Effects of sulfide on sulfate reducing bacteria in response to Cu(II), Hg(II) and Cr(VI) toxicity

Abstract

Sulfate reducing bacteria (SRB) is identified as the primary organisms responsible for the treatment of heavy metal wastewater. However, most heavy metals can inhibit the growth of SRB during heavy metal treatment processes. Sulfide is a metabolic product of SRB and it can precipitate or reduce heavy metals. This study focused on the effects of sulfide on SRB resistance to Cu(II), Hg(I) and Cr(VI) toxicity. First, we considered the existence style of various heavy metals with and without sulfide addition by sequential extraction experiments. Second, the particle size distribution was evaluated and the cell structure during the metabolism of a SRB culture, containing different heavy metals, was analyzed by particle size distribution and TEM analyses. Third, the evolution of sulfate under the influence of different concentrations of heavy metals with and without sulfide addition was investigated to evaluate SRB activity. The results indicated that sulfide played an important role in alleviating and even eliminating the toxicity of Cu(II), Hg(II) and Cr(VI). We also discuss the mechanism of sulfide on SRB resistance to Cu(II), Hg(I) and Cr(VI) toxicity. With the development of metallurgy-related industries like metal finishing and electroplating, massive amounts of acid wastewater are generated and released into the environment [1]. These waste streams commonly contain high levels of sulfate and dissolved metals. The discharge of this heavy metal contaminated wastewater into the environment can be devastating to aquatic and terrestrial ecosystems [2]. Conventionally, the most widely used method to treat these effluents is chemical neutralization with hydroxide followed by the precipitation of metals. However, this method has serious limitations due to the production of large amounts of unstable metal hydroxides leading to high disposal and dewatering costs for the produced sludge [3]. The biological treatment of acidic and metal-containing wastewater is an attractive alternative. The main advantage of this process over chemical neutralization is that less sludge is generated *Corresponding author (email: hbcao@home.ipe.ac.cn) and insoluble compounds such as metal oxides or sulfides are produced that are easily separated and recycled [4][5][6]. SRB have been identified as the primary bacteria for use in the biological treatment of heavy metal containing wastewater. While SRB are capable of various metal transformations, metals can also inhibit their growth [7][8][9]. Sulfide which is produced biologically during sulfate reduction by SRB could precipitate [10,11] or reduce [12,13] heavy metal cation. This decreases or even eliminates the toxicity of the heavy metals toward SRB. To our knowledge, few systematic investigations on the effects of sulfide on SRB resistance to heavy metal ion toxicity and of biologically produced precipitates on SRB metabolism have been conducted. We, therefore, studied the toxic metal ions Cu(II), Hg(II) and Cr(VI), which are usually found in waste streams. The mechanism of sulfides in...

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“…Bioprecipitation of copper as well as sulphate reduction occurred maximally at lower concentrations of metal (1 and 5 ppm) and decreased retrogressively as the concentration of the dissolved metal increased (from 10 to 15 ppm). These results were in accordance with the data reported previously (Sani et al 2001 ; Utgikar et al 2003 ; Cabrera et al 2006 ; Azabou et al 2007 ; Sheng et al 2011 ). Various researchers have proved the stimulatory effects of heavy metals on SRB at lower concentrations and inhibitory (causing a reduction of metabolic activity) or even toxic (causing death) at higher concentrations (Utgikar et al 2002 ; Sani et al 2003 ).…”

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