Arsenic removal from water using iron-impregnated granular activated carbon in the presence of bacteria.

This study investigated the adsorption of arsenite [As(III)] and arsenate [As(V)] to iron-impregnated granular activated carbon (Fe-GAC), focusing on the effects of bacteria on arsenic removal. Characteristics of Fe-GAC were analyzed using field emission scanning electron microscopy along with energy dispersive X-ray spectrometry. Batch experiments were performed under various experimental conditions to determine the adsorption of As(III) and As(V) to Fe-GAC in the absence and presence of bacteria (Enterococcus faecalis, Escherichia coli, or Bacillus subtilis). In addition, biosorption of As(III) and As(V) to bacteria was observed with batch experiments. Experimental results showed that Fe-GAC was characterized by mosaic-like deposition layers separated by interspacing on the surface. Iron impregnation increased the removal of As(III) and As(V) in GAC. Biosorption experiments indicated that a small amount of As(V) adsorbed to bacteria while no adsorption of As(III) was observed. This phenomenon can be attributed to interactions of anionic As(V) with positively-charged amine groups present on bacterial surfaces. Results also showed that the influence of bacteria on arsenic removal in Fe-GAC was not eminent in our experimental conditions even though bacteria could occupy surface adsorption sites on iron (hydr)oxides. This study demonstrated that hindrance effects of bacteria on arsenic adsorption to the surfaces of Fe-GAC were minimal.

Bacterial attachment to iron-impregnated granular activated carbon.

Bacterial attachment to iron-impregnated granular activated carbon (Fe-GAC) was investigated in this study using Enterococcus faecalis ATCC 10100 and charcoal-based GAC. Two sets of column experiments were performed under different ionic strengths and pH conditions. Breakthrough curves of bacteria were obtained by monitoring effluent. Mass recoveries and attachment rate coefficients were quantified from these curves. In addition, characteristics of Fe-GAC were analyzed using field emission scanning electron microscopy (FESEM) and X-ray spectrometry (EDS). Results show that Fe-GAC was characterized by mosaic-like deposition layers of iron oxides with about 2 microm in thickness. Color mapping with FESEM visualized the spatial distribution of carbon (yellow-green) and iron (red) on Fe-GAC. EDS indicates that iron was distinctly found from Fe-GAC at three peak positions. Results also reveal that bacterial attachment to Fe-GAC was affected by ionic strength and pH. Bacterial mass recoveries decreased from 62.9 to 41.7% with increasing ionic strength from 1 to 50 mM. This indicates that bacterial attachment to the surfaces of Fe-GAC was enhanced with increasing ionic strength. With increasing pH from 6.46 to 9.19, mass recoveries increased from 50.5 to 84.2%, indicating that bacterial attachment to Fe-GAC was reduced with increasing pH. This study demonstrates that iron oxides offer favorable attachment sites for bacteria on the surfaces of Fe-GAC and further improves the knowledge of bacterial removal in Fe-GAC.

Determination of bacterial mass recovery in iron-coated sand: influence of ionic strength.

Column experiments were performed in this study to investigate the influence of ionic strength on the mass recovery of Escherichia coli in iron-coated sand. The first set of the experiments was performed in the coated sand under various NaCl concentrations. The second experiments were carried out in the coated sand under various NaCl concentrations with a fixed phosphate concentration. Bacterial mass recoveries were quantified from breakthrough curves. The mass recoveries were compared with those obtained from the experiments in quartz sand under the same ionic strength/composition. Experimental results show that the mass recovery in quartz sand decreased from 76.7 to 9.2% with increasing effective ionic strength (I(e)) from 0 to 149.4 mM using NaCl. In the coated sand, however, the mass recovery remained constant in the range between 2.7 and 3.7% even though I(e) increased in the same range. This indicates that bacterial adhesion to the coated sand may not be affected by ionic strength in the presence of NaCl. Results also illustrate that the mass recovery in quartz sand decreased from 64.7 to 13.3% with increasing I(e) from 0.97 to 149.6 mM using NaCl under a fixed phosphate concentration (0.97 mM as I(e)). In the coated sand, the mass recovery increased sharply to 58.5% in 0.97 mM phosphate concentration compared to the case in deionized water (3.0%). This indicates that in the coated sand bacterial mass recovery can increase due to the presence of phosphate. In addition, the mass recovery in the coated sand decreased from 58.5 to 6.7% with increasing I(e) from 0.97 to 149.6 mM using NaCl under a fixed phosphate concentration (0.97 mM as I(e)). This demonstrates that bacterial adhesion to the coated sand may be influenced by ionic strength in the presence of phosphate.