Academic literature on the topic 'Arsenic cycle'
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Journal articles on the topic "Arsenic cycle"
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Miyashita, Shin-ichi, Shoko Fujiwara, Mikio Tsuzuki, and Toshikazu Kaise. "Cyanobacteria produce arsenosugars." Environmental Chemistry 9, no. 5 (2012): 474. http://dx.doi.org/10.1071/en12061.
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Environmental contextAlthough arsenic is known to accumulate in both marine and freshwater ecosystems, the pathways by which arsenic is accumulated and transferred in freshwater systems are reasonably unknown. This study revealed that freshwater cyanobacteria have the ability to produce arsenosugars from inorganic arsenic compounds. The findings suggest that not only algae, but cyanobacteria, play an important role in the arsenic cycle of aquatic ecosystems. AbstractMetabolic processes of incorporated arsenate in axenic cultures of the freshwater cyanobacteria Synechocystis sp. PCC 6803 and Nostoc (Anabaena) sp. PCC 7120 were examined. Analyses of arsenic compounds in cyanobacterial extracts using a high-performance liquid chromatography–inductively coupled plasma mass spectrometry system showed that both strains have an ability to biotransform arsenate into oxo-arsenosugar-glycerol within 20 min through (1) reduction of incorporated arsenate to arsenite and (2) methylation of produced arsenite to dimethylarsinic acid by methylarsonic acid as a possible intermediate product. In addition, Synechocystis sp. PCC 6803 cells are able to biosynthesise oxo-arsenosugar-phosphate from incorporated arsenate. These findings suggest that arsenosugar formation as well as arsenic methylation in cyanobacteria possibly play a significant role in the global arsenic cycle.
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HANAOKA, Ken'ichi. "Arsenic Cycle in Marine Ecosystmes." Kagaku To Seibutsu 37, no. 10 (1999): 653–59. http://dx.doi.org/10.1271/kagakutoseibutsu1962.37.653.
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Borges Freitas, S. C., D. van Halem, M. M. Rahman, J. Q. J. C. Verberk, A. B. M. Badruzzaman, and W. G. J. van der Meer. "Hand-pump subsurface arsenic removal: the effect of groundwater conditions and intermittent operation." Water Supply 14, no. 1 (September 12, 2013): 119–26. http://dx.doi.org/10.2166/ws.2013.180.
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Hand-pump subsurface arsenic removal (SAR) has been investigated in rural Bangladesh with different groundwater conditions and intermittent operation modes. Multiple injection-abstraction cycles were performed after injection of 1 m3 of aerated water. From these experiments it can be concluded that hand-pump SAR, in the traditional injection-abstraction design, does not provide drinking water below the WHO arsenic guideline of 10 μg/L. Results show that arsenic removal was not enhanced by: (i) injection of O2-rich water, (ii) higher Fe:As ratios in the groundwater, or by (iii) multiple injection-abstraction cycles, i.e. at location 1, the breakthrough occurred at abstraction-injection ratios of Va/Vi = 2, for cycle 23. It is proposed that dissolved organic carbon (DOC), bicarbonate and phosphate have a significant effect on the arsenic adsorption process. However, iron removal was very efficient and abstraction-injection ratios increased within successive cycles, with Va/Vi > 8 for cycle 23. Furthermore, intermittent operation reduced arsenic concentrations after stop and restart, suggesting insufficient contact time between soluble arsenic and oxidized iron surfaces around the tube well.
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Saunders, Jaclyn K., Clara A. Fuchsman, Cedar McKay, and Gabrielle Rocap. "Complete arsenic-based respiratory cycle in the marine microbial communities of pelagic oxygen-deficient zones." Proceedings of the National Academy of Sciences 116, no. 20 (April 29, 2019): 9925–30. http://dx.doi.org/10.1073/pnas.1818349116.
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Microbial capacity to metabolize arsenic is ancient, arising in response to its pervasive presence in the environment, which was largely in the form of As(III) in the early anoxic ocean. Many biological arsenic transformations are aimed at mitigating toxicity; however, some microorganisms can respire compounds of this redox-sensitive element to reap energetic gains. In several modern anoxic marine systems concentrations of As(V) are higher relative to As(III) than what would be expected from the thermodynamic equilibrium, but the mechanism for this discrepancy has remained unknown. Here we present evidence of a complete respiratory arsenic cycle, consisting of dissimilatory As(V) reduction and chemoautotrophic As(III) oxidation, in the pelagic ocean. We identified the presence of genes encoding both subunits of the respiratory arsenite oxidase AioA and the dissimilatory arsenate reductase ArrA in the Eastern Tropical North Pacific (ETNP) oxygen-deficient zone (ODZ). The presence of the dissimilatory arsenate reductase gene arrA was enriched on large particles (>30 um), similar to the forward bacterial dsrA gene of sulfate-reducing bacteria, which is involved in the cryptic cycling of sulfur in ODZs. Arsenic respiratory genes were expressed in metatranscriptomic libraries from the ETNP and the Eastern Tropical South Pacific (ETSP) ODZ, indicating arsenotrophy is a metabolic pathway actively utilized in anoxic marine water columns. Together these results suggest arsenic-based metabolisms support organic matter production and impact nitrogen biogeochemical cycling in modern oceans. In early anoxic oceans, especially during periods of high marine arsenic concentrations, they may have played a much larger role.
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Nadar, S. Venkadesh, Masafumi Yoshinaga, Palani Kandavelu, Banumathi Sankaran, and Barry P. Rosen. "Crystallization and preliminary X-ray crystallographic studies of the ArsI C–As lyase fromThermomonospora curvata." Acta Crystallographica Section F Structural Biology Communications 70, no. 6 (May 10, 2014): 761–64. http://dx.doi.org/10.1107/s2053230x14008814.
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Arsenic is a ubiquitous and carcinogenic environmental element that enters the biosphere primarily from geochemical sources, but also through anthropogenic activities. Microorganisms play an important role in the arsenic biogeochemical cycle by biotransformation of inorganic arsenic into organic arsenicals andvice versa. ArsI is a microbial nonheme ferrous-dependent dioxygenase that transforms toxic methylarsonous acid to the less toxic inorganic arsenite by C–As bond cleavage. An ArsI ortholog from the thermophilic bacteriumThermomonospora curvatawas expressed, purified and crystallized. The crystals diffracted to 1.46 Å resolution and belonged to space groupP43212 or its enantiomerP41212, with unit-cell parametersa=b= 42.2,c= 118.5 Å.
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Rhine, E. Danielle, Elizabeth Garcia-Dominguez, Craig D. Phelps, and L. Y. Young. "Environmental Microbes Can Speciate and Cycle Arsenic." Environmental Science & Technology 39, no. 24 (December 2005): 9569–73. http://dx.doi.org/10.1021/es051047t.
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Han, Yong Hwan, Sung Zoo Kim, Suhn Hee Kim, and Woo Hyun Park. "Arsenic trioxide inhibits growth of As4.1 juxtaglomerular cells via cell cycle arrest and caspase-independent apoptosis." American Journal of Physiology-Renal Physiology 293, no. 2 (August 2007): F511—F520. http://dx.doi.org/10.1152/ajprenal.00385.2006.
