Kinetics of microbial selenite reduction by novel bacteria isolated from activated sludge.

A total of three bacteria isolated from activated sludge of a wastewater treatment plant were found to reduce selenite to elemental selenium nanoparticles as both amorphous nanospheres and monoclinic nanocrystals. The three isolated strains, which are potential candidates for bioremediation of selenite-contaminated water sources, were designated as Citrobacter sp. NVK-2, Providencia sp. NVK-2A, and Citrobacter sp. NVK-6 based on 16S rRNA sequencing. Despite belonging to the same genus, the kinetics of selenite reduction by strain NVK-2 (Vmax = 58.82 µM h-1, Km = 3737.12 µM) completely differed from that of strain NVK-6 (Vmax = 19.23 µM h-1, Km = 1300.17 µM). The selenite reduction rate by strain NVK-2A (Vmax = 9.26 µM h-1, Km = 3044.73 µM) was the slowest among the investigated microorganisms. The microbial selenite reduction rates according to various organic sources indicated that simple organic sources such as acetate and lactate were better than more complex organic sources such as propionate, butyrate, and glucose for selenite removal. Interestingly, the selenite reduction rate was significantly enhanced when the organic source was strategically divided into small portions and consecutively supplied to the culture.

Electrochemical effect on bioleaching of arsenic and manganese from tungsten mine wastes using Acidithiobacillus spp.

Mine wastes from tungsten mine which contain a high concentration of arsenic (As) may expose many environmental problems because As is very toxic. This study aimed to evaluate bioleaching efficiency of As and manganese (Mn) from tungsten mine wastes using the pure and mixed culture of Acidithiobacillus ferrooxidans and A. thiooxidans. The electrochemical effect of the electrode through externally applied voltage on bacterial growth and bioleaching efficiency was also clarified. The obtained results indicated that both the highest As extraction efficiency (96.7%) and the highest Mn extraction efficiency (100%) were obtained in the mixed culture. A. ferrooxidans played a more important role than A. thiooxidans in the extraction of As whereas A. thiooxidans was more significant than A. ferrooxidans in the extraction of Mn. Unexpectedly, the external voltage applied to the bioleaching did not enhance metal extraction rate but inhibited bacterial growth, resulting in a reverse effect on bioleaching efficiency. This could be due to the low electrical tolerance of bioleaching bacteria. However, this study asserted that As and Mn could be successfully removed from tungsten mine waste by the normal bioleaching using the mixed culture of A. ferrooxidans and A. thiooxidans.

Biological selenite removal and recovery of selenium nanoparticles by haloalkaliphilic bacteria isolated from the Nakdong River.

Microbial selenite reduction has increasingly attracted attention from the scientific community because it allows the separation of toxic Se from waste sources with the concurrent recovery of Se nanoparticles, a multifunctional material in nanotechnology industries. In this study, four selenite-reducing bacteria, isolated from a river water sample, were found to reduce selenite by > 85% within 3 d of incubation, at ambient temperature. Among them, strain NDSe-7, belonging to genus Lysinibacillus, can reduce selenite and produce Se nanospheres in alkaline conditions, up to pH 10.0, and in salinity of up to 7.0%. This strain can reduce 80 mg/L of selenite to elemental Se within 24 h at pH 6.0-8.0, at a temperature of 30-40 °C, and salinity of 0.1-3.5%. Strain NDSe-7 exhibited potential for use in Se removal and recovery from industrial saline wastewater with high alkalinity. This study indicates that extremophilic microorganisms for environmental remediation can be found in a conventional environment.

Bioleaching for environmental remediation of toxic metals and metalloids: A review on soils, sediments, and mine tailings.

Owing to industrial evolution, a huge mass of toxic metals, including Co, Cu, Cr, Mn, Ni, Pb, and Zn, and metalloids, such as As and Sb, has inevitably been released into the natural environment and accumulated in soils or sediments. Along with modern industrialization, many mineral mines have been explored and exploited to provide materials for industries. Mining industries also generate a vast amount of waste, such as mine tailings, which contain a high concentration of toxic metals and metalloids. Due to the low economic status, a majority of mine tailings are simply disposed into the surrounding environments, without any treatment. The mobilization and migration of toxic metals and metalloids from soils, sediments, and mining wastes to water systems via natural weathering processes put both the ecological system and human health at high risk. Considering both economic and environmental aspects, bioleaching is a preferable option for removing the toxic metals and metalloids because of its low cost and environmental safety. This chapter reviews the recent approaches of bioleaching for removing toxic metals and metalloids from soils, sediments, and mining wastes. The comparison between bioleaching and chemical leaching of various waste sources is also discussed in terms of efficiency and environmental safety. Additionally, the advanced perspectives of bioleaching for environmental remediation with consideration of other influencing factors are reviewed for future studies and applications.

Biological Manganese Removal by Novel Halotolerant Bacteria Isolated from River Water.

Manganese-oxidizing bacteria have been widely investigated for bioremediation of Mn-contaminated water sources and for production of biogenic Mn oxides that have extensive applications in environmental remediation. In this study, a total of 5 Mn-resistant bacteria were isolated from river water and investigated for Mn removal. Among them, Ochrobactrum sp. NDMn-6 exhibited the highest Mn removal efficiency (99.1%). The final precipitates produced by this strain were defined as a mixture of Mn2O3, MnO2, and MnCO3. Optimal Mn-removal performance by strain NDMn-6 was obtained at a temperature range of 25-30 °C and the salinity of 0.1-0.5%. More interestingly, strain NDMn-6 could be resistant to salinities of up to 5%, revealing that this strain could be possibly applied for Mn remediation of high salinity regions or industrial saline wastewaters. This study also revealed the potential of self-detoxification mechanisms, wherein river water contaminated with Mn could be cleaned by indigenous bacteria through an appropriate biostimulation scheme.