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Colloidal iron and manganese in water affecting RO operation
Abstract
The finding of various forms of iron, and less commonly of manganese, in numerous reverse osmosis (RO) membrane autopsies we have performed, have led us to call attention to the diverse forms of iron and manganese species in natural waters. Correlation of elemental composition analyses of foulants with contaminants in RO feedwater and pretreatment steps led to successful solutions of fouling problems by the modification of pretreatments, such as substitution of oxidation filtration strategies for iron and manganese reduction with sequestration with appropriate antiscalants. Cases where iron and manganese fouling failed to respond to sequestration with antiscalants, the existence in the RO feedwater of pre-existing colloidal iron and manganese particles are suspected. To fully control such fouling, speciation of the different forms of iron and manganese that exist in natural, industrial and wastewaters are central to process design, troubleshooting and RO system operation and maintenance. We have undertaken a literature review of iron and manganese colloidal chemistry as it pertains to the RO membrane process. This paper reviews the background for the association of iron with manganese in water treatment, natural sources of colloidal iron and manganese, early works on methods for the reduction of iron and manganese in traditional municipal waterworks where colloidal particles may be formed and not removed, speciation of forms of iron and manganese in water treatment, and the effects of colloidal iron and manganese on RO operation. The overall conclusion is that methods for the speciation and quantitation of colloidal forms of iron and manganese need to be fully developed and employed for the validation of methods useful for the control and/or removal of such foulants in RO feedwaters.
... Iron and manganese ions in feed solutions can act as coagulants in natural waters and form positively charged colloidal particles that adhere to the reverse osmosis membrane. Consequently, there is a reduction in flux and permeability and an increase in transmembrane pressure, polarization, and fouling effects, and a decrease in membrane efficiency (Ning 2009). ...
The presence of metallic ions in raw freshwater is a problem that occurs with greater intensity in periods of drought, due to the intensification of water withdrawal from lower levels of the dams, where there is a higher percentage of organic matter and concentration of metallic ions, including manganese and iron. High levels of these dissolved metals, in addition to altering the organoleptic properties of water, also cause deleterious effects on human and animal health. Given this, the present study aimed to evaluate the use of reverse osmosis in the removal of Mn⁺² and Fe⁺² from raw freshwater, to comply with the MS 5/2017 regulation (Brazilian standard), which establishes the maximum allowable values for Mn⁺² and Fe⁺² ions in drinking water. Three synthetic feed solutions were evaluated to study the retention alone and together of the metals, as well as the water permeability before and after the retention tests with each studied solution. The results showed that the reverse osmosis process retained 99 % of Mn⁺², 93 % of Fe⁺², and 98 % of the two ions together. Regarding the cleaning process, it increased the water permeability of the membrane after exposure to Fe⁺² and the mixture of Mn⁺² and Fe⁺², being reduced after exposure to Mn⁺² only. For the three types of feed, the post-cleaning fouling was estimated at 9.14 − 13.65 % in terms of permeability. Thus, reverse osmosis can be considered a promising process for the treatment of drinking water, and further studies are needed to implement this process in water treatment plants.
... During the desalination process, particularly in the pretreatment phase and due to the contact of water with air or the increase in pH, Fe 2+ ions can, easily, oxidized into Fe 3+ and generate iron oxides, that can cause a buildup in RO devices and cause them to foul [23]. If iron is not fully removed during the pretreatment stage, residual colloids can form a cake layer on the membrane surface [24], which contributes to the overall hydraulic resistance to the permeate flux and enhances concentration polarization. ...
Fouling is an inherent challenge in the Reverse Osmosis (RO) desalination process. Inorganic and colloidal compounds are frequently encountered on RO membrane surfaces. Although fouling is the topic of various studies, combined fouling notably by gypsum and iron oxides and their interaction is not yet studied. Therefore, the aim of this work is to study the combined fouling by gypsum and iron oxides and their interaction with the surface of the RO membrane. Gypsum and iron scaling were compared, and it was demonstrated that gypsum scaling caused severe water flux decline and induced membrane wetting. An important flux decline was also observed for iron scaling when the pH of feed solution is close to 6. Flux decline caused by combined fouling was compared with an individual fouling. A membrane fouling trials showed a synergistic effect between the dissolved calcium sulfate and iron oxide particles, which aggravated and accentuated RO the membrane fouling. The drop in normalized flux, caused by the combined fouling, was compared to the two-individual fouling (with gypsum and iron oxides), it appears that the combined one was 50% higher. The molecular interactions between iron oxides and gypsum as well as the properties of the formed crystals were determined by SEM/EDX and X-Ray Diffraction.
... Recent review articles indicated that the most common foulant types of seawater RO desalination are colloidal iron and silica ( Badruzzaman et al., 2019 ;Jiang et al., 2017 ). Generally, iron fouling on RO membranes is mostly colloidal, usually as silicates ( Ning, 2009 ). The foulant composition of the membrane used in the Nitsanim natural (reduced) SGW experiment showed high contents of silicon, calcium and magnesium ( Table 2 ). ...
Reverse osmosis (RO) seawater desalination is a widely applied technological process to supply potable water worldwide. Recently, saline groundwater (SGW) pumped from beach wells in coastal aquifers that penetrate beneath the freshwater-seawater interface is considered as a better alternative water source to RO seawater desalination as it is naturally filtered within the sediments which reduces membrane fouling and pre-treatment costs. The SGW of many coastal aquifers is anoxic – and thus, in a low redox stage – has elevated concentrations of dissolved manganese, iron and sulfides. We studied the influence of the SGW redox stage and chemistry on the performance - permeate flux and fouling properties - of RO desalination process. SGWs from three different coastal aquifers were sampled and characterized chemically, and RO desalination experiments were performed under inert and oxidized conditions. Our results show that all three aquifers have anoxic saline groundwater and two of them have intensive anaerobic oxidation of organic matter. Two aquifers were found to be in the denitrification stage or slightly lower and the third one in the sulfate reduction stage. Our results indicate that the natural redox stage of SGWs from coastal aquifers affects the performance of RO desalination. All SGW types showed better RO performance over seawater desalination. Furthermore, air oxidation of the SGW was accompanied with pH elevation, which increased the membrane fouling. Hence, keeping the feed water unexposed to atmospheric conditions for maintaining the natural reducing stage of the SGW is crucial for low fouling potential. The observed benefits of using naturally reduced SGW in RO desalination have significant implications for reduction in overall process costs.
