(735h) A New Approach for NOx Control Based On the Chelate Absorption-Biofilm Electrode Integrated System

Nitric oxides (NO_x) are hazardous air pollutants that may cause acid rain, acid fog, photochemical smog, health risks of flora and fauna, etc. More and more attention has been paid to the control of NO_x. To date, only Selective Catalytic Reduction (SCR) and Selective Non-Catalytic Reduction (SNCR) obtained industrial applications widely. However, researchers never stopped in studying efficient, economic and green approach for NO_x control. Chemical absorption-biological reduction integrated system is one of the promising approaches which well integrates biological treatment with physicochemical methods. In order to break through the limitation of biological reduction rate, electrochemical action was introduced into this system in recent years. Biofilm electrode method combines biofilm process with electrochemical process, and enhances the reduction of Fe(II)EDTA-NO and Fe(III)EDTA by the cathodic hydrogen production.

Based on the biofilm electrode method, a chelate absorption–biofilm electrode integrated approach was innovatively utilized for the removal of nitrogen monoxide (NO) from the simulated flue gas. The feasibility of this system and parameters that may affect its performance were investigated. It was hoped that this study could provide theoretical foundation and basic data for the industrial application of this new approach.

A reliable chelate absorption–biofilm electrode integrated system was built up. The simulated flue gas with an inlet gas flow rate of 1 L/min contained 500 ppm of NO, 1%~10% of O₂, 15% of CO₂ and N₂. An absorption tower was used to absorb the simulated flue gas and a three-dimensional biofilm electrode reactor was used to regenerate the absorption liquid. Denitrifying bacteria (Pseudomonas sp. DN-2) and iron-reducing bacteria (Escherichia coli FR-2) were mixed cultivated to form biofilm. After inoculation process, the integrated system could maintain steady removal efficiency (90%) during long-term continuous operation. The electric current has an obvious impact on the NO removal efficiency during startup phase, and a relative small effect during steady state.

Effects of several key parameters such as gas residence time, inlet concentration of NO and O₂, and concentration of Fe(II)EDTA in the absorption liquid on the NO removal efficiency were also investigated in the integrated system. The inlet concentration of NO and O₂ had little effects on the NO removal, but a relatively obvious effects on the concentration of Fe(II)EDTA. The fall in the concentration of Fe(II)EDTA showed the greatest when concentration of inlet O₂ was increased. The decrease of gas residence time had the greatest impact on the NO removal efficiency.

Compared to the chemical absorption-biological reduction integrated system, this new approach has several evident advantages. The reduction rates of Fe(II)EDTA-NO and Fe(III)EDTA are enhanced, tolerance of O₂ in the flue gas is improved, processing load of NO is increased. Therefore, chelate absorption–biofilm electrode integrated system could provide better performance in the NO removal and larger processing load than the biological packed tower in the almost same or even harder conditions.