Chapter 7

NOM Removal by Adsorption

Mika Sillanpää∗,  and Amit Bhatnagar∗∗     ∗Lappeenranta University of Technology, LUT Faculty of Technology, LUT Chemtech, Laboratory of Green Chemistry, Sammonkatu 12, 50130 Mikkeli, Finland     ∗∗University of Eastern Finland, Department of Environmental Science, Faculty of Science and Forestry, P.O. Box 1627, 70211 Kuopio, Finland

Abstract

The removal of natural organic matter (NOM) and its constituents from water is an emerging issue, and a robust treatment technology is needed to achieve this goal. Interest in research to overcome this problem has been growing steadily, and many technologies have been proposed for the removal of NOM from water. This chapter focuses on the removal of NOM and its constituents from water using adsorption technology, which has proved to be one of the best technologies for the removal of diverse types of aquatic pollutants. The principal NOM removal results obtained with different adsorbents have been summarized.

Keywords

Adsorption; Carbon adsorbent; Hydroxide adsorbent; Metal oxide adsorbent; Nanoadsorbent; Natural organic matter (NOM); Water treatment
Abbreviations
AOPs
   Advanced oxidation processes
CNT
   Carbon nanotube
CSZ
   Chitosan/zeolite composite
CUR
   Carbon usage rate
DBP
   Disinfection by-product
DBPFP
   Disinfection by-product formation potential
DOC
   Dissolved organic carbon
DOM
   Dissolved natural organic matter
EBCT
   Empty bed contact time
FTIR
   Fourier transform infrared
GAC
   Granular activated carbon
HA
   Humic acids
HAAs
   Haloacetic acids
HPIA-DEAE
   Hydrophilic acid-weak ionic exchange resin
HPLC
   High performance liquid chromatography
HPSEC
   High performance size exclusion chromatography
IOCS
   Iron oxide-coated sand
IOP
   Iron oxide particle
LDH
   Layered double hydroxide
Mag-PCMAs
   Magnetic permanently confined micelle arrays
MWCNT
   Multiwalled carbon nanotube
NMR
   Nuclear magnetic resonance
NOM
   Natural organic matter
PAC
   Powdered activated carbon
ROM
   Residual organic matter
SAM
   Self-assembled monolayer
SEC
   Size exclusion chromatography
SPTHMFP
   Simulated plant trihalomethane formation potential
SUVA
   Specific UV absorbance
THMFP
   Trihalomethane formation potential
THM
   Trihalomethane
TOC
   Total organic carbon

7.1. Introduction

The choice of water treatment process depends on the characteristics of the water and the treatment method costs (Richardson et al., 2007). An improved understanding of the chemical properties of aquatic natural organic matter (NOM) sheds light on choosing the most appropriate treatment strategies for removing NOM from raw drinking waters (Owen et al., 1985). A great variety of NOM removal processes have been investigated and employed, such as coagulation (Bell-Ajy et al., 2000; Crozes et al., 1995; Matilainen et al., 2010), membrane filtration (Siddiqui et al., 2000; Metsämuuronen et al., 2014), advanced oxidation processes (Matilainen and Sillanpää, 2010), and adsorption (Karanfil et al., 1999; Genz et al., 2008). However, all these methods have their own shortcomings or limitations; for example, inorganic coagulants such as aluminum- or iron-based salts remove only a portion of NOM (Chow et al., 2009). Furthermore, the removal of NOM by conventional and advanced treatment processes (flocculation, oxidation, and membrane processes) is not always adequate with regard to removal efficiency, chemical and energy consumption, and management of residuals (Genz et al., 2008). The adsorption process, the focus of this chapter, is generally considered one of the best water treatment technologies because of its convenience, ease of operation, and simplicity of design.

7.2. Adsorption

Adsorption can be described as the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface. In other words, adsorption is a mass transfer process that includes the accumulation of substances at the interface of two phases, such as the liquid–liquid, gas–liquid, gas–solid, or liquid–solid interface (Dąbrowski, 2001). The substance being adsorbed is the adsorbate, and the adsorbing material is the adsorbent. In a real adsorption system, equilibrium is achieved between the adsorbent, which is in contact with the bulk phase, and the so-called interfacial layer. In contrast, desorption denotes the converse process. Adsorption is different from absorption, where the adsorbate molecules penetrate the bulk solid phase. The term sorption—together with the terms sorbent, sorbate, and sorptive—is also used to represent both adsorption and absorption, when both occur simultaneously or cannot be distinguished (Dąbrowski, 2001). An adsorption isotherm—the equilibrium relation between the quantity of the adsorbed material and the pressure (for gas) or concentration (for liquids) in the bulk fluid phase at constant temperature—is widely used to explain the adsorption process. In the literature, readers can find several models describing the adsorption process, namely the Freundlich isotherm (Freundlich, 1906), Langmuir isotherm (Langmuir, 1916), and Brunauer–Emmett–Teller (BET) isotherm (Brunauer et al., 1938). Adsorption can be distinguished as either physical adsorption (or physisorption, from the universal van der Waals interactions) or chemical adsorption (or chemisorption, which can have the character of a chemical process) (Dąbrowski, 2001). It may also occur due to electrostatic attraction. Physical adsorption is a reversible process that takes place at a temperature lower or close to the critical temperature of an adsorbed substance. In contrast, chemical adsorption usually occurs at temperatures much higher than the critical temperature, and is a specific process that can only take place on some solid surfaces for a given gas/liquid (Dąbrowski, 2001). Under favorable conditions, both processes can occur simultaneously or alternately. Physical adsorption is accompanied by a decrease in free energy and entropy of the adsorption system, so this process is exothermic (Dąbrowski, 2001). It has been argued that in view of the higher bonding strength in chemisorption, it is difficult to remove chemisorbed species from the solid surface. A brief discussion of historical developments in adsorption science and engineering is presented below.
The credit for the first quantitative observations on adsorption goes to Scheele (Mantell, 1951) in 1773, who reported some experiments on the uptake of gases by charcoal and clays. This was followed by observations made by Lowitz in 1785 on the reversible removal of color and odor-producing compounds from water by wood charcoal. Larvitz in 1792 and Kehl in 1793 observed similar phenomena with vegetable and animal charcoals, respectively. The term adsorption was proposed by du Bois-Reymond but introduced into the literature by Kayser (Dąbrowski, 2001). Kayser also developed some theoretical concepts that became basic to monomolecular adsorption theory (Dąbrowski, 2001). Systematic studies of adsorption were conducted by de Saussure and, based on the results of these studies, he concluded that all types of gases are taken up by porous substances (sea foam, cork, charcoal, asbestos), and this process is accompanied by the evolution of heat (Dąbrowski, 2001). Thus, he discovered the exothermic character of adsorption processes, and he was the first to note the commonness of adsorption. The term absorption was introduced by McBain (McBain, 1909) to determine an uptake of hydrogen by carbon much slower than adsorption. He proposed the term sorption for adsorption and absorption. Practical application of adsorption processes is based mainly on the selective uptake of individual components from their mixtures by other substances. Selective adsorption, which has many industrial applications, was discovered by Tswett in 1903 (Dąbrowski, 2001). Later, he took advantage of this phenomenon to separate chlorophyll and other plant pigments by means of silica materials. The technique proposed by Tswett has been called column solid/liquid adsorption chromatography. This discovery was not only the beginning of a new analytical technique, but also the origin of a new field of surface science. Readers interested in a detailed discussion of the theory and applications of adsorption should refer to an excellent comprehensive review by Dąbrowski (Dąbrowski, 2001).

7.3. Adsorbents and Their Characteristics

To achieve the best performance in adsorption systems, knowledge of various types of adsorbents is essential. The most important properties of a good adsorbent are a well-developed porous structure and high surface area. Another feature of a good adsorbent is a short equilibration time so that it can be used to remove contaminants more quickly. Thus, the best adsorbents for pollutant removal have a high surface area and porosity, and demonstrate fast adsorption kinetics. Commercial sorbents used in cyclic adsorption processes should ideally meet several important requirements (Deng, 2006), including high selectivity derived from equilibrium, kinetic, or steric effects; large adsorption capacity; fast adsorption kinetics; easy regenerability; good mechanical strength; and low cost. The above adsorbent performance requirements can be expressed simply as adsorbent characteristic requirements as follows (Deng, 2006): large internal pore volume; large internal surface area; controlled surface properties through selected functional groups; controlled pore size distribution, preferably in the micropore range; weak interactions between adsorbate and adsorbent (mostly on physical sorbents); inorganic or ceramic materials to enhance chemical and mechanical stability; and low-cost raw materials. In recent decades, a number of materials from different sources have been extensively investigated as adsorbents in water pollution control. Some of the important ones include silica gel, activated alumina, zeolites, and activated carbon.

