Characterization of the enhancement of zero valent iron on microbial azo reduction.

Yun Fang,Guoping Sun,Meiying Xu,Wei-Min Wu,Xingjuan Chen,Xueduan Liu,Jun Guo

doi:10.1186/s12866-015-0419-3

Abstract

BackgroundThe microbial method for the treatment of azo dye is promising, but the reduction of azo dye is the rate-limiting step. Zero valent iron (Fe0) can enhance microbial azo reduction, but the interactions between microbes and Fe0 and the potential mechanisms of enhancement remain unclear. Here, Shewanella decolorationis S12, a typical azo-reducing bacterium, was used to characterize the enhancement of Fe0 on microbial decolorization.ResultsThe results indicated that anaerobic iron corrosion was a key inorganic chemical process for the enhancement of Fe0 on microbial azo reduction, in which OH−, H2, and Fe2+ were produced. Once Fe0 was added to the microbial azo reduction system, the proper pH for microbial azo reduction was maintained by OH−, and H2 served as the favored electron donor for azo respiration. Subsequently, the bacterial biomass yield and viability significantly increased. Following the corrosion of Fe0, nanometer-scale Fe precipitates were adsorbed onto cell surfaces and even accumulated inside cells as observed by transmission electron microscope energy dispersive spectroscopy (TEM-EDS).ConclusionsA conceptual model for Fe0-assisted azo dye reduction by strain S12 was established to explain the interactions between microbes and Fe0 and the potential mechanisms of enhancement. This model indicates that the enhancement of microbial azo reduction in the presence of Fe0 is mainly due to the stimulation of microbial growth and activity by supplementation with elemental iron and H2 as an additional electron donor. This study has expanded our knowledge of the enhancement of microbial azo reduction by Fe0 and laid a foundation for the development of Fe0-microbial integrated azo dye wastewater treatment technology.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-015-0419-3) contains supplementary material, which is available to authorized users.

Highlights

The microbial method for the treatment of azo dye is promising, but the reduction of azo dye is the rate-limiting step
Because azo dyes are decolorized by functional microorganisms, characterizing the Fe0-assisted decolorization of azo dyes using a pure decolorizing bacterium may provide some exact information about the reaction mechanism, and understanding how the microbes interacts with Fe0 will facilitate the elucidation of the mechanisms of enhancement and optimize the biodecolorization process
Effects of Fe0 on azo dye decolorization by strain S12 To confirm that Fe0 enhanced the anaerobic bioreduction of azo dye, decolorization by strain S12 was performed at six different dosages (0, 10, 20, 30, 40, and 60 mM) of Fe0 at pH 7.0 (Figure 1)

Summary

Introduction

The microbial method for the treatment of azo dye is promising, but the reduction of azo dye is the rate-limiting step. Zero valent iron (Fe0) can enhance microbial azo reduction, but the interactions between microbes and Fe0 and the potential mechanisms of enhancement remain unclear. Zero valent iron (Fe0) can enhance anaerobic microbial azo reduction, but the exact mechanism of Fe0assisted microbial reduction remains unclear [9,10,11]. Because azo dyes are decolorized by functional microorganisms, characterizing the Fe0-assisted decolorization of azo dyes using a pure decolorizing bacterium may provide some exact information about the reaction mechanism, and understanding how the microbes interacts with Fe0 will facilitate the elucidation of the mechanisms of enhancement and optimize the biodecolorization process.

Methods

Results

Conclusion