| 11. |
- Ahmad, Arslan
(författare)
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Evaluation and optimization of advanced oxidation coagulation filtration (AOCF) to produce drinking water with less than 1 μg/L of arsenic
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Arsenic is an extremely poisonous element. It has been reported to cause contamination of drinking water sources in many parts of the world. The current drinking water permissible limit for arsenic in the European Union is 10 μg/L. The World Health Organization has a general rule that no substance may have a higher lifetime risk of more than 1 in 100,000. However, several studies on toxicity of arsenic suggest that purely based on health effects the arsenic limit of 10 μg/L is not sufficient. The main goal of this research was to develop an efficient arsenic removal technology that could be able to produce drinking water with an arsenic concentration of less than 1 μg/L. For this purpose, an innovative three step technique, Advanced Oxidation - Coagulation - Filtration (AOCF), was investigated through bench-scale and pilot scale experiments in the Netherlands at the water treatment plant of Dorst. Firstly, prior to the investigations on AOCF, the existing arsenic removal at the water treatment plant was investigated. Secondly, through a series of bench-scale experiments, the optimum type of coagulant, its combination dose with the selected chemical oxidant and optimum process pH were determined. Eventually, the partially optimized technique from the bench-scale was implemented at the pilot scale physical model of water treatment plant Dorst where AOCF was evaluated for arsenic removal and its effect on the removal of other common undesirable groundwater constituents. The optimized AOCF technology consistently removed arsenic from groundwater to below 1 ug/L when implemented at pilot scale. The overall effluent quality also remained acceptable. The method is efficient with both types of filtration media tested in this research i.e., virgin sand and metal oxide coated sand, however virgin sand media showed slightly better arsenic removal efficiency.
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| 12. |
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| 13. |
- Ahmad, Arslan, et al.
(författare)
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Impact of phosphate, silicate and natural organic matter on the size of Fe(III) precipitates and arsenate co-precipitation efficiency in calcium containing water
- 2020
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Ingår i: Separation and Purification Technology. - : ELSEVIER. - 1383-5866 .- 1873-3794. ; 235
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Tidskriftsartikel (refereegranskat)abstract
- Removal of arsenic (As) from water by co-precipitation with Fe(III) (oxyhydr)oxides is a widely used technique in water treatment. Nevertheless, As removal efficiency appears to be sensitive to the composition of the water matrix. The aim of this study was to gain a deeper understanding of the independent and combined effects of silicate (Si), phosphate (P), natural organic matter (NOM) and calcium (Ca) on arsenate [As(V)] co-precipitation efficiency and the size of Fe(III) precipitates. We found that, in complex solutions, containing multiple solutes and high levels of Ca, (variations in) Si and P concentrations reduce As(V) removal to some extent, mainly due to a decreased adsorption of As(V) onto Fe(III) precipitates. On the other hand, NOM concentrations reduced As(V) removal to a much greater extent, due to possible formation of mobile Fe(III)-NOM complexes that were difficult to remove by filtration. These findings have a great significance for predicting As(V) removal as a function of seasonal and process-related water quality changes at water treatment plants.
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| 14. |
- Ahmad, Arslan, et al.
(författare)
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Mechanisms of arsenate removal and membrane fouling in ferric based coprecipitation-low pressure membrane filtration systems
- 2020
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Ingår i: Separation and Purification Technology. - : ELSEVIER. - 1383-5866 .- 1873-3794. ; 241
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Tidskriftsartikel (refereegranskat)abstract
- Ferric based coprecipitation-low pressure membrane filtration is a promising arsenic (As) removal method, however, membrane fouling mechanisms are not fully understood. In this study we investigated the effect of feed water composition and membrane pore size on arsenate [As(V)] removal and membrane fouling. We observed that As removal efficiency was independent of the membrane pore size because the size of the Fe(III) particles was larger than the pore size of the membranes, attributed to a high calcium concentration in the feed water. Arsenic coprecipitation with Fe(III) (oxyhydr)oxides rapidly reached equilibrium before membrane filtration, within 1 min. Therefore, As removal efficiency was not improved by increasing residence time before membrane filtration. The removal of As(V) was strongly dependent on feed water composition. A higher Fe(III) dose was required to reduce As(V) to sub-mu g/L levels for feed water containing higher concentration of oxyanions such as phosphate and silicate, and lower concentration of cations such as calcium. Cake-layer formation was observed to be the predominant membrane fouling mechanism.