7.3.1. Silica Gel

Silica gel is most commonly encountered in everyday life as beads in a small paper packet. In this form, it is used as a desiccant to control local humidity to avoid spoilage or degradation of some goods. Silica gels are classified into three types: regular, intermediate, and low density gels. Regular density silica gel is prepared in an acid medium and has a high surface area (e.g., 750 m2 g−1). Intermediate and low density silica gels have low surface areas (300–350 and 100–200 m2 g−1, respectively). Modified forms of silica have also been widely explored for the removal of different pollutants (Najafi et al., 2011; Wang et al., 2009; Zaitseva et al., 2013).

7.3.2. Activated Alumina

Activated alumina comprises a series of nonequilibrium forms of partially hydroxylated alumina oxide, Al2O3. In general, as a hydrous alumina precursor is heated, hydroxyl groups are driven off, leaving a porous solid structure of activated alumina. This process is also used to remove water from organic liquids, including gasoline, kerosene, oils, aromatic hydrocarbons, and many chlorinated hydrocarbons, with a surface area ranging from 200 to 300 m2 g−1. Activated alumina has received wide attention as an adsorbent, and a number of reports are available on its adsorption characteristics. Readers interested in a detailed discussion of the application of alumina in water treatment should refer to comprehensive reviews by Kasprzyk-Hordern (2004) and Kumar et al. (2014).

7.3.3. Zeolites

Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. About 40 natural and over 200 synthetic zeolites have been identified so far. Zeolite based materials are extremely versatile, and their main applications include ion-exchange resins, catalytic applications in the petroleum industry, separation process, and as an adsorbent for water, carbon dioxide, and hydrogen sulfide. Zeolites have been extensively used for the removal of diverse pollutants (Grieco and Ramarao, 2013; Xie et al., 2013; Martucci et al., 2012; Lin et al., 2013). Wang and Peng (2010) presented a review on the role of natural zeolites as effective adsorbents in water and wastewater treatment.

7.3.4. Activated Carbon

Activated carbon has undoubtedly been the most popular and widely used adsorbent in wastewater treatment worldwide. It is produced by a process consisting of raw material dehydration and carbonization followed by activation. The product obtained generally has a very porous structure with a large surface area ranging from 600 to 2000 m2 g−1. Activated carbon has proved a versatile adsorbent that can remove diverse types of pollutants from water and wastewater (Marsh and Rodríguez-Reinoso, 2006; Bansal and Goyal, 2005; Bhatnagar et al., 2013).
The performance of the adsorption process depends on many factors, including (1) surface area, (2) nature and initial concentration of the adsorbate, (3) solution pH, (4) temperature, (5) interfering substances, and (6) nature and dose of the adsorbent. The physicochemical nature of the adsorbent significantly affects both adsorption rate and capacity. The solubility of the solute also considerably influences the adsorption equilibrium. In general, an inverse relationship can be expected between the extent of adsorption of a solute and its solubility in the solvent where the adsorption takes place. The presence of (in)organic compounds can also limit the adsorption process.

7.4. NOM Removal from Water by Adsorption

7.4.1. Carbon Adsorbents

Granular activated carbon (GAC) adsorption is one of the best technologies employed for the removal of NOM and other diverse aquatic pollutants. The most common adsorbent used for water treatment is activated carbon, which can be applied as powdered activated carbon (PAC) or GAC. While PAC can be applied at various stages of water treatment, GAC is typically utilized after coagulation–filtration/sedimentation but before postdisinfection (Bond et al., 2011). Residual humic substances after the coagulation process are most likely fragments of lower size and charge. Owing to the hydrophobicity of remaining NOM, in situations where they retain significant disinfection by-product formation potential (DBPFP), activated carbon adsorption is recommended for their removal (Bond et al., 2011). Vidic and Suidan (1991) demonstrated the role of dissolved oxygen in the adsorptive capacity of activated carbon for both synthetic matter and NOM. The adsorption isotherm tests were conducted using an initial NOM concentration of 7.6 mg of DOC L−1. The results indicate that the adsorptive capacity of GAC for this particular NOM increased as much as twofold as a result of the presence of molecular oxygen. The effectiveness of GAC adsorption for the removal of NOM and trihalomethanes (THM) from the drinking water treated at Ivedik Water Treatment Plant in Ankara City was investigated (Capar and Yetis, 2001). The Freundlich Isotherm constants, K and n, were determined as 17.61 (mg g−1) (L mg−1)1 = n and 1.66, respectively. Bench-scale GAC columns were run with empty bed contact times (EBCT) varying from 0.40 to 2.67 min to evaluate adsorption performance and to investigate the effect of EBCT on service life. The treated volumes of water increased with EBCT, showing a linear increase in GAC service life. A 5-fold increase in EBCT resulted in an almost 16-fold increase in service life. Correspondingly, the carbon usage rate decreased, and the optimal bed depth was observed to be 10 cm. The capacities calculated by the isotherm equation and achieved in columns were also compared. The column capacities were within 43–65% of the isotherm capacities at complete breakthrough. However, they were only within 8–17% of the isotherm capacities at 50% breakthrough. GAC was also studied by Iriarte-Velasco et al. (2008) for the adsorption of NOM. Three different carbons of different origin were initially used. Their physical properties were studied by means of N2 adsorption. Their chemical properties were studied by means of thermogravimetric analysis, acid–base titrations, and Fourier transform infrared spectroscopy (FTIR). Only one of the carbons showed a broad absorption band in the 1300—1000 cm−1 region in FTIR spectra, which was assigned to the C–O stretching and O–H bending modes of alcoholic, phenolic, and carboxylic groups. Adsorption of NOM was studied by batch adsorption experiments, and uptake of NOM by the different carbons was evaluated by UV absorbance, DBPFP tests, and high-performance liquid chromatography–size exclusion chromatography (HPLC–SEC). The Freundlich equation was used to fit equilibrium data. Point of zero charge (pHPZc) and overall surface basicity were shown to improve the removal of THM precursors. Differences were reported in the molecular weight distribution of the adsorbed material by different carbons. A clear correlation was found between a reduction in the THM formation capacity of the sample and the reduction in intensity of a specific peak in SEC chromatograms. Furthermore, trihalomethane formation potential (THMFP) tests showed the existence of some fractions of NOM that were not adsorbable with activated carbons and undetected by measurement of DOC.
The removal of NOM from lake water was studied in two pilot-scale adsorbers containing GAC with different physical properties (Velten et al., 2011). In both GAC adsorbers, the adsorbability of the remaining NOM fractions, compared on the basis of partition coefficients, increased with decreasing molecular size, suggesting that increasingly large portions of the internal GAC surface area could be accessed as the size of NOM decreased. Overall DOC uptake at pseudosteady-state differed between the two tested GACs (18.9 and 28.6 g-C kg−1 GAC); the percentage difference in DOC uptake closely matched the percentage difference in the volume of pores with widths in the 1–50 nm range that was measured for the two fresh GACs. Despite the differences in NOM uptake capacity, the two GACs removed individual NOM fractions in similar proportions.
Besides GACs, PACs were also applied in combination with aluminum sulfate to improve NOM removal from high-DOC source water (Fabris et al., 2004). The treated water quality was analyzed using absorbance at 254 nm, DOC, THMFP, rapid fractionation, C13 NMR, and molecular weight distribution by high performance size exclusion chromatography. Carbon C (steam activated, coal based carbon), and B (chemically activated, wood based carbon, which is primarily mesoporous (2–50 nm pore width)) offered equivalent DOC removal, but carbon C was considered superior because it reduced treated water THMFP. It is postulated that an organic fraction of around 1000 Da is responsible for the differences in THMFP shown in the treated waters.
Modified carbons have also been used for NOM removal. Several pathways have been employed to systematically modify two GACs, F400 (coal based) and Macro (wood based), for examining the adsorption of dissolved natural organic matter (DOM) from natural waters (Dastgheib et al., 2004). A total of 24 activated carbons with different physical and chemical characteristics were produced. The impact of carbon treatment on DOM adsorption was examined by conducting isotherm experiments at a neutral pH using the modified carbons and a DOM isolated from the influent to a drinking water treatment plant in Myrtle Beach, South Carolina, USA. Adsorption of the DOM by two activated carbon fibers (ACFs) with relatively uniform pore size distributions showed that only pores with widths larger than 1 nm were accessible to the DOM macromolecules. Increases in the carbon supermicropore and mesopore volume (i.e., >1 nm) increased the DOM uptake, if the surface chemistry was favorable. Normalized on a surface area basis, the isotherms showed the significance of carbon surface chemistry for DOM uptake. At neutral pH, the adsorption of negatively charged DOM molecules was favored by basic and positively charged surfaces, while DOM uptake was minimized when the surface had acidic characteristics. High-temperature ammonia treatment of oxidized carbons considerably enhanced DOM uptake, mainly due to the increase in accessible surface area and surface basicity. Iron-impregnated carbons indicated an enhanced affinity of the iron-laden carbon surface toward the DOM species, if the surface was not negatively charged. DOM adsorption by virgin and modified GACs was studied by Cheng et al. (2005). DOM samples were obtained from two water treatment plants before (i.e., raw water) and after coagulation/flocculation/sedimentation processes (i.e., treated water). GACs were modified by high-temperature helium or ammonia treatment, or iron impregnation followed by high-temperature ammonia treatment. Two ACFs were also used, with no modification, to examine the effect of carbon porosity on DOM adsorption. Size exclusion chromatography (SEC) and specific ultraviolet absorbance (SUVA254) were employed to characterize the DOMs before and after adsorption. Iron-impregnated (HDFe) and ammonia-treated (HDN) activated carbons showed significantly higher DOM uptakes than the virgin GAC. The enhanced DOM uptake by HDFe was due to the presence of iron species on the carbon surface. The higher uptake of HDN was attributed to the enlarged carbon pores and basic surface created during ammonia treatment. The SEC and SUVA254 results showed no specific selectivity in the removal of different DOM components as a result of carbon modification. The removal of DOM from both raw and treated waters was negligible by ACF10, with 96% of its surface area in pores smaller than 1 nm. Low molecular weight (MW) DOM components were preferentially removed by ACF20H, with 33% of its surface area in 1–3 nm pores. ACF20H pores excluded DOM components with MWs larger than 1600, 2000, and 2700 Da of Charleston raw, Charleston treated, and Spartanburg treated waters, respectively. In contrast to carbon fibers, DOM components from the entire MW range were removed from waters by virgin and modified GACs.

