Thesis

New applications of Fine-Grained Iron Oxyhydroxides as Cost-effective Arsenic Adsorbents in Water Treatment

Thesis

New applications of Fine-Grained Iron Oxyhydroxides as Cost-effective Arsenic Adsorbents in Water Treatment

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Abstract

Arsenic pollution of drinking waters across the world is one of the most serious water-related problems due to its well-established consequences on human health even at very low concentrations in the lower µg/L range. Among different well-established options for arsenic remediation, the adsorption onto highly efficient commercial iron oxyhydroxide-based adsorbent such as granular ferric hydroxide (GFH) has proven to be effective and persuasive. However, GFH is a cost-extensive material. During the industrial production of granular fractions of conventional adsorbents, the fine-grained fraction (individual particle size of < 250 µm) is generated as by-product/waste as this fraction of granular adsorbents cannot be applied in fixed-bed adsorption filters because of high clogging potential in filter-bed. In this doctoral thesis, an integrated water process combining the adsorption and submerged microfiltration (MF) unit (abbreviated as SMAHS) was investigated to employ fine-grained iron oxyhydroxides. Air bubbling was applied in the slurry reactor of a SMAHS to introduce shear at the membrane surface for fouling control. Moreover, the powdered-sized fractions (individual particle size of ~ 3 µm) of iron oxyhydroxides were applied to form the pre-deposited dynamic membrane (DM) and the effectiveness of the formed DM was assessed in MF process. n addition to the fine fraction of the GFH, arsenic adsorption on µTMF (fine-grained tetravalent manganese feroxyhyte) was investigated through batch adsorption tests at pH 8 in three different water matrices and different adsorption isotherms were applied. The physical and chemical characteristics of the adsorbents were also fully investigated. The Freundlich isotherm describes the equilibrium isotherm data better than Langmuir isotherm, indicating a heterogeneous nature of the applied adsorbents. The isotherm data shows characteristics of favorable arsenic adsorption onto µGFH and µTMF. Further, adsorption efficiency of applied adsorbents depends strongly on the water quality parameters (pH and water matrix). Arsenic adsorption onto both adsorbents is mostly reversible, with a small proportion of irreversible adsorption. The findings from SMAHS indicate that the arsenic adsorption efficiency is comparable to that found in a fixed-bed adsorption filter packed with conventional adsorbents of the same type, with potential benefits of simultaneous removal of micro-organisms and turbidity. The material cost is estimated to be as low as 0.30 €/m3 of product water when the arsenic concentration in the product water is below the drinking water regulation limit (10 µg/L). The outcomes further suggest that iron oxyhydroxides as forming materials of DMs may be applied in water treatment to achieve arsenic removal rates of greater than 90 % if operating conditions are well controlled. Moreover, arsenic removal rates of the SMAHS and DM can be predicted/modeled using a mathematical model based on a homogenous surface diffusion model (HSDM). In conclusion, it is expected that the new applications of fine-grained iron oxyhydroxides would not only increase the sustainable footprint of the conventional adsorbent production process as the by-product will be utilized but also be efficient solutions for arsenic remediation using the highly efficient low-cost adsorbents in water treatment.

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Chapter
Adsorption is one of the most widely applied unit operations to separate molecules that are present in a fluid phase using a solid surface. Adsorption kinetic aspects should be evaluated in order to know more details about its mechanisms, characteristics, and possibilities of application. These data can determine the residence time to reach the required concentration of the adsorbate, making possible the design and operation of an adsorption equipment and defining the performance in batch and continuous systems. This chapter presents the particularities of adsorption kinetics in liquid phase. Batch and fixed-bed systems are considered. For discontinuous batch systems, diffusional mass transfer models and adsorption reaction models are discussed. For fixed-bed systems, the shape of breakthrough curves is studied on the basis of mass balance equations and empirical models. Furthermore, the design and scale up of fixed-bed columns are detailed according to the length of unused bed (LUB) and bed depth service time (BDST) concepts. Several numerical methods are presented in order to solve the required models for batch and fixed-bed systems. Some parameter estimation techniques are discussed in order to obtain the fundamental parameters for adsorption purposes, like mass transfer coefficients and empirical parameters.
