Reduction of Selenium Oxyanions in Wastewater Using Two Bacterial Strains

Abstract

The biological reduction of selenium oxyanions is capable of reducing both selenate and selenite to insoluble elemental selenium. In this process, however, bacteria inevitably require expensive chemicals such as yeast extract in almost all cases. Therefore, the reduction of selenium oxyanions with inexpensive alcohol would be more practical. A Pseudomonas sp. strain 4C-C isolated from a sludge in a wastewater treatment facility was able to reduce selenate to selenite using ethanol as an electron donor for its anaerobic respiration, but could not reduce selenite to elemental selenium. Paracoccus denitrificans JCM-6892, on the other hand, was observed to be able to reduce selenite to elemental selenium in the presence of ethanol, but not selenate to selenite. Therefore, a mixture containing a suspension of Pseudomonas sp. strain 4C-C and P. denitrificans JCM-6892 cells allowed selenate to be reduced to insoluble elemental selenium via selenite in the presence of ethanol and was also capable of reducing nitrate to nitrogen gas. Aiming at simplicity of the recovery process of insoluble elemental selenium, a polymeric gel immobilized mixture of the two bacterial strains was examined using ethanol as an electron donor. The immobilized mixture could therefore reduce not only selenate to elemental selenium, but also nitrate to nitrogen gas in a single step. The gel that immobilized the microbial mixture changed its color during the process to bright red and no red elemental selenium was left in the wastewater. This indicates that the reduced elemental selenium was completely absorbed in the gel. This simple bacterial combination would therefore be effective in the presence of ethanol to reduce selenium oxyanions in various wastewaters containing selenium and the other oxyanions.

Selenium removal from drinking water by adsorption to chitosan–clay composites and oxides: Batch and columns tests

“…Membrane filtration is expensive, due to low selectivity and fouling problems [5][6][7]. Microbial treatment, based on reduction to elementary selenium [8,9], is sensitive to oxygen and nitrate and high carbon concentrations are required [10,11]. Ionexchange resins show selectivity for selenate or selenite [6], but sulfate reduces removal and its precipitation with barium prior to filtration is therefore recommended [12].…”

Green-Synthesis of Selenium Nanoparticles Using Garlic Cloves (Allium sativum): Biophysical Characterization and Cytotoxicity on Vero Cells

“…Biological synthesis of selenium nanowires and nanorods have been done using bacteria, Rhizobium selenireducens, Dechlorosoma, pseudomonas, Paracoccus, Enterobacter, Thaurea, Sulfurospirillium, Desulfovibrio and Shewanella [25][26][27], while the extracellular synthesis of selenium nanoparticles was made using Aspergillus terreus fungi [28]. Moreover, microbes like Klebsiella pneumoniae [29] and Pseudomonas alcaliphila [30] have been employed for synthesizing selenium nanoparticles with quite increased amount of yield.…”

Nanomicrobiology

“…When the newly isolated Pseudomonas strain 4C-C was grown anaerobically on ethanol, selenate was reduced to selenite but selenite was not reduced to Se 0 (Morita et al 2007). Under anaerobic growth with ethanol, P. denitrificans JCM-6892 was capable of reducing selenite to Se 0 , but this bacterium could not reduce selenate to selenite.…”

“…Under anaerobic growth with ethanol, P. denitrificans JCM-6892 was capable of reducing selenite to Se 0 , but this bacterium could not reduce selenate to selenite. However, when these two organisms were grown as co-culture in the presence of selenate, Se 0 was produced (Morita et al 2007). …”