7.4.2. Nanoadsorbents

Nanotechnology has emerged as one of the promising technologies in water treatment. In light of this, nanoscale carbon black was employed to remove NOM in water in the presence and absence of coagulation (Wang et al., 2010). In the absence of coagulation, more than 60% of NOM removal was achieved by carbon black adsorption. A lower pH (3–5) was favorable for NOM removal. More than 35% of NOM was removed by carbon black adsorption in the first 20 min, and the adsorption of NOM onto carbon black occurred within about 2 h. Mixing intensity was found to be essential for the mixture of NOM and carbon black, while insufficient stirring or over-stirring decreased NOM removal efficiency. When low dosages of coagulants were used in combination with carbon black at pH 6–7, the removal efficiency of NOM increased significantly. Depending on the coagulant, the sequencing of adsorption and coagulation can be important. Almost 90% of NOM was removed in 15 min by carbon black adsorption and alum coagulation, which is a higher removal rate than for conventional treatment. This study indicated that carbon black might be an important adsorbent for NOM removal in water treatment in combination with low doses of alum.
Multiwalled carbon nanotubes (MWCNTs) were thermally treated and employed as adsorbents to study their characterizations and adsorption performance for NOM in aqueous solutions (Lu and Su, 2007). The physiochemical properties of CNTs, such as the structure and nature of the carbon surface, were changed after thermal treatment, which made CNTs adsorb more NOM. The amount of NOM adsorbed onto CNTs increased with a rise in initial NOM concentration and solution ionic strength, but decreased with a rise in solution pH. A comparative analysis of the NOM adsorption of CNTs and GAC was also conducted. Under the same conditions, treated CNTs have the best NOM adsorption performance, followed by raw CNTs and then GAC, suggesting that the CNTs are efficient NOM adsorbents and possess good potential for applications to maintain high-quality water. Further research on the toxicity of CNTs and CNT-related nanomaterials is needed to promote safe and optimized applications of CNTs in water treatment. MWCNTs were also used by Naghizadeh et al. (2013) for the adsorption of hydrophobic NOM from aqueous solution under different operational conditions, including contact time, pH, initial concentration of NOM, and temperature. MWCNTs with an average diameter of 10–50 nm were synthesized via chemical vapor deposition. The results illustrated that both as-prepared and functionalized MWCNTs had high adsorption capacity for the NOM studied. Functionalization of MWCNT affected the surface area and introduced oxygen-containing functional groups onto its surface, which depressed the adsorption of NOM onto MWCNTs–COOH. The obtained data had the best conformity to the Freundlich isotherm. Kinetic studies were performed and the adsorption kinetics successfully followed the pseudosecond-order kinetic model. Adsorption of three NOM analogues, including salicylic acid, phthalic acid, and catechol on MWCNTs as well as commercial PAC were investigated (Liu et al., 2013). All adsorption isotherms fit the Freundlich isotherm model well. PAC possessed 2–10 times higher adsorption capacities toward the three compounds than MWCNTs, indicating a pore-filling effect. Hydrophobic interaction, electrostatic interaction, hydrogen bond and π–π interaction acted simultaneously, but made different contributions to the adsorption of the three NOM analogues on PAC and MWCNTs. Also, magnetic chitosan nanoparticles have proven effective in humic acid (HA) removal (Dong et al., 2014).