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We investigated the in vitro effects of arsenic trioxide on cell growth, cell cycle regulation, and apoptosis in As4.1 juxtaglomerular cells. Arsenic trioxide inhibited the growth of As4.1 cells with an IC50of ∼5 μM. Arsenic trioxide induced S phase arrest of the cell cycle and very efficiently stimulated apoptosis in As4.1 cells, as evidenced by flow cytometric detection of sub-G1DNA content, annexin V binding assay, and 4′-6-diamidino-2-phenylindole staining. This apoptotic process was accompanied by the loss of mitochondrial transmembrane potential (ΔΨm), a decrease in Bcl-2, the activation of caspase-3, and cleavage of poly(ADP-ribose) polymerase. However, all of the caspase inhibitors tested in this experiment failed to rescue As4.1 cells from arsenic trioxide-induced cell death in view of sub-G1cells and annexin V positive-staining cells. However, a caspase-8 inhibitor (Z-IETD-FMK) noticeably decreased the loss of ΔΨmin arsenic trioxide-treated cells. When we examined the changes in reactive oxygen species (ROS), H2O2, or O2•−in arsenic trioxide-treated cells, H2O2was significantly decreased and O2•−was increased. In addition, we detected a decreased GSH content in arsenic trioxide-treated cells. Taken together, we have demonstrated that arsenic trioxide as a ROS generator potently inhibited the growth of As4.1 JG cells through S phase arrest of the cell cycle and caspase-independent apoptosis.
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Dey, Arindam, Sandip Chattopadhyay, Suryashis Jana, Mukul Kumar Giri, Shamima Khatun, Moumita Dash, Hasina Perveen, and Moulima Maity. "Restoration of uterine redox-balance by methanolic extract of Camellia sinensis in arsenicated rats." Acta Biologica Szegediensis 62, no. 1 (August 23, 2018): 7–15. http://dx.doi.org/10.14232/abs.2018.1.7-15.
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Arsenic, an environmental and industrial pollutant causes female reproductive disturbances and female infertility. Several researchers found that the use of Camellia sinensis (CS) (green tea) is effective as an alternative therapeutic strategy in the management of several health ailments. This study explores the role of CS extract against arsenic-induced rat uterine tissue damage. Methanolic extract of CS (10 mg/kg BW) was tested concomitantly in arsenic-treated (10 mg/kg BW) rats for a duration of two-oestrous cycle length (8 days). CS effectively attenuated arsenic-induced antioxidantdepletion and necrosis in uterine tissue. Rats treated with sodium arsenite showed significantlyreduced activities of enzymatic antioxidants like superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) in uterine tissue as evidenced by the results of spectrophotometric and electrozymographic analysis. Co-administration of CS significantly reversed the above oxidative stress markers in uterine tissue along with the histopathological changes in ovarian and uterine tissue. Moreover, an increase in the level of transcription factor NF-κB in the uterine tissue in association with reduced serum levels of vitamin B12 and folic acid were mitigated in arsenic fed rats following CS co-administration.
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Ryan, P. C., F. J. Huertas, L. N. Pincus, and W. Painter. "ARSENIC-BEARING SERPENTINE-GROUP MINERALS: MINERAL SYNTHESIS WITH INSIGHTS FOR THE ARSENIC CYCLE." Clays and Clay Minerals 67, no. 6 (December 2019): 488–506. http://dx.doi.org/10.1007/s42860-019-00040-1.
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Oremland, Ronald S., John F. Stolz, and James T. Hollibaugh. "The microbial arsenic cycle in Mono Lake, California." FEMS Microbiology Ecology 48, no. 1 (April 2004): 15–27. http://dx.doi.org/10.1016/j.femsec.2003.12.016.
Full textDissertations / Theses on the topic "Arsenic cycle"
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Benkherouf, M. (Moaadh). "Life cycle assessment of arsenic removal methods." Master's thesis, University of Oulu, 2018. http://urn.fi/URN:NBN:fi:oulu-201812043210.
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The presence of arsenic in drinking water has been a major concern for years, due to its concentration being above the maximum allowable limit of 10 μg/l. Ingestion of arsenic-contaminated water causes different types of cancer, cardiovascular diseases, skin lesion and more. Many techniques have been developed and used to reduce arsenic levels to the maximum allowable limit. The conventional methods to do so are adsorption, membrane filtration, coagulation-flocculation, oxidation, and ion exchange. The most common adsorption material is activated carbon produced from hard coal, but there is a shift towards using agro-waste materials in order to produce a more environmentally-friendly adsorbent with high rejection levels. Such materials include cocoa pod husk, ice cream beans, and red mombin seeds, where cocoa pod husk AC was able to remove 80% of arsenate, and red mombin seeds AC removed arsenate almost completely. Nanofiltration membranes were reportedly effective for arsenic removal, reaching a removal percentage of 90%. In this work, a life cycle assessment analysis using SimaPro was conducted for arsenic removal using red mombin seeds activated carbon and spiral wound nanofiltration membranes, as they are able to reach high removal efficiencies. The methods were then compared based on their impacts on the different environmental and damage categories to determine which is the better option. The results showed that nanofiltration had the lowest environmental impacts over the different impact categories by a huge differenceJuomaveden sisältämä arseeni on ollut merkittävä ongelma jo pitkään, sillä arseenipitoisuus ylittää usein sille asetun raja-arvon 10 μg/l. Arseenipitoisen juomaveden käyttö aiheuttaa muun muassa syöpä- ja verenkiertoelimistön sairauksia sekä iho-ongelmia. Juomaveden arseenipitoisuuden vähentämiseksi on kehitetty useita menetelmiä, joista tavallisimpia ovat adsorptio, kalvoerotus, koagulaatio ja flokkaus, hapetus ja ioninvaihto. Yleisin adsorptiomateriaali on aktiivihiili, joka on valmistettu kivihiilestä, mutta nykyisin maatalousjätteestä valmistetut adsorbentit ovat kiinnostuksen kohteena, sillä ne ovat ympäristöystävällisempiä ja niiden avulla voidaan saavuttaa korkea haitta-aineiden poistoprosentti. Tällaisia materiaaleja ovat muun muassa kaakaopavun kuoret ja punamombinin siemenet. Tutkimuksissa on saavutettu kaakaopavun kuorista valmistetun adsorbentin avulla 80 %:n poistuma arseenille ja punamombinin siemenet ovat poistaneet vedestä arseenin lähes kokonaan. Nanosuodatuksessa kalvot ovat tutkimusten mukaan poistaneet arseenista 90 %. Tässä tutkimuksessa suoritettiin SimaPro-ohjelmiston avulla elinkaariarviointi kahdelle vedenkäsittelymenetelmälle: adsorptiolle, jossa käytettiin punamombinin siemenistä valmistettua adsorbenttia, sekä nanosuodatukselle, jossa käytettiin spiraalikalvoja. Menetelmiä verrattiin niiden ympäristövaikutusten perusteella parhaan vaihtoehdon löytämiseksi. Tulosten perusteella nanosuodatuksen ympäristövaikutukset kaikissa vaikutusluokissa olivat merkittävästi alhaisemmat
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McCaffery, Kevin A. "Isolation and Characterization of a Microorganism from Groundwater that Reduces Arsenate." Fogler Library, University of Maine, 2002. http://www.library.umaine.edu/theses/pdf/McCafferyKA2002.pdf.
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Rodríguez-Freire, Lucía. "The Role of Microorganisms in the Biogeochemical Cycle of Arsenic in the Environment." Diss., The University of Arizona, 2014. http://hdl.handle.net/10150/333167.
