Re-acclimation performance and microbial characteristics of a thermophilic biofilter for NOx removal from flue gas

Abstract

Currently, a novel chemical absorption-biological reduction (CABR) integrated process, employing Fe(II)EDTA as a solvent, is being under development to reduce the cost of NOx removal from flue gas. In this work, the NO removal profile, re-acclimation performance, and microbial characteristics in a thermophilic biofilter were investigated at the conditions typical to CABR process. The biofilter comprised of four layers of packing material with a surface area of 1200 m(2) m(-3). Experimental results revealed that the biofilter could remove 95 % of the fed NO at typical flue gas conditions. As the gas residence time varied from 90 to 15 s, the NO removal efficiency decreased from 100 to 56.5 % due to the NO mass transfer limitation. The longer period of the biofilter shutdown required more time for its re-acclimation. For example, after 8-day shutdown, the biofilter was re-acclimated in 32 h. Denaturing gradient gel electrophoresis analysis of PCR-amplified product showed that Pseudomonas, a group of denitrifier, was dominant in the biofilter. Because the Pseudomonas was abundant at the bottom layer of packed-bed, the bottom layer contributed to 60-70 % of the total NO removal. In addition, Pseudomonas gradually faded away along the gas flow path from the bottom to the top of biofilter, resulting in a significant decrease in NO removal at the other three packed-bed layers. These observed results will provide the process engineering and scale-up data with respect to the biofilter operations to help advance the CABR process to pilot-scale testing.

A Biophysicochemical Model for NO Removal by the Chemical Absorption–Biological Reduction Integrated Process

“…The calculation of physicochemical constants and the estimation of biokinetic parameters for the modeling refer to the Supporting Information, and the results under the typical operating conditions can be found in the Supporting Information, Table S1, Figure S1, and Table S2 10 Experimental Procedure. A thermophilic biofilter with an inner diameter of 0.08 m and a height of 0.6 m started up in our previous work 15 was used for NO absorption in this study. The volume of the packing layers was 1.5 L, and the specific surface area (a t ) of the packings was 1200 m 2 m −3 .…”

“…It has been demonstrated that the CABR process features higher NO removal efficiency compared to the conventional biological denitrification, 11 which showed over 90% in the long term operation under the typical CABR conditions. 15 Parametric tests revealed that the gas residence time and the concentration of Fe(II)EDTA were critical to achieve a high NO removal efficiency. 15−17 It has been confirmed that the main end product of the NO reduction in the CABR system was nitrogen gas while N 2 O was an intermediate.…”

Simultaneous Biological and Chemical Removal of Sulfate and Fe(II)EDTA-NO in Anaerobic Conditions and Regulation of Sulfate Reduction Products

“…In recent years, moving-bed biofilm reactor (MBBR) has been widely used in the fields of sulfate reduction, sulfur autotrophic denitrification, nitrification and denitrification due to its comparatively low footprint and efficient treatment performance [17,18]. The MBBR process principle is based on the basic principle of the biofilm process, making full use of the advantages of the activated sludge process and overcoming the shortcomings of the traditional activated sludge process and the fixed biofilm process.…”

Pathway of FeEDTA transformation and its impact on performance of NOx removal in a chemical absorption-biological reduction integrated process

“…The reduction rate of Fe(III)EDTA was 5.17 × 10 −5 mol m −2 min −1 , which was only half of that of the bound NO 15 . Zhang et al 16 reported that during the operation of the CABR process, the total iron concentration in the recirculated solution dropped gradually in a biofilter. Based on the iron mass balance, the average iron loss in the biofilter was 0.83 M d −1 in the first 28 days in presence of 3% (v/v) oxygen 16 .…”

“…Zhang et al 16 reported that during the operation of the CABR process, the total iron concentration in the recirculated solution dropped gradually in a biofilter. Based on the iron mass balance, the average iron loss in the biofilter was 0.83 M d −1 in the first 28 days in presence of 3% (v/v) oxygen 16 . van der Maas et al 17 also showed that 2 mM d −1 of EDTA degradation occurred during the long-term operation of NO removal in presence of 3.5–3.9% (v/v) oxygen.…”