... In water supplies, iron(II) and manganese (II) salts are unsTable and are precipitated as insoluble hydroxide, which settles out as a rust-coloured silt and such water causes staining in laundry. When water containing high amount of iron and manganese are used for industrial purposes like textile and paper production, the quality of the paper and textile produced are greatly reduced [5]. Therefore, removal of manganese and iron from water is necessary. ...
Silica-coated magnetite nanoparticle was synthesized as model adsorbent for the removal of Fe(II) and Mn(II) which are major contaminants of surface water. Prepared adsorbent was fully characterized using Fourier Transform Infra-red spectroscopy, Scanning Electron Microscopy, X-Ray Diffraction and X-Ray Fluorescence. The optimum conditions of adsorption were determined by investigating the effect of initial metal ion concentration, contact time, adsorbent dose, pH of aqueous solution and temperature. Adsorption equilibrium time was found to be 60 min for both Fe(II) and Mn(II). The equilibrium adsorption experimental data for the two metals were found to fit the Langmuir adsorption isotherms best with a regression value of 0.989 and 0.979 for Fe(II) and Mn(II) respectively. The pseudo second order kinetic model was found to describe the adsorption kinetics for both metals more effectively. The adsorption processes involving both metals were endothermic. The adsorbent was finally applied to typical raw water with initial manganese and iron concentrations of 1.45 mg/l and 3.67 mg/l, respectively, and the removal efficiency was 90 % for Mn and 47 % for Fe.
... Excess concentration of manganese affects colour, taste and odour of water. In addition, human exposure to toxic manganese adversely affects the nervous system, with symptoms such as anxiety, ataxia, dementia and manganism, a syndrome similar to Parkinson's disease (Ning 2009). Therefore, it is pertinent for environmentalists to develop novel treatment techniques that can effectively reduce Mn to its minimum or to allowable limit (Abdeen et al. 2015). ...
In the present study, a new composite adsorbent, chitosan/bentonite/manganese oxide (CBMnO) beads, cross-linked with tetraethyl-ortho-silicate (TEOS) was applied in a fixed-bed column for the removal of Mn (II) from water. The adsorbent was characterised by scanning electron microscopy (SEM), Fourier transform infra-red (FT-IR), N2 adsorption-desorption and X-ray photoelectron spectroscopy (XPS) techniques, and moreover the point of zero charge (pHpzc) was determined. The extend of Mn (II) breakthrough behaviour was investigated by varying bed mass, flow rate and influent concentration, and by using real environmental water samples. The dynamics of the column showed great dependency of breakthrough curves on the process conditions. The breakthrough time (tb ), bed exhaustion time (ts ), bed capacity (qe ) and the overall bed efficiency (R%) increased with an increase in bed mass, but decreased with the increase in both influent flow rate and concentration. Non-linear regression suggested that the Thomas model effectively described the breakthrough curves while large-scale column performance could be estimated by the bed depth service time (BDST) model. Experiments with environmental water revealed that coexisting ions had little impact on Mn (II) removal, and it was possible to achieve 6.0 mg/g breakthrough capacity (qb ), 4.0 L total treated water and 651 bed volumes processed with an initial concentration of 38.5 mg/L and 5.0 g bed mass. The exhausted bed could be regenerated with 0.001 M nitric acid solution within 1 h, and the sorbent could be reused twice without any significant loss of capacity. The findings advocate that CBMnO composite beads can provide an efficient scavenging pathway for Mn (II) in polluted water.
... The use of a 0.2 μm filter has been suggested by some authors Sallanko et al. 2005), whereas 100 kilodalton (kDa) (Sallanko et al. 2005) or 30 kDa ultrafiltration (Carlson et al. 1997;Carlson and Knocke 1999;Gregory and Carlson 2001;Sallanko et al. 2005) was set as a limit for soluble, nonoxidized manganese by others. In addition, iron and manganese colloidal oxides are commonly found on water purification membranes as foulants (Choo et al. 2005), even in reverse osmosis (RO) operations, in which pretreatment steps, such as manganese greensand or oxidation/filtration, have been applied to control iron and manganese levels in RO feed waters (Ning 2009). Incomplete removal of colloidal iron and manganese particles in the pretreatment steps may cause severe fouling problems for RO/Nanofiltration (NF) plants. ...
Iron and manganese are commonly found in natural waters, particularly in groundwater. Because of the importance of particle size distribution (PSD) on the performance of removal processes, this research focuses on understanding the PSD andζ-potentials of oxidized iron/manganese in water, as a function of pH, ionic strength, and hardness. After rapid oxidation of dissolved iron/manganese, laser diffraction (LD), dynamic light scattering (DLS), and fractionation through serial membrane filtration techniques were used to define the PSD. For manganese dioxide, theζ-potential was found to decrease as the pH decreased and as the ionic strength and hardness increased, resulting in a higher aggregate size. The aggregation rate of manganese dioxide strongly increased with hardness. On the other hand, ferric hydroxide PSD was not significantly altered by ionic strength or hardness at pH values relevant to typical natural waters. A combination of several techniques was found to be essential for providing a complete picture of the PSD. The DLS and LD techniques were generally well adapted for nano-scale and micron-scale particles, respectively. The serial membrane filtration technique was suggested for water practitioners working toward the selection of an appropriate process for iron/manganese control in drinking waters.