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Arsenic (As) is a highly toxic chemical that is widely distributed in groundwater around the world. As-bearing sulfide minerals (ASM) are known to contribute to high background concentrations of As in groundwater in regions where the geochemistry of the parent material is dominated by sulfide minerals. The fate of As in groundwater depends on the activity of microorganisms which can oxidize arsenite (Asᴵᴵᴵ), or reduce arsenate (Asᵛ). In oxidizing environments, Asᵛ is the predominant species, and the accumulation of As is limited by the sorption of As onto iron (Fe) oxides and hydroxides. Under reducing environments, Asᴵᴵᴵ is the predominant specie, and while the sorption strength of Asᴵᴵᴵ on the Fe-surface of Fe (oxy)hydroxides is weaker, the accumulation of As in water can be limited by the precipitation of As as part of an ASM. The main aim of this research is to study the impact of microbial activity on the mobilization and immobilization of As in the environment. The first objective of this research was to characterize the metabolic activity of three Asᴵᴵᴵ-oxidizing bacteria, Azoarcus sp. pb-1 strain EC1, Azoarcus sp. pb-1 strain EC3 and Diaphorobacter sp. pb-1 strain MC, isolated from a non-contaminated, pristine environment. These Asᴵᴵᴵ-oxidizing bacteria demonstrated a great metabolic flexibility to use oxygen and nitrate to oxidize Asᴵᴵᴵ as well as organic and inorganic substrates as alternative electron donors (e-donors) explains their presence in non-As-contaminated environments. The findings suggest that at least some Asᴵᴵᴵ-oxidizing bacteria are flexible with respect to electron-acceptors and e-donors and that they are potentially widespread in low As concentration environments. The second objective of this research was to investigate the stability of orpiment (As₂S₃) and arsenopyrite (FeAsS), at circumneutral pH and 30°C, under aerobic- and or anoxic conditions (nitrate amended as electron acceptor (e-acceptor)), in order to assess the feasibility of immobilizing As by formation of ASM as a long-term option for the bioremediation of As contamination. The percentage of As released from the minerals ranged from zero when FeAsS was biologically incubated to 87% for As₂S₃(s) under anoxic abiotic conditions. While the dissolution of ASM was greater in biological conditions, the presence of inoculum provided as sludge served as a sink for As, limiting the mobilization of As into aqueous phase. Thus, the mobilization of As from ASM can be controlled by altering the environmental conditions such as the redox conditions or by stimulating microbial activity. Further research investigated the formation of ASM catalyzed by biological reduction of Asᵛ and sulfate (SO₄²⁻). In particular, the third objective of this research was to study the effect of the pH on the removal of As due to the biological-mediated formation of ASM in an iron-poor system. A series of batch experiments were performed to study the reduction of SO₄²⁻ and Asᵛ by an anaerobic mixed culture in a range of pH conditions (6.1-7.2), using ethanol as the e-donor. A marked decrease of the total aqueous concentrations of As and S and the formation of a yellow precipitate was observed in the inoculated treatments amended with ethanol, but not in the non-inoculated controls, indicating that the As-removal was biologically mediated. The pH dramatically affected the extent and rate of As removal, as well as the stoichiometric composition of the precipitate. The precipitate was composed of a mixture of orpiment and realgar, and the proportion of orpiment in the sample increased with increasing pH. The results suggest that ASM formation is greatly enhanced at mildly acidic pH conditions. The fourth objective was to investigate the biomineralization of As through simultaneous Asᵛ and SO₄²⁻ reduction in a minimal iron environment for the As-contaminated groundwater bioremediation. A continuous bioreactor, inoculated with an anaerobic sludge was maintained at circumneutral pH (6.25-6.50) and fed with Asᵛ and SO₄²⁻, utilizing ethanol as an e-donor for over 250 d. A second bioreactor running under the same conditions but lacking SO₄²⁻ was operated as a control to study the fate of As removal. The reactor fed with both Asᵛ and SO₄²⁻ removed on the average 91.2% of the total soluble As, while less than 5% removal was observed in the control bioreactor without S. The biomineralization of As in the bioreactor was also evident from the formation of a yellow precipitate made of a mixture of As₂S₃ and AsS minerals. These results taken as a whole indicate that a bioremediation process relying on the addition of a simple, low-cost e-donor offers potential to promote the removal of As from groundwater by precipitation of ASM. The fifth objective was to evaluate the toxic impact that the exposure to soluble As or the formation of ASM could have on the anaerobic mixed culture used as inocula. The methanogenic community on the reactors was impacted by addition of As. The biogenic ASM inhibited the acetoclastic methanogens causing an accumulation of acetate. In the SO₄²⁻-free bioreactor, the methanogens were initially highly sensitive to Asᴵᴵᴵ (formed from Asᵛ reduction) but quickly adapted to its toxicity. Consequently, the formation of ASM would impact the methanogenic activity of an anaerobic biofilm, while the exposure to Asᴵᴵᴵ would not have a negative impact if the biofilm undergoes adaptation. The sixth and final objective was to study the stability of a biogenic ASM at two different pH values (6.5 and 7.5) and under different redox conditions. The long-term stability was evaluated in three different bioreactors that operated for 145 d: aerobic (R1), anoxic (nitrate as alternative e-acceptor (R2) and anaerobic (R3). The dissolution of ASM was greatly affected by the pH, and slightly by the presence and nature of the e-acceptor. The ASM was very stable at pH 6.5, however, the As mobilization rate was up to 7-fold higher at pH 7.5, likely due to the formation of thioarsenic species. The stability of ASM was also impacted by the e-acceptor present. The As mobilization rate was 77% higher under anaerobic conditions than under aerobic conditions, most likely due to the formation of secondary As-bearing minerals. Therefore, the stability of ASM depends on the conditions of the operation, and it can be controlled by altering the environmental conditions, such as the pH or the presence of the e-acceptor.
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Igboamalu, Tony E. "Kinetic studies of Cr(VI) reduction in an indigenous mixed culture of bacteria in the presence of As(III)." Diss., University of Pretoria, 2014. http://hdl.handle.net/2263/46240.
Full textAbstract:
An indigenous mixed culture of bacteria collected from a Wastewater Treatment Plant (Brits,
North West Province, South Africa), biocatalytically reduced Cr(VI) in the presence of
As(III). Both the reduced chromium (Cr(III)) and the oxidised arsenic (As(V)) readily form
amorphous hydroxides that can be easily separated or precipitated from the aqueous phase as
part of the treatment process. Treatment of Cr(VI) and As(III) before disposal of wastewater
is critical since both compounds are known to be carcinogenic and mutagenic at very low
concentrations, and acutely toxic at high concentrations.
Batch experiments were conducted to evaluate the rate of Cr(VI) reduction under anaerobic
condition in the presence of its co-contaminant As(III) typically found in the groundwater
and mining effluent. Results showed near complete Cr(VI) reduction under initial Cr(VI)
concentrations up to 70 mg/L in a batch amended with 20 mg/L As(III). However, increasing
Cr(VI) concentrations up to 100 mg/L resulted in the inhibition of Cr(VI) reduction activity.
Further investigation was conducted in a batch reactor amended with 70 mg/L Cr(VI)
concentration at different As(III) concentrations ranging from 5-70 mg/L to evaluate the
effect of varying As(III) concentration on Cr(VI) reduction efficiency. Results showed that
Cr(VI) reduction efficiency increased as As(III) concentrations increased from 5-40 mg/L.
However, further increase in As(III) concentration up to 50 mg/L resulted in incomplete
Cr(VI) reduction and decrease in Cr(VI) reduction efficiency. These results suggest that the
rate of Cr(VI) reduction depends on the redox reaction of As(III) and As(V) with Cr(VI).
