Arsenite Oxidation Research Articles

FERROCENYL ALKYLAMMONIUM N-SUBSTITUTED POLYPYRROLE CONTAINING Pt AND Pd AND ITS APPLICATION ON ELECTROANALYSIS OF ARSENITE

Arsenic occurs in a variety of forms and oxidation states and is a very toxic element. The main inorganic arsenic species present in natural waters are arsenate (oxidation state V) and arsenite ions (oxidation state III). Arsenite is more toxic and mobile than arsenate. Therefore, it is important the development of new materials for analysis and control of these toxic species. This research proves that polymer-metal composite electrode materials synthesized by incorporation of Pt0 and Pd0 nanoparticles into a poly(pyrrole-ferrocenyl alkylammonium) matrix present electrocatalytic properties towards the oxidation of arsenite to arsenate. The polymer films displayed a stable electrochemical response in aqueous solution. However, when the polymer film modified electrode were transferred to aqueous solution in presence of arsenite anions, the CV curves for polymer films were deeply modified by the decrease in the electroactivity of the film. It can be concluded that the cationic polymer films present a strong affinity toward arsenite anions. The composite films containing Pt0 or Pd0 showed catalytic activity towards oxidation of As(III) to As(V) due to the presence of metal catalyst particles into the polymer films.

Adsorption and oxidation study on arsenite removal from aqueous solutions by polyaniline/polyvinyl alcohol composite

In this study, the Polyaniline/Polyvinyl Alcohol (PANi/PVA) composite was examined for arsenite (As(III)) removal from aqueous solution. The effect of several parameters including PVA concetration (0–5g/L), pH (1–13), adsorbent dosage (0.5–6g/L), contact time (0–120min), initial As(III) concentration (0.5–100mg/L), and As(III) oxidation were evaluated on the adsorption efficiency. The results indicated that PVA has an effective role in increasing adsorptive capacity of PANi, by changing its morphology and extending its active surface sites. The adsorption process was pH dependent and As(III) removal consistently improved by increasing solution pH. Adsorption reached equilibrium within 1h and Kinetics study showed that the adsorption process followed the pseudo-second-order rate model. Maximum arsenite removal efficiency was obtained when 2g/L of PANi/PVA was added to the solution. The equilibrium adsorption data were well fitted to Langmuir isoterm model, and the maximum adsorption capacity of arsenite was 27.25mg/g. Furthermore, arsenite oxidation led to 65% adsorption enhancement at the neutral aqueous system and also decreased the sensitivity of adsorption to pH.

Kinetics of arsenite oxidation by Sinorhizobium sp. M14 under changing environmental conditions

Many arsenite oxidizing bacteria show potential for application in bioremediation of arsenic-contaminated waters, but most can be used effectively only under conditions similar to those prevailing at their isolation site. This problem may be overcome by the use of the plasmid pSinA, which provides its hosts arsenite oxidation ability. However, the application potential of the natural host strain, Sinorhizobium sp. M14, has not been assessed under environmental conditions, which may readily affect the efficiency of the oxidation process. Thus, the aim of this study was to investigate the impact of several factors (e.g. pH, temperature, arsenic concentration) on the growth kinetics and arsenite oxidation abilities of Sinorhizobium sp. M14. Batch experiments were carried out to determine the adaptability of the strain. Subsequently, growth kinetics were tested and verified in continuous cultures, under environment-like conditions. The obtained results indicate that the strain is capable of intensive growth (doubling time = 9.2 h) and efficient biooxidation in a wide range of conditions, including low temperatures (As(III) oxidation rate = 0.533 mg L−1 h−1 at 10 °C). It was shown that aeration of the cultures may increase both growth and biooxidation rates, when appropriate supplementation with organic nutrients is provided. The obtained qualitative indicators allow for the comparison of arsenite-oxidizing abilities of M14 with other strains, proving its potential for application in arsenic-contaminated water treatment technologies.