... The high levels of iron and manganese can discolor the water, stain the plumbing fixtures, and give water an unpleasant metallic taste (California State University, (2004). The iron and manganese elements in water occur in various forms (Ning, 2009); (Ning, 1997) and (Ning and Shen, 1998). In the water tap, the iron and manganese are present in dissolved forms. ...
This paper presents the maximum performance capabilities of our antiscalants and antifoulants that in many cases would permit the elimination of unnecessary pretreatment unit operations, resulting in significant operation and maintenance cost savings. The cost savings accrue also from the avoidance of carry-over foulants resulting from these pretreatment steps, as well as higher RO recoveries made possible, thus increasing water productivity and reducing the volume of RO reject and pretreatment waste needing disposal. Higher control limits on scaling and fouling potentials also facilitate the work on development of zero-liquid-discharge or minimum waste discharge projects needed in many locations.
A novel two-dimensional carbon-based magnetic nano-material, magnetic graphene oxide (MGO), was prepared and then used as an efficient adsorbent. MGO showed rapid and complete removal of iron(II) (Fe) and manganese(II) (Mn) from micro-polluted water bodies in a wide pH range. After saturated adsorption, MGO could be rapidly separated from water under an external magnetic field. Results of the adsorption equilibrium study indicated that adsorptions of Fe and Mn by MGO were monolayer heterogeneous and spontaneous processes resulting from the heterogeneity of the MGO surface as well as the electrostatic interactions between surface acidic groups of MGO and metal ions. In addition, both the Fe and Mn uptakes of MGO were very slightly affected by NaCl, although they decreased with increased humic acid in solutions. In an Fe/Mn binary aqueous system, both metal ions can be efficiently removed at low concentrations, but MGO showed preferential adsorption of Fe in a concentrated aqueous mixture. The adsorption behavior in the binary system was due to different affinities of surface oxygen-containing functional groups on MGO to Fe and Mn. Finally, unlike traditional approaches in recycling and reusing an adsorbent, the Fe- and Mn-loaded MGO can be directly applied as a new adsorbent to achieve the efficient removal of fluoride from aqueous solutions.
This study examined the effect of initial manganous ion (Mn 2+) concentration and oxidant dose on the oxidation of Mn 2+ to Mn oxide during water treatment. The oxidants studied were chlorine dioxide (ClO 2), potassium permanganate (KMnO 4), and ozone. Initial Mn 2+ concentrations were 60, 200, and 1,000 μg/L, and the goal of the treatment was a final Mn 2+ <10 μg/L. Bench-scale experiments were performed by applying different doses of each oxidant to a raw surface water and measuring Mn 2+ residuals overtime. For all experiments, the ambient raw water conditions were pH 7.0, 9°C, and total organic carbon = 3.4 mg/L. Oxidation kinetics for low initial Mn 2+ concentrations (60 and 200 μg/L) were significantly slower than for high concentrations (1,000 μg/L). For the lower initial Mn 2+ levels, ClO 2 was the only oxidant that consistently produced final Mn 2+ <10 μg/L, generally within 60-120 s. All oxidants produced final Mn 2+ <10 μg/L when the initial Mn 2+ concentration was 1,000 μg/L. Oxidation with ozone consistently resulted in soluble Mn 2+ >20 μg/L after 5 min, with the formation of permanganate ion in many cases. For low Mn2t concentrations, 90% oxidation by KMnO 4 required 15-30 min.
A series of filtration steps was used to seperate iron (Fe) and manganese (Mn) into soluble, colloidal, and particulate fractions. Two case studies demonstrate how fractionation data can improve understanding of the origins and removal of Fe amd Mn. The Mn species present in one water source were shown to be regulated by a biogeochemical cycle in which the natural oxidation and reduction of Mn appeared to be microbially mediated. Mn removal was improved by adjusting the application of potassium permanganete to account for this cycle. A groundwater treatment plant was suffering from high postfilter Fe and Mn concentrations. Fractionation data identified the problem as inadequate solids capture, not oxidant dosage, allowing a quick solution. The unexpected oxidation of Mn with chlorine (Cl2) was attributed to Fe oxide surface catalysis. Without adequate particle removal (no coagulant added), applying Cl2 on top of the filters exhibited superior removal to adding Cl2 before a detention basin.
Initial coagulation rates of colloidal hematite (-Fe2O3) particles (diameter less than 0.1 m) were measured experimentally in well-defined laboratory systems at constant temperature. The relative stability ratio,W, was obtained at various ionic strengths in NaCl medium and at pH values in the range from 3 to 12. ExperimentalW values ranged from 1 to 104 in various systems. The results delineate the roles ofspecific andgeneralized coagulation mechanisms for iron oxides. Among the specifically-interacting species (G
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) studied were phosphate, monomeric organic acids of various structures, and polymeric organic acids. The critical coagulation-restabilization concentrations of specifically-interacting anions (from 10–7 to 10–4 molar) can be compared with the general effects of non-specific electrolyte coagulants (10–3 to 10–1 molar). The laboratory results are interpreted with the help of a Surface Complex Formation/Diffuse Layer Model (SCF/DLM) which describes variations of interfacial charge and potential resulting from variations of coagulating species in solution. Comparison of these laboratory experiments with observations on iron behavior in estuarine and lake waters aids in understanding iron removal mechanisms and coagulation time scales in natural systems.
In northern Camden and northwestern Burlington Counties, NJ, the pH of groundwater in the Potomac Group and the Raritan and Magothy Formations of Cretaceous age ranges from 5 to 6 in the outcrop area to eight several miles downdip to the southeast. Iron is present in the groundwater as dissolved FeU2 and FeOHU1, and is as suspended ferric oxhyhydroxides, presumably formed by oxidation of ferrous species already in solution. The oxyhydroxides are probably a mixture of amorphous material and goethite with small amounts of hematite. in the outcrop area the concentration of dissolved ferrous or suspended ferric species is less than 0. 5 mg/liter in unpolluted waters. Just downdip from the outcrop area, ferrous and ferric iron species increase abruptly to about 6 to 7 mg/liter and 6 to 11 m/liter, respectively.