Moreover, the inhibitory effect observed at high Cr(VI) and As(III) concentration may also be attributed to the dual toxicity effect of Cr(VI) and As(III) on microbial cell. From the
above batch kinetic studies lethal concentration of Cr(VI) and As(III) for these strains was
evaluated and established.
Initial evaluation of the bacteria using 16S rRNA partial sequence method showed that cells
in the mixed culture comprised predominantly of the Gram-positive species: Staphylococcus
sp., Enterobacter sp., and Bacillus sp. The biokinetic parameters of these strains were
estimated using a non-competitive inhibition model with a computer programme for
simulation of the Aquatic System “AQUASIM 2.0”.
Microbial reduction of Cr(VI) in the presence of As(III) was further investigated in
continuous-flow bioreactors (biofilm reactor) under varying Cr(VI) loading rates. The reactor
achieved Cr(VI) removal efficiency of more than 96 % in the first three phases of continuous
operation at lower Cr(VI) concentration ranging from 20-50 mg/L. However, 20 % decrease
in Cr(VI) removal efficiency was observed as Cr(VI) concentration increase up to 100 mg/L.
The reactor was able to recover from Cr(VI) and As(III) overloading phase after establishing
the resilient nature of the microorganism. Similarly to the batch reactor studies the overall
performance of the reactor also demonstrated that the presence of As(III) greatly enhance
Cr(VI) reduction in a bioreactor. This was evident by near complete removal of Cr(VI)
concentration up to 50 mg/L. The basic mass balance expressions on Cr(VI) along with the
non-competitive inhibition model were used to estimate the biokinetic parameters in the
continuous flow bioreactor system.
Cr(VI) reduction efficiency along the longitudinal column was also evaluated in this study.
Results showed that Cr(VI) efficiency increased as Cr(VI) concentration travels along the
longitudinal column. Other important factors such as oxygen and pH during biological Cr(VI)
reduction in the presence of As(III) oxidation were also evaluated.Dissertation (MEng)--University of Pretoria, 2014.
tm2015
Chemical Engineering
MEng
Unrestricted
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Eppili, Venkatesh. "Electrospinning of Polymeric Solutions Using Opuntia ficus-indica Mucilage and Iron Oxide for Nanofiber Membranes for Treating Arsenic Contaminated Water." Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6232.
Full textAbstract:
Water is the essential part of every organism and it is also a vital constituent of healthy living and diet. Unfortunately water contamination over the past decade has increased dramatically leading to various diseases. As technology advances, we are detecting many pollutants at smaller levels of concentrations. Arsenic (As) is one of those major pollutants, and Arsenic poisoning is a condition caused due to excess levels of arsenic in the body. The main basis for Arsenic poisoning is from ground water which naturally contains high concentrations of arsenic. A case study from 2007 states that over 137 million people in 70 countries were affected by arsenic poisoning from drinking water [1]. This thesis work is motivated by this study and investigates the fabrication, characterization, and testing of Opuntia ficus-indica mucilage nanofiber membranes formed using a mucilage, polystyrene (PS) and iron oxide (Fe2O3) solution by an electrospinning process. Cactus mucilage is a jelly-like substance, which is extracted from the cactus pad, and is an inexpensive, biodegradable and biocompatible material. It is also an abundant material available in nature. Polystyrene is a synthetic aromatic polymer prepared from monomer styrene. Polystyrene is further dissolved using D-Limonene as a solvent. D-Limonene is a non-toxic solvent and is a citrus extract of orange peelings. In an effort to enhance adsorption capacity for the mucilage nanofiber membranes, iron oxide nanopowder is incorporated into the polymeric solution. A mucilage and polystyrene-iron oxide solution is mixed in different ratios and electrospun to obtain nanofibers. The fibers will be characterized by certain techniques such as Scanning electron microscopy (SEM), contact angle measurements, viscosity and Fourier transform infrared spectroscopy (FTIR). The fibers obtained from mucilage and PS-Fe2O3 will be further tested under Atomic fluorescence spectrometry (AFS) for testing the removal of arsenic from water. Also, a life cycle analysis (LCA) is conducted to evaluate the environmental impacts of the fabrication of the membranes by using SimaPro® software.
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Muppaneni, Rasudha. "Investigation of Opuntia ficus-indica Mucilage Nanofiber Membrane Filtration for Water Systems." Scholar Commons, 2015. https://scholarcommons.usf.edu/etd/5541.
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This work investigates the fabrication, characterization and testing of Opuntia ficus-indica mucilage nanofibers to be utilized in water filtration systems. These mucilage nanofibers are formed using different polymers through a process called electrospinning. The polymers used to promote the formation of nanofibers are poly vinyl alcohol (PVA) and polystyrene (PS). The mucilage is a jelly like substance extracted from the pads of the cactus plant. It is a mixture of proteins, complex polysaccharides and monosaccharaides. It is an inexpensive, non-toxic, biodegradable and biocompatible material which is present in abundance. The mucilage extracted from the pads is mixed with acetic acid to form the mucilage solution. The mucilage solution is then mixed by volume with co-spinning polymers, PVA and PS. PVA is a synthetic polymer that is water-soluble, and this work considers two types of PVA differentiated based upon molecular weight, such as low molecular weight PVA and high molecular weight PVA. Polystyrene is a synthetic polymer extracted from a monomer styrene, and it is inexpensive, biodegradable, and abundant. The polystyrene, in its solid form, is further decomposed using a solvent called D-Limonene. D-Limonene is a biodegradable, non-toxic solvent formed from the citrus extract of orange peelings. The PVA and PS solutions are mixed in several different volume ratios with the mucilage solutions. These solutions were electrospun and consistent nanofibers were obtained using the low molecular weight PVA solutions and the polystyrene solutions. The fibers and polymeric solutions were characterized by scanning electron microscopy (SEM), contact angle measurements, viscosity, and FTIR. Resulting mucilage nanofiber membranes were characterized by atomic fluorescence spectrometry (AFS) filtration testing. In addition, a life cycle analysis using the SimaPro software was performed to understand the environmental impact of solutions used to fabricate the mucilage nanofiber membranes. Characterization results confirm the formation of PVA:mucilage and PS:mucilage nanofibers. Filtration testing of the nanofiber membranes indicates better performance with membranes formed by PS: mucilage solutions as compared to PVA: Mucilage solutions. Overall, this work has shown that natural materials, such as cactus mucilage, can be synthesized with polymeric solutions to form environmentally friendly water filters.
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Kirby, Jason K., and n/a. "Trace metal and metalloid accumulation, distribution, and, speciation in Lake Macquarie, N.S.W., Australia." University of Canberra. Resource, Environmental & Heritage Sciences, 2005. http://erl.canberra.edu.au./public/adt-AUC20051129.124508.
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THESIS ORGANISATION
This thesis is organised into nine chapters that include seven international and
national publications (six accepted and one submitted for publication). The initial
overview chapter outlines the justification and direction for this thesis. With the
exception of chapter 8 (accepted for publication on the 1st May 2005); all chapters are
exact duplicates of published articles in international and national refereed journals
(chapters 2 to 7). The initial chapters (2 and 3) presents research findings using a
marine fish species, mullet (Mugil cephalus), to measure trace metal bioavailability in
Lake Macquarie, NSW Australia. While subsequent chapters (4 to 8) are presenting
research under taken to improve the understanding of arsenic cycling in marine and
estuarine environments. The final chapter (chapter 9) is a synopsis of the major
findings presented in this thesis. Due to the publication nature of this thesis, an
unavoidable degree of replication exists within chapters (publications).
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Parsons, Christopher. "Distribution et mobilité de l'arsenic dans les sols : effets de cycles redox successifs." Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00637484.