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| 15. |
- Ahmad, Arslan, et al.
(författare)
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Mobility and redox transformation of arsenic during treatment of artificially recharged groundwater for drinking water production
- 2020
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Ingår i: Water Research. - : Elsevier. - 0043-1354 .- 1879-2448. ; 178
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Tidskriftsartikel (refereegranskat)abstract
- In this study we investigate opportunities for reducing arsenic (As) to low levels, below 1 mu g/L in produced drinking water from artificially infiltrated groundwater. We observe that rapid sand filtration is the most important treatment step for the oxidation and removal of As at water treatment plants which use artificially recharged groundwater as source. Removal of As is mainly due to As co-precipitation with Fe(III)(oxyhydr)oxides, which shows higher efficiency in rapid sand filter beds compared to aeration and supernatant storage. This is due to an accelerated oxidation of As(III) to As(V) in the filter bed which may be caused by the manganese oxides and/or As(III) oxidizing bacteria, as both are found in the coating of rapid sand filter media grains by chemical analysis and taxonomic profiling of the bacterial communities. Arsenic removal does not take place in treatment steps such as granular activated carbon filtration, ultrafiltration or slow sand filtration, due to a lack of hydrolyzing iron in their influent and a lack of adsorption affinity between As and the filtration surfaces. Further, we found that As reduction to below 1 mu g/L can be effectively achieved at water treatment plants either by treating the influent of rapid sand filters by dosing potassium permanganate in combination with ferric chloride or by treating the effluent of rapid sand filters with ferric chloride dosing only. Finally, we observe that reducing the pH is an effective measure for increasing As co-precipitation with Fe(III)(oxyhydr)oxides, but only when the oxidized arsenic, As(V), is the predominant species in water.
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| 16. |
- Ahmad, Muhammad Arslan, et al.
(författare)
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Estimating the Permeability of Naturally Structured Soil From Percolation Theory and Pore Space Characteristics Imaged by X-Ray
- 2018
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Ingår i: Water Resources Research. - 0043-1397 .- 1944-7973. ; 54, s. 9255-9263
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Tidskriftsartikel (refereegranskat)abstract
- The saturated hydraulic conductivity of soil, K-s, is a critical parameter in hydrological models that remains notoriously difficult to predict. In this study, we test the capability of a model based on percolation theory and critical path analysis to estimate K-s measured on 95 undisturbed soil cores collected from contrasting soil types. One parameter (the pore geometry factor) was derived by model fitting, while the remaining two parameters (the critical pore diameter, d(c), and the effective porosity) were derived from X-ray computed tomography measurements. The model gave a highly significant fit to the K-s measurements (p<0.0001) although only 47% of the variation was explained and the fitted pore geometry factor was approximately 1 to 2 orders of magnitude larger than various theoretical values obtained for idealized porous media and pore network models. Apart from assumptions in the model that might not hold in reality, this could also be attributed to experimental error induced by, for example, air entrapment and changes in the soil pore structure occurring during sample presaturation and the measurement of K-s. Variation in the critical pore diameter, d(c), was the dominant source of variation in K-s, which suggests that d(c) is a suitable length scale for predicting soil permeability. Thus, from the point of view of pedotransfer functions, it could be worthwhile to direct future research toward exploring the correlations of d(c) with basic soil properties and site attributes.
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| 17. |
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Arsenic Research and Global Sustainability: Proceedings of the Sixth International Congress on Arsenic in the Environment (As2016), June 19-23, 2016, Stockholm, Sweden
- 2016
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Proceedings (redaktörskap) (refereegranskat)abstract
- The Congress "Arsenic in the Environment" offers an international, multi- and interdisciplinary discussion platform for research and innovation aimed towards a holistic solution to the problem posed by the environmental toxin arsenic, with considerable societal impact. The congress has focused on cutting edge and breakthrough research in physical, chemical, toxicological, medical, agricultural and other specific issues on arsenic across a broader environmental realm. The Congress "Arsenic in the Environment" was first organized in Mexico City (As2006) followed by As2008 in Valencia, Spain, As2010 in Tainan, Taiwan, As2012 in Cairns, Australia and As2014 in Buenos Aires, Argentina. The 6th International Congress As2016 was held June 19-23, 2016 in Stockholm, Sweden and was entitled Arsenic Research and Global Sustainability.