Effects of manganese oxide-modified biochar composites on arsenic speciation and accumulation in an indica rice (Oryza sativa L.) cultivar

A pot experiment was used to investigate arsenic (As) speciation and accumulation in rice, as well as its concentration in both heavily contaminated and moderately contaminated soils amended with manganese oxide-modified biochar composites (MBC) and biochar alone (BC). In heavily As-contaminated soil, application of BC and MBC improved the weight of above-ground part and rice root, whereas in moderately As-contaminated soil, the application of MBC and low rate BC amendment increased rice root, grain weight and the biomass of the plant. Arsenic reduction in different parts of rice grown in MBC-amended soils was greater than that in plants cultivated in BC-amended soils. Such reduction can be attributed to the oxidation of arsenite, As(III), to arsenate, As(V), by Mn-oxides, which also had a strong adsorptive capacity for As(V). MBC amended to As-contaminated soil had a positive effect on amino acids. The Fe and Mn levels in the iron-manganese plaque that formed on the rice root surface differed among the treatments. MBC addition significantly increased Mn content (p < 0.05); the application of 2.0% MBC increased Mn content 36- and 10-fold compared to the control in heavily and moderately As-contaminated soils, respectively. The results indicate that application of Mn oxide-modified biochar to As-contaminated paddy soil could effectively remediate contaminated soil and reduce As accumulation in edible parts of rice.

Biological arsenite oxidation with nitrate as sole electron acceptor

ABSTRACT The potential of anoxic biological arsenite oxidation with nitrate as the sole electron acceptor was tested by using the acclimatized activated sludge which was chronically exposed under arsenite and nitrate coexisted aquatic environment. The activated sludge cultivated in a sequencing batch reactor was fed with arsenite and nitrate as the main substrates over six months. A series of batch experiments were conducted with acclimated sludge. Results showed that no obvious inhibition was observed in the anoxic arsenite oxidation linked to nitrate and nitrite reduction at the concentration of arsenite up to 35 mg AsIII L−1. Moreover, it was found that nitrite was accumulated over the reaction probably due to limited availability of arsenite. The kinetic study further suggested that the maximum specific arsenite oxidation rates (q obs, max) with nitrate and nitrite as the electron acceptors were found to be 0.55 ± 0.10 mg AsIII g−1VSS min−1 and 0.40 ± 0.04 mg AsIII g−1VSS min−1, respectively.

Genome Sequence of the Photoarsenotrophic Bacterium Ectothiorhodospira sp. Strain BSL-9, Isolated from a Hypersaline Alkaline Arsenic-Rich Extreme Environment.

The full genome sequence of Ectothiorhodospira sp. strain BSL-9 is reported here. This purple sulfur bacterium encodes an arxA-type arsenite oxidase within the arxB2AB1CD gene island and is capable of carrying out “photoarsenotrophy” anoxygenic photosynthetic arsenite oxidation. Its genome is composed of 3.5 Mb and has approximately 63% G+C content.

Oxidation of arsenite to arsenate on birnessite in the presence of light.

The effect of simulated solar radiation on the oxidation of arsenite [As(III)] to arsenate [As(V)] on the layered manganese oxide, birnessite, was investigated. Experiments were conducted where birnessite suspensions, under both anoxic and oxic conditions, were irradiated with simulated solar radiation in the presence of As(III) at pH 5, 7, and 9. X-ray absorption spectroscopy (XAS) was used to determine the nature of the adsorbed product on the surface of the birnessite. The oxidation of As(III) in the presence of birnessite under simulated solar light irradiation occurred at a rate that was faster than in the absence of light at pH 5. At pH 7 and 9, As(V) production was significantly less than at pH 5 and the amount of As(V) production for a given reaction time was the same under dark and light conditions. The first order rate constant (kobs) for As(III) oxidation in the presence of light and in the dark at pH 5 were determined to be 0.07 and 0.04 h−1, respectively. The As(V) product was released into solution along with Mn(II), with the latter product resulting from the reduction of Mn(IV) and/or Mn(III) during the As(III) oxidation process. Post-reaction XAS analysis of As(III) exposed birnessite showed that arsenic was present on the surface as As(V). Experimental results also showed no evidence that reactive oxygen species played a role in the As(III) oxidation process.Electronic supplementary materialThe online version of this article (doi:10.1186/s12932-016-0037-5) contains supplementary material, which is available to authorized users.

