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Magnetic ion exchange: Is there potential for international development?

Authors:

Abstract

Magnetic ion exchange (MIEX®) is an ion exchange resin developed as an additive to existing water treatment plants where additional organic matter is to be removed. The smaller size, magnetic properties and simple regeneration using NaCl distinguishes MIEX® from conventional ion exchange resins and hence its use in international development applications is investigated in this review article. MIEX® has been demonstrated to remove varying levels of dissolved organic matter, inorganic anions such as nitrate and sulphate and micropollutants including non-ionic pesticides. The removal efficiency can also be influenced by temperature, pH and presence of other anions. As MIEX® is unable to disinfect water, the most likely application within international development is as pre-treatment before disinfection or membrane filtration.
Magnetic Ion Exchange: Is There Potential for International Development?
P. A. Neale, A. I. Schäfer
School of Engineering and Electronics, University of Edinburgh, Edinburgh, EH9 3JL,
United Kingdom, email: p.neale@ed.ac.uk
Submitted to Desalination
Date Submitted: January 2008
Date Re-submitted: May 2008
Abstract: Magnetic ion exchange (MIEX®) is an ion exchange resin developed as an additive to
existing water treatment plants where additional organic matter is to be removed. The smaller size,
magnetic properties and simple regeneration using NaCl distinguishes MIEX® from conventional
ion exchange resins and hence its use in international development applications is investigated in
this review article. MIEX® has been demonstrated to remove varying levels of dissolved organic
matter, inorganic anions such as nitrate and sulphate and micropollutants including non-ionic
pesticides. The removal efficiency can also be influenced by temperature, pH and presence of other
anions. As MIEX® is unable to disinfect water, the most likely application within international
development is as pre-treatment before disinfection or membrane filtration.
Keywords: Magnetic ion exchange, international development, natural organic matter removal,
micropollutant removal
1. Introduction
Magnetic ion exchange (MIEX®) is a strong base anion exchange resin with magnetic properties
that can be used to adsorb weak organic acidic ions from water [1]. The magnetic properties
differentiate it from other ion exchange resins, as it allows for faster resin agglomeration and
recovery [2]. The resin was developed with the purpose of removing dissolved organic carbon
(DOC) from drinking water supplies [3]. While DOC by itself is relatively harmless, problems can
occur when DOC is combined with chlorine, a common drinking water disinfectant, or bromide as
they can form disinfection by-products (DBP), which are potential carcinogens [2]. In addition, the
removal of DOC from water reduces the need for residual disinfection of bacterial regrowth during
distribution, as well as customer complaints relating to taste, odour and colour of the water [4]
The objective of this paper is to review potential applications of this ion exchange resin in
international development. One of the main problems facing international development is the
provision of safe drinking water, with over 1.1 billion people lacking access to this basic need [5].
Waterborne diseases, associated with pathogenic bacteria, viruses and protozoa, are the most
common cause of illness and death related to water and sanitation within developing countries [6].
Therefore, improved microbiological safety through the removal of pathogens is essential for
international development. While MIEX® can not be used to disinfect or physically remove bacteria
or viruses, it can remove DPB precursors, reduce chlorine demand, and therefore reduce DPB risk
[7]. In addition, it can be coupled with disinfection processes such as ozonation or membrane
filtration such as ultrafiltration.
This review will describe the principles of MIEX® and focus on its applicability to international
development by discussing its ability to remove DOC, as well as a range of inorganic and organic
contaminants from water and examine the possibility of MIEX® integration with existing water
treatment options. The issue of brine waste disposal options will conclude the paper.
2. Process Principles
2.1. Resin Characteristics
MIEX® is an anionic exchange resin which consists of a magnetic core with a polymer shell (Fig. 1)
[8]. The polymer, polyacrylate, is macroporous and contains quaternary amide functional groups,
which assist with DOC removal through ion exchange [9]. MIEX® differs from traditional ion
exchange resins due to its small size and magnetic properties. These changes were implemented to
maximise organic removal and resin reuse. The resin beads have a mean diameter of 150 – 180 µm
which is approximately 2 to 5 times smaller than other ion exchange resins [10]. As a result it has
an increased surface area to volume ratio compared to other resins, meaning there are more
exchange sites which increases exchange kinetics, therefore more DOC can be removed [2, 7]. The
magnetic core enables fast agglomeration and settling of resin particles, and this leads to high (up to
99.9%) resin recovery rates [11].
Figure 1: Light microscope image of MIEX® resin
2.2. Adsorption and Desorption
Adsorption and desorption are the chemical reactions that allow the process to function (Fig. 2).
The DOC is adsorbed to the resin through ion exchange with the chloride ions at the active sites on
the surface. Quaternary amide moieties act as DOC chloride exchange sites [12]. The presence of
negatively charged carboxylic groups in DOC enables removal as they are attracted to the active
sites [12]. The resin is not limited to the adsorption of DOC. MIEX® also has the ability to adsorb
other anions, including nitrate, sulphate, bromide, chromium, arsenic and certain pesticides [13, 14].
The removal efficiency of these compounds will depend on the anion competition for exchange
sites.
Figure 2: MIEX® adsorption and desorption chemistry with NR+3 representing the quaternary
amide exchange sites (Adapted from [15])
Brine&
Raw&Water&
DESORPTION&
DOC&ADSORPTION&
-OOC
NR+
3%
NR+
3%
Cl(%
Cl(%
H+%
H+%
DOC&
DOC&
Cl(%
NR+
3%
NR+
3%
Na+%
DOC&
DOC&
Neale, P.A. ; Schäfer, A.I. (2009) Magnetic ion exchange: Is there potential for
international development?, Desalination, 248, 160–168. doi:10.1016/j.desal.
2008.05.052
The resin is regenerated through desorption, which is a reversal of the adsorption process.
