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The mechanisms responsible for the fast granulation of anaerobic sludge caused by Mg and Ca addition was examined in four lab-scale expanded granular sludge bed (EGSB) reactors. Results indicated that both Mg and Ca accelerated the sludge-granulation process and increased the amount of polysaccharides and proteins in the sludge. Energy dispersive x-ray spectrometry (EDX) analysis revealed that, in a mature granule, both Mg and Ca composed as phosphate and calcium was distributed primarily in the periphery of the granule, while magnesium distributed mainly in the interior. The addition of Mg was more favorable for the nuclei formation, whereas the addition of Ca was more favorable for subgranule growth and maintaining the granules' rigid structure. Results showed that the addition of Mg in the nuclei formation stage and Ca in the granule-growth stage accelerated granulation more than adding only one of them in the granulation process. [ABSTRACT FROM AUTHOR]

Given that the consumption of organic substances entails costly biodesulfurization, the characteristics of the bacterial community in a reactor should be determined to increase the desulfurizing rate under low organic loading condition. In this study, the bacterial community distribution in the expanded granular sludge bed reactor used to treat sulfate-containing wastewater with low organic loading rate was determined by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and 16S rDNA clone library analyses. DGGE results showed that the predominant bacteria were stable and accounted for ~90 % sulfate removal efficiency. Differences in band positions and intensities indicated that the distribution and abundance of bacteria were affected by their positions in the reactor. Typical bands were identified in the bacterial community comprising Desulfovibrio, Desulfomicrobium, Thiomonas, Acinetobacter, Bacteroidetes, and Chloroflexi. Their functions in the reactor were also discussed. The possible links between the functional and microbial responses were also investigated based on the characteristic and spatial distribution of each bacterium in consortium. [ABSTRACT FROM AUTHOR]

A novel technique for internal structure and elemental distribution analyses of granular sludge is presented. Sludge samples were freeze-dried and embedded in epoxy resin to form a module, which were then ground and polished to obtain sequential cross-sections. The cross-sections were analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). SEM observations showed that one granule was formed having several cores with different inorganic minerals, rather than a single core. EDX results indicate that the main elements of the granules are O, Ca, Mg, and P. In addition, the distribution areas of calcium and magnesium in the granule do not coincide. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

large volume of bacterially produced precipitates are generated during the bio-treatment of heavy metal wastewater. The composition of the bacterially produced precipitates and its effects on sulfate reducing bacteria (SRB) in copper-containing waste stream were evaluated in this study. The elemental composition of the microbial precipitate was studied using electrodispersive X-ray spectroscopy (EDX), and it was found that the ratio of S:Cu was 1.12. Combining with the results of copper distribution in the SRB metabolism culture, which was analyzed by the sequential extraction procedure, copper in the precipitates was determined as covellite (CuS). The bacterially produced precipitates caused a decrease of the sulfate reduction rate, and the more precipitates were generated, the lower the sulfate reduction rate was. The particle sizes of bacterially generated covellite were ranging from 0.03 to 2 μm by particles size distribution (PSD) analysis, which was smaller than that of the SRB cells. Transmission electron microscopy (TEM) analysis showed that the microbial covellite was deposited on the surface of the cell. The effects of the microbial precipitate on SRB metabolism were found to be weakened by increasing the precipitation time and adding microbial polymeric substances in later experiments. These results provided direct evidence that the SRB activity was inhibited by the bacterially produced covellite, which enveloped the bacterium and thus affected the metabolism of SRB on mass transfer. [ABSTRACT FROM AUTHOR]