The genetic basis of anoxygenic photosynthetic arsenite oxidation.

'Photoarsenotrophy', the use of arsenite as an electron donor for anoxygenic photosynthesis, is thought to be an ancient form of phototrophy along with the photosynthetic oxidation of Fe(II), H2 S, H2 and NO2-. Photoarsenotrophy was recently identified from Paoha Island's (Mono Lake, CA) arsenic-rich hot springs. The genomes of several photoarsenotrophs revealed a gene cluster, arxB2AB1CD, where arxA is predicted to encode for the sole arsenite oxidase. The role of arxA in photosynthetic arsenite oxidation was confirmed by disrupting the gene in a representative photoarsenotrophic bacterium, resulting in the loss of light-dependent arsenite oxidation. In situ evidence of active photoarsenotrophic microbes was supported by arxA mRNA detection for the first time, in red-pigmented microbial mats within the hot springs of Paoha Island. This work expands on the genetics for photosynthesis coupled to new electron donors and elaborates on known mechanisms for arsenic metabolism, thereby highlighting the complexities of arsenic biogeochemical cycling.

Functions and Unique Diversity of Genes and Microorganisms Involved in Arsenite Oxidation from the Tailings of a Realgar Mine.

This study focused on the functional and molecular characterizations of microbial communities from the tailings of the Shimen realgar mine. We fully explored, for the first time, the arsenite-oxidizing activities and the functional gene diversities of microorganisms from the tailings, as well as the correlation of the microbial activities/diversities with environmental factors. The findings of this study help us to better understand the diversities of the arsenite-oxidizing bacteria and the geochemical cycle of arsenic in the tailings of the Shimen realgar mine and gain insights into the microbial mechanisms by which the secondary minerals of the tailings were formed. This work also offers a set of unique arsenite-oxidizing bacteria for basic research of the molecular regulation of arsenite oxidation in bacterial cells and for the environmentally friendly bioremediation of arsenic-contaminated groundwater.

Tremendous effect of oxygen vacancy defects on the oxidation of arsenite to arsenate on cryptomelane-type manganese oxide

Manganese oxide as a benign and low-cost oxidant has been widely investigated for the oxidation of As(III) to As(V), but its As(III) oxidation rate is easily hindered due to the thermodynamically favorable adsorption of the As(V) species produced and coexisting ions. Herein, we develop a novel strategy of tremendously increasing the As(III) oxidation activity via tuning the concentration of oxygen vacancy defects (OVD) in cryptomelane-type manganese oxides (OMS-2). The result of the batch experiment of the As(III) oxidation on OMS-2 shows that increasing the concentration of oxygen vacancy defects in OMS-2 remarkably increases the specific As(III) oxidation rate from 0.12 to 0.22μmolm−2min−1, and dramatically reduces the unfavorable effect of the As(V) adsorption on the As(III) oxidation activity. The origin of the tremendous effect of OVD in OMS-2 on the As(III) oxidation activity is experimentally and theoretically investigated by the adsorption of the As(III) and As(V) species on OMS-2, the point of zero charge (pHPZC), the evolution of the concentration of Mn2+ ions dissolved in the solution, and density functional theory (DFT) calculations. The results reveal that the presence of OVD in OMS-2 not only makes the adsorption of As(III) on OMS-2 more thermodynamically favorable, but also accelerates the charge transfer from As(III) to Mn atom, thus significantly improving the As(III) oxidation activity.

Advantages of aeration in arsenic removal and arsenite oxidation by structural Fe(II) hydroxides in aqueous solution