Desorption is achieved with the assistance of a 10% w/w NaCl brine. Through a reverse of the ion
exchange process, the DOC sorbed to the quaternary amide active sites are substituted for chloride
ions, and the exchanged DOC goes to the brine [10]. This process occurs due to the high chloride
concentration, as the chloride ions have a strong affinity for the exchange sites and force the DOC
from the resin [15]. Depending on water quality 2% w/w NaOH can be added to assist regeneration,
as the increase in pH increases the solubility of DOC [15]. Conventional ion exchange resins are
fouled by organic matter, and thus can not be reused effectively. Therefore, the ability to regenerate
is advantageous to application in international development where ease of operation is crucial.
3. Contaminant Removal
3.1. Natural Organic Matter
Natural organic matter (NOM) is a complex mixture of different types of organic molecules
including fulvic and humic acids, hydrophilic acids and various low molecular weight compounds
[16]. The origins of NOM in water supplies include soil, swamps and plant decomposition, as well
as wastewater effluent if present. NOM has colour, taste and odour implications for drinking water,
and can also pose a threat to human health when combined with chlorine disinfection as NOM is a
DBP precursor [2].
MIEX® was developed for the purpose of removing the dissolved fraction of NOM from water.
Previous studies have demonstrated that it effectively removes the ultraviolet absorbing and acidic
fractions of DOC over a wider molecular weight range compared to alternative treatment options,
such as coagulation [1, 10, 11]. In addition, the resin can also effectively remove both hydrophobic
and hydrophilic fractions of DOC [7].
The removal of DOC from raw water using MIEX® is generally around 80% [2, 11]. However, the
removal efficiency of DOC can be affected by the quality of the raw water as well as the solution
chemistry. Due to the presence of carboxylic groups [12], DOC is in an anionic form from pH 4 - 5.
At low pH (<4) it cannot be used to effectively remove DOC, however as most applications are in
the pH range of 6.5 7.5 it can remove DOC rich in carboxylic groups. However, the removal
efficiency would also be greatly reduced if the raw water came from a source rich in tannins.
Tannins primarily contain phenolic hydroxyl groups, which are not in an anionic form until
approximately pH 8 - 9 [1]. Temperature also has the potential to affect removal. Humbert et al.
[14] found no significant difference in DOC removal between 6 and 26°C, however removal
increased slightly as the temperature increased to 36°C. This is because an increase in temperature
leads to an augmentation of reaction kinetics.
There are several factors that can impair DOC removal by the resin. Firstly, there is the issue of
seasonal variations in the quantity of DOC in raw water. After periods of high rainfall the level of
DOC in water supplies can increase [11]. In these situations it may be necessary to alter the dosage
of resin, or increase the contact time, to ensure that it can successfully remove DOC. This may
make this process vulnerable in international development applications where trained personnel and
monitoring may not be easily available. In addition, a high concentration of inorganic anions in the
raw water can compete for ion exchange sites, reducing DOC removal [2]. This indicates the studies
with specific waters are important before process adaptation.
3.2. Inorganic Matter
MIEX® has the potential remove inorganic anions from water, and the presence of anions such as
fluoride or nitrate are common problems in many developing countries. Inorganic anions such as
bromide can increase the formation of DBP [3], while trace metal anions such as chromium and
arsenic can have serious implications for human health as they are carcinogenic [13]. Several
studies have shown that inorganic anion removal is dependant on MIEX® resin concentration [9,
14]. At high resin doses (8 mL/L) as much as 65% of bromide can be removed, while this decreases
significantly at lower doses (0.5 mL/L) to 8% removal [14]. The removal efficiency of bromide is
further dependant on pH. A study by Singer and Bilyk [7] showed that bromide removal decreased
significantly as alkalinity increased. At high pH there is a higher concentration of bicarbonate ions
and these compete with bromide for ion exchange sites, reducing the bromide removal.
Removal of sulphate and nitrate has also been studied. The presence of sulphate in the water can
cause problems for DOC removal, as it can compete with DOC for exchange sites [3]. Sulphate
removal has been shown to be concentration dependant, with 92% removal by MIEX® at 2 mL/L
resin concentration, decreasing to 42% removal at 0.5 mL/L concentrations [14]. The resin can
contribute significantly to nitrate removal, up to 94% [10, 14].
In addition, the application of MIEX® to removal trace metal anions such as arsenic (As(V)) and
chromium (Cr(VI)) has been studied, and showed 37% removal of arsenic and 58% removal of
chromium [13]. As arsenic contamination is a problem in some developing countries such as
Bangladesh [17] the ability of MIEX® to remove moderate amounts of arsenic is very relevant and
promising for international development.
3.3.Micropollutants
Micropollutants, which include pesticides, natural and synthetic hormones and pharmaceutically
active products, can be considered ubiquitous in surface and wastewater [18]. Low concentrations
of many micropollutants (ng/L to µg/L) can have a significant effect on vertebrate and ecosystem
health. Such compounds are of concern where water reuse is practiced intentionally or
unintentionally because of polluted waters serving as water supplies downstream. Such sewage-
water supply cross-connections are very common in international development due to open sewers,
pit latrines and usage streams for disposal and water supply. In developing countries the usage of
pesticides that may be banned in developed countries is commonplace and it is likely that this is the
most severe micropollutant threat. In addition, many micropollutants are not removed effectively
using conventional water treatment, where such treatment schemes exist, and therefore MIEX® may
be applied to assist their removal. Within the literature, MIEX® has been applied to remove
micropollutants including pesticides atrazine and isoproturon [14, 19] and natural hormones such
as estrone [20, 21]. The removal of pesticides from water is particularly applicable to international
development due to extensive pesticide use in many developing countries [22].