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L'arsenic est un metalloïde toxique et cancérigène. Ubiquiste dans la pedosphere, il est très sensibleaux fluctuations des conditions redox du sol, ce qui influe significativement sa toxicité et mobilité. Nousétudions le cycle biogéochimique global de l'arsenic, en tenant compte de l'usage croissant des ressources, etpassons en revue l'importance respective de l'arsenic geogénique et anthropogénique dans l'environnement.La contamination à l'arsenic est souvent diffuse dans les bassins sédimentaires de l'Europe. Cependant, desconcentrations dans l'eau interstitielle du sol peuvent être élevées lors de périodes de saturation du solcausées par la monté des eaux souterraines ou les inondations, prévues d'augmenter dû aux changementsclimatiques. La spectrométrie de fluorescence X quantitative et sans standard a été utilisée pour analyserl'arsenic dans des sols relativement contaminés de la plaine alluviale de la Saône au moyen de protocoles depréparation d'échantillons conçus pour optimiser la précision d'analyse et l'exactitude in situ aux bassesconcentrations d'arsenic. L'arsenic dans ces sols est associe aux (hydr)oxydes du fer et de manganèse de lataille d'argile colloïdale. Ceux-ci subissent une dissolution réductrice par les microorganismes lors desinondations, libérant une importante concentration d'arsenic dans la phase aqueuse. Si, par la suite, l'arsenicdégagé n'est pas éliminé avec l'eau de crue évacuée, il est ré-immobilisé pendant l'oxydation du sol et lareprécipitation des oxydes métalliques. Grâce à une combinaison novatrice d'analyses chimiques par voiehumide, d'écologie microbienne, de spectroscopie ainsi que de modélisation thermodynamique et cinétique,nous démontrons que les cycles d'oxydo-réduction séquentiels entraînent une atténuation d'arsenic aqueuxdans des conditions réductrices dû à la coprécipitation croissante, et a une diminution de l'activitémicrobienne causée par l'appauvrissement en matière organique labile. Des processus d'atténuationsimilaires sont observés en l'absence d'activité microbienne pour Cr et As dans des argiles pyriteuses lorsquecelles-ci sont exposés aux oscillations redox provoquées par l'ajout de substances humiques réduites. Ainsi,nous montrons que les effets cumulatifs de cycles redox successifs sont extrêmement importants pour lamobilité de divers contaminants dans l'environnement.
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Fernandez, Rojo Lidia. "Vers un traitement passif des drainages miniers acides (DMA) riches en arsenic par oxydation biologique du fer et de l'arsenic." Thesis, Montpellier, 2017. http://www.theses.fr/2017MONTT153.
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Les déchets sulfurés issus de l’extraction des minerais métalliques génèrent des drainages miniers acides (DMA) contenant des éléments toxiques tels que l’arsenic. Les procédés de traitement passifs basés sur l’oxydation bactérienne du fer et de l’arsenic, en favorisant la précipitation de ces éléments sous une forme stable, pourraient représenter une solution efficace et économique pour traiter cette pollution. Dans ce contexte, l’objectif général de cette thèse était de mieux comprendre les facteurs environnementaux et opérationnels qui contrôlent l’efficacité d’élimination de l’arsenic. Une approche en pilote à flux continu a été mise en oeuvre afin de se rapprocher des conditions réelles d’un traitement. L’étude a été conduite d’abord à l’échelle d’un bioréacteur de paillasse en conditions contrôlées (température, lumière, débit, temps de séjour et hauteur d’eau), puis dans un dispositif de taille supérieure, fonctionnant de manière totalement passive et in situ. Ces dispositifs ont été alimentés avec de l’eau d’un DMA riche en arsenic, issue de l’ancien site minier de Carnoulès, dans le Gard. Les caractéristiques de l’eau et des bioprécipités au sein de ces pilotes, en particulier le rédox du fer et de l’arsenic, ont été suivis dans différentes conditions environnementales et d’opération par des méthodes de spéciation liquide et solide (HPLC-ICP-MS, EXAFS, XANES), des analyses minéralogiques (DRX) et des analyses microbiologiques (ARISA, séquençage haut débit du gène de l'ARNr 16S, quantification du gène aioA). Les résultats issus des expériences en laboratoire ont mis en évidence l’effet de différents paramètres opérationnels (hauteur d’eau, temps de rétention hydraulique, et présence/absence d’une pellicule flottante) sur les performances du traitement, ainsi que sur la microbiologie et la minéralogie des bioprécipités formés. Le dispositif de terrain a permis de tester les performances du procédé dans des conditions environnementales fluctuantes (variabilité de la physico-chimie de l’eau d’entrée et de la température) et d’acquérir des connaissances nouvelles sur l’évolution des bioprécipités au cours de six mois de traitement. Les connaissances acquises dans cette thèse pourront servir de base à la conception d’une étape d’élimination de l’arsenic dans les processus de traitement des DMAAcid mine drainage (AMD) are produced by sulfuric tailings from mining of metal ores. They are characterized by high contents of toxic elements like arsenic. One efficient and economical solution for the treatment of As in these tailings could be the use of a passive method based on iron and arsenic bacterial oxidation, and the subsequent precipitation of these elements in a stable form. In this context, the objective of this PhD thesis was to better understand the environmental and operational factors controlling the efficiency of As removal processes. A continuous-flow pilot approach was implemented in order to better reproduce the real treatment conditions. This study was first performed in a bench-scale bioreactor with controlled conditions (temperature, light, flow, residence time and water height). Then, it was performed in a field-scale bioreactor installed in situ, reproducing a passive treatment in real conditions. These devices were fed with As-rich AMD waters from the ancient mine of Carnoulès (Gard, France). Water and bioprecipitate properties were monitored in both devices, specially the redox speciation of iron and arsenic. This monitoring was held for different environmental and operational conditions. Iron and arsenic speciation in liquid and solid phases was measured by different analytical techniques such as HPLC-ICP-MS, EXAFS and XANES. Mineral identification was made by XRD analysis, while microbiological characterization was made by ARISA, high-throughput sequencing of 16S rRNA gene, and aioA gene quantification. Results from the lab-scale experiments evidenced the effects of the different operational parameters (water height, hydraulic retention time and the presence/absence of a floating film) on the treatment performance, as well as on the microbiology and mineralogy of the produced bioprecipitates. The field device was used to test the treatment performance under fluctuating environmental conditions (variability of the physico-chemistry of the feed water and of the temperature) and to gain new knowledge about the evolution of the bioprecipitates during six months of treatment. All the knowledge acquired in this PhD thesis could serve as a basis for the design of an arsenic removal stage in DMA treatment processes
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Thouin, Hugues. "Transfert de polluants inorganiques dans un technosol de brûlage d’armes organo-arséniées soumis à un apport de matière organique et à des cycles de saturation/désaturation : expérimentation en mésocosme." Thesis, Orléans, 2016. http://www.theses.fr/2016ORLE2069/document.