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Conventional drinking water treatment processes have faced several obstacles that are severely affected by water pollution and shortage, which makes it difficult to produce potable water effectively. Low-pressure membrane filtration, which includes ultrafiltration (UF) and microfiltration (MF), is one of the most promising treatment technologies for improving water quality. Periodic hydraulic backwashing is a necessity for the routine operation of UF/MF membranes, but only sparse data are available regarding the optimization of backwashing procedures, while more attention has been directed toward membrane fouling and cleaning. In the current work, we critically review the backwashing parameters of UF/MF membranes used in municipal water supplies. These parameters include pressure, flux, permeability (or resistance), mass balance, and membrane characterization techniques. The factors affecting backwash performance, which include membrane properties, feed water properties and operating conditions, are discussed in detail. The pretreatments of feed water, such as peroxidation, adsorption, coagulation and filtration influence the performance of UF/MF membranes to varying extents. The impacts of the backwash interval, backwash duration, backwash strength, air-assisted backwashing, chemically enhanced backwashing, and backwash water quality on backwash performance are summarized to provide more comprehensive data, which can improve backwash performance in full-scale drinking water and water reuse treatment plants.
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This work studied the impact of humic and fulvic acids on the removal kinetics of arsenic (V) by granular ferric hydroxide (GFH) and the adsorption capacity of arsenic (V) onto GFH at equilibrium. The Freundlich and DubininRadushkevich models describe the arsenic (V) adsorption behavior onto GFH reasonably well ( ). The removal kinetics were studied by fitting the experimental data to both first-order and second-order models. The lowest adsorption capacity was observed in the presence of fulvic acids (FA), and conversely, the adsorption capacity in the presence of humic acids (HA) was lower than that without humic substances (WHS). The removal kinetics of arsenic (V) were well defined for the second-order model, with correlation coefficients ranging from 0.951 to 0.977. This study suggests that the presence of humic substances negatively impacts the removal of arsenic from water.
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We show that amyloid fibrils-based membranes purify water from arsenic, adsorbing both the arsenate(+5) and arsenite(+3) oxidation forms at efficiencies of ~99%. Binding isotherms indicate that amyloid fibrils possess multiple binding residues capable of strongly adsorbing arsenic ions via metal-ligand interactions, delaying the saturation of the membrane. We also show that these membranes can be reused for several cycles without any efficiency drop, and validate our technology in purifying real contaminated ground water by removing arsenic with an efficiency as high as 99.6%. These result make this technology promising for inexpensive, efficient and low-energy removal of arsenic from contaminated water.
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Arsenic contamination in drinking water is a major issue in the present world. Arsenicosis is the disease caused by the regular consumption of arsenic contaminated water, even at a lesser contaminated level. The number of arsenicosis patients is increasing day-by-day. Decontamination of arsenic from the water medium is the only one way to regulate this and the arsenic removal can be fulfilled by water treatment methods based on separation techniques. Electrocoagulation (EC) process is a promising technology for the effective removal of arsenic from aqueous solution. The present review article analyzes the performance of the EC process for arsenic removal. Electrocoagulation using various sacrificial metal anodes such as aluminium, iron, magnesium, etc. is found to be very effective for arsenic decontamination. The performances of each anode are described in detail. A special focus has been made on the mechanism behind the arsenite and arsenate removal by EC process. Main trends in the disposal methods of sludge containing arsenic are also included. Comparison of arsenic decontamination efficiencies of chemical coagulation and EC is also reported.