The removal of atrazine and isoproturon using MIEX® was studied by Humbert et al. [14, 19]. The
results demonstrated only 7% of atrazine and 5% of isoproturon could be removed using MIEX®
after a contact time of 30 minutes [14]. By increasing the contact time to 24 hours slightly higher
(approximately 12%) removal was observed [19]. The poor performance was attributed to the non-
ionic nature of the pesticides. However, MIEX® may have greater applicability in pesticide removal
when used as a pre-treatment to powdered activated carbon (PAC). Humbert et al. [19] found the
use of MIEX® prior to PAC lead to a 20% increase in pesticide removal compared to removal by
PAC alone.
The removal of steroidal hormones from drinking water is also of importance. Hormones, such as
estradiol and estrone, are naturally excreted by humans, and they are amongst some of the most
potent endocrine disrupting chemicals [23]. Mastrup and Schäfer [20] and Schäfer et al. [21] studied
estrone removal by MIEX® and found removal was influenced by pH, temperature and ionic
strength. The charge of some hormones is affected by pH. For example, estrone changes from a
neutral to a negative charge above its acid dissociation constant of 10.4. At pH 11, MIEX® could
remove approximately 70% of negatively charged ionic estrone from solution, compared to only
30% when estrone has a neutral charge and is non-ionic [21]. This suggests that while ion exchange
interactions are important for estrone removal by MIEX®, estrone must still interact with MIEX®
through either specific (e.g. hydrogen bonding) or non-specific (eg van der Waal forces)
interactions as 30% is still removed below pH 11.
4. Process Integration
MIEX® can be added to water treatment processes in similar ways to coagulants or PAC. Its
magnetic characteristics allow accelerated floc formation and settling. The process, from the input
raw water to the output DOC removed water, is shown below in Fig. 3 and it can be divided into
three key parts, DOC removal, resin recovery and resin regeneration. In addition, MIEX® can be
retrofitted to existing treatment plants.
Figure 3: The MIEX® process (adapted from [23]).
4.1. MIEX Process
The raw water enters a stirred contact, and resin is added. The contractor is stirred to allow the resin
to disperse to provide maximum surface area for DOC adsorption [11]. The amount of resin added
is typically 5 to 10 mL/L, however this can vary depending on the quality of the raw water [15].
The contact time is typically 30 minutes, however a study by Humbert et al. [14] suggested
maximum DOC removal can be reached within 15 minutes using 8 mL/L of MIEX® resin.
However, a longer contact time may be required depending on water quality, as it has been
suggested by Fearing, et al., [11] that a contact time of 60 minutes is required for optimal DOC
removal. In addition, as demonstrated in the case of atrazine and isoproturon, the contact time for
optimal removal will vary depending on the contaminant. After detention in the contactor, the resin
and water flow under gravity to the separator. Due to its magnetic properties, the resin rapidly
agglomerates and forms large particles which settle quickly, allowing fast separation from the
supernatant [10]. Only a small amount (<0.1%) is lost during the process, so the rate of resin
recovery is greater 99.9% [11], however any resin carryover can increase the turbidity of the treated
water [7]. Therefore, an additional water treatment process such as coagulation may be required
after to remove any turbidity [3]. Approximately 85 90% of the recovered resin is reused in the
process, while the remaining resin is regenerated using NaCl brine.
4.2. Pre-treatment
MIEX® cannot be used as a stand alone process to treat drinking water as it does not have the
capacity to remove turbidity, particulate matter or pathogens from water. However, it can be
coupled with existing water treatment options to produce safe drinking water. Recently research has
focused the usage of the resin as a pre-treatment step to coagulation (Fig. 4) ozonation and
membrane filtration [1, 2, 11]. Fearing et al. [11] compared DOC removal with MIEX® itself to the
resin combined with ferric sulphate coagulation, and found DOC removal increased by as much as
20% in the combined process. In contrast, Boyer and Singer [2] found there was no significant
difference in DOC removal between MIEX® itself and for a combined process with alum
coagulation. There are several advantages to applying the resin as a pre-treatment. Typically
MIEX® removes low to moderate molecular weight fractions of DOC, while coagulation is better
suited to remove high molecular weight fractions [24]. Allpike et al. [1] found that the use of
MIEX® pre-treatment before alum coagulation lead to a wider molecular weight range of DOC
removed compared to the resin or coagulation alone. In addition, pre-treatment with the resin can
reduce the coagulation dose required for treatment significantly (up to 85%) [7]. However, as
neither MIEX® nor coagulation can disinfect water, even the combined process is not suitable for
Contactor%
Resin%Separation%%
Resin%Regeneration%
Treated%
Water%
Raw%
Water%
Recovered%Resin%
international development alone, and would need to be coupled with chemical or physical
disinfection processes.
Figure 4: MIEX® pre-treatment option for alum coagulation (adapted from [15])
Ozonation is a water treatment method that disinfects water without the need for chlorine, however
there are some drawbacks which prevents greater ozonation application. Firstly, carcinogenic
bromate and bromate DBPs can form when using ozone to disinfect water containing bromide ions
[12]. Secondly, energy demand is high, and thirdly, any DOC present in the raw water can increase
the ozone demand, which reduces the effectiveness of ozonation [9]. Based on its ability to remove
approximately 80% DOC and up to 65% bromide, MIEX® is an attractive pre-treatment option for
ozonation. Johnson and Singer [9] found that MIEX® pre-treatment significantly increased the
dissolved ozone concentration following ozonation, compared to untreated water. Therefore, with
the removal of the majority of DOC the ozone demand could be reduced. MIEX® pre-treatment also
has implications for the ozone decay, as Wert et al. [12] demonstrated that MIEX® pre-treatment
decreased the ozone decay rate compared to untreated water which can lead to an increase in
bacteria and protozoan inactivation. In addition, bromate formation due to ozonation decreased
significantly when MIEX® was used for pre-treatment [9]. This is due to the removal of bromide
ions, as well as the reduced ozone demand. A hybrid MIEX® - ozonation process could be an option
to treat water in developing countries, however the operational and maintenance requirements of
ozonation may make it an inappropriate technology option at this stage [6].
