A pilot study on the regeneration of ferrous chelate complex in NOx scrubber solution by a biofilm electrode reactor.

A chemical absorption-biological reduction integrated process has been proposed for the removal of nitrogen oxides (NO(x)) from flue gases. In this study, we report a new approach using biofilm electrode reactor (BER) to regenerate Fe(II)EDTA via simultaneously reducing Fe(II)EDTA-NO and Fe(III)EDTA in NO(x) scrubber solution. Biofilm formed on the surface of the cathode was confirmed by Environmental Scan Electro-Microscope. Experimental results demonstrated that it was effective and feasible to utilize the BER to promote the reduction of Fe(II)EDTA-NO and Fe(III)EDTA simultaneously. The reduction efficiency of Fe(II)EDTA-NO and Fe(III)EDTA was up to 85% and 78%, respectively when the BER was continuously operated with electricity current at 30 mA. The absence of electricity induced an immediate decrease in reduction efficiency, indicating that the bio-regeneration of ferrous chelate complex was electrochemically accelerated. The present approach is considered advantageous for the enhanced bio-reduction in the NO(x) scrubber solution.

A new approach for Fe(III)EDTA reduction in NO(x) scrubber solution using bio-electro reactor.

A new process for the removal of NO(x) by a combined Fe(II)EDTA absorption and microbial reduction has been demonstrated, in which part of the Fe(II)EDTA will be oxidized by oxygen in the flue gas to form Fe(III)EDTA. In former studies, strain FR-2 has been found to reduce Fe(III)EDTA efficiently. Otherwise, it has been reported that bio-electro reactor could efficiently provide a chance for simultaneous denitrification and metal ion removal. Therefore, a use of bio-electro reactor is suggested to promote the reduction of Fe(III)EDTA by strain FR-2 in this paper. The results showed that the concentration of Fe(III)EDTA decreased rapidly when electric current was applied, and that as the current density rose, the Fe(III)EDTA reduction rate increased while followed by a decrease afterward. The formation of the biofilm on the electrode was observed by ESEM (Environmental Scan Electro-Microscope). In addition, the Fe(III)EDTA reduction rate obviously decreased with the existence of NaNO(2).

NO(x) removal from simulated flue gas by chemical absorption-biological reduction integrated approach in a biofilter.

A chemical absorption-biological reduction integrated approach, which combines the advantages of both the chemical and biological technologies, is employed to achieve the removal of nitrogen monoxide (NO) from the simulated flue gas. The biological reduction of NO to nitrogen gas (N2) and regeneration of the absorbent Fe(II)EDTA (EDTA:ethylenediaminetetraacetate) take place under thermophilic conditions (50 +/- 0.5 degrees C). The performance of a laboratory-scale biofilter was investigated for treating NO(x) gas in this study. Shock loading studies were performed to ascertain the response of the biofilter to fluctuations of inlet loading rates (0.48 approximately 28.68 g NO m(-3) h(-1)). A maximum elimination capacity (18.78 g NO m(-3) h(-1)) was achieved at a loading rate of 28.68 g NO m(-3) h(-1) and maintained 5 h operation at the steady state. Additionally, the effect of certain gaseous compounds (e.g., O2 and SO2) on the NO removal was also investigated. A mathematical model was developed to describe the system performance. The model has been able to predict experimental results for different inlet NO concentrations. In summary, both theoretical prediction and experimental investigation confirm that biofilter can achieve high removal rate for NO in high inlet concentrations under both steady and transient states.

Evaluation of complexed NO reduction mechanism in a chemical absorption-biological reduction integrated NO(x) removal system.

Biological reduction of nitric oxide (NO) from Fe(II) ethylenediaminetetraacetic acid (EDTA)-NO to dinitrogen (N(2)) is a core process for the continual nitrogen oxides (NO(x)) removal in the chemical absorption-biological reduction integrated approach. To explore the biological reduction of Fe(II)EDTA-NO, the stoichiometry and mechanism of Fe(II)EDTA-NO reduction with glucose or Fe(II)EDTA as electron donor were investigated. The experimental results indicate that the main product of complexed NO reduction is N(2), as there was no accumulation of nitrous oxide, ammonia, nitrite, or nitrate after the complete depletion of Fe(II)EDTA-NO. A transient accumulation of nitrous oxide (N(2)O) suggests reduction of complexed NO proceeds with N(2)O as an intermediate. Some quantitative data on the stoichiometry of the reaction are experimental support that reduction of complexed NO to N(2) actually works. In addition, glucose is the preferred and primary electron donor for complexed NO reduction. Fe(II)EDTA served as electron donor for the reduction of Fe(II)EDTA-NO even in the glucose excessive condition. A maximum reduction capacity as measured by NO (0.818 mM h(-1)) is obtained at 4 mM of Fe(II)EDTA-NO using 5.6 mM of glucose as primary electron donor. These findings impact on the understanding of the mechanism of bacterial anaerobic Fe(II)EDTA-NO reduction and have implication for improving treatment methods of this integrated approach.