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Arsenic removal by low pressure-driven membrane operations
Published in Alberto Figoli, Jan Hoinkis, Jochen Bundschuh, Membrane Technologies for Water Treatment: Removal of Toxic Trace Elements with Emphasis on Arsenic, Fluoride and Uranium, 2016
Wickramasinghe et al. (2004) evaluated the removal of As from USA and Bangladesh groundwater by using a combined approach coagulation/MF. Ferric chloride or ferric sulfate was used as coagulant. In addition, a cationic polyelectrolyte (CY 2461, Cytec Industries, Stamford, CT) was also tested as a coagulant aid (doses were of 0.02 and 0.3 mg L−1). MF was performed by using hollow-fiber membranes from A/G Technology (Needham, MA) with nominal pore size of 0.1 μm. Results of bench-scale experiments indicated that the As removal is highly dependent on the raw water quality and the used coagulants gave efficient results; however, the use of ferric sulfate led to a lower residual turbidity in the treated water. The addition of polyelectrolyte as a coagulant aid improved the permeate flux but had no effect on the As residual concentration. In a pH range of 6.2–8.7 the As removal was improved by decreasing the pH value (Fig. 2.5). This result can be explained assuming that when pH is lowered, the As adsorption is increased leading to an increased particle size (Jain and Loeppert, 2000; Meng et al., 2000). Consequently, also the membrane rejection towards precipitate particles at a given ferric ion dose is increased by decreasing pH. Therefore, pH adjustment may be necessary in order to reduce the ferric ion dose required.
Geochemical Environments
Published in Arthur W. Hounslow, Water Quality Data, 2018
Iron has a high natural abundance, is ubiquitous, and exists in two valence states, Fe2+ (ferrous), the reduced form, and Fe3+ (ferric), the oxidized form. Iron forms low solubility oxides, hydroxides, and sulfides. At a pH greater than 3, ferric iron is insoluble and forms colloidal hydroxides. This means that in the presence of dissolved oxygen or hydrogen sulfide iron forms insoluble compounds. In their absence, iron may occur in water in the ferrous state. Of great significance with respect to many trace metals is the fact that the iron colloids have high adsorption capacity. The transformation of ferric hydroxide to limonite and hematite is basically one of dehydration, namely:
Coagulation and Mixing
Published in Paul N. Cheremisinoff, Handbook of Water and Wastewater Treatment Technology, 2019
Ferric sulfate is usually stored in the dry state either in the shipping bags or in bulk in concrete or steel bins. Bulk storage bins should be as tight as possible to avoid moisture absorption, but dust collector vents are permissible; and desirable. Hoppers on bulk storage bins should have a minimum slope of 36 degrees; however, a greater angle is preferred. Bins may be located inside or outside and the material transferred by bucket elevator, screw, or air conveyors. Ferric sulfate stored in bins usually absorbs some moisture and forms a thin protective crust which retards further absorption until the crust is broken.
Effect of solar radiation on natural organic matter composition in surface waters and resulting impacts on drinking water treatment
Published in Environmental Technology, 2023
I. Slavik, D. Kostrowski, W. Uhl
Coagulation jar test experiments were performed according to the Deutscher Verein des Gas- und Wasserfachs (DVGW) [64], with volumes of 1.8 L in 2 L beakers supplied with baffles. Ferric chloride was used as a coagulant. The temperature was kept at 20°C. Considering recommendations by Dennet et al. [65] and Vilgé-Ritter et al. [66] and preliminary experiments, a coagulation pH of 5 was chosen for maximum exploitation of the coagulant. A dosage of 14 mg Fe L–1 or higher had been determined in preliminary experiments to yield maximum DOC removal, and thus the dosage was set to this minimum value. The coagulation pH was adjusted with sodium hydroxide. For instantaneous dispersion of the coagulant and destabilisation of the particles, an Ultra Turrax Disperser (T 25 digital, IKA, Staufen, Germany) was used for the fast-stirring phase (G > 1000 s–1; t = 30 s). Mixing in the following slow-stirring phase (G = 40 s–1; t = 20 min) was performed using a Heidolph RZR 2041 single mixer.
Attenuation of organics contamination in polymers processing effluent using iron-based sludge: process optimization and oxidation mechanism
Published in Environmental Technology, 2022
Ultimately, wastewater effluent loaded with heavy metals is one of the main environmental concerns on a world scale [20,21]. Besides their natural occurrence, heavy metals may enter the ecological system through mining activities. Although the mining activities contribute to the world’s economy and international trade between countries, they cause severe environmental damage through contamination of freshwater. Acid mine drainage (AMD) effluents come from the mining areas when water is loaded with iron sulphide (pyrite) [22–24]. Through oxidation, pyrite is converted into ferrous ions, which is undergoing for further oxidation on exposure to atmospheric oxygen to form ferric ions [25]. Therefore, the acid content in water is increased as the ferric ions react directly with pyrite and thus causing an environmental damage. Therefore, tools can be integrated for environmental management.
Cellular stress strategies and harvesting methods to improve the feasibility of microalgae biofuel
Published in International Journal of Green Energy, 2022
Luciane Maria Colla, Munise Zaparoli, Francine de Souza Sossella, Naiara Elisa Kreling, Alan Rempel
Aluminum sulfate (Al2(SO4)3) is a low cost product, and is the most used in water treatment. However, wastewater with a high solid content requires a high dosage of Al2(SO4)3 and does not provide an adequate efficiency, which restricts its use. Ferric chloride (FeCl3) is often used in the treatment of effluents as a coagulant because it can operate in a wider pH range when compared to others (between 5 and 11). The disadvantage of using ferrous sulfate (FeSO4.7H2O) is the need for aeration of the medium because the formation of ferrous hydroxide, which is required for harvesting, occurs only in the presence of dissolved oxygen (Nunes 2004).