Membrane filtration such as ultrafiltration (UF) may be a suitable water treatment option for
international development as it disinfects water by physically removing bacteria and viruses, and
has a lower chemical requirement compared to conventional treatment [25]. However, organic,
biological and particulate fouling which reduces the treated water output and increases costs
through high cleaning and maintenance requirements which again may be difficult to achieve in
international development. As MIEX® can remove significant amounts of DOC it may prevent
some of this membrane fouling. However, studies by Son et al. [26] and Humbert et al. [27] using
dead-end filtration configurations found that MIEX® pre-treatment for UF only lead to a minor
decrease in membrane fouling compared to no pre-treatment. Son et al. [26] showed that
coagulation was a better pre-treatment for UF, suggesting that more fouling was caused by high
molecular weight fractions which coagulation can remove, compared to low to moderate fractions
MIEX® typically removes. In addition, Schäfer et al. [21] has suggested that MIEX® resin is prone
to break up, and this may in fact contribute to membrane fouling. Zhang et al. [28] pre-treated
submerged UF membranes with MIEX® and PAC, and MIEX pre-treatment showed no increase in
transmembrane pressure, and allowed the process to run for longer, while PAC lead to an increase
in transmembrane pressure. Submerged membranes typically require lower pressure and less
cleaning than dead-end or cross flow membrane configurations [28], therefore submerged
membranes with MIEX® pre-treatment may be more manageable in international development
applications.
5. Brine Disposal and Treatment
Alum%Coagulation%Clarification%
Sand%Filtration%
MIEX®%Pre(Treatment%
In the final phase of the MIEX® process the DOC saturated resin is regenerated with 10% w/w
NaCl solution [10]. The by-product of regenerate is a waste brine containing NaCl as well as any
DOC, inorganics and micropollutants removed from the raw water and recovered from the resin.
Such brines are similar in characteristic to reverse osmosis concentrates from desalination or
wastewater reuse facilities. As such disposal or treatment can be expensive and have significant
environmental impacts it is important to consider brine disposal options suitable for developing
countries.
When geographically possible, the majority of such waste brines is disposed to the ocean [29]. This
disposal method is applied due to low cost, however disposal can be problematic, as the brine
salinity is considerably higher than seawater, disturbing the sea floor [29], while the presence of
micropollutants in the brine is likely to have negative implications for aquatic organisms. In
situations when ocean disposal is not suitable, such as for inland water treatment, other brine
disposal options include solar evaporation, landfill and bore injection [30]. For inland disposal,
solar evaporation ponds are the most suitable disposal method in warm or arid developing countries.
They are low cost, require little maintenance, and when the ponds are properly sealed there is no
contamination of surrounding soil or groundwater [31], unlike the other inland disposal options.
Another option is to treat the brine to separate the organic matter from brine. Using anion exchange
brine from a sugar refinery Wadley et al. [32] used nanofiltration to separate NaCl from organic
matter. The DOC concentration in brine can be as high as 20 g/L [15], therefore it could be used as
a soil supplement, while the NaCl could be reused to regenerate MIEX®. However, due to the
higher costs and complexities associated with brine treatment compared to disposal it is unlikely it
would be suitable for international development.
6. Integration in Developing Countries
As waterborne diseases are a major cause of mortality in developing countries [33] it is essential to
disinfect or physically remove pathogenic bacteria and viruses. As a result MIEX® can not be used
alone for international development. However, depending on levels of water turbidity and
particulate matter type, MIEX® can be coupled with either chlorine disinfection or submerged
ultrafiltration. Some advantages and disadvantages of MIEX® in the context of international
development are shown in Table 1. As well as the advantages of removing DBP precursors and
reducing chlorine demand, the ability of MIEX® to remove inorganic anions shows great potential
for international development in particular where physio-chemical water quality are of concern.
While MIEX® can not remove turbidity, and can even increase it, the presence of turbidity does not
affect removal of DOC. High turbidity waters are very common in developing countries,
particularly during rainy season, hence this is an important characteristic of MIEX® for international
development. Finally, waste brine produced by the process can create environmental problems if
not properly disposed of, however in arid or warm countries brine can be disposed of with low cost
and environmental impact using solar evaporation. Therefore, MIEX can be suitable for
international development, provided it is coupled with disinfection or membrane filtration and the
waste is dealt with responsibly.
Table 1: Advantages and disadvantages of MIEX® in international development
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ADVANTAGES
DISADVANTAGES
Effective removal of dissolved organic carbon
(up to 80%), and hence disinfection by-product
precursors
Cannot disinfect water, therefore cannot be used
alone for international development
applications where microbiology contaminants
are significant
Reduced chlorine demand and hence reduce
disinfection costs
Cannot remove turbidity or particulate matter,
therefore filtration or coagulation is required for
turbid raw water
Significant removal of inorganic anions, such as
nitrate and sulphate, and certain micropollutants,
such as ionic pesticides, pharmaceuticals and
hormones
Any resin carryover in the process can increase
turbidity of the treated water
Potential to couple MIEX® with other water
treatment applications, such as disinfection,
coagulation and membrane filtration
Seasonal fluctuations in DOC concentration can
require different MIEX® doses or retention
times, therefore the process requires monitoring
MIEX® waste brine can be disposed of through
solar evaporation at low cost and low
environmental impact
MIEX® waste brine requires treatment and
disposal
Presence of turbidity and particulate matter do
not affect removal of DOC by MIEX, which is
good characteristic for international development
where surface waters often have extreme
turbidity values
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... Magnetic ion exchange resins (MIEX) are quaternary ammonium-type strong base anion resins with parent polypropylene polymer shells . They possess small sizes, larger surface area to volume ratio and magnetic properties which differentiate them from conventional ion exchange resins (Neale and Schäfer, 2009). The magnetic properties of MIEX make them easily cluster at the bottom of the container after adsorption reducing adsorbent losses and enhancing recovery (up to 99.9%) and regeneration (Boyer and Singer, 2005). ...