The world's increasing need for economically purified water and the advent of 50 to 100 million gallons per day (mgd) reverse osmosis (RO) plants capable of producing potable water at competitive prices demand the simplest possible pretreatment processes. Recent advances in antiscalant and anti-foulant design and applications now allow for significant simplifications in pretreatment steps necessary for RO feedwaters (1-3). Improved capabilities of antiscalants and antifoulants provide a vista of an ultimately simple pretreatment process for RO using minute dosages of chemicals. In addition to simplicity and economy in equipment, continuous operation of RO plans with no stoppages for cleaning and very long membrane service lives is a worthy and viable goals.
The chemistry of the interaction of iron, silica and organic polymers causing fouling of reverse osmosis prefilters and membranes is examined. The elemental analysis of the foulants is presented. A case study is described at the Nevada Cogen water treatment facilities in Las Vegas. The use of several antiscalants appeared to be associated with the frequent clogging of the prefilters and of the elements. Following analysis of the deposits, a replacement antiscalant was used with no ferric silicate flocculation activity.
This comprehensive, fully illustrated survey of the structures of crystalline silicates is largely the result of the author's own crystal-chemical classification of silicates, based on Bragg's classic system. Much emphasis is placed on nomenclature and classification, involving a passing acquaintance with ancient Greek (oligosilicates), German (zweier or zehner single chains) and mathematical symbolism. In general, few details will be found on the structure of individual silicates, the approach being mainly the development of a comprehensive treatment.-R.A.H.
Major sources of wastewater generated on land can benefit from, and often are in need of, processes for the complete recovery of water, having only solid by-products or waste for disposal. This applies to municipal and industrial wastewater and brackish water reverse osmosis (RO) plants and agricultural irrigation. High recovery of water with RO membranes is by far the most efficient method of processing waste and brackish water. Recoveries ranging from 70 to 90% are possible, limited by precipitation of insoluble salts and coagulation of colloidal particles. If emerging intermediate precipitative treatments of the limiting foulants can become widely successful, a tandom second RO step of similar recovery rates will reach an overall water recovery of 97–99%. The remaining 1–3% of the original water volume can be addressed with evaporative concentrators. Based on our initial successes, we clearly see this tandom RO process to be of universal utility. Precipitated salts from the treatment of the primary RO concentrate are mainly divalent cations (Ca, Mg, Sr, Ba) with coagulated silica and colloidal matter. Solutes that survive the secondary RO are mainly soluble monovalent cations (Na, K). The overall tandom RO process thus constitutes a way to fractionate divalent cation salts from the monovalent cation salts. Both salt fractions may find commercial use and not be entirely wasted. We currently are actively assisting municipal RO plants in California in maximizing the percent recovery in the primary ROs, and for the moment, minimizing the volumes of raw water needed and volumes of concentrate that have to be discharged. To illustrate the necessity of dealing with the unique water chemistry of each RO plant, we present the well water analyses of three municipal systems within a 25-mile radius of Riverside, CA. In each case, due to the high cost of discharging concentrate into a brine line to the sea, close to limiting primary RO recoveries have been reached. The results of autopsies and foulant analyses performed on membranes from these three plants identify the foulants that need to be precipitatively removed before treatment with secondary RO. Further work is being considered along these lines.
Experiments were performed to establish directly the extent of association of Fe and Mn with dissolved organic matter in anoxic pore waters from the sediments of Loch Duich, Scotland. Of the dissolved Fe, 74–84% was retained by an ultrafiltration membrane (MW ⩾ 1000), in the high molecular weight (HMW) phase, compared with 3–17% of the dissolved Mn. After u.v. oxidation the measured total concentration of Fe increased by 43–70% while that in the HMW phase was reduced to 27–44%. Simultaneously, the concentration of dissolved Mn increased by only 1–12%. It was concluded that most if not all the Fe was organically bound while Mn was present mainly as labile inorganic complexes.
showed very similar size distributions. This is consistent with the presence of preferential flow paths and suggests that colloids, and to the consumer. Soil-derived biocolloids such as bacte- colloid-associated contaminants, can be transported rapidly through riaandvirusesmayalsoposeahealthriskiftheybecome the vadose zone with minimal interaction with the soil matrix. The mobile: the literature on this is quite extensive (e.g., Sd FFF-ICP-MS analysis showed variation in element ratios (Fe/Al, Kim and Corapcioglu 1996, Jin et al. 1997). Mg/Al), which were used to detect changes in surface coatings and Movement of colloids is a three-stage process involv- mineralogy over the colloid size range. The study demonstrated the ing dispersion (or mobilization), transport and depo- utility of Sd FFF-ICP-MS for examining the influence of colloid size sition. Much is known about dispersion processes in onelementcompositionandonelucidatingcolloidtransportprocesses surfacesoilsbecauseaggregatestabilityhasalargeinflu- in soils. ence on: seedling emergence and plant viability, the resistance of soils to erosion, and water permeability (QuirkandSchofield,1955).Lessisknownaboutcolloid
Bench-scale tests were conducted to investigate the removal of dissolved manganese from Delaware River water. Prior pilot-plant results had indicated that manganese was not effectively removed by ozonation, sludge blanket clarification, and filtration, because of the breakthrough or resolubilization of colloidal manganese dioxide [MnO₂(s)] species. Increasing the alkalinity was not an effective means of controlling manganese. But application of potassium permanganate after ozonation and at the beginning of coagulation considerably improved the removal of soluble manganese.