Structural Fe(II) Hydroxide (SFH) was used to remove As(III) and As(V) from aerated synthetic wastewater with initially 30mg/L As at neutral pH values. Batch experiments were performed to investigate the influence of O2, pH and coexisting HPO42⿿ on As removal by 0.5g (Fe)/L SFH. The results suggested that removal efficiency for As(III) and As(V) were ⿼60% and ⿼50% under anoxic conditions at initial pH 7.0 and 9.0, respectively. However, the efficiency increased to over 90% for both As(III) and As(V) under oxic conditions. The in situ mineral transformation of SFH to newly formed Fe(II/III) and FeOOH was responsible for the robust removal. As(III) removal was nearly unaffected by HPO42⿿ (1.0mM), while obviously inhibition was observed in the case of As(V). The microstructure of fresh and reacted SFH was characterized by FTIR and XPS and these results indicate that As was removed via inner-sphere complexation and precipitation. XPS studies showed that As(III) was converted to As(V) after 2h of reaction in the pH range of 7.0⿿9.0, which is attributable to enhanced formation of Fe(IV) by the Fenton reaction during mineral transformation. In practice, results of this study suggest that aeration is advantageous to significantly enhancement of As(III) oxidation and removal with highly reactive SFH.

Simultaneous arsenite oxidation and nitrate reduction at the electrodes of bioelectrochemical systems.

Arsenic and nitrate contaminations in the soil and groundwater have urged the scientific community to explore suitable technologies for treatment of both contaminants. This study reports, for the first time, a novel application of bioelectrochemical systems for coupling As detoxification at the anode and denitrification at the cathode. A similar As(III) oxidation efficiency was achieved when anode potential was controlled by a potentiostat or a direct current (DC) power supply. However, a slightly lower nitrate reduction rate was obtained in reactors using DC power supply during simultaneous operation of nitrate reduction and As(III) oxidation. Microbial community analysis by denaturing gradient gel electrophoresis indicated the presence of some autotrophic As(III)-oxidizing bacteria, including Achromobacter spp., Ensifer spp., and Sinorhizobium spp., that can flexibly switch their original metabolism of using oxygen as sole electron acceptor to a new metabolism mode of using solid-state anode as sole electron acceptor driving for As(III) oxidation under anaerobic conditions. Although further research is required for validating their applicability, bioelectrochemical systems represent a brilliant technology for remediation of groundwater contaminated with nitrate and/or arsenite.

Arsenite oxidizing multiple metal resistant bacteria isolated from industrial effluent: their potential use in wastewater treatment.

Arsenite oxidizing bacteria, isolated from industrial wastewater, showed high resistance against arsenite (40mM) and other heavy metals (10mM Pb; 8mM Cd; 6mM Cr; 10mM Cu and 26.6mM As(5+)). Bacterial isolates were characterized, on the basis of morphological, biochemical and 16S rRNA ribotyping, as Bacillus cereus (1.1S) and Acinetobacter junii (1.3S). The optimum temperature and pH for the growth of both strains were found to be 37°C and 7. Both the strains showed maximum growth after 24h of incubation. The predominant form of arsenite oxidase was extracellular in B. cereus while in A. junii both types of activities, intracellular and extracellular, were found. The extracellular aresenite oxidase activity was found to be 730 and 750µM/m for B. cereus and A. junii, respectively. The arsenite oxidase from both bacterial strains showed maximum activity at 37°C, pH 7 and enhanced in the presence of Zn(2+). The presence of two protein bands with molecular weight of approximately 70 and 14kDa in the presence of arsenic points out a possible role in arsenite oxidation. Arsenite oxidation potential of B. cereus and A. junii was determined up to 92 and 88% in industrial wastewater after 6days of incubation. The bacterial treated wastewater improved the growth of Vigna radiata as compared to the untreated wastewater. It indicates that these bacterial strains may find some potential applications in wastewater treatment systems to transform toxic arsenite into less toxic form, arsenate.

MS title: Catalytic oxidation and removal of arsenite in the presence of Fe ions and zero-valent Al metals