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In recent years, adsorption science and technology for water and wastewater treatment has attracted substantial attention from the scientific community. However, the number of publications containing inconsistent concepts is increasing. Many publications either reiterate previously discussed mistakes or create new mistakes. The inconsistencies are reflected by the increasing publication of certain types of article in this field, including “short communications”, “discussions”, “critical reviews”, “comments”, “letters to the editor”, and “correspondence (comment/rebuttal)”. This article aims to discuss (1) the inaccurate use of technical terms, (2) the problem associated with quantities for measuring adsorption performance, (3) the important roles of the adsorbate and adsorbent pKa, (4) mistakes related to the study of adsorption kinetics, isotherms, and thermodynamics, (5) several problems related to adsorption mechanisms, (6) inconsistent data points in experimental data and model fitting, (7) mistakes in measuring the specific surface area of an adsorbent, and (8) other mistakes found in the literature. Furthermore, correct expressions and original citations of the relevant models (i.e., adsorption kinetics and isotherms) are provided. The authors hope that this work will be helpful for readers, researchers, reviewers, and editors who are interested in the field of adsorption studies.
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Arsenic is a semi-metal element that can enter in water bodies and drinking water supplies from natural deposits and from mining, industrial and agricultural practices. The aim of the present work was to propose an alternative process for removing As from water, based on adsorption on a brown seaweed (Sargassum muticum), after a simple and inexpensive treatment: coating with iron-oxy (hydroxides). Adsorption equilibrium and kinetics were studied and modeled in terms of As oxidation state (III and V), pH and initial adsorbate concentration. Maximum adsorption capacities of 4.2 mg/g and 7.3 mg/g were obtained at pH 7 and 20 °C for arsenite and arsenate, respectively. When arsenite was used as adsorbate, experimental evidences pointed to the occurrence of redox reactions involving As(III) oxidation to As(V) and Fe(III) reduction to Fe(II), with As(V) uptake by the adsorbent. The proposed adsorption mechanism was then based on the assumption that arsenate was the adsorbed arsenic species. The most relevant drawback found in the present work was the considerable leaching of iron to the solution. Arsenite removal from a mining-influenced water by adsorption plus precipitation was studied and compared to a traditional process of coagulation/flocculation. Both kinds of treatment provided practically 100% of arsenite removal from the contaminated water, leading at best in 12.9 μg/L As after the adsorption and precipitation assays and 14.2 μg/L after the coagulation/flocculation process.
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The top layer of natural rapid sand filtration was found to effectively oxidise arsenite (As(III)) in groundwater treatment. However, the oxidation pathway has not yet been identified. The aim of this study was to investigate whether naturally formed manganese oxide (MnO2), present on filter grains, could abiotically be responsible for As(III) oxidation in the top of a rapid sand filter. For this purpose As(III) oxidation with two MnO2 containing powders was investigated in aerobic water containing manganese(II) (Mn(II)), iron(II) (Fe(II)) and/or iron(III) (Fe(III)). The first MnO2 powder was a very pure - commercially available - natural MnO2 powder. The second originated from a filter sand coating, produced over 22 years in a rapid filter during aeration and filtration. Jar test experiments showed that both powders oxidised As(III). However, when applying the MnO2 in aerated, raw groundwater, As(III) removal was not enhanced compared to aeration alone. It was found that the presence of Fe(II)) and Mn(II) inhibited As(III) oxidation, as Fe(II) and Mn(II) adsorption and oxidation were preferred over As(III) on the MnO2 surface (at pH 7). Therefore it is concluded that just because MnO2 is present in a filter bed, it does not necessarily mean that MnO2 will be available to oxidise As(III). However, unlike Fe(II), the addition of Fe(III) did not hinder As(III) oxidation on the MnO2 surface; resulting in subsequent effective As(V) removal by the flocculating hydrous ferric oxides.
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This work aims to modify zein, a corn protein, to be a biocompatible adsorbent for the removal of As(V) from water. This adsorbent was prepared by the incorporation of iron(III) chloride into 50%(w/v) of zein in ethanol and water (70:30 (v/v)) and dropping into cold water (5 °C) to form adsorbent beads. In the batch operation, various parameters, i.e. pH of solution, iron loading concentration, competing ions and adsorption time, were studied. Under the optimum conditions, the As(V) adsorption appeared to follow the Langmuir isotherm model with the maximum adsorption capacity of 1.95 mg/g.