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| 18. |
- Arslan, Muhammad, et al.
(författare)
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Impact of Varying Load Conditions and Cooling Energy Comparison of a Double-Inlet Pulse Tube Refrigerator
- 2020
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Ingår i: Processes. - : MDPI. - 2227-9717. ; 8:3
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Tidskriftsartikel (refereegranskat)abstract
- Modeling and optimization of a double-inlet pulse tube refrigerator (DIPTR) is very difficult due to its geometry and nature. The objective of this paper was to optimize-DIPTR through experiments with the cold heat exchanger (CHX) along the comparison of cooling load with experimental data using different boundary conditions. To predict its performance, a detailed two-dimensional DIPTR model was developed. A double-drop pulse pipe cooler was used for solving continuity, dynamic and power calculations. External conditions for applicable boundaries include sinusoidal pressure from an end of the tube from a user-defined function and constant temperature or limitations of thermal flux within the outer walls of exchanger walls under colder conditions. The results of the system's cooling behavior were reported, along with the connection between the mass flow rates, heat distribution along pulse tube and cold-end pressure, the cooler load's wall temp profile and cooler loads with varied boundary conditions i.e. opening of 20% double-inlet and 40-60% orifice valves, respectively. Different loading conditions of 1 and 5W were applied on the CHX. At 150 K temperature of the cold-end heat exchanger, a maximum load of 3.7 W was achieved. The results also reveal a strong correlation between computational fluid dynamics modeling results and experimental results of the DIPTR.
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| 19. |
- Aullón Alcaine, Anna, et al.
(författare)
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Hydrogeochemical controls on the mobility of arsenic, fluoride and other geogenic co-contaminants in the shallow aquifers of northeastern La Pampa Province in Argentina
- 2020
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Ingår i: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 715
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Tidskriftsartikel (refereegranskat)abstract
- Elevated Arsenic (As) and Fluoride (F) concentrations in groundwater have been studied in the shallow aquifers of northeastern of La Pampa province, in the Chaco-Pampean plain, Argentina. The source of As and co-contaminants is mainly geogenic, from the weathering of volcanic ash and loess (rhyolitic glass) that erupted from the Andean volcanic range. In this study we have assessed the groundwater quality in two semi-arid areas of La Pampa. We have also identified the spatial distribution of As and co-contaminants in groundwater and determined the major factors controlling the mobilization of As in the shallow aquifers. The groundwater samples were circum-neutral to alkaline (7.4 to 92), oxidizing (Eh similar to 0.24 V) and characterized by high salinity (EC = 456-11,400 mu S/cm) and Na+-HCO3- water types in recharge areas. Carbonate concretions ("tosca") were abundant in the upper layers of the shallow aquifer. The concentration of total As (5.6 to 535 mu g/L) and F (0.5 to 14.2 mg/L) were heterogeneous and exceeded the recommended WHO Guidelines and the Argentine Standards for drinking water. The predominant As species were arsenate As(V) oxyanions, determined by thermodynamic calculations. Arsenic was positively correlated with bicarbonate (HCO3-), fluoride (F), boron (B) and vanadium (V), but negatively correlated with iron (Fe), aluminium (Al), and manganese (Mn), which were present in low concentrations. The highest amount of As in sediments was from the surface of the dry lake. The mechanisms for As mobilization are associated with multiple factors: geochemical reactions, hydrogeological characteristics of the local aquifer and climatic factors. Desorption of As(V) at high pH, and ion competition for adsorption sites are considered the principal mechanisms for As mobilization in the shallow aquifers. In addition, the long-term consumption of the groundwater could pose a threat for the health of the local community and low cost remediation techniques are required to improve the drinking water quality.
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| 20. |
- Bhattacharya, Prosun, 1962-, et al.
(författare)
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Editors’ foreword
- 2016
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Ingår i: Arsenic Research and Global Sustainability. - London : CRC Press. - 9781315629438 ; , s. xlv-xlvi, s. xlvii-xlviii
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Konferensbidrag (refereegranskat)
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