Arsenic immobilization in acid mine drainage (AMD) is required prior to its discharge to safeguard aquatic organisms. Zero-valent aluminum (ZVAl) such as aluminum beverage cans (AlBC) was used to induce the oxidation of As(III) to As(V) and enhance the subsequent As removal from an artificially prepared AMD. While indiscernible As(III) oxidation was found in aerated ZVAl systems, the addition of 0.10–0.55mM Fe(II) or Fe(III) into the AMD significantly promoted the As(V) production. Reactions between Fe(II) and H2O2, which was produced through an oxidative reaction of ZVAl with dissolved oxygen, generated OH radicals. Such OH radicals subsequently induced the As(III) oxidation. Over the course of the Fenton like reaction, ZVAl not only directly generated the H2O2, but indirectly enhanced the OH radical production by replenishing Fe(II). Arsenite oxidation in the aerated ZVAl/Fe and AlBC/Fe systems followed zero- and first-order kinetics. Differences in the kinetic reactions of ZVAl and AlBC with respect to As(III) oxidation were attributed to higher productive efficiency of the oxidant in the AlBC systems. After the completion of As(III) oxidation, As(V) could be removed simultaneously with Al(III) and Fe(III) by increasing solution’s pH to 6 to produce Al/Fe hydroxides as As(V) scavengers or to form Al/Fe/As co-precipitates.

Long-term performance of rapid oxidation of arsenite in simulated groundwater using a population of arsenite-oxidizing microorganisms in a bioreactor

A population of arsenite-oxidizing microorganisms enriched from the tailing of the Shimen realgar mine was used to generate biofilms on the surfaces of perlites. This bioreactor is able to completely oxidize 1100 μg/L As(III) dissolved in simulated groundwater into As(V) within 10 min; after 140 days of operation, approximately 20 min were required to completely oxidize the same concentration of As(III). Analysis for the 16S rRNA genes of the microbial community showed that Bacteroidetes and Proteobacteria are dominant in the reactor. Six different bacterial strains were randomly isolated from the reactor. Function and gene analysis indicated that all the isolates possess arsenite-oxidizing activity, and five of them are chemoautotrophic. Further analysis showed that a large diversity of AioAs and two types of RuBisCOs are present in the microbial community. This suggests that many chemoautotrophic arsenite-oxidizing microorganisms were responsible for quick oxidation of arsenite in the reactor. We also found that the reactor is easily regenerated and its number is readily expanded. To the best of our knowledge, the arsenite-oxidizing efficiency, which was expressed as the minimum time for complete oxidization of a certain concentration of As(III) under a single operation, of this bioreactor is the highest among the described bioreactors; it is also the most stable, economic and environment-friendly.

High-Quality Draft Genomes from Thermus caliditerrae YIM 77777 and T.tengchongensis YIM 77401, Isolates from Tengchong, China.

The draft genomes of Thermus tengchongensis YIM 77401 and T. caliditerrae YIM 77777 are 2,562,314 and 2,218,114 bp and encode 2,726 and 2,305 predicted genes, respectively. Gene content and growth experiments demonstrate broad metabolic capacity, including starch hydrolysis, thiosulfate oxidation, arsenite oxidation, incomplete denitrification, and polysulfide reduction.

The Arsenite Oxidation Potential of Native Microbial Communities from Arsenic-Rich Freshwaters.

Microorganisms play an important role in speciation and mobility of arsenic in the environment, by mediating redox transformations of both inorganic and organic species. Since arsenite [As(III)] is more toxic than arsenate [As(V)] to the biota, the microbial driven processes of As(V) reduction and As(III) oxidation may play a prominent role in mediating the environmental impact of arsenic contamination. However, little is known about the ecology and dynamics of As(III)-oxidizing populations within native microbial communities exposed to natural high levels of As. In this study, two techniques for single cell quantification (i.e., flow cytometry, CARD-FISH) were used to analyze the structure of aquatic microbial communities across a gradient of arsenic (As) contamination in different freshwater environments (i.e., groundwaters, surface and thermal waters). Moreover, we followed the structural evolution of these communities and their capacity to oxidize arsenite, when experimentally exposed to high As(III) concentrations in experimental microcosms. Betaproteobacteria and Deltaproteobacteria were the main groups retrieved in groundwaters and surface waters, while Beta and Gammaproteobacteria dominated the bacteria community in thermal waters. At the end of microcosm incubations, the communities were able to oxidize up to 95% of arsenite, with an increase of Alphaproteobacteria in most of the experimental conditions. Finally, heterotrophic As(III)-oxidizing strains (one Alphaproteobacteria and two Gammaproteobacteria) were isolated from As rich waters. Our findings underlined that native microbial communities from different arsenic-contaminated freshwaters can efficiently perform arsenite oxidation, thus contributing to reduce the overall As toxicity to the aquatic biota.