... The interaction between MIEX and PFOA has been established to involve both chemisorption and physical adsorption . MIEX resins are easily regenerated via desorption using 10% w/w NaCl brine, the adsorbed ions on the resin are replaced with chloride ions (Neale and Schäfer, 2009). ...
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Perfluoroalkyl carboxylic acids (PFCAs) are sub-class of perfluoroalkyl substances commonly detected in water matrices. They are persistent in the environment, hence highly toxic to living organisms. Their occurrence at trace amount, complex nature and prone to matrix interference make their extraction and detection a challenge. This study consolidates current advancements in solid-phase extraction (SPE) techniques for the trace-level analysis of PFCAs from water matrices. The advantages of the methods in terms of ease of applications, low-cost, robustness, low solvents consumption, high pre-concentration factors, better extraction efficiency, good selectivity and recovery of the analytes have been emphasized. The article also demonstrated effectiveness of some porous materials for the adsorptive removal of the PFCAs from the water matrices. Mechanisms of the SPE/adsorption techniques have been discussed. The success and limitations of the processes have been elucidated.
... In contrast to activated carbon adsorption, which has low DBP precursor removal for low DOC content water, magnetic ion exchange (MIEX®) adsorption reported better removal (Jutaporn et al., 2022). MIEX® resin is an anion exchange resin with quaternary amide functional groups with a strong base and microporous (Neale and Schäfer, 2009) that could effectively eliminate DOM, including DBP precursors (Arias-Paic et al., 2016). For Southeast Asian water sources, research using ion exchange resin for DBP removal is still lacking. ...
Article
This review discusses disinfection by-products’ (DBPs) potential precursors, formation, and toxicity, alongside available research on the treatment of DBPs in Southeast Asian countries' water sources. Although natural organic matter (NOM) in the form of humic and fulvic acids is the major precursor of DBPs formation, the presence of anthropogenic organic matter (AOM) also plays essential roles during disinfection using chlorine. NOM has been observed in water sources in Southeast Asian countries, with a relatively high concentration in peat-influenced water sources and a relatively low concentration in non-peat-influenced water sources. Similarly, AOMs, such as microplastics, pharmaceuticals, pesticides, and endocrine-disrupting chemicals (EDCs), have also been detected in water sources in Southeast Asian countries. Although studies regarding DBPs in Southeast Asian countries are available, they focus on regulated DBPs. Here, the formation potential of unregulated DBPs is also discussed. In addition, the toxicity associated with extreme DBPs' formation potential, as well as the effectiveness of treatments such as conventional coagulation, filtration, adsorption, and ozonation in reducing DBPs’ formation potential in Southeast Asian sources of water, is also analyzed.
... With the application of MIEX pretreatment in drinking water plants, the dosage of subsequent coagulants (Shuang et al., 2013;J. Wang et al., 2015;Watson et al., sodium chloride (NaCl) solution to restore its exchange activity (Neale & Schäfer, 2009), leaving the high salt desorption fluid containing a large amount of organic pollutants in the regeneration tank. This mixed system of liquids can easily cause serious corrosion to subsequent metal pipes and water treatment structures at all levels, affecting the service life of equipment and the safe operation of the production system (Y. ...
Article
Magnetic ion exchange resin (MIEX) pretreatment has been widely used to enhance the performance of waterworks, but the high-salinity organic desorbent produced during the resin regeneration is difficult to be safely disposed of. The present study aimed to investigate the removal of DOM and retention of salts from MIEX desorbent via zero-valent iron (ZVI)-assisted Fenton reaction. ZVI/H2O2 mediated Fenton reaction was further validated by various analytical approaches such as 3D-EEM, Molecular weight distribution, Zeta potential, size, dissolution of iron ions, etc. In batch experiments, 73.26% reduction of DOC and 97.66% of UV254 were achieved in 40 min at optimal H2O2 concentration (20 mM), 2 g/L dose of ZVI, and pH of 3, respectively. The removal of organics was ascribed to the direct oxidation of ZVI/H2O2 and flocculation of the iron released during the oxidation. It should be noted that the high concentration of Cl⁻ in system favored the organic removal and its enhanced performance lied in the production and oxidation of HOCl/OCl⁻. The treated liquid can be reused to regenerate the saturated resin with only a small amount of salt supplementation to obtain a similar recovery performance to that of a freshly configured 10% NaCl solution. Moreover, the retrieval and utilization of ZVI particles and other properties of MIEX desorbent after ZVI/H2O2 treatment were all promising and up to the mark: after four reuses, the mineralization of organic matter differs by 8.81% from the first time, which could be compensated by supplying new ZVI. This research will facilitate the recycling of resin desorbate and expand the market for MIEX applications.
... Magnetic ion exchange (MIEX®) resin is a strong base, macroporous, anion exchange resin with quaternary amide functional groups (Neale and Schäfer, 2009) that has been increasingly used for DBP precursor control. First-generation MIEX® DOC resin effectively removes DOM, including DBP precursors, from various water sources and has been successfully employed in many full-scale WTPs (Arias-Paic et al., 2016;Gan et al., 2013). ...