This article describes research to quantify the kinetics of Mn(II) and Fe(II) oxidation by potassium permanganate and chlorine dioxide; illustrates the effects of reduced metal ion concentration, pH, temperature, and the presence of dissolved organic carbon (DOC) on these kinetics; and investigates aspects of oxidation through modeling analyses. Among conclusions based on experimental results were the following: oxidation of reduced Mn(II) was rapid except at low solution temperatures; rates of Mn(II) oxidation are acceptable in the presence of humic or fulvic acids, but those acids strongly inhibit Fe(II) oxidation efficiency; poor manganese removal may be caused by inefficient capture of colloidal MnOx (s). The sequence in which oxidants are added may be an important issue for design and operation. Este articulo describe la investigación hecha para cuantificar la cinética de la oxidación del Mn(II) y del Fe(II) por medio del KMnO₄ y del CLO₂; demuestra los efectos de la reducción de la concentración de iones metálicos, el pH, la temperatura, y la presencia de carbón orgánico disuelto en esta cinética; e investiga los aspectos de la oxidación por medio de modelos de análisis. Entre las conclusiones que se obtuvieron basados en los resultados de la experimentación, se encuentran los siguientes: las tasas de oxidacion del Mn(II) son aceptables en la presencia de ácido húmicos y fúlvicos, pero estos ácidos restringen bastante la eficiencia de oxidación del Fe(II); y la pobre remoción del manganeso puede ser causada por la ineficiente captura de coloides de MnOx (s). La sequencia segón la cual se añaden los oxidantes puede ser un elemento importante para el diseño y la operación.
In this study, non-filamentous heterotrophic bacteria with the ability to cause iron precipitation were isolated from water in a ferric ammonium citrate medium. Aerobacter aerogenes was the most common of the organisms found, especially in surface waters. All the bacteria appeared to have two characteristics in common, the ability to utilize citrate as a carbon source and the production of capsular material. Microscopic observations showed a large capsule which appeared to be encrusted with iron. Much of the iron can be removed with the capsule by sonication. In the ferric ammonium citrate medium where the iron is bound with citrate and ammonia, it is hypothesized that this complex material is absorbed into the cell, the carbon from the citrate is utilized, and the remaining iron is absorbed in the capsule. Although different types of organisms were isolated, three cultures were chosen and studied, Aerobacter aerogenes, Serratia indica, and Bacillus pumilus. As in much of the previously reported work, ferric ammonium citrate was used as the organic iron complex. The advantage of this compound is that iron is held in solution under alkaline conditions as high as pH 9.0-9.5. None of the cultures produced a pH high enough to cause iron precipitation.
This article presents methods developed for applications in laboratory studies on the fundamental chemistry of manganese in the II and IV oxidation states. These methods should also apply to the study of manganese in water supplies and other natural waters. The studies described may be grouped under the following headings: separation of solid manganese oxides and soluble manganous manganese; spectrophotometric determination of manganous manganese after separation from higher-valent forms; and, spectrophotometric determination of manganese in higher oxidation tastes.
Various microorganisms are known to concentrate iron and manganese in water supplies by depositing hydroxides of these elements in sheaths and stalks or in the slime layer adjacent to the microorganism cell. Iron bacteria are commonly found in waters that provide a continuous supply of ferrous ions and are most troublesome in water supplies in which the iron content is 1 ppm or greater. A large ensheathed bacterium has been studied that concentrates iron and manganese in its sheaths and that flourishes in a water supply containing, by chemical analysis, no detectable manganese and less than 0.02 ppm iron.
This paper attempts to introduce the work described in this special section on colloid transport within a more general perspective of the evolution of our understanding of the importance of colloids in subsurface systems. The focus will be on the transport of colloidal particles in natural (i.e., chemically and physically heterogeneous) geological settings because the complexity imposed by these situations represents the greatest challenge to current and future understanding. Great progress has been made in addressing many of the key questions related to colloid transport. However, as in most areas of science, increased knowledge also serves to reveal new and more complex challenges that must be addressed.
Manganese is a commonly found substance in groundwater in Finland. As a powerful oxidant, ozone can be used for the oxidizing of manganese even without raising the pH. The SFS (Finnish Standards Association) standard has set the accepted limit for soluble manganese to 0.45 μm. However, some research papers have used the limit of 30 kD (kilodalton) for soluble manganese. This research concentrates on the size fractions of manganese in four samples of untreated groundwater and in four samples of ozonized groundwater when treated with 0.45 μm, 0.20 μm, 100 kD, 30 kD, and 10 kD filters. In all tests, nearly all manganese contained in raw water penetrated all filters. There were slight variations in the flocculation of manganese in ozonized groundwater; nevertheless, hardly any reduction in manganese levels took place beyond 100 kD. After ozonation, there were two water samples which surpassed the manganese limit of 50 μgl set for domestic water when the filtration was 0.20 μm and another two samples when the filtration was 100 kD.
The common technique for the control and removal of iron consists of oxidation followed by solid /liquid separation. The effects of ionic strength and chloride concentration on the oxidation kinetics of ferrous iron in the mg/L range by dissolved oxygen are reported here. The rate constant at 25° C in infinitely dilute solution is about 6 × 1013 M−2 atm−1 min−1 and in seawater-like conditions, 4 × 1012 M−2 atm−1 min−1. With atmospheric partial pressures of oxygen and pH > 6, the chemical half-life of ferrous iron is on the order of minutes to hours. The particle size distribution of some ferric oxyhydroxide precipitates are reported. The use of other oxidants such as chlorine and potassium permanganate versus oxygen is reviewed.
Fouling of membranes by colloidal organic and inorganic particles continues to be documented as the most common and challenging obstacle in attaining stable continuous operation of reverse osmosis (RO) and ultrafiltration (UF) systems. Much current research is being conducted on physical parameters to mitigate such fouling. The focus has been on membrane synthesis and element design; microfiltration and ultrafiltration pretreatment; electromagnetic devices; correlation with physical factors such as Silt Density Index, zeta potential and critical flux; technique of direct observation of fouling process through a membrane; and classification of macromolecular organics for correlation with fouling characteristics. We report initial successes with chemical control of colloidal fouling. Through screening with a large number of observable coagulations of natural colloids, we have developed a group of proprietary anticoagulants and dispersants that would, at less than 10 ppm dosage to the RO feedwater, control various classes of colloidal foulants. Case studies of the control of humic matter, elemental sulfur and colloidal silicate in problematic RO systems that became stabilized are briefly presented. We conclude that a great need and potential exists in economically controlling the myriads of fouling interactions of colloidal particles during concentration within the brine channels of RO membrane elements. Low dosages of antifoulants can in many cases obviate the need for installation and maintenance of pretreatment unit or operations designed to remove such colloidal foulants from the process stream.