Photocatalytic oxidation and simultaneous removal of arsenite with CuO/ZnO photocatalyst

Abstract We investigated the photocatalytic oxidation and simultaneous removal of arsenite in synthetic aqueous As solution with high concentration. The process was performed by using CuO/ZnO nanoparticles under UV irradiation at around neutral pH. The effects of CuO addition, initial arsenite concentration and photocatalyst loading on the treatment efficiency were investigated. Adsorption of arsenic onto catalytic surface was evaluated with fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Batch results showed it that CuO has a significant effect on the photocatalytic performance of ZnO. The rate constant of photocatalytic oxidation with CuO(20%)/ZnO was 4 times better than those obtained with pristine ZnO. The removal amount (mg g −1 ) of arsenic increased with an increase in initial arsenic concentration. As(III) solution of 30 mg L −1 could be completely removed with photocatalyst of 0.67 g L −1 during 10 h of irradiation time. The maximum As(III) removal amount by photocatalytic oxidation and simultaneous removal was 6.5 times larger relative to that observed in the adsorption in dark. The excellent photocatalytic oxidation and high uptake performances make CuO/ZnO a potentially attractive candidate for the removal of As(III) from highly arsenic contaminated water.

In Situ Oxidation and Efficient Simultaneous Adsorption of Arsenite and Arsenate by Mg–Fe–LDH with Persulfate Intercalation

Inorganic arsenic occurs mainly in As(III) and As(V) states in water environment, but arsenite is more toxic and difficult to remove than arsenate by usual adsorption processes. To achieve the in situ oxidation of As(III) and simultaneous removal of both As(III) and As(V) in water, a novel-layered double hydroxide (Mg–Fe–S2O8–LDH) with the intercalation of persulfate has been designed and synthesized by a calcination-reconstruction method. The arsenic adsorption performances and removal mechanism with the Mg–Fe–S2O8–LDH material were studied. The experimental result showed that, since the strong oxidation ability of the exchangeable persulfate ions from the LDH, the As(III) species in water were almost completely oxidized to the As(V) state and simultaneously adsorbed onto the Mg–Fe–S2O8–LDH. It was found that the maximum adsorption capacity for As(III) and As(V) in single-pollutant system was 75.00 and 75.63 mg·g−1, respectively. When the adsorbent dosage was 0.5 g·L−1 for a mixed As(III) and As(V) solution, the batch experiment showed that the residual arsenic concentration can be reduced from 1 mg·L−1 to lower than the limit value of drinking water standard recommended by WHO. It indicated that the synthesized Mg–Fe–S2O8–LDH is a potential attractive adsorbent for simultaneous removal of As(III) and As(V) in water.

Role of Acinetobacter sp. in arsenite As(III) oxidation and reducing its mobility in soil

ABSTRACTMicrobial arsenite oxidation was observed by Acinetobacter sp. XS21, this strain oxidised arsenite As(III) up to 80 mM within 48–72 h of incubation. The present strain XS21 oxidised As(III) at a very high concentration in a shorter interval of time than any of the previous reported microbes. Further, XS21 was applied to the soil to observe its ability in reducing the mobility of As(III), and we found that Acinetobacter sp. XS21 efficiently removed arsenite from soluble-exchangeable fraction and removed 70% of the arsenite as compared to control. This feature makes it a potential candidate for bioremediation. Arsenic-resistant bacteria with strong As(III)-oxidising ability may have potential to improve bioremediation of As(III)-contaminated sites. To understand their basis of resistance and transformation we found the As(III) oxidase gene using degenerate primer and amplified ∼550 bp of aioA gene. Amplified aioA gene sequence exhibiting 52% identity in terms of gene and deduced protein sequence to Uncultured bacterium, and Achromobacter sp. arsenite oxidase of larger subunit. Arsenite oxidase, an enzyme, was also observed in this isolate, which may provide a resistance and transforming ability. This bacterium was identified as Acinetobacter sp., by sequencing 16s rRNA gene sequence analysis.