Article
The characteristics of dissolved organic matter (DOM) play an important role in the formation and speciation of carcinogenic disinfection byproducts. This study investigated changes in the characteristics and reactivity of DOM caused by the magnetic ion exchange resins, MIEX® DOC and MIEX® GOLD, using fluorescence excitation-emission matrix (EEM) with parallel factor (PARAFAC) analysis and Orbitrap mass spectrometry (Orbitrap MS) with unknown screening analysis. A five-component PARAFAC model was developed and validated from 208 EEMs of raw and MIEX®-treated water samples. The two resins exhibited preferential removal of the humic-like components (67-87% removal) and successfully removed protein-like components to a lesser extent (5-61% removal). Unknown screening analysis indicated removal of most condensed aromatic structures and lignin-like features that had high O/C values and refractory characteristics of lipid-like features by MIEX® treatments. MIEX® preferentially removed DOM molecules with more oxidized and shorter CH2 chains. The two resins had similar performance in trihalomethanes formation potential removal, but MIEX® GOLD achieved greater haloacetonitriles formation potential removal owing to its larger pore opening. Over 100 CHOCl DBP features were commonly found in all the samples while tens of CHOCl DBPs were uniquely formed in the samples with and without pre-treatments by MIEX®. Treatments by MIEX® before chlorination resulted in more intermediate CHOCl DBPs formed after chlorination compared to chlorinated raw waters. By optical spectroscopic analysis together with Orbitrap MS molecular characterization, we were able to confirm both quantitative and qualitative changes in DOM properties by MIEX® treatment related to DBP formation.
... The high salinity in the AIX spent brine could also harm the biodegradation efficacy. Several methods to conventionally dispose of the AIX spent brine, such as discharge after dilution, deep well injection, landfill, discharge in the sewer or other surface water bodies, sea and ground storage, and evaporation pounds, have been investigated [7][8][9]. However, these methods either cause secondary pollution such as severe groundwater, surface water, soil and sea contamination, causing the destruction of marine ecological balance and soil salinization [3,4,10], or high energy consumption and operation costs [11]. ...
Article
Full-text available
The anion exchange (AIX) spent brine, generated during the NDMP-3 resin regeneration process, highly loaded with organic substances mainly humic substances (HSs) and salts (mainly NaCl) remains an environmental concern. In this study, pilot-scale electro dialysis (ED) and ultrafiltration (UF) hybrid technologies were first used to recover NaCl solution as a resin regeneration agent and HSs, which could be utilized as a vital ingredient of organic fertilizer, from the AIX spent brine. Recovered ≈ 15% w/w NaCl solution obtained by two-stage pilot-scale ED can be used to regenerate saturated NDMP-3 anion exchange resins; the regeneration–readsorption performance of NDMP-3 resins was equivalent to that of fresh ≈ 15% w/w NaCl solution. The two-stage dilute solution with low-salt content (0.49% w/w) was further concentrated by pilot-scale UF, so that the HS content in the retentate solution was >30 g/L, which meets the HS content required for water-soluble organic fertilizers. The HS liquid fertilizer could significantly stimulate the growth of green vegetables with no phytotoxicity, mainly due to special properties of HSs. These results demonstrate that ED + UF hybrid technologies can be a promising approach for the sustainable treatment and resource recovery of AIX spent brine.
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With the continuous development of society, industrialization, and human activities have been producing more and more pollutants. Fluoride discharge is one of the main causes of water pollution. This review summarizes various commonly used and effective fluoride removal technologies, including ion exchange technology, electrochemical technology, coagulation technology, membrane treatment, and adsorption technology, and points out the outstanding advantages of adsorption technology. Various commonly used fluoride removal techniques as well as typical adsorbent materials have been discussed in published papers, however, the relationship between different adsorbent materials and adsorption models has rarely been explored, therefore, this paper categorizes and summarizes the various models involved in static adsorption, dynamic adsorption, and electrosorption fluoride removal processes, such as pseudo-first-order and pseudo-second-order kinetic models, Langmuir and Freundlich isotherm models, Thomas and Clark dynamic adsorption models, including the mathematical equations of the corresponding models and the significance of the models are also comprehensively summarized. Furthermore, this comprehensive discussion delves into the fundamental adsorption mechanisms, quantification of maximum adsorption capacity, evaluation of resistance to anion interference, and assessment of adsorption regeneration performance exhibited by diverse adsorption materials. The selection of the best adsorption model not only predicts the adsorption performance of the adsorbent but also provides a better description and understanding of the details of each part of the adsorption process, which facilitates the adjustment of experimental conditions to optimize the adsorption process. This review may provide some guidance for the development of more cost-effective adsorbent materials and adsorption processes in the future.
Conference Paper
In this study, degradation of pharmaceutical and personal care products (PPCPs) i.e. acetaminophen- commonly known as paracetamol (ACT) and ciprofloxacin (CIP) using electro-chemical and photo-chemical techniques were investigated. For electro-chemical degradation of Act and CIP, the effect of operational parameters viz. treatment time (0-300 min), voltage (5-25 V), PPCPs concentration (1-25 mg/L), solution pH (3-11), electrode material (stainless steel: SS and aluminium: Al), inter-electrode distance (1-2 cm) and combination of electrodes on removal efficiency were analyzed. Meanwhile, the photo-chemical degradation of ACT and CIP were carried using visible light (450-495 nm) and the effect of operational parameters such as treatment time (0-120 min), light intensity (1020 W), catalyst dose (Fe2SO4 and H2O2) was examined. Subsequently, the rate of ACT and CIP degradation was investigated using first-order and second-order kinetic models for both electro-chemical and photo-chemical techniques. From results, it was observed that the electro-chemical degradation of ACT and CIP using Al electrode was better in comparison with Fe electrode i.e., 95.15% of ACT and 95.52% of CIP removal was observed at an optimum voltage of 15V at 60 min for four number of Al electrodes. On the other hand, for photo-chemical degradation using visible light, the maximum removal of ACT and CIP was observed to be 85.25% and 96.70%, respectively within 60 min using 20W visible light and at an optimum catalyst dose of 0.5 g/L FeSO4 and 0.067 mL/L H2O2. Furthermore, kinetic study revealed that the degradation of ACT and CIP was better represented by second-order model for electro-chemical treatment. Meanwhile, for photo-chemical degradation of ACT and CIP was better represented by first-order kinetic model. In conclusion, both electro-chemical and photo-chemical techniques could degrade both the ACT and CIP effectively.