7.4.3. Metal Oxide and Hydroxide Based Adsorbents

Besides carbon adsorbents, metal oxides and hydroxides have also been investigated for NOM removal. Fe and Al oxyhydroxides have been found effective in adsorbing NOM from solutions. Three types of iron oxide particles (IOPs) viz. ferrihydrite, goethite, and hematite, were prepared to remove residual organic matter (ROM) from secondary effluents (Choo and Kang, 2003). Of the three types of IOPs tested, the most amorphous, ferrihydrite, was found to be the most effective adsorbent in the removal of ROM from the secondary effluent. Regarding the ROM removal efficiency of ferrihydrite, the chemical oxygen demand and DOC removal were relatively low and were stabilized at a relatively low dose of IOPs; UV removal, however, gradually increased, even at higher IOP dosages, which might be associated with the IOP removal of phenolic compounds from the ROM pool. The optimal pH level (approximately pH 6.0) for maximum ROM removal by iron oxide adsorption could be attributed to the association and dissociation of ferrihydrite and ROM depending on solution pH.
Mechanisms contributing to the adsorption of NOM on surfactant-modified iron oxide-coated sand (IOCS) were explored by microscopic surface characterization techniques and adsorption tests (Ding and Shang, 2010). Electrostatic interactions that were thought to originate from the positively charged, surfactant-coated surface, hexadecyl trimethyl ammonium (HDTMA) seemed to be unimportant, probably because the outward-pointing tail groups of the surface-coated HDTMA monolayers hindered the interactions. Improved hydrophobic interactions followed by ligand exchange are believed to be the dominant mechanisms. Atomic force microscopy analysis with chemically modified tips was used to explore the adsorption mechanisms between NOM and IOCS, where an iron oxide-coated mica surface was utilized as a substitute for the IOCS surface. This demonstrated the changes in pull-on forces and the increases in hydrophobic interactions from the modification of IOCS with HDTMA. IOCS was modified with HDTMA and tested as an adsorbent for the removal of NOM from water (Ding et al., 2010). The modification did not change the physical properties of the IOCS but coated HDTMA onto its surface. The HDTMA-modified IOCS displayed a faster initial NOM adsorption and substantially higher capacity than the unmodified IOCS over a wide pH range in both batch and column adsorption. The enhancement was more pronounced at higher pH. Compared to unmodified IOCS, the HDTMA-modified IOCS removed more hydrophobic and larger NOM molecules and its NOM adsorption was less sensitive to changes in ionic strength. The adsorption capacity of the modified IOCS was regenerated in situ with NaOH solution and ex situ with HDTMA solution. HDTMA-modified IOCS adsorption may be a promising alternative technology for NOM removal.
Bolto et al. (2001) investigated the effect of adding suspended matter in the form of clay or metal oxide when a cationic polymer was employed as the primary coagulant. The solids provide both an adsorbent for NOM and a nucleating species for precipitating the NOM-polymer complex. Metal oxides in conjunction with a cationic polymer were more promising than clay, with effectiveness in the order Fe2O3 > Fe3O4 > Al2O3 > MnO2. Magnesium oxide at a much lower dose was nearly as effective as ferric oxide, but raised the pH level significantly. Using simple self-assembled monolayer (SAM) techniques, a silica substrate was modified as an adsorbent and tested for its potential for reduction of water quality parameters such as UV absorbance, color, and DOC (Chow et al., 2009). Silica particles that were coated with an aminosiloxane SAM (NH2-SAM) were evaluated in both a high surface area powder form and a more realistic granular sand form. Initial results using direct stirred contact with powdered NH2-SAM showed promising results, with 60% reduction of UV254 after 1 h and up to 70% removal of DOC with increased doses and contact times. NH2-SAM powder removed NOM in a broader and less selective MW range than coagulation treatment, and this removal was enhanced by pH control at 6, especially for medium MW components. When NH2-SAM sand was applied, the significantly reduced effective surface area resulted in lower DOC removal, but color removal was still considerable for realistic treatment plant contact times. Attempted regeneration with acidic solutions showed greater effectiveness at lower applied pH, but recovery of adsorption capacity reduced with successive adsorption/regeneration cycles, highlighting the need for further refinement of operating conditions for more effective application of this relatively simple water treatment technology.
The effect of mixed oxidants and PAC on the removal of NOM was studied (Álvarez-Uriarte et al., 2010). Results obtained in this work indicated that mixed oxidants promote conversion of humic matter to hydrophilic matter. Hydrophilic acid-weak ionic exchange resin (HPIA-DEAE) fraction accounted for 8% in raw water whereas it increased to 20% in finished water, based on THMFP results. The results also indicated that hydrophilic fraction was an important source of THM formation in water treatment plant effluent. Extraction and quantification of humic substances from surface waters was more effective with DEAE ionic resin. The authors pointed out that the addition of PAC during the coagulation of natural surface waters preoxidized with electrochemically generated oxidants could significantly improve process efficiency for the removal of low MW and hydrophilic NOM fractions. Based on THMFP and simulated plant trihalomethane formation potential (SPTHMFP) results, this would allow an important reduction in THM formation during the final disinfection step. The addition of a small amount of PAC (50 mg L−1) allowed for a 50% reduction of the coagulant dose, whereas the removal of high MW fractions of NOM was maintained and that of small fractions was significantly increased. Chlorination tests confirmed the trend that showed improvement in the removal of THMFPF and SPTHMFP. PAC was especially effective for the removal of fast-reacting precursors, as deduced from the SPTHMFP results. The presence of PAC in suspension aids in the formation of the flocs. This way, the minimum dose needed for coagulation can be reduced without affecting process performance.