The statistical treatment of more than 1500 water analyses indicated that the natural water during its hydrologic cycle can dissolve much higher amounts of minerals than those found in seawater and able to keep it in solution under normal physiochemical conditions. The present study proved that the dissolution of minerals in natural water show relative and variable solubility as salinity, chloride in particular, increasing. Several statistical relationships were obtained and many equations had developed for predicting the natural upper concentration limits (UCL) of dissolving calcite, gypsum and silica at any given chloride, this is in order to conclude realistic and descriptive mineral saturation factors. A similar approach had also applied to explore the suitability of the currently used reference pH-scale. It was found that the currently measured pH against the fixed highest dissociation constant of zero salinity water may lead to erroneous conclusions, while measuring against the natural lower water dissociation rate that changes considerably with increasing salinity and decreasing hydration number is more reasonable. It is obvious that the fixed universal constants are not suitable bases for hydrochemical interpretation. This new perspective offers better understanding of the natural water dissolving capacity. The answer to the heading question is yes, the seawater is under saturation and slightly acidic.
RO membrane colloidal fouling experiments were performed in the laboratory under well controlled and realistic conditions. Iron oxide was selected as a typical inorganic colloidal foulant, due to its importance, as evidenced from well known manufacturer recommendations on iron concentrations in feed waters and from frequently encountered problems in membrane installations. A range of iron concentrations was identified where a linear relationship existed between flux reduction rate and concentration. The performance of the Silt Density Index (SDI) was tested on the basis of the RO fouling data obtained. The range of iron concentrations where measurable and meaningful SDI values could be obtained was remarkably close to membrane manufacturer recommendations. A notable sensitivity of the SDI was also observed with particles for which retention is negligible. However, on the basis of the RO fouling data obtained, it appears that the SDI is not conservative enough. Furthermore, since the SDI cannot predict fouling rates, it cannot discriminate between different types of membranes.
Since not all water supplies respond to a standard iron removal process, it is often necessary to carry out pilot testing in order to determine a method that is effective, as well as economical.
Near complete recovery of water from desalination of brackish and wastewater on land using a reverse osmosis (RO) system followed in tandem by a seawater RO system is highly desirable. Such a tandem RO process is being demonstrated for overall recovery of water in the range of 96%–98%, and fractionation of dissolved salts aimed at zero liquid discharge for municipal water plants. Serious issues of RO concentrate disposal, scaling of waste disposal lines, and salinity contamination of aquifers and soils are being addressed with such an approach. A wide range of differentiated antiscalant formulations is applied towards the task of maximizing water recovery of current municipal RO plants for maximized productivity and minimized concentrate disposal costs. Primary RO concentrates resulting from maximized recoveries are realized in the 70%–90% range. The concentrates from the primary ROs are being tested at pilot demonstration scales with seawater ROs for the highest possible recoveries of water limited by the high-pressure pumps to drive against the osmotic pressures of the resultant brine. We are providing a summary report on the limits of controls of our antiscalants for brackish water, the overall tandem RO recoveries attained in the initial pilot demonstration plants, and laboratory data pointing to our expectation that the tandem RO process is a universally usable process to generate super-concentrates from which the principal dissolved divalent salts of Ca and Mg can be separated from the mono-valent Na and K salts with commercial utility. Such zero liquid discharge processes will represent the ultimate environmentally friendly water treatment for large municipal plants.
Geochemical and microbiological studies support the hypothesis that bacteria mediate man- ganese oxidation in aerobic bottom waters of Oneida Lake, N.Y. In lake water samples main- tained in the laboratory, decreases in soluble Mn2+ and the formation of oxidized manganese (MnO,) occurred only in summer samples which supported metabolically active Mn-oxidizing bacteria. The effect of initial Mn2+ concentrations on Mn oxidation and on the disappearance of soluble Mn2+ (binding) was studied in water enriched from natural levels (1.2 k 0.4 PM in June and 0.48 PM in August 1979) to 9.1-200 PM Mn 2i. Highly enriched lake water (265 @4 Mn2+) inhibited Mn oxidation. Binding and oxidation of Mn was inhibited in filtered samples when particles X.4 pm were removed, ancl inhiljition persisted when the particles were first ethanol treated and then reintroduced into filtered lake water. Within the range of O-20 PM Mn2+ rates of Mn 2+ binding varied with the initial Mn2+ concentrations in August water samples.
This paper attempts to introduce the work described in this special section on colloid transport within a more general perspective of the evolution of our understanding of the importance of colloids in subsurface systems. The focus will be on the transport of colloidal in natural (i.e., chemically and physically heterogeneous) geological settings because the complexity imposed by these situations the greatest challenge to current and future understanding. Great progress has been made in addressing many of the key questions related to colloid transport. However, as in most areas of science, increased knowledge also serves to reveal new and more complex challenges that must be addressed.
A new method is described which enables determination of the concentration of truly dissolved forms of trace elements in natural waters without substantial influence of adsorption on the walls of apparatus and vessels. The method also simplifies further analysis of the ionic and molecular forms of trace elements. It consists in immersing a dialysis bag, filled with pure water, directly into the natural water in situ and allowing the dialysis and adsorption equilibriu to be established. Conditions for the use of this method are discussed and results of the determination of the dissolved fraction of 20 elements in river water, as compared with the results by filtration and ultrafiltration are presented. Neutron activation analysis was used for the elemental determinations.
Contaminants originating from human activities have entered the subsurface environment through waste disposal practices, spills, and land application of chemicals. The establishment of effective disposal and isolation procedures for chemical wastes, the protection of public health, and the amelioration of subsurface contamination rely on the ability to predict the velocity at which contaminants move through the vadose (unsaturated) and saturated zones. However, attempts to describe and predict contaminant transport cannot succeed if major pathways and mechanisms for transport are not defined.