Conference Paper
In this study, performance evaluation of two adsorbents synthesized using invasive weed i.e. Prosopis juliflora was chemically activated using hydrochloric acid (HPJ) and sodium hydroxide (NPJ) and applied for adsorptive removal of methyl orange (MO) and Rhodamine B (RB) dyes from mono-component (MO/RB) and multicomponent (MO+RB) systems in batch mode. The synthesized adsorbents were characterized using SEM, EDX, XRD, FTIR TGA and porosimetry analysis. From the porosimetry analysis the surface area, pore volume and pore size of HPJ was found to be 352.425 m²/g, 0.178 cc/g and 1.929 nm. Meanwhile, the effect of operational parameters such as contact time, adsorbent dose, dye concentration and solution pH on removal of MO and RB dyes was investigated. Subsequently, kinetic and equilibrium studies were modelled by different kinetic and isotherm models in mono-component system. One the other hand, multi-component adsorption system was modelled using Langmuir competitive model. Furthermore, the effect of presence of one dye on removal of other and vice versa, i.e. synergistic and antagonistic nature of adsorption process were investigated. From results, it was observed that pseudo-first-order kinetic and Langmuir isotherm models best fit the experimental kinetic and equilibrium data for removal of MO and RB dyes using both HPJ and NPJ adsorbents. The Langmuir’s maximum adsorption capacity (qm) of HPJ for the removal of MO and RB dyes was found to be 12.77 mg/g and 9.95 mg/g, respectively. On the other hand, the maximum adsorption capacity of NPJ for the removal of MO and RB dyes was observed to be 10.51 mg/g and 8.69 mg/g, respectively. In conclusion, the HPJ and NPJ could be effectively used as adsorbents for removal of dyes from effluents.
Article
Full-text available
In this study, pretreatment of organic matters with MIEX® was evaluated using bench-scale experimental procedures on three organic matters to determine its effect on subsequent UF or MF membrane filtration. For comparison, a coagulation process was also used as a pretreatment of UF or MF membrane filtration. Moreover, the membrane fouling potential was identified using different fractions and molecular weights (MW) of organic matter. From the removal property of MW organic matter by the coagulation process for the sample water NOM and AOM, the removal efficiencies of high MW organic matter were much higher than those of low MW organic matter. It was shown that the removal efficiency of high MW organic matter (more than 10 kDa) was lower than that of low MW organic matter for the MIEX® process. For the change of permeate flux by the pretreatment process, the MIEX®-UF process showed high removal efficiency of organic matter compared with the coagulation-UF processes, but a high reduction rate of permeate flux was presented through the reduction of removal efficiency of high MW organic matter. From sequential filtration test results to examine the effect of MW of organic matter on membrane fouling, we found that the membrane fouling occurred with high MW organic matter, and the DOC of organic matter less than 0.5 mg/L was acting as the membrane foulant. In sample water composed of low MW organic matter (less than 10 kDa), because the low MW organic matter of less than 10 kDa has a high removal efficiency by MIEX®, a low reduction rate of permeate flux is obtained compared with the coagulation-UF processes. In summary, research on the physical/chemical characteristics of original water is needed before a membrane pretreatment process is selected, and a pertinent pretreatment process should be used based on the physical/chemical characteristics of the original water.
Article
The contamination of groundwater by arsenic in Bangladesh is the largest poisoning of a population in history, with millions of people exposed. This paper describes the history of the discovery of arsenic in drinking-water in Bangladesh and recommends intervention strategies. Tube-wells were installed to provide "pure water" to prevent morbidity and mortality from gastrointestinal disease. The water from the millions of tube-wells that were installed was not tested for arsenic contamination. Studies in other countries where the population has had long-term exposure to arsenic in groundwater indicate that 1 in 10 people who drink water containing 500 mu g of arsenic per litre may ultimately die from cancers caused by arsenic, including lung, bladder and skin cancers. The rapid allocation of funding and prompt expansion of current interventions to address this contamination should be facilitated. The fundamental intervention is the identification and provision of arsenic-free drinking water. Arsenic is rapidly excreted in urine, and for early or mild cases, no specific treatment is required. Community education and participation are essential to ensure that interventions are successful; these should be coupled with follow-up monitoring to confirm that exposure has ended. Taken together with the discovery of arsenic in groundwater in other countries, the experience in Bangladesh shows that groundwater sources throughout the world that are used for drinking-water should be tested for arsenic.
Article
Two South Australian reservoir waters, Hope Valley and Myponga, were selected in this study based on the differences in the character of their organic matter. Four treatment options: (a) alum coagulation without pH adjustment; (b) alum coagulation at pH 6; (c) magnetic ion-exchange (MIEX®) resin; and (d) combined alum/MIEX® treatment, were used to compare the removal of dissolved organic carbon (DOC) and treated water quality, particularly the formation of disinfection by-products and bacterial regrowth potential. Improved DOC removal was achieved with the inclusion of MIEX® treatment in the process. Removal of DOC under optimised treatment conditions indicated combined alum and MIEX® treatment was very similar to MIEX® alone but much better than conventional and enhanced coagulation with alum. Combined treatment (alum and MIEX®) removed 2.3 and 1.4 times the DOC of enhanced coagulation with alum from Hope valley and Myponga respectively. The DOC remaining after each treatment strategy was different in character. The molecular weight distribution results indicated that MIEX® treatment removed a broad range of compounds, whilst alum treatment targeted the removal of high molecular weight compounds. In addition, the DOC remaining after MIEX® treatment consisted of compounds with lower specific UV absorbance (SUVA). Including MIEX® in the treatment stream provided better DOC and bromide removal thus reducing chlorine decay and trihalomethane (THM) formation. The ability of the water to support bacterial growth as measured by bacterial regrowth potential (BRP) was the lowest after MIEX® treatment (option c) compared with the three other treatments (options a, b & d). In summary, laboratory tests show that including MIEX® in the treatment process can improve treated water quality.