7.4.4. Composite, Modified and/or Miscellaneous Adsorbents

A composite adsorbent was prepared with chitosan and PAC (Zhang and Liu, 2010). Jar tests were carried out to investigate effects of pH, adsorption time, temperature, and initial concentration of NOM on the adsorbent’s NOM removal efficiency. UV absorbance at 254 nm wavelength (UV254) was used as a surrogate parameter for NOM concentration. It was demonstrated that NOM removal by chitosan-PAC composite adsorbent could be as high as 69% under optimal conditions. Pseudofirst-order rate expression and pseudosecond-order rate expression were fitted to the experimental results, and the latter was found to fit the experimental results quite well. The adsorption isotherm of NOM onto the adsorbent under various initial NOM concentrations was also experimentally determined. The Freundlich isotherm was found to fit the adsorption data well. NOM and its interaction with anion exchanger and adsorber resins were investigated to optimize the uptake of organics (Pürschel and Ender, 2008). Four different starches (one of them 14C-labelled) with different molecular size distributions and L-phenylalanine (L-Phe) were selected as model substances for the high-MW biopolymer and the low-MW neutral/amphiphilic fractions of NOM. The uptake of starches by various ion exchangers and adsorbers was measured in column experiments. Results were discussed in terms of size exclusion, anion exchange, adsorption, and hydrophilic/hydrophobic repulsion. In summary, at neutral pH, starch has been most effectively removed by size exclusion followed by adsorption, whereas ion exchange resins show higher uptake capacities than “pure” adsorber due to the stronger attraction between starch and the polar functional groups of the ion exchangers. At acidic pH, the uptake of sulfate, as a competitive adsorptive, leads to an earlier starch breakthrough at ion exchangers. Therefore, adsorbers are more effective. For L-Phe, ion exchange is the main uptake mechanism. It was found for both organics that the higher the water content of the resins, the more effective the uptake.
Natural pumice particles were used as granular support media and coated with iron oxides to investigate their adsorptive NOM removal from waters (Kitis et al., 2007). The study examined the impacts of natural pumice source, particle size fraction, pumice dose, pumice surface chemistry and specific surface area, and NOM source on the ultimate extent and rate of NOM removal. All adsorption isotherm experiments were conducted using the variable dose completely mixed batch reactor bottle point method. Iron oxide coating overwhelmed the surface electrical properties of the underlying pumice particles. Surface areas as high as 20.6 m2 g−1 were achieved after iron coating of pumice samples, which are greater than those of IOC samples reported in the literature. Iron coating of natural pumices significantly increased the NOM uptakes both on an adsorbent mass- and surface area basis. The smallest size fractions (<63 μm) of coated pumice generally exhibited the highest NOM uptakes. A strong linear correlation between the iron content of coated pumices and their Freundlich affinity parameters (KF) indicated that the enhanced NOM uptake is due to iron oxides bound on the pumice surfaces. Iron oxide-coated pumice surfaces preferentially removed high UV-absorbing fractions of NOM, with UV absorbance reductions of up to 90%. Control experiments indicated that iron oxide species bound on pumice surfaces are stable, and potential iron release to the solution is not a concern at the pH values of typical natural waters. Based on high NOM adsorption capacities, iron oxide-coated pumice may be a promising novel adsorbent for NOM removal from waters. Furthermore, due to preferential removal of high UV-absorbing NOM fractions, iron oxide-coated pumice may also be effective in controlling the formation of disinfection by-products in drinking water treatment.
Natural organic polyelectrolytes, such as HAs and fulvic acids (FAs), were removed by adsorption onto silicate rocks (Kaneco et al., 2003). Tobermorite, zeolite, and molecular sieves 5A were used as the adsorbents. Tobermorite was more efficient by 40–50% in the removal of FAs, and by 30–50% for HA than zeolite or molecular sieves, respectively. HA removal from the solution by adsorption onto silicate rocks occurred more readily than FA removal. From the determined heat of adsorption, the adsorption process in the present study may be chemisorption (ligand exchange). Metal/HA complexes were effectively removed by adsorption onto tobermorite. Because tobermorite (a silicate rock) can be easily synthesized and obtained commercially, the adsorption method of removal of FAs and HAs is superior to their precipitation. Magnetic permanently confined micelle arrays (Mag-PCMAs) were synthesized by coating the surface of Fe3O4 particles with a silica/surfactant mesostructured hybrid layer for NOM removal (Wang et al., 2011a). It was determined that NOM removal efficiency by Mag-PCMAs could be as high as 80% at a wide range of initial pH values (∼6.0–10.0). The adsorption isotherm fitted a Langmuir model well. Although Fe3O4 had a high positive charge and Mag-PCMAs a small negative charge, Mag-PCMAs had a higher NOM removal efficiency than uncoated Fe3O4 particles (which are also magnetic), indicating that the adsorption of NOM onto Mag-PCMAs was not dominated by electrostatic interactions. Possible mechanisms for the adsorption of NOM onto Mag-PCMAs were hydrophobic interactions and hydrogen bonding. It was feasible to reuse Mag-PCMAs after regeneration.
The main NOM component in several waters is attributed to humic substances (HS), which have several characteristics that influence how NOM may be removed from water (Fabris et al., 2008; Eikebrokk et al., 2007). Many researchers specifically focused on the removal of HS by adsorption processes. Granules with positive surface charges were prepared by coating glass beads with polypyrrole (PPy) (Bai and Zhang, 2001). Studies were conducted with batch and fixed-bed HA adsorption experiments using coated glass beads as adsorbents. X-ray photoelectron spectroscopy showed that 28% of the nitrogen atoms in the PPy coating were protonated, leading to a highly positively charged surface at pH < 10.5. The results also showed that the amount of protonated nitrogen atoms decreased by up to 25% due to HA adsorption, suggesting that HA uptake by the PPy-coated glass beads was affected at least partly by charge neutralization. HA adsorption also resulted in a reverse of the positive zeta potential of the PPy coating, indicating the importance of macromolecular adsorption in the process. Both pH and ionic concentration were found to affect the extent of HA adsorption by the PPy-coated granules. Chitosan was coated on the surface of polyethylene terephthalate granules through a dip and phase inversion process, and was examined for HA removal by batch adsorption experiments (Zhang and Bai, 2003). A zeta potential study indicated that the chitosan-coated granules had positive zeta potentials at pH < 6.6 and negative zeta potentials at pH > 6.6. Adsorption of HA onto the chitosan-coated granules was found to be strongly pH dependent. Significant amounts of HA were adsorbed under acidic and neutral pH conditions, but the adsorption capacity was reduced remarkably with increasing solution pH values. X-ray photoelectron spectroscopy revealed that the amino groups of the chitosan layer were protonated due to HA adsorption, suggesting the formation of an organic complex between the protonated amino groups and HA. A kinetic study indicated that the adsorption process was transport limited at low-solution pH values, but became both transport and attachment limited at high-solution pH values.
Aminated polyacrylonitrile fibers (APANFs) were prepared by surface modification of polyacrylonitrile fibers (PANFs) with diethylenetriamine in a solution, and the APANFs were studied as an adsorbent for HA removal (Deng and Bai, 2003). The surface modification reaction introduced the amine groups on the surface of the fibers, and the APANFs had a zero point of ζ potentials at pH 8.1, in contrast to pH 3.5 for the PANFs. Adsorption experiments indicated that the APANFs were very effective in removing HA from aqueous solutions in the pH range of 2–10, whereas the PANFs did not adsorb HA at all under the same conditions. It was found that both electrostatic interaction and surface complexation mechanisms played important roles in HA adsorption on the APANFs, although the relative importance of each of the adsorption mechanisms varied with solution pH values.
A chitosan/zeolite composite (CSZ) and surfactant-modified CSZ (SMCSZ) were prepared and tested for HA adsorption (Lin and Zhan, 2012). SMCSZ exhibited a higher HA adsorption capacity than CSZ. The HA adsorption capacities for CSZ and SMCSZ decreased with increasing solution pH from 4 to 12. The HA molecules adsorbed on CSZ and SMCSZ could only be partially desorbed in 1 mol L−1 NaOH solution. The mechanisms for the adsorption of HA on CSZ at pH 7 might include electrostatic interaction and hydrophobic interaction. The mechanisms for the adsorption of HA on SMCSZ at pH 7 might include electrostatic interaction, organic partitioning, and hydrogen bonding. Polyaniline/attapulgite composite (ATP–PANI) was prepared by in situ chemical oxidation and studied for HA adsorption (Wang et al., 2011b). The maximum adsorption amounts were found to be 43.01, 52.91, and 61.35 mg g−1 at 15, 25, and 35 °C, respectively. The HA molecules adsorbed on ATP–PANI can be effectively desorbed in 2 M NaOH solution, and regenerated adsorbent can be used repeatedly in the subsequent four adsorption–regeneration cycles with little loss of HA adsorption amount.
The use of rice husk ash (RHA) as an adsorbent of HA from water was studied (Imyim and Prapalimrungsi, 2010). RHA was also functionalized with 3-aminopropyltriethoxysilane. The adsorption capacity of RHA-NH2 was higher than that of RHA. Experimental adsorption data fitted well with the Langmuir equation and the maximum adsorption capacity was 8.2 mg g−1 at pH 6. Pillared bentonite was prepared for the removal of HA from water (Peng et al., 2005). It was found to be effective for the removal of HA with a high adsorption capacity of 537 mg g−1, and adsorption was favored under acid conditions. Pillared bentonite was regenerated with NaOH, and the regeneration efficiency reached 83% and 85% when the concentration of NaOH reached 0.025 and 0.05 mol L−1. Surfactant-modified bentonite (SMB) in removing HA from wastewaters was evaluated (Anirudhan and Ramachandran, 2007). HDTMA chloride was used to modify the surface of the clay mineral. The SMB exhibits very high adsorption potential for HA, and at pH 3.0 more than 99% removal was achieved from an initial concentration of 25 μmol L−1. The maximum adsorption capacity was 73.52 μmol g−1 with the binding constant, b = 0.155 L μmol−1 at 30 °C and pH 3.0. The adsorbent was suitable for repeated use (more than three cycles) without any noticeable loss of capacity. The ability of organo-layered double hydroxides (LDHs) was studied to remove HA from an aqueous medium (Zhang et al., 2012). Organo-LDHs with different Mg/Al molar ratios (2:1, 3:1 and 4:1) containing dodecyl sulfonate (DSO) as the interlamellar anions were prepared through coprecipitation. The maximum HA removal capacities for 2:1, 3:1, and 4:1 type LDH-DSO were 594.3, 646.7, and 428.4 mg g−1, respectively, while a carbonate-based LDH only removed 23.77 mg g−1. The adsorption of HA on cross-linked chitosan-epichlorohydrin (chitosan–ECH) beads was investigated by Wan Ngah et al. (2008). The maximum adsorption capacity determined from the Langmuir model was 44.84 mg/g. More than 60% of HA could be desorbed from the adsorbent using 1.0 M HCl for 180 min. Bhattacharya et al. (2012) examined the suitability of poly(amidoamine) (PAMAM) dendrimers for HA removal. Researchers have demonstrated efficient removal of dissolved HA using biocompatible PAMAM dendrimers. A study was conducted using ATR-FTIR to identify the specific chemical groups involved in the dendrimer–HA complexation. Upon raising the pH of the dendrimer-bound HA to 10, wherein dendrimers become neutral (pKa of primary amine) and HA remains highly negatively charged, regeneration of the dendrimers is possible as a result of the much weakened electrostatic interaction between the two species. Besides the above mentioned studies, other researchers have also used various adsorbents for HA (Shaker et al., 2012; Moussavi et al., 2013; Omri et al., 2013; Wang et al., 2012; Tang et al., 2012; Liu et al., 2011a,b; Zhan et al., 2010, 2011; Doulia et al., 2009; Zhao et al., 2008) or for NOM removal from water (Humbert et al., 2008; Matilainen et al., 2006; Korshin et al., 1997; Gu et al., 1994; Smith et al., 2012; Hyung and Kim, 2008; Wu et al., 2013; Al-Naseri and Abbas, 2009; Lambert and Graham, 1995; Smith, 1994; Jung et al., 2007; Shi et al., 2009; Matsui et al., 1998, 2004; Bjelopavlic et al., 1999; Qi and Schideman, 2008; Fettig, 2005; Day et al., 1994; McMeen and Benjamin, 1997; Heijman et al., 1999; Davis, 1982; Joseph et al., 2012; Kim et al., 2013; Ng et al., 2014). Figure 7.1 shows some of the important adsorbents used for NOM removal from water. Table 7.1 lists the summary of the main findings of NOM removal from water by adsorption.
image
Figure 7.1 List of some of the important adsorbents used for natural organic matter (NOM) removal from water.