Most approaches to describing and predicting the movement of contaminants treat groundwater as a two-phase system in which contaminants partition between immobile solid constituents and the mobile aqueous phase. Contaminants that are sparingly soluble in water and that have a strong tendency to bind to aquifer media are assumed to be retarded (to move much more slowly than the rate at which groundwater flows) (Figure la).
Many contaminants readily sorb to immobile aquifer media and therefore are considered to be virtually immobile in the subsurface and to present little danger to groundwater supplies. For example, in soil and aquifer material, many metals and radionuclides bind strongly to mineral components; furthermore, many nonpolar organic contaminants tend to bind to particulate organic matter. Colloids in the solid phase, however, also may be mobile in subsurface environments. Because the composition of colloids is expected to be chemically similar to that of the surfaces of immobile aquifer material, these particles also could sorb organic and inorganic contaminants and stabilize them in the mobile phase. The colloids act as a third phase that can increase the amount of contaminant that the flow of groundwater can transport (see Figure 1 b) .
Oxidation of Mn(II) by potassium permanganate and chlorine dioxide was investigated for the environmental conditions of pH, temperature, and initial Mn(II) concentrations typically observed in water treatment. For the conditions examined, oxidation reactions are rapid, with completion of the reactions within approximately 30 s. A kinetic model based on solution-phase oxidation, adsorption, and surface oxidation mechanisms was developed that successfully simulates experimental data. The model was capable of simulating the experimental data (r2 = 0.90 and 0.75 for KMnO4 and ClO2, respectively) over a range of solution pH (5.5-8), temperature (2-25-degrees-C), and initial Mn(II) concentrations (0.4-1.25 mg/L). The kinetic model was solved numerically, and rate constants and activation energies (10-50 kJ/mol) were derived for the three mechanisms simulated. For reactive oxidants such as KMnO4 and ClO2, adsorption of Mn(II) to the oxide surface is the rate-limiting step. Because of rapid surface oxidation reactions, concentrations of adsorbed Mn(II) were predicted to be low for the conditions studied. This result is in contrast to less reactive oxidants where surface adsorption is rapid relative to solution and surface oxidation reactions.
ABSTRACTA method for the simultaneous quantification of the various forms of iron added or endogenous to foods has been developed. The total, elemental, and soluble iron are determined with minimal pre-treatment by atomic absorption spectrophotometry. The iron valences and complexed iron are measured spectrophotometrically using the bathophenanthroline reagent. The method was both reproducible and accurate in measuring iron added to plant material and to a formulated instant beverage. The procedure may be applied to determination of possible changes in the iron-fortified processed foods.
Destabilization-flocculation is often used as a pretreatment before ultrafiltration of drinking water and secondary wastewater effluent. The fouling of ultrafiltration membranes by colloidal iron hydroxide-oxide has been studied by measuring the pore streaming potential of a series polysulfone type UF membranes with 10 KDa–50 KDa NMWCO. SEM–EDX was carried out on the fouled membranes and the iron distribution in and on the fouled membrane was determined. Fouling of the membrane as measured by flux reduction was usually accompanied by a positive change in zeta potential and iso-electric point (IEP) of the membrane. Severity of fouling seems to correlate with the presence of some pores of size larger than part of the iron colloid particle size distribution. SEM-EDX confirmed presence of iron within those membranes (20 KDa) suffering the most fouling. An initially large change in zeta potential was seen even after relatively small amounts of solution were filtered through the membrane. A control experiment showed this is not due to iron adsorption equilibrium, but should probably be attributed to fouling.
Major municipal wastewater reclamation plants in California, USA, Singapore, and many built or planned for other regions of the world use the high pathogen reduction properties of microfiltration/ultrafiltration (MF/UF) membranes followed by reverse osmosis (RO) membranes. Operational experiences in these plants suggest that while MF and UF membranes encounter pore and cake fouling by colloidal particles (0.1 micron down to molecular sizes, ie. nanoparticles), a significant fraction of the smaller colloidal particles pass through the MF and UF membranes, and end up on RO membranes as cake-layer foulants. Autopsies, foulant analyses and cleaning studies performed on fouled RO membranes from the plants and pilot plants showed that colloidal natural organic matter, colloidal calcium phosphate and some times colloidal silicates are the main components. These colloidal particles have great affinity towards aggregation with each other. Due to incomplete removal by MF and even UF, fouling of RO membranes downstream becomes measurable by trend-charts of normalized values of permeate flow, differential pressure and salt passage. Normalized permeate flow is the most sensitive, and an early indicator of such fouling. In this paper we will provide some details of our studies and provide literature evidences that support the conclusion that calcium phosphate in foulants originated as nanoparticles in the wastewater.
We have applied laser-induced breakdown spectroscopy to quantitative analysis of colloidal and particulate iron in water. A coaxial sample flow apparatus developed in our previous work, which allowed us to control the atmosphere of laser-induced plasma, was used. Using sequential laser pulses from two Q-switched Nd:YAG lasers as excitation sources, the FeO(OH) concentration in the tens of ppb range was determined with an optimum interval between two laser pulses and an optimum delay time of a detector gate from the second pulse. The detection limit of Fe decreased substantially using two sequential laser pulse excitations: the 0.6 ppm limit of single pulse excitation to 16 ppb with sequential pulse excitation. The effects of the second laser pulse on the plasma emission were studied. The concentration of iron in fine particles in boiler water sampled from a commercially operated thermal power plant has been determined successfully by this method. The results show the capability of laser-induced breakdown spectroscopy in determining suspended colloidal and particulate impurities in a simple and quick way.