Chapter
The purpose of this chapter is to acquaint the reader with the importance of biochemical processes in organic geochemistry. Unfortunately, it is not possible to explain in detail all of the biochemical processes that affect organic solutes. Therefore, this chapter introduces basic concepts of biochemical processes. First, the chapter discusses the general decomposition of organic carbon, which is a major biogeochemical pathway in natural systems. The chemical processes of life put together amino acids, carbohydrates, and fatty acids to build specific compounds, such as proteins, polysaccharides, and lipids. When the death of an organism occurs, then the biochemical processes of decay and decomposition take over, and an entirely different suite of fragmented compounds occur. The general decomposition of organic carbon is a broad view of this complicated process.
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Magnetic ion exchange resin, known by its commercial name (MIEX®) provides one pretreatment alternative that could maximize ozonation disinfection while decreasing bromate formation in bromide-containing waters. During a 5-week pilot study, the MIEX® process removed up to 30 % of the dissolved organic carbon (DOC) and reduced ultraviolet absorbance at 254 nm (UV 254) by up to 60%. When MIEX® pretreated water was ozonated, ozone decay rates were reduced, increasing the CT achieved by 40% to 65%. The increased disinfection capability reduced the transferred ozone dosages required for Cryptosporidium inactivation by 15% to 25% and bromate formation by 35%.
Article
A continuous flow colloidal affinity magnetic separation device is used for the removal of As(V) and Cr(VI) from aqueous solutions. Langmuir isotherms fit the adsorption behavior of the individual ions on Orica MIEX ion exchange particles. In a mixture of equal weight percent As(V) and Cr(VI), the adsorption of As(V) begins only above a critical cut‐off concentration, implying preferential adsorption of the higher valence ion at the available sites. Cr(VI) is removed selectively from the mixture in the continuous flow device, consistent with the presence of a higher concentration of the higher valence ion in the proximity of a charged (anion‐exchange) surface.
Article
One of the most critical problems in developing countries is the lack of drinking water. People in these regions are supplied with surface water, which contains a significant amount of microorganisms that can cause several diseases. In fact, one of the main causes of infantile mortality is the high incidence of diarrhoeic diseases and other illnesses related to impure drinking water. Ultrafiltration (UF) is a pressure-driven membrane process that separates on the basis of size and can remove bacteria and viruses from water. Therefore, OF can be applied for disinfecting water, avoiding some illnesses or epidemics where people consume ultrafiltrated water. The Chemical and Nuclear Engineering Department of the Polytechnic University of Valencia in Spain is working in cooperation with a non-governmental organisation to develop a system to make water drinkable in a region of Ecuador. The system consists of an OF plant with one spiral-wound module, equipped with a pressure pump driven by a petrol engine. Before the application of the process, the OF plant has to be completely tested and fine-tuned in order to assure that it will successfully perform once in Ecuador. One of the stages of these preliminary tests was the selection of the most suitable OF membrane from the point of view of kind of material and cut-off, bearing in mind the following points: quality of ultrafiltrated water, performance conditions, membrane fouling and cleaning and maintenance conditions. This paper describes the preliminary tests carried out with different UF membranes to select the most suitable one for disinfecting surface water.
Article
The primary objective of this work was to evaluate the effectiveness of the MIEX® process in removing natural organic matter (NOM) from selected drinking water sources of the City of Istanbul. Raw water samples from five drinking water treatment plants (Elmalı, B.Çekmece, Ömerli, İkitelli, and Kağıthane) serving to about 10 million people were collected and jar-tested in laboratory. The kinetics of NOM removal at various MIEX® dose and contact times, the extent of resin saturation in multiple-loading experiments, and the impacts of MIEX® pretreatment prior to coagulation on coagulant demands were investigated. After a resin dose of 5–10ml settled resin/l and contact time of 10–20min, dissolved organic carbon (DOC) concentrations and specific UV absorbance (SUVA254) values obtained for all waters were
Article
Natural organic matter (NOM) in water sources is undesirable for customers because it reacts with chlorine to form trihalomethanes (THMs), which can be harmful to health, and other organochlorine compounds that can cause taste complaints. A new Magnetic Ion EXchange process (MIEX® DOC) has been reported as being successful in removing NOM from raw water. The aim of this research was (a) to evaluate the performance of the MIEX® process in removing NOM from hard, lowland water on a pilot plant scale and (b) to compare the performance of the MIEX® process with low pH coagulation DAF, in particular, with respect to reducing THM levels. A 45 and 40% reduction in the amount of NOM and in the levels of THMs, respectively, in chlorine-dosed water was achieved when the MIEX® process was used with dissolved air flotation (DAF).
Article
The implementation of a computer model to simulate reverse osmosis in systems with several components is described. The model was based on the Spiegler-Kedem theory of reverse osmosis. The results of a pilot-scale investigation of the use of nanofiltration to recover sodium chloride from waste brine from the regeneration of anion exchange resin were used in this study. This effluent contains around 50 g/l of sodium chloride and 5 g/l (as total carbon) of organic colourants, many of which are negatively charged. When using the SelROTM MPT-30 or MPT-31 membrane at an operating pressure of 3 MPa, temperatures between 45°C and 60°C, and linear feed flow rates around 1.6 m/s, the retention of sodium chloride was found to be between 0% and 20%, while the organic compounds had an overall retention of 80% to 97%. The experimental results were used to obtain a set of parameters relating to the system, which were then used to generate design data for a full-scale plant. Suitable module arrangements were proposed and the system performance for each case was predicted.