Table 7.1

Summary of the main findings on natural organic matter (NOM) removal from water by adsorption

AdsorbentMain findingsReferences
Iron-impregnated activated carbonsHigher DOM uptake due to the presence of iron species on the carbon surfaceCheng et al. (2005)
Ammonia-treated activated carbonsHigher DOM uptake due to the enlargement of carbon pores and basic surface creation during ammonia treatmentCheng et al. (2005)
Nanoscale carbon blackA lower pH (3–5) was found to be favorable for NOM removal; more than 35% of NOM was removed in the first 20 minWang et al. (2010)
Iron oxide particlesOptimal pH 6.0 helped to remove a maximum amount of residual organic matter by iron oxide adsorption, which was attributed to the association and dissociation of ferrihydrite and residual organic matter depending on solution pHChoo and Kang (2003)
Iron oxide-coated sand (IOCS) was modified with HDTMAA faster initial NOM adsorption and substantially higher capacity was observed than the unmodified IOCS over a wide pH range in both batch and column adsorptionDing et al. (2010)
Silica particles coated with an aminosiloxane SAM (NH2-SAM)60% reduction of UV254 after 1 h and up to 70% removal of dissolved organic carbon with higher doses and contact timesChow et al. (2009)
Chitosan-PAC composite adsorbentRemoval of NOM was as high as 69% under optimal conditionsZhang and Liu (2010)
Tobermorite, zeolite, and molecular sieves 5ATobermorite was more efficient by 40–50% in the removal of fulvic acids, and by 30–50% for humic acid (HA)Kaneco et al. (2003)
Magnetic permanently confined micelle arraysNOM removal efficiency could be as high as 80% at a wide range of initial pH values (∼6.0–10.0)Wang et al. (2011a)
Table Continued

image

AdsorbentMain findingsReferences
Aminated polyacrylonitrile fibers (APANFs)Found to be very effective in removing HA from aqueous solutions in the pH range of 2–10; both electrostatic interaction and surface complexation mechanisms played important roles in HA adsorption on the APANFsDeng and Bai (2003)
Polyaniline/attapulgite compositeHA adsorption was found to be in the range of 43–61 mg g−1 at different temperaturesWang et al. (2011b)
Rice husk ash functionalized with 3-aminopropyltriethoxysilaneAdsorption capacity was reported as 8.2 mg g−1 for HA at pH 6Imyim and Prapalimrungsi (2010)
Pillared bentoniteAdsorption capacity was reported as 537 mg g−1 for HAPeng et al. (2005)
Surfactant-modified bentoniteShowed very high adsorption potential for HA; more than 99% removal was achieved at pH 3.0 from an initial concentration of 25 μmol L−1. The maximum adsorption capacity was 73.52 μmol g−1 with binding constant, b = 0.155 L μmol−1 at 30 °C and pH 3.0Anirudhan and Ramachandran (2007)
LDH-DSOHA removal capacities were reported as 428–646 mg g−1Zhang et al. (2012)
Cross-linked chitosan-epichlorohydrin (chitosan–ECH) beadsHA adsorption was 44 mg g−1Wan Ngah et al. (2008)
Almond shell activated carbonHA adsorption was reported as 169 mg g−1Omri et al. (2013)
Amine functionalized magnetic mesoporous composite microspheresHA adsorption was found to be 128 mg g−1Tang et al. (2012)

image

DOM, dissolved natural organic matter; PAC, powdered activated carbon; LDH, layered double hydroxide; DSO, dodecyl sulfonate.

7.5. Conclusions

This chapter has attempted to cover a wide range of existing literature on NOM removal from water by adsorption technology. It is evident that a great variety of adsorbents (GACs, PACs, modified carbons, single walled and multiwalled carbon nanotubes, IOPs (ferrihydrite, goethite, and hematite), IOCS, chitosan and PAC composite, polypyrrole-coated glass beads, APANFs, CSZ, RHA, SMB, etc.) have been tested thus far, with varying degrees of success, for the removal of NOM and its constituents from water. The literature also reveals that in some cases the modification of the adsorbent increased NOM removal efficiency. However, very little work has been carried out in this direction, especially on the mechanism of NOM adsorption by the modified adsorbents. A variety of adsorbents are used for the removal of NOM and its constituents from water; therefore, the type of adsorbent that is best for a specific purpose is a critical issue requiring detailed and systematic research. No definite conclusion can yet be reached, since each of the adsorbents has its own advantages and disadvantages. There is great potential for improvement in this field in the hope that new and selective adsorbents can be applied for NOM removal not only on a laboratory scale, but also commercially.

References

Al-Naseri S.K, Abbas T.R. Predicting NOM removal by fixed-bed GAC adsorbers. Jordan J. Civ. Eng. 2009;3:172–183.

Álvarez-Uriarte J.I, Iriarte-Velasco U, Chimeno-Alanís N, González-Velasco J.R. The effect of mixed oxidants and powdered activated carbon on the removal of natural organic matter. J. Hazard. Mater. 2010;181:426–431.

Anirudhan T.S, Ramachandran M. Surfactant-modified bentonite as adsorbent for the removal of humic acid from wastewaters. Appl. Clay Sci. 2007;35:276–281.

Bai R, Zhang X. Polypyrrole-coated granules for humic acid removal. J. Colloid Interface Sci. 2001;243:52–60.

Bansal R.C, Goyal M. Activated Carbon Adsorption. Boca Raton: CRC Press; 2005.

Bell-Ajy K, Abbaszadegan M, Ibrahim E, Verges LeChevallier D. Conventional and optimized coagulation for NOM removal. J. Am. Water Works Assoc. 2000;92:44–58.

Bhatnagar A, Hogland W, Marques M, Sillanpää M. An overview of the modification methods of activated carbon for its water treatment applications. Chem. Eng. J. 2013;219:499–511.

Bhattacharya P, Conroy N, Rao A.M, Powell B.A, Ladner D.A, Ke P.C. PAMAM dendrimer for mitigating humic foulant. RSC Adv. 2012;2:7997–8001.

Bjelopavlic M, Newcombe G, Hayes R. Adsorption of NOM onto activated carbon: effect of surface charge, ionic strength, and pore volume distribution. J. Colloid Interface Sci. 1999;210:271–280.

Bolto B, Dixon D, Eldridge R, King S. Cationic polymer and clay or metal oxide combinations for natural organic matter removal. Water Res. 2001;35:2669–2676.

Bond T, Goslan E.H, Parsons S.A, Jefferson B. Treatment of disinfection by‐product precursors. Environ. Technol. 2011;32:1–25.

Brunauer S, Emmett P.H, Teller E. Adsorption of gases in multimolecular layers. J. Am. Chem. Soc. 1938;60:309–319.

Capar G, Yetis U. Removal of natural organic matter and trihalomethanes from the drinking water of Ankara City. Turk. J. Eng. Environ. Sci. 2001;25:527–535.

Cheng W, Dastgheib S.A, Karanfil T. Adsorption of dissolved natural organic matter by modified activated carbons. Water Res. 2005;39:2281–2290.

Choo K.-H, Kang S.-K. Removal of residual organic matter from secondary effluent by iron oxides adsorption. Desalination. 2003;154:139–146.

Chow C.W.K, Majewski P, Bauer S, Fabris R, Drikas M. Removal of natural organic matter using self-assembled monolayer technology. Desalin. Water Treat. 2009;12:344–351.

Crozes G, White P, Marshall M. Enhanced coagulation: its effect on NOM removal and chemical costs. J. Am. Water Works Assoc. 1995;87:78–89.

Dąbrowski A. Adsorption — from theory to practice. Adv. Colloid Interface Sci. 2001;93:135–224.

Dastgheib S.A, Karanfil T, Cheng W. Tailoring activated carbons for enhanced removal of natural organic matter from natural waters. Carbon. 2004;42:547–557.

Davis J.A. Adsorption of natural dissolved organic matter at the oxide/water interface. Geochim. Cosmochim. Acta. 1982;46:2381–2393.

Day G.M, Hart B.T, McKelvie I.D, Beckett R. Adsorption of natural organic matter onto goethite. Colloids Surf. A Physicochem. Eng. Aspects. 1994;89:1–13.