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La destruction par brûlage de munitions chimiques de la Première Guerre Mondiale a provoqué une contamination importante de la partie supérieure du sol du site de la Place-à-Gaz par l’arsenic, le zinc, le cuivre et le plomb. Le traitement thermique a eu pour effet de minéraliser l’As des agents de guerre organoarséniés, et de former un assemblage minéral inattendu composé d’arséniates de Zn, Cu et Fe, et d’une phase amorphe riche en Fe, As, Zn, Cu et Pb. Ce matériel amorphe est la principale phase porteuse de l’As et des métaux dans la zone la plus polluée. Le site est sujet à des changements environnementaux pouvant affecter la stabilité des contaminants inorganiques. Afin d’évaluer l’impact d’épisodes de saturation en eau et de l’apport de matière organique sur les cycles biogéochimiques des métaux et de l’As, une étude en mésocosme a été menée. Les résultats montrent que la phase amorphe est instable en conditions saturées, et libère des contaminants dans l’eau interstitielle du sol. Comme sur le site, les contaminants les plus mobiles sont le Zn et l’As. L’addition de matière organique a induit une immobilisation de l’As, par piégeage de l’As V sur les oxyhydroxydes de fer, dans la partie saturée du sol. La caractérisation du compartiment microbien a été effectuée via des dénombrements, une analyse de la diversité bactérienne et des tests d’activités d’oxydation de l’As III et de respiration et. Les résultats montrent que les microorganismes ont contribué activement au métabolisme du C et de l’As. L’apport de matière organique a promu la croissance des microorganismes As III-oxydants et As Vréducteurs et modifié la structure des communautés bactériennes. Cependant, un effet négatif de la matière organique sur la vitesse d’oxydation de l’As III a été observé, entrainant une augmentation des concentrations d’As III en solution. Cette étude en mésocosme a montré que le dépôt naturel de litière organique a des conséquences antagonistes sur le transfert des contaminants inorganiques. Ces résultats fournissent de plus amples informations sur l’impact environnemental de la Grande Guerre et, de façon plus générale, sur les processus biogéochimiques contrôlant le comportement des métaux/métalloïdes sur les sites polluésThe thermal destruction of chemical munitions from World War I, on the site of “Place-à-Gaz”, induced intense local top soil contamination by arsenic and heavy metals. The heat treatment mineralized As from organoarsenic warfare agents, resulting in a singular mineral assemblage, composed of Zn, Cu and Fe arsenates and of an amorphous phase rich in Fe, As, Zn, Cu and Pb. The amorphous material was the principal carrier of As and metals in the central part of the site. The site undergoes environmental changes which may alter the stability of inorganic contaminants. To assess the impact of water saturation episodes and input of bioavailable organic matter on the biogeochemical cycles of metal(loid)s, a mesocosm study was conducted. Results showed that amorphous phase was instable in saturated conditions, and released contaminants in soil water. As previously observed on site, the most mobile contaminants were Zn and As. The addition of organic matter induced the immobilization of As by trapping of As V onto hydrous ferric oxides in the saturated soil. Microbial characterizations including counting, bacterial community structure, respiration, and determination of As IIIoxidizing activities were performed. Results showed that microorganisms actively contribute to the metabolisms of C and As.The addition of organic matter induced the increase of As III-oxidizing and As V-reducing microorganisms concentrations and modified the bacterial diversity. However, a negative effect of organic matter on the activity of As III oxidation was observed resulting in higher As III concentration in soil water. This study showed that the natural deposition of forest organic litter on the site, induced antagonist effects on the transfer of inorganic pollutants did not immobilize all the Zn and As and even contributed to As III transport to the surrounding environment. These results provide more information about the environmental impact of the Great War and more generally about the processes driving the behavior of metals/metalloids on polluted sites
Books on the topic "Arsenic cycle"
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The metabolism of arsenite. Boca Raton, FL: CRC Press, 2012.
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Cai, Yong, and Olin C. Braids. Biogeochemistry of Environmentally Important Trace Elements (Acs Symposium Series). An American Chemical Society Publication, 2002.
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1961-, Cai Yong, Braids O. C, and American Chemical Society Meeting, eds. Biogeochemistry of environmentally important trace elements. Washington, D.C: American Chemical Society, 2002.
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Smith, Benjamin T. Mexican Press and Civil Society, 1940-1976. University of North Carolina Press, 2018. http://dx.doi.org/10.5149/northcarolina/9781469638089.001.0001.
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Mexico today is one of the most dangerous places in the world to report the news, and Mexicans have taken to the street to defend freedom of expression. As Benjamin T. Smith demonstrates in this history of the press and civil society, the cycle of violent repression and protest over journalism is nothing new. He traces it back to the growth in newspaper production and reading publics between 1940 and 1976, when a national thirst for tabloids, crime sheets, and magazines reached far beyond the middle class. As Mexicans began to view local and national events through the prism of journalism, everyday politics changed radically. Even while lauding the liberty of the press, the state developed an arsenal of methods to control what was printed, including sophisticated spin and misdirection techniques, covert financial payments, and campaigns of threats, imprisonment, beatings, and even murder. The press was also pressured by media monopolists tacking between government demands and public expectations to maximize profits, and by coalitions of ordinary citizens demanding that local newspapers publicize stories of corruption, incompetence, and state violence. Since the Cold War, both in Mexico City and in the provinces, a robust radical journalism has posed challenges to government forces.
Book chapters on the topic "Arsenic cycle"
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Chatterjee, Soumya, Roxana Moogoui, and Dharmendra K. Gupta. "Arsenic: Source, Occurrence, Cycle, and Detection." In Arsenic Contamination in the Environment, 13–35. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-54356-7_2.
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Dhuldhaj, Umesh Praveen, Ishwar Chandra Yadav, Surendra Singh, and Naveen Kumar Sharma. "Microbial Interactions in the Arsenic Cycle: Adoptive Strategies and Applications in Environmental Management." In Reviews of Environmental Contamination and Toxicology Volume 224, 1–38. New York, NY: Springer New York, 2012. http://dx.doi.org/10.1007/978-1-4614-5882-1_1.
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"The global arsenic cycle revisited." In Arsenic, 3–26. CRC Press, 2011. http://dx.doi.org/10.1201/b10772-3.
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"Transfer and transformation of arsenic in food chain cycle." In Arsenic in Geosphere and Human Diseases; Arsenic 2010, 196–205. CRC Press, 2010. http://dx.doi.org/10.1201/b10548-13.
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Rensing, C., and B. P. Rosen. "Heavy Metals Cycle (Arsenic, Mercury, Selenium, others)." In Encyclopedia of Microbiology, 205–19. Elsevier, 2009. http://dx.doi.org/10.1016/b978-012373944-5.00053-5.
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Bergmann, M., and W. Goessler. "Arsenobetaine a possible methyl donor in the one carbon cycle?" In Arsenic in the Environment - Proceedings, 301–2. CRC Press, 2016. http://dx.doi.org/10.1201/b20466-146.
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"II.2 Recent advances in arsenic toxicology / biochemistry and food web transfer Pathways of arsenic biotransformations: The arsenic methylation cycle." In Understanding the Geological and Medical Interface of Arsenic - As 2012, 235–38. CRC Press, 2012. http://dx.doi.org/10.1201/b12522-78.
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Wang, D., B. Li, L. Lin, and G. F. Sun. "Effects of folate on arsenic methylation pattern and methionine cycle in sub chronic arsenic-exposed mice." In Environmental Arsenic in a Changing World, 361–62. CRC Press, 2019. http://dx.doi.org/10.1201/9781351046633-142.
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Roy, Dibakar, Dasari Sreekanth, Deepak Pawar, Himanshu Mahawar, and Kamal K. Barman. "Phytoremediation of Arsenic Contaminated Water Using Aquatic, Semi-Aquatic and Submerged Weeds." In Biodegradation [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.98961.
