Study on arsenic biosorption using Fe(III)-treated biomass of Staphylococcus xylosus
Introduction
Arsenic is among the most abundant elements in the earth's crust, it can be naturally found in soil and water, due to leaching from rocks and sediments and also as a result of anthropogenic sources, such as mining and processing sulfide ores, combustion of fossils fuel and use of pesticides [1]. Inorganic and organic arsenic species are found in natural waters whereas inorganic arsenic species are the dominant form in most of the groundwater and surface water sources [2]. Arsenic exists mainly in two inorganic forms, trivalent As(III) and pentavalent As(V) [3]. As(III) can be found in groundwater, whereas As(V) exists in oxygenated surface waters [4]. The presence of arsenic in natural waters is of primary concern, due to its lethal effects, whereas As(III) is 25 to 60 times more toxic than As(V) as well as several hundreds times more toxic than organic arsenic species [5]. Several countries around the world, such as Taiwan, India, Hungary, Mexico, Argentina, Chile and United States are reported to contain high arsenic concentrations in their groundwater [1], [6].
The International Agency for Research on Cancer classifies arsenic in Class A of human carcinogens (prone to cancer of the bladder, lungs, skin, kidney, liver and prostate). Due to its acute lethal effects on human health, World Health Organization promulgated the maximum contaminant level (MCL) for arsenic in drinking water not to exceed 10 μg·l−1 [7].
In order to keep arsenic limit below 10 μg·l−1 several methods have been developed, including coagulation and flocculation, precipitation, adsorption, ion exchange and membrane filtration [7]. However, the standard methods developed to remove arsenic from industrial effluents are often expensive or fail to concentrate arsenic in small waste volumes [8].
Accordingly, there is an urgent need to develop a cost efficient treatment technology capable of separating arsenic from both drinking water and industrial effluents. One method that recently has gained attention is biosorption, where living or dead biomasses, as well as cellular products are used for the removal of metal or metalloid species. In that way, the problem of toxicity can be eliminated whereas no additional cost of nutrient supply and culture maintenance is required [9].
Several biosorbents including plant biomass such as Moringa oleifera, or sorghum, as well as bacteria, fungi, yeasts or algae have been used to remove As(III) and As(V) from aqueous solutions [9], [10], [11], [12]. The capacity of the biomass used has been increased in some cases, applying several modification methods [13], [14]. A chitosan-coated biosorbent has been used successfully for the removal of both forms of arsenic from aqueous solutions [15].
Iron and arsenic may co-exist in natural water sources [6]. Recently iron has been selected for the modification of biomass or other materials since it possesses a natural affinity towards arsenic species, exhibiting high removal efficiencies [16]. Pretreated tea fungus with FeCl3 was found to be an effective biosorbent for As(III), As(V) and Fe(II) removal from ground water samples [12]. In addition, non-viable fungal biomass of Aspergillus niger, coated with iron oxide showed good removal efficiencies of As(III) and As(V) from aqueous solutions [4].
The main objective of this study was the removal of As(III) and As(V) from aqueous solution using Fe(III)-pretreated biomass of Staphylococcus xylosus. The adsorption capacity of Staphylococcus xylosus was determined using both Langmuir and Freundlich isotherm models. Potentiometric titration of the biomass along with FT-IR studies were carried out to identify the functional groups on the biomass surface that participate in Fe(III) and arsenic species binding. Desorption studies of As(III) and As(V) along with the extend of Fe(III) leaching were also attempted, whereas biomass reuse was further investigated and the results are reported here.
Section snippets
Bacteria and media
Staphylococus xylosus was isolated from contaminated soil in a mining industry near Stratoni, Chalkidiki, Greece and identified according to the criteria described in Bergey's Manual of Systematic Bacteriology [17], by professor E. Litopoulou Tzannetaki in the Microbial Laboratory of Agricultural School of Aristotle University, Thessaloniki, Greece. Staphylococcus xylosus was cultivated in Luria-Bertani broth containing 1.0% tryptone, 0.5% yeast extract and 0.5% NaCl (Scharlau Chemie,
Biomass treatment with Fe(III)
The first series of biosorption were conducted with raw biomass of Staphylococcus xylosus and the results did not show any significant removal of both arsenic species. In an attempt to increase biosorption capacity, Staphylococcus xylosus cells were treated with Fe(III) solutions first. Among the parameters affecting the efficiency of biosorption treatment, pH is concerned to be the most critical. Here, at higher than 2.0 pH values, a sharp increase in the percentage of Fe(III) sorption was
Conclusions
Arsenic biosorption using Staphylococcus xylosus biomass pretreated with Fe(III) solutions was successful with both arsenic species studied, suggesting the potential use of this biomass in detoxification of Fe(III) containing industrial effluents. No significant differences were observed between As(III) and As(V) studied here, concerning the biosorption capacity of the biomass. The attractiveness of biosorption process was enhanced when desorption studies showed full recovery of As(III) and
Acknowledgement
The authors are grateful to State Scholarships Foundation (I.K.Y.), Greece for Mahendra Aryal's doctorate scholarship.
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