In this study, removal efficiency of heavy metals such as iron, manganese, copper and nickel were surveyed in various units of water treatment plant in IsfahanCity. Samples were taken from influent, before and after sedimentation and after filtration under standard condition. Concentration of heavy metals in each sample was measured by atomic absorption spectrophotometer. The results showed that removal efficiency of iron, manganese, copper and nickel were 71, 60, 79 and 40 percent, respectively. Experimental results currently showed low efficiency for the suitable removal of aluminum. So, the aluminum concentration in all the samples from the influent (2.03 mg l-1) and effluent (2 mg l-1) of the water treatment plant exceeded the EPA drinking water standard (50 μg l-1). It is concluded that using conventional treatment technology can reduce metal concentrations conform to internationally approved guidelines except for aluminum. @ JASEM
Subsurface aeration is used to oxidise Fe in situ in groundwater that is used to make drinking water potable. In a groundwater system with pH>7 subsurface aeration results in non-mobile Fe precipitate and mobile Fe colloids. Since originally the goal of subsurface aeration is to remove iron in situ, the formation of non-mobile iron precipitate, which facilitates the metal's removal, is the desired result. In addition to this intended effect, subsurface aeration may also strongly enhance the microbiological removal of ammonium (NH(4)(+)) in the purification station. Mobile iron colloids could be the link between subsurface aeration and the positive effect on the NH(4)(+) removal process. Therefore, the objective of this study was to assess whether synthetic iron colloids could improve the NH(4)(+) removal process. The effect of synthetic iron colloids on the NH(4)(+) removal process was studied using an artificial purification set-up on a laboratory scale. Columns that purified groundwater with or without added synthetic iron colloids were set up in duplicate. The results showed that the NH(4)(+) removal was significantly ( alpha = 0.05 ) increased in columns treated with the synthetic iron colloids. Cumulative after 4 months about 10% more NH(4)(+) was nitrified in the columns that was treated with the groundwater containing synthetic iron colloids. The results support the hypothesis that mobile iron colloids could be the link between subsurface aeration and the positive effect on the NH(4)(+) removal process.
The literature was reviewed with respect to metal speciation methods in aquatic samples specifically emphasizing speciation of heavy metals in landfill leachate. Speciation here refers to physical fractionation (particulate, colloidal, dissolved), chemical fractionation (organic complexes, inorganic complexes, free metal ions), as well as computer-based thermodynamic models. Relatively few landfill leachate samples have been speciated in detail (less than 30) representing only a few landfills (less than 15). This suggests that our knowledge about metal species in landfill leachate still is indicative. In spite of the limited database and the different definitions of the dissolved fraction (< 0.45 microm or < 0.001 microm) the studies consistently show that colloids as well as organic and inorganic complexes are important for all heavy metals in landfill leachate. The free metal ion constitutes less than 30%, typically less than 10%, of the total metal concentration. This has significant implications for sampling, since no standardized procedures exist, and for assessing the content of metals in leachate in the context of its treatment, toxicity and migration in aquifers.
In this review article, the authors present up-to-date developments on experimental, modeling and field studies on the role of subsurface colloidal fines on contaminant transport in saturated porous media. It is a complex phenomenon in porous media involving several basic processes such as colloidal fines release, dispersion stabilization, migration and fines entrapment/plugging at the pore constrictions and adsorption at solid/liquid interface. The effects of these basic processes on the contaminant transport have been compiled. Here the authors first present the compilation on in situ colloidal fines sources, release, stabilization of colloidal dispersion and migration which are a function of physical and chemical conditions of subsurface environment and finally their role in inorganic and organic contaminants transport in porous media. The important aspects of this article are as follows: (i) it gives not only complete compilation on colloidal fines-facilitated contaminant transport but also reviews the new role of colloidal fines in contaminant retardation due to plugging of pore constrictions. This plugging phenomenon also depends on various factors such as concentration of colloidal fines, superficial velocity and bead-to-particle size ratio. This plugging-based contaminant transport can be used to develop containment technique in soil and groundwater remediation. (ii) It also presents the importance of critical salt concentration (CSC), critical ionic strength for mixed salt, critical shear stressor critical particle concentration (CPC) on in situ colloidal fines release and migration and consequently their role on contaminant transport in porous media. (iii) It also reviews another class of colloidal fines called biocolloids and their transport in porous media. Finally, the authors highlight the future research based on their critical review on colloid-associated contaminant transport in saturated porous media.
Fractionation of Metals in Water, Sediment, and Soil Systems
- H Borg
H. Borg, in L. Landner, ed., Fractionation of Metals in Water, Sediment, and Soil Systems. Springer–Verlag, Berlin, 1987.
Process selection and design of a dual-membrane treatment plant treating brackish surface water
- B Yallaly
- R Bergman
- B Fuerst
- R Foster
B. Yallaly, R.Bergman, B.Fuerst and R. Foster, Process selection and design of a dual-membrane treatment plant treating brack-ish surface water. Annual Conf. Proc., AWWA, Washington, DC, June 17–21, 2001. Downloaded by [Florida State University] at 19:39 28 December 2014
Iron and manganese removal
- L D Benefield
- J F Judkins
L.D. Benefield and J.F. Judkins, Iron and manganese removal, in Process Chemistry for Water and Wastewater Treatment, Prentice-Hall, New York, NY, 1982.
A bench-scale approach to optimize of reverse osmosis systems treating silica and iron bearing groundwater
- A Zacheis
A. Zacheis, A bench-scale approach to optimize of reverse osmosis systems treating silica and iron bearing groundwater. AWWA Inorganic Contaminants Workshop, Austin, TX, 2006.
Microfiltration and ultrafiltration: novel pretreatments for iron and manga-nese removal from a reverse osmosis feedwater. Water Quality Technology Conf
- M A Mann
- D Thomson
- E Jabari
- D Rohe
M.A. Mann, D.Thomson, E. Jabari and D. Rohe, Microfiltration and ultrafiltration: novel pretreatments for iron and manga-nese removal from a reverse osmosis feedwater. Water Quality Technology Conf. AWWA, Seattle, WA, November 10–14, 2002.