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Arsenic (As) is the one the most toxic element present in earth which poses a serious threat to the environment and human health. Arsenic contamination of drinking water in South and Southeast Asia reported one of the most threatening problems that causes serious health hazard of millions of people of India and Bangladesh. Further, use of arsenic contaminated ground water for irrigation purpose causes entry of arsenic in food crops, especially in Rice and other vegetable crops. Currently various chemical technologies utilized for As removal from contaminated water like adsorption and co-precipitation using salts, activated charcoal, ion exchange, membrane filtration etc. are very costly and cannot be used for large scale for drinking and agriculture use. In contrast, phytoremediation utilizes green plats to remove pollutants from contaminated water using various mechanisms such as rhizofiltration, phytoextraction, phytostabilization, phytodegrartion and phytovolatilization. A large numbers of terrestrial and aquatic weed flora have been identified so far having hyper metal, metalloid and organic pollutant removal capacity. Among the terrestrial weed flora Arundo donax, Typha latifolia, Typha angustifolia, Vetivaria zizinoids etc. are the hyper As accumulator. Similarly Eicchornea crassipes (Water hyacinth), Pistia stratiotes (water lettuce), Lemna minor (duck weed), Hyrdilla verticillata, Ceratophyllum demersum, Spirodella polyrhiza, Azola, Wolfia spp., etc. are also capable to extract higher amount of arsenic from contaminated water. These weed flora having As tolerance mechanism in their system and thus remediate As contaminated water vis-à-vis continue their life cycle. In this chapter we will discuss about As extraction potential of various aquatic and semi aquatic weeds from contaminated water, their tolerance mechanism, future scope and their application in future world mitigating As contamination in water resources.
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Andala, Dickson Mubera, Erick Mobegi, Mildred Nawiri, and Geoffrey Otieno. "Fabrication of Metal Oxide-Biopolymer Nanocomposite for Water Defluoridation." In Advances in Environmental Engineering and Green Technologies, 242–71. IGI Global, 2020. http://dx.doi.org/10.4018/978-1-7998-1871-7.ch013.
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Fluoride contamination in groundwater affects about 150 million people worldwide. In this study, the authors focused on synthesizing biopolymer metal oxide nanocomposite for fluoride removal. Nanocomposite material was done using SEM. As(V), Al, Ti, Zr, and Fe water samples were analysed by ICP-MS (inductively coupled plasma-mass spectrometry). Fluoride level was determined using the standard method – Ion-Selective Electrode method. Preliminary results indicate arsenic (V) removal was below the 10 ppb and fluoride less than 1.5 ppm as prescribed by WHO. The removal efficiency was after 60-70 minutes with recyclability of 11 cycles. The nanocomposite worked well in all pH ranges 6.5-8.5. A filter cartridge biopolymer metal oxide nanocomposite constituting of template aluminium homogenized in the aggregated network of chitosan was developed as an adsorbent for fluoride from the water with better adsorption limit.
Conference papers on the topic "Arsenic cycle"
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Simingalam, Sina, Priyalal Wijewarnasuriya, and Mulpuri V. Rao. "Thermal cycle annealing and its application to arsenic-ion implanted HgCdTe." In 2014 20th International Conference on Ion Implantation Technology (IIT). IEEE, 2014. http://dx.doi.org/10.1109/iit.2014.6940053.
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Kumar, Sanjay, Clement Yedjou, and Paul B. Tchounwou. "Abstract 2291: Arsenic trioxide induces cell cycle arrest, apoptosis and MAPKinase signaling cascade in acute promyelocytic leukemia cells." In Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA. American Association for Cancer Research, 2014. http://dx.doi.org/10.1158/1538-7445.am2014-2291.
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Marval, Paula L. Miliani de, Sun Hye Kim, and Marcelo L. Rodriguez-Puebla. "Abstract 3186: Transplacental arsenic exposure modifies the number of hair follicle keratinocytes stem cells and alters their cell-cycle control." In Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA. American Association for Cancer Research, 2014. http://dx.doi.org/10.1158/1538-7445.am2014-3186.
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Kumar, Sanjay, and Paul B. Tchounwou. "Abstract 3811: Arsenic trioxide induces cell cycle arrest, apoptosis through interaction of DAXX and degradation of MDM2 in acute leukemia cells." In Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA. American Association for Cancer Research, 2015. http://dx.doi.org/10.1158/1538-7445.am2015-3811.
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Lee, Won Sup, Jeong Won Yun, Min Jeong Kim, Arulkumar Nagappan, Jing Nan Lu, Seong-Hwan Chang, Jae-Hoon Jeong, GonSup Kim, Jin-Myung Jung, and Soon Chan Hong. "Abstract 2107: Tetra-arsenic hexoxide induces G2/M cell cycle arrest, apoptosis, and autophagy via p38 MAPK- and AKT-mediated pathways in SW620 human colon cancer cells." In Proceedings: AACR Annual Meeting 2017; April 1-5, 2017; Washington, DC. American Association for Cancer Research, 2017. http://dx.doi.org/10.1158/1538-7445.am2017-2107.
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Bansal, Iqbal K. "Hydrophobic Silicon-Direct Bonding for Fabrication of RF Microwave Devices." In ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-41161.
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Direct wafer bonding (DWB) is an operation of ultra-fine alignment, joining and thermal bonding of two silicon wafers. The first silicon wafer “handle” substrate is a Czochralski (<CZ>) substrate with N+ arsenic dopant with very low bulk resistivity, whereas second wafer “device” is a float-zone (<FZ>) having extremely high resistivity N-phosphorus dopant. Prior to the joining step, silicon wafers are chemically cleaned in order to minimize surface contamination. The wafer surface is “hydrophobic” which is achieved using an insitu oxide etching process. The surface quality is also characterized in terms of sub-micron light point defects (LPD’s) counts and haze concentration using a laser beam scanning system. After chemical clean, none of the LPD’s counts is greater than 1.0 μ size. The joining step is performed in a Class 100 or better environment by employing a commercial joiner. Then, thermal bonding operation is carried out by employing an extended stream oxidation cycle at elevated temperatures. Typical failure modes of DWB are misalignment errors and “voided” or “disbonded” regions. The area of “voided” regions for each bonded pair is determined by employing a scanning acoustic microscope. Detailed product throughtput and yield data are presented in this paper. A spreading resistivity profile (SRP) system is employed for accurate measurement of doping carrier concentration as a function of the depth. The superior uniformity for capacitance-voltage characteristics of a Si-Si bonded wafer versus an inverse epitaxial silicon wafer substrate is shown in terms of the device performance. The applications of silicon-direct wafer bonded substrates provide a quantum jump in the device electrical performance of PIN diodes.
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Baughn, Terry V., and Shea Chen. "Low Cycle Fatigue in RF Microwave Module Housings." In ASME 2003 International Electronic Packaging Technical Conference and Exhibition. ASMEDC, 2003. http://dx.doi.org/10.1115/ipack2003-35263.
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Hermetic housings are required for the vast majority of electronics used in RF microwave electronics to protect the gallium arsenide and silicon devices from the environment. A common housing style includes a metal ring frame that is brazed onto a metal or ceramic base. The housing is populated with electronic devices and circuits and then hermetically sealed with a thin metal lid. For high volume manufacturing, lids are often attached by a resistance weld using a seam seal process. The interior hermitic volume is sealed at or near one atmosphere internal pressure. Since the housing may be subjected to a substantial number of pressure cycles that can yield the lid material, a low cycle fatigue evaluation is required to establish the long-term reliability of the hermetic housing. Kovar is a common lid and housing material because of a good coefficient of thermal expansion match with glass, ceramic and other materials used in RF circuitry. Unfortunately only high cycle fatigue data is available for kovar. A method is proposed to generate an estimate of high cycle end of the low cycle fatigue response from the high cycle fatigue data. The proposed method is verified by comparing a predicted fatigue life with experimental results from hermetic housings subjected to pressure cycling.