Deng S. Sorbent technology. In: Encyclopedia of Chemical Processing. New York: Taylor & Francis; 2006.

Deng S, Bai R.B. Aminated polyacrylonitrile fibers for humic acid adsorption: behaviors and mechanisms. Environ. Sci. Technol. 2003;37:5799–5805.

Ding C, Shang C. Mechanisms controlling adsorption of natural organic matter on surfactant-modified iron oxide-coated sand. Water Res. 2010;44:3651–3658.

Ding C, Yang X, Liu W, Chang Y, Shang C. Removal of natural organic matter using surfactant-modified iron oxide-coated sand. J. Hazard. Mater. 2010;174:567–572.

Dong C, Chen W, Liu C. Preparation of novel magnetic chitosan nanoparticle and its application for removal of humic acid from aqueous solution. Appl. Surf. Sci. 2014;292:1067–1076.

Doulia D, Leodopoulos C, Gimouhopoulos K, Rigas F. Adsorption of humic acid on acid-activated Greek bentonite. J. Colloid Interface Sci. 2009;340:131–141.

Eikebrokk B, Fabris R, Drikas M, Chow C. NOM characteristics and treatability by coagulation. In: Hahn H.H, Hoffman E, Ødegaard H, eds. Chemical Water and Wastewater Treatment IX. London: IWA Publishing; 2007.

Fabris R, Chow C.W.K, Drikas M. Practical application of a combined treatment process for removal of recalcitrant NOM – alum and PAC. Water Sci. Technol. Water Supply. 2004;4:89–94.

Fabris R, Chow C.W.K, Drikas M, Eikebrokk B. Comparison of NOM character in selected Australian and Norwegian drinking waters. Water Res. 2008;42:4188–4196.

Fettig J. Modelling the uptake of natural organic matter (NOM) by different granular sorbent media. J. Water Supply Res. Technol. Aqua. 2005;54:83–93.

Freundlich H.M.F. Over the adsorption in solution. J. Phys. Chem. 1906;57:385–471.

Genz A, Baumgarten B, Goernitz M, Jekel M. NOM removal by adsorption onto granular ferric hydroxide: equilibrium, kinetics, filter and regeneration studies. Water Res. 2008;42:238–248.

Grieco S.A, Ramarao B.V. Removal of TCEP from aqueous solutions by adsorption with zeolites. Colloids Surf. A Physicochem. Eng. Aspects. 2013;434:329–338.

Gu B, Schmitt J, Chen Z, Liang L, McCarthy J.F. Adsorption and desorption of natural organic matter on iron oxide: mechanisms and models. Environ. Sci. Technol. 1994;28:38–46.

Heijman S.G.J, van Paassen A.M, van der Meer W.G.J, Hopman R. Adsorptive removal of natural organic matter during drinking water treatment. Water Sci. Technol. 1999;40:183–190.

Humbert H, Gallard H, Suty H, Croué J.-P. Natural organic matter (NOM) and pesticides removal using a combination of ion exchange resin and powdered activated carbon (PAC). Water Res. 2008;42:1635–1643.

Hyung H, Kim J.-H. Natural organic matter (NOM) adsorption to multi-walled carbon nanotubes: effect of NOM characteristics and water quality parameters. Environ. Sci. Technol. 2008;42:4416–4421.

Imyim A, Prapalimrungsi E. Humic acids removal from water by aminopropyl functionalized rice husk ash. J. Hazard. Mater. 2010;184:775–781.

Iriarte-Velasco U, Álvarez-Uriarte J.I, Chimeno-Alanís N, González-Velasco J.R. Natural organic matter adsorption onto granular activated carbons: implications in the molecular weight and disinfection byproducts formation. Ind. Eng. Chem. Res. 2008;47:7868–7876.

Joseph L, Flora J.R.V, Park Y.-G, Badawy M, Saleh H, Yoon Y. Removal of natural organic matter from potential drinking water sources by combined coagulation and adsorption using carbon nanomaterials. Sep. Purif. Technol. 2012;95:64–72.

Jung H.R, Seo S.D, Choi H.C. Preparation of mesostructured carbon (MSC) for removal of natural organic matter (NOM) in aqueous solution. Mater. Sci. Forum. 2007;544–545:123–126.

Kaneco S, Itoh K, Katsumata H, Suzuki T, Masuyama K, Funasaka K, Hatano K, Ohta K. Removal of natural organic polyelectrolytes by adsorption onto tobermorite. Environ. Sci. Technol. 2003;37:1448–1451.

Karanfil T, Kitis M, Kilduff J.E, Wigton A. Role of granular activated carbon surface chemistry on the adsorption of organic compounds. 2. Natural organic matter. Environ. Sci. Technol. 1999;33:3225–3233.

Kasprzyk-Hordern B. Chemistry of alumina, reactions in aqueous solution and its application in water treatment. Adv. Colloid Interface Sci. 2004;110:19–48.

Kim S, Kim J, Seo G. Iron oxide nanoparticle-impregnated powder-activated carbon (IPAC) for NOM removal in MF membrane water treatment system. Desalin. Water Treat. 2013;51:1–9.

Kitis M, Kaplan S.S, Karakaya E, Yigit N.O, Civelekoglu G. Adsorption of natural organic matter from waters by iron coated pumice. Chemosphere. 2007;66:130–138.

Korshin G.V, Benjamin M.M, Sletten R.S. Adsorption of natural organic matter (NOM) on iron oxide: effects on NOM composition and formation of organo-halide compounds during chlorination. Water Res. 1997;31:1643–1650.

Kumar E, Bhatnagar A, Hogland W, Marques M, Sillanpää M. Interaction of anionic pollutants with Al-based adsorbents in aqueous media – a review. Chem. Eng. J. 2014;241:443–456.

Lambert S.D, Graham N.J.D. Removal of non-specific dissolved organic matter from upland potable water supplies—I. Adsorption. Water Res. 1995;29:2421–2426.

Langmuir I. The adsorption of gases on plane surface of glass, mica and platinum. J. Am. Chem. Soc. 1916;40:1361–1368.

Lin J, Zhan Y. Adsorption of humic acid from aqueous solution onto unmodified and surfactant-modified chitosan/zeolite composites. Chem. Eng. J. 2012;200–202:202–213.

Lin L, Lei Z, Wang L, Liu X, Zhang Y, Wan C, Lee D.-J, Tay J.H. Adsorption mechanisms of high-levels of ammonium onto natural and NaCl-modified zeolites. Sep. Purif. Technol. 2013;103:15–20.

Liu F, Xu Z, Wan H, Wan Y, Zheng S, Zhu D. Enhanced adsorption of humic acids on ordered mesoporous carbon compared with microporous activated carbon. Environ. Toxicol. Chem. 2011;30:793–800.

Liu F.-F, Fan J.-L, Wang S.-G, Ma G.-H. Adsorption of natural organic matter analogues by multi-walled carbon nanotubes: comparison with powdered activated carbon. Chem. Eng. J. 2013;219:450–458.

Liu Z, Zu Y, Meng R, Xing Z, Tan S, Zhao L, Sun T, Zhou Z. Adsorption of humic acid onto carbonaceous surfaces: atomic force microscopy study. Microsc. Microanal. 2011;17:1015–1021.

Lu C, Su F. Adsorption of natural organic matter by carbon nanotubes. Sep. Purif. Technol. 2007;58:113–121.

Mantell C.L. Adsorption. New York: McGraw-Hill Book Company; 1951.

Marsh H, Rodríguez-Reinoso F. Activated Carbon. Oxford: Elsevier; 2006.

Martucci A, Pasti L, Marchetti N, Cavazzini A, Dondi F, Alberti A. Adsorption of pharmaceuticals from aqueous solutions on synthetic zeolites. Microporous Mesoporous Mater. 2012;148:174–183.

Matilainen A, Sillanpää M. Removal of natural organic matter from drinking water by advanced oxidation processes. Chemosphere. 2010;80:351–365.

Matilainen A, Vepsäläinen M, Sillanpää M. Natural organic matter removal by coagulation during drinking water treatment: a review. Adv. Colloid Interface Sci. 2010;159:189–197.

Matilainen A, Vieno N, Tuhkanen T. Efficiency of the activated carbon filtration in the natural organic matter removal. Environ. Int. 2006;32:324–331.