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Oil/water (O/W) emulsion is daily produced and difficult to be treated effectively. Ceramic membrane ultrafiltration is one of reliable processes for the treatment of O/W emulsion, yet still hindered by membrane fouling. In this study, two types of Fe2O3 dynamic membranes (i.e., pre-coated dynamic membrane and self-forming dynamic membrane) were prepared to mitigate the fouling of support ceramic membrane in O/W emulsion treatment. Pre-coated dynamic membrane (DM) significantly reduced the fouling of ceramic membrane (i.e., 10% increase of flux recovery rate), while self-forming dynamic membrane aggravated ceramic membrane fouling (i.e., 8.6% decrease of flux recovery rate) after four filtration cycles. A possible fouling mechanism was proposed to explain this phenomenon, which was then confirmed by optical images of fouled membranes and the analysis of COD rejection. In addition, the cleaning efficiency of composite membranes (i.e., Fe2O3 dynamic membrane and support ceramic membrane) was enhanced by substitution of alkalescent water backwash for deionized water backwash. The possible reason for this enhancement was also explained. Our result suggests that pre-coated Fe2O3 dynamic membrane with alkalescent water backwash can be a promising technology to reduce the fouling of ceramic membrane and enhance membrane cleaning efficiency in the treatment of oily wastewater.
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Three treatment technologies for removing arsenic from groundwater in Albuquerque, N.M., were compared: ion exchange (IX), iron hydroxide coagulation followed by microfiltration (C/MF), and activated alumina (AA) adsorption. For an 8,700-m(3)/d (2.3-mgd) arsenic treatment facility, capital costs of the three processes were similar: $5.2 million, $4.1 million, and $4.6 million, respectively. Annual operations and maintenance costs were $447,000, $273,000 and $444,000, respectively. The principal differences were the result of large salt requirements for the IX process and the need to reduce the pH to 6 for AA adsorption, followed by base addition to stabilize the water. The C/MF system was selected for a demonstration facility in Albuquerque.
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Membrane fouling is considered a serious obstacle for operation and cost efficiency in wastewater treatment using nanofiltration (NF). However, pretreatment is the most practical way to reduce this prior to NF. In this research, two types of wastewaters were pretreated with different methods prior to NF to examine the effect of pretreatment on membrane fouling in terms of turbidity, chemical oxygen demand (COD) and permeate flux. Turbidity and COD were measured to assess solid foulants and organic species in the wastewater, respectively. First sample was secondary treated sewage which was pretreated using coagulation­flocculation­sedimentation (CFS) only. Steady flux was increased from 24 L/m h for wastewater without pretreatment to 32.1 L/m h with pretreatment. COD was also eliminated after CFS/NF, and turbidity was reduced to 0.6 NTU. Second sample was diluted biodiesel wastewater which was pretreated using a combination of powdered­activated carbon (PAC) adsorption and CFS (PAC/CFS). Steady flux was increased from 22.3 L/m h for wastewater without pretreatment to 28.7 L/m h with pretreatment, biodiesel wastewater quality also improved. Turbidity was reduced from 12 to 0.6 NTU, and COD was reduced from 526 to 4 mg/L after NF with PAC/CFS pretreatment, while COD was reduced from 526 to 95 mg/L using NF without pretreatment.
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Arsenic represents a natural drinking water contaminant that can deteriorate health due to its extreme toxic nature. Infant mortality, neuropathies, liver disease, cancer, eye diseases, cardiovascular disease and different skin alterations can stem from chronic arsenic exposure. The predominant species of arsenic comprise of arsenite and arsenate. Arsenite is more toxic in nature as compared to arsenate. Arsenic pollution is mainly caused by natural process such as weathering of rocks and minerals followed by leaching and industrial activities that lead to contamination of soil and groundwater. The WHO guideline permits the maximum limit of arsenic as 10 μg/L in drinking water. This review provides a comprehensive overview on arsenic mode of action, its sources and health related effects. The effect of toxicity, biomarkers of arsenic toxicity and the mechanism of arsenic dangers on humans are also discussed.