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Layne, Abbie W., Mary Anne Alvin, Evan Granite, Henry W. Pennline, Ranjani V. Siriwardane, Dale Keairns, and Richard Newby. "Overview of Contaminant Removal From Coal-Derived Syngas." In ASME 2007 International Mechanical Engineering Congress and Exposition. ASMEDC, 2007. http://dx.doi.org/10.1115/imece2007-42165.
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Gasification is an important strategy for increasing the utilization of abundant domestic coal reserves. DOE envisions increased use of gasification in the United States during the next 20 years. As such, the DOE Gasification Technologies Program, including the FutureGen initiative, will strive to approach a near-zero emissions goal, with respect to multiple pollutants, such as sulfur, mercury, and nitrogen oxides. Since nearly one-third of anthropogenic carbon dioxide emissions are produced by coal-powered generation facilities, conventional coal-burning power plants, and advanced power generation plants, such as IGCC, present opportunities in which carbon can be removed and then permanently stored. Gas cleaning systems for IGCC power generation facilities have been effectively demonstrated and used in commercial operations for many years. These systems can reduce sulfur, mercury, and other contaminants in synthesis gas produced by gasifiers to the lowest level achievable in coal-based energy systems. Currently, DOE Fossil Energy’s goals set for 2010 direct completion of R&D for advanced gasification combined cycle technology to produce electricity from coal at 45–50% plant efficiency. By 2012, completion of R&D to integrate this technology with carbon dioxide separation, capture, and sequestration into a zero-emissions configuration is targeted with a goal to provide electricity with less than a 10% increase in cost of electricity. By 2020, goals are set to develop zero-emissions plants that are fuel-flexible and capable of multi-product output and thermal efficiencies of over 60% with coal. These objectives dictate that it is essential to not only reduce contaminant emissions into the generated synthesis gas, but also to increase the process or system operating temperature to that of humid gas cleaning criteria conditions (150 to 370 °C), thus reducing the energy penalties that currently exist as a result of lowering process temperatures (−40 to 38 °C) with subsequent reheat to the required higher temperatures. From a historical perspective, the evolution of advanced syngas cleaning systems applied in IGCC and chemical and fuel synthesis plants has followed a path of configuring a series of individual cleaning steps, one for each syngas contaminant, each step controlled to its individual temperature and sorbent and catalyst needs. As the number of syngas contaminants of interest has increased (particulates, hydrogen sulfide, carbonyl sulfide, halides such as hydrogen chloride, ammonia, hydrogen cyanide, alkali metals, metal carbonyls, mercury, arsenic, selenium, and cadmium) and the degree of syngas cleaning has become more severe, the potential feasibility of advanced humid gas cleaning has diminished. A focus on multi-contaminant syngas cleaning is needed to enhance the potential cost savings, and performance of humid gas cleaning will focus on multi-contaminant syngas cleaning. Groups of several syngas contaminants to be removed simultaneously need to be considered, resulting in significant gas cleaning system intensification. Intensified, multi-contaminant cleaning processes need to be devised and their potential performance characteristics understood through small-scale testing, conceptual design evaluation, and scale-up assessment with integration into the power generation system. Results of a 1-year study undertaken by DOE/NETL are presented to define improved power plant configurations and technology for advanced multi-contaminant cleanup options.
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Pakzadeh, Behrang, Jay Wos, and Jay Renew. "Flue Gas Desulfurization Wastewater Treatment for Coal-Fired Power Industry." In ASME 2014 Power Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/power2014-32278.
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The United States Environmental Protection Agency (USEPA)’s announcement that it will revise the effluent limitation guidelines for steam electric power generating units could affect not only how power plants use water, but also how they discharge it. The revised guidelines may lower discharge limits for various contaminants in flue gas desulfurization (FGD) wastewater including mercury, selenium, arsenic, and nitrate/nitrite. Although the specific details of the guidelines are unknown at present, the power industry is evaluating various technologies that may address the new effluent limitation guidelines and promote water conservation. Moreover, the power industry is looking for avenues to increase water usage efficiency, reuse and recycle throughout its plant processes. Final rule approval is expected by the middle of 2014 and new regulations are expected to be implemented between 2017 and 2022 through 5-year NPDES permit cycles. discharge limits for various contaminants including arsenic, mercury, selenium, and nitrate/nitrite [1]. These pollutant limits may be below the levels achievable today with conventional treatment [2]. A growing interest exists in zero liquid discharge (ZLD) facilities and processes in power plant operations. Potentially stringent discharge limits along with water conservation and reuse efforts are two of the major drivers to achieve ZLD. Potential pollutant levels are so low that ZLD may be the best option, if not an outright requirement [1]. Thermal ZLD systems have been the subject of increased interest and discussion lately. They employ evaporating processes such as ponds, evaporators and crystallizers, or spray dryers to produce a reusable water stream and a solid residue (i.e. waste). Evaporators and crystallizers have been employed in the power industry for a number of years. However, typical A growing interest exists in zero liquid discharge (ZLD) facilities and processes in power plant operations. Potentially stringent discharge limits along with water conservation and reuse efforts are two of the major drivers to achieve ZLD. Potential pollutant levels are so low that ZLD may be the best option, if not an outright requirement. A key disadvantage of thermal ZLD is its high capital cost. One way to reduce this cost is to pre-treat the liquid stream using innovative membrane technologies and reverse osmosis (RO).
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Vadhwana, N. M., and W. Chen. "Effect of Loading History on Hydrogen Content in Pipeline Steels." In 2002 4th International Pipeline Conference. ASMEDC, 2002. http://dx.doi.org/10.1115/ipc2002-27298.
Full textAbstract:
The application of high strength pipeline steels for oil and gas transmission is believed to provide greater gas flow capacity due to increased design pressure, and reduced line pipe cost due to material tonnage savings. However, the use of high strength pipeline steels is concerned with high risk of brittle failures such as hydrogen induced cracking, fractures due to low ductility. In this study, three grades of modern pipeline steel (X65, X80, X100) were examined to determine their susceptibility to hydrogen permeation and hydrogen trapping under the influence of various mechanical loading conditions. The steel samples were placed in a solution of sulfuric acid poisoned with arsenic trioxide to create an environment where hydrogen can enter the steel. Initially, round bar samples were charged for various times at a low current density to establish that 24 hours was a sufficient charging time for the three steels. Tensile samples were loaded and held at stress levels corresponding to the respective yield strength and the amount of hydrogen entering the steel was then measured. The stress, normalized to the yield strength, and hydrogen contents, normalized to as received contents, were used to rank the three steel grades and to find the steel that was the most susceptible to hydrogen entry. For the samples charged prior to loading, two times as much diffusible hydrogen was found in the X100 as compared to the other steels, but the trapped hydrogen content was equivalent. Four loading conditions were used for each grade of steel: 1) 2% strain; 2) 2% strain and hold at load for 24 hours; 3) 2% strain then 100 cycles at R = 0.1; and 4) 2% strain, 100 cycles at R = 0.1 then hold at load for 24 hours. For the loaded samples, the amount of hydrogen, both diffusible and trapped increased with load severity, with the highest amounts found in the highest grades of steel. The most pronounced increase was not found in the X100, but in the X-80 steel. Micro structural features, such as banded structure, seemed to have a more prominent role on the hydrogen content of the X100 than in the other steels as it seemed less affected by the loading condition than by charging time.