Matsui Y, Murase R, Sanogawa T, Aoki N, Mima S, Inoue T, Matsushita T. Micro-ground powdered activated carbon for effective removal of natural organic matter during water treatment. Water Sci. Technol. Water Supply. 2004;4:155–163.

Matsui Y, Yuasa A, Li F. Overall adsorption isotherm of natural organic matter. J. Environ. Eng. 1998;124:1099–1107.

McBain J.W. The mechanism of the adsorption (“sorption”) of hydrogen by carbon. Philos. Mag. Ser. 1909;6:916–935.

McMeen C.R, Benjamin M.M. NOM removal by slow sand filtration through iron oxide-coated olivine. J. Am. Water Works Assoc. 1997;89:57–71.

Metsämuuronen S, Sillanpää M, Bhatnagar A, Mänttäri M. Natural organic matter removal from drinking water by membrane technology. Sep. Purif. Rev. 2014;43:1–61.

Moussavi S.P, Ehrampoush M.H, Mahvi A.H, Ahmadian M, Rahimi S. Adsorption of humic acid from aqueous solution on single-walled carbon nanotubes. Asian J. Chem. 2013;25:5319–5324.

Naghizadeh A, Nasseri S, Rashidi A.M, Kalantary R.R, Nabizadeh R, Mahvi A.H. Adsorption kinetics and thermodynamics of hydrophobic natural organic matter (NOM) removal from aqueous solution by multi-wall carbon nanotubes. Water Sci. Technol. Water Supply. 2013;13:273–285.

Najafi M, Rostamian R, Rafati A.A. Chemically modified silica gel with thiol group as an adsorbent for retention of some toxic soft metal ions from water and industrial effluent. Chem. Eng. J. 2011;168:426–432.

Ng M, Kho E, Liu S, Lim M, Amal R. Highly adsorptive and regenerative magnetic TiO2 for natural organic matter (NOM) removal in water. Chem. Eng. J. 2014;246:196–203.

Omri A, Benzina M, Trabelsi W, Ammar N. Adsorptive removal of humic acid on activated carbon prepared from almond shell: approach for the treatment of industrial phosphoric acid solution. Desalin. Water Treat. 2013:1–12.

Owen D.M, Amy G.L, Chowdhury Z.K, Paode R, McCoy G, Viscosil K. NOM characterization and treatability. J. Am. Water Works Assoc. 1985;87:46–63.

Peng X, Luan Z, Chen F, Tian B, Jia Z. Adsorption of humic acid onto pillared bentonite. Desalination. 2005;174:135–143.

Pürschel M, Ender V. Sorption of natural organic matter by adsorber and ion exchange resins – investigations with starch and phenylalanine as model substances. In: 15th International Conference on the Properties of Water and Steam (15th ICPWS), Radisson SAS Hotel Berlin. 2008.

Qi S, Schideman L.C. An overall isotherm for activated carbon adsorption of dissolved natural organic matter in water. Water Res. 2008;42:3353–3360.

Richardson S.D, Plewa M.J, Wagner E.D, Schoeny R, DeMarini D.M. Occurrence, genotoxicity, and carcinogenicity of regulated and emerging disinfection by-products in drinking water: a review and roadmap for research. Mutat. Res. 2007;636:178–242.

Shaker A.M, Komy Z.R, Heggy S.E.M, El-Sayed M.E.A. Kinetic study for adsorption humic acid on soil minerals. J. Phys. Chem. A. 2012;116:10889–10896.

Shi D, Xie S, Wen D, Xi D. Removal of bromate and natural organic matter by using biologically activated carbon. Int. J. Environ. Pollut. 2009;38:180–192.

Siddiqui M, Amy G, Ryan J, Odem W. Membranes for the control of natural organic matter from surface waters. Water Res. 2000;34:3355–3370.

Smith B, Yang J, Bitter J.L, Ball W.P, Fairbrother D.H. Influence of surface oxygen on the interactions of carbon nanotubes with natural organic matter. Environ. Sci. Technol. 2012;46:12839–12847.

Smith E.H. Bench-scale tests and modeling of adsorption of natural organic matter by activated carbon. Water Res. 1994;28:1693–1702.

Tang Y, Liang S, Yu S, Gao N, Zhang J, Guo H, Wang Y. Enhanced adsorption of humic acid on amine functionalized magnetic mesoporous composite microspheres. Colloids Surf. A Physicochem. Eng. Aspects. 2012;406:61–67.

Velten S, Knappe D.R.U, Traber J, Kaiser H.-P, von Gunten U, Boller M, Meylan S. Characterization of natural organic matter adsorption in granular activated carbon adsorbers. Water Res. 2011;45:3951–3959.

Vidic R.D, Suidan M.T. Role of dissolved oxygen on the adsorptive capacity of activated carbon for synthetic and natural organic matter. Environ. Sci. Technol. 1991;25:1612–1618.

Wan Ngah W.S, Hanafiah M.A.K.M, Yong S.S. Adsorption of humic acid from aqueous solutions on crosslinked chitosan–epichlorohydrin beads: kinetics and isotherm studies. Colloids Surf. B Biointerfaces. 2008;65:18–24.

Wang H, Kang J, Liu H, Qu J. Preparation of organically functionalized silica gel as adsorbent for copper ion adsorption. J. Environ. Sci. 2009;21:1473–1479.

Wang H, Keller A, Li F. Natural organic matter removal by adsorption onto carbonaceous nanoparticles and coagulation. J. Environ. Eng. 2010;136:1075–1081.

Wang H, Keller A.A, Clark K.K. Natural organic matter removal by adsorption onto magnetic permanently confined micelle arrays. J. Hazard. Mater. 2011;194:156–161.

Wang J, Han X, Ma H, Ji Y, Bi L. Adsorptive removal of humic acid from aqueous solution on polyaniline/attapulgite composite. Chem. Eng. J. 2011;173:171–177.

Wang M, Liao L, Zhang Z, Li Z. Adsorption of low concentration humic acid from water by palygorskite. Appl. Clay Sci. 2012;67–68:164–168.

Wang S, Peng Y. Natural zeolites as effective adsorbents in water and wastewater treatment. Chem. Eng. J. 2010;156:11–24.

Wu C.N, Wang L, Ling Q, Tang Y.C, Huang J, Pan F.K. Removal of natural organic matter of artificial lake by modified fly ash. Adv. Mater. Res. 2013;690–693:1020–1023.

Xie Q, Xie J, Wang Z, Wu D, Zhang Z, Kong H. Adsorption of organic pollutants by surfactant modified zeolite as controlled by surfactant chain length. Microporous Mesoporous Mater. 2013;179:144–150.

Zaitseva N, Zaitsev V, Walcarius A. Chromium(VI) removal via reduction–sorption on bi-functional silica adsorbents. J. Hazard. Mater. 2013;250–251:454–461.

Zhan Y, Lin J, Qiu Y, Gao N, Zhu Z. Adsorption of humic acid from aqueous solution on bilayer hexadecyltrimethyl ammonium bromide-modified zeolite. Front. Environ. Sci. Eng. China. 2011;5:65–75.

Zhan Y, Zhu Z, Lin J, Qiu Y, Zhao J. Removal of humic acid from aqueous solution by cetylpyridinium bromide modified zeolite. J. Environ. Sci. 2010;22:1327–1334.

Zhang G, Wu T, Li Y, Huang X, Wang Y, Wang G. Sorption of humic acid to organo layered double hydroxides in aqueous solution. Chem. Eng. J. 2012;191:306–313.

Zhang J, Liu F. Adsorption of natural organic matter onto a composite adsorbent prepared with chitosan and powdered activated carbon. Desalin. Water Treat. 2010;20:291–296.

Zhang X, Bai R. Mechanisms and kinetics of humic acid adsorption onto chitosan-coated granules. J. Colloid Interface Sci. 2003;264:30–38.

Zhao L, Luo F, Wasikiewicz J.M, Mitomo H, Nagasawa N, Yagi T, Tamada M, Yoshii F. Adsorption of humic acid from aqueous solution onto irradiation-crosslinked carboxymethylchitosan. Bioresour. Technol. 2008;99:1911–1917.

..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.
Reset