABR) integrated approach has been developed recently for the nitrogen oxides (NO(x)) removal from flue gases. The major challenge for this approach is how to enhance the rate of the biological reduction step. To tackle the challenge, a three-dimensional biofilm-electrode reactor (3D-BER) was utilized. This reactor provides not only considerable amount of sites for biofilm, but also many electron donors for bioreduction. Factors affecting the performance of 3D-BER were optimized, including material of the third electrode (graphite), glucose concentration (1000 mg·L(-1)), and volume current density (30.53 A·m(-3) NCC). Experimental results clearly demonstrated that this method significantly promotes the bioreduction rate of Fe(II)EDTA-NO (0.313 mmol·L(-1)·h(-1)) and Fe(III)EDTA (0.564 mmol·L(-1)·h(-1)) simultaneously. Experiments on the mechanism showed that Fe(II)EDTA serves as the primary electron donor in the reduction of Fe(II)EDTA-NO, whereas the reduction of Fe(III)EDTA took advantage of both glucose and electrolysis-generated H(2) as electron donors. High concentration of Fe(II)EDTA-NO or Fe(III)EDTA interferes the bioreduction of the other one. The proposed methodology shows a promising prospect for NO(x) removal from flue gas.