Pre‐deposited dynamic membrane adsorber formed of microscale conventional iron oxide‐based adsorbents to remove arsenic from water: Application study and mathematical modeling


BACKGROUND: This study reports the development of a dynamic membrane (DM) adsorber by the pre‐depositing powdered‐sized fraction of iron oxide‐based adsorptive material on the surface of a microfiltration(MF) membrane. The aim is to use the developed DM adsorber for arsenate (As(V)) remediation from water by a combined mechanism of adsorptive and membrane filtration. The two applied iron oxide‐based adsorptive materials are micro‐sized granular ferric hydroxide and micro‐sized tetravalent manganese feroxyhyte, and are available at an affordable price. RESULTS: The results show that As(V) removal efficiency strongly depends on the physicochemical properties of the depositing material such as specific surface area, isoelectric point, and particle size of the pre‐depositing material. The experimentally determined As(V) removal rates were mathematically modeled using a homogeneous surface diffusion model (HSDM) that incorporates the equilibrium parameters and mass transport coefficients of the adsorption process. The simulations showed that the mathematical model could describe the As(V) removal rates accurately over a broad range of operating conditions. The results further showed that the longer filtration times with very low normalized As(V) permeate concentration (C/Cf = 0.1 for example) can be prolonged by operating DM adsorber at lowermost membrane water flux of 31 L/(m2·h) and large amount of pre‐depositing material on MF membrane surface (Ma= 14 mg/cm2). CONCLUSION: The results presented in this study confirm that use of these inexpensive materials (side‐product of granular iron‐oxide‐based adsorbents) in treating As(V) polluted water would enhance the sustainability of the industrial production process of conventional granular adsorbents by utilizing the wastes created during the process of adsorbent production.
Research Article
Received: 18 December 2020 Revised: 4 March 2021 Accepted article published: 5 March 2021 Published online in Wiley Online Library:
( DOI 10.1002/jctb.6728
Pre-deposited dynamic membrane adsorber
formed of microscale conventional iron oxide-
based adsorbents to remove arsenic from
water: application study and mathematical
Muhammad Usman,a
Aida Idrissi Belkasmi,aIoannis A Kastoyiannisband
Mathias Ernsta
BACKGROUND: This study reports the development of a dynamic membrane (DM) adsorber by pre-depositing powdered-sized-
fraction of iron oxide-based adsorptive material on the surface of a microltration(MF) membrane. The aim is to use the devel-
oped DM adsorber for arsenate (As(V)) remediation from water by a combined mechanism of adsorptive and membrane
ltration. The two applied iron oxide-based adsorptive materials are micro-sized granular ferric hydroxide and micro-sized tet-
ravalent manganese feroxyhyte, and are available at affordable price.
RESULTS: The results show that As(V) removal efciency strongly depends on the physicochemical properties of the depositing
material such as specic surface area, isoelectric point and particle size of the pre-depositing material. The experimentally
determined As(V) removal rates were mathematically modeled using a homogeneous surface diffusion model, which incorpo-
rates the equilibrium parameters and mass transport coefcients of the adsorption process. The simulations showed that the
mathematical model could describe the As(V) removal rates accurately over a broad range of operating conditions. The results
further showed that the longer ltration times with very low normalized As(V) permeate concentration (C/C
=0.1, for example)
can be prolonged by operating the DM adsorber at the lowermost membrane water ux of 31 L m
and a large amount of
pre-depositing material on the MF membrane surface (M
=14 mg cm
CONCLUSION: The results presented in this study conrm that use of these inexpensive materials (side-product of granular iron
oxide-based adsorbents) in treating As(V)-polluted water would enhance the sustainability of the industrial production process
of conventional granular adsorbents by utilizing the wastes created during the process of adsorbent production.
© 2021 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society
of Chemical Industry (SCI).
Supporting information may be found in the online version of this article.
Keywords: arsenate; adsorption; granular ferric hydroxide; membrane adsorber; homogenous surface diffusion model; water treatment
Dynamic membranes (DMs) were rst narrated in 1965 by a
research group from the Oak Ridge National Laboratory.
a membrane manufactured through a casting membrane solution
or melting spinning technique, a DM lter, which is referred to as a
secondary membrane, can be developed in situ. The DM lter
builds up as a layer of particles such as metal oxides, soil-based
compounds and powdered activated carbon (PAC) deposited
via permeation drag onto surfaces of meshes, nylon, polyethersul-
fone (PES) and ceramic-based microltration (MF) and ultraltra-
tion (UF).
This suggests that a DM lter technology
predominantly involves two layers, namely the primary
membrane as a supporting layer and the deposited cake layer of
microparticles as the secondary membrane. The primary mem-
brane offers the foundation to the deposited layer, while the
*Correspondence to: M Usman, Institute for Water Resources and Water Supply,
Hamburg University of Technology, Am Schwarzenberg-Campus 3, 20173
Hamburg, Germany. E-mail:
aInstitute for Water Resources and Water Supply, Hamburg University of Tech-
nology, Hamburg, Germany
bLaboratory of Chemical and Environmental Technology, Department of
Chemistry, Aristotle University of Thessaloniki, Thessaloniki, Greece
© 2021 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical
Industry (SCI).
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and
reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
deposited layer, consisting of nano- and microparticles, acts as
the dominant functional part for decontamination of water.
deposited layer of particles then determines the removal rates
and efciency of the DM lter towards a target trace pollutant,
when the primary membrane does not have a rejection capacity
towards the specic target pollutant.
For example, dissolved
inorganic trace contaminants such as arsenic and antimony are
not retained by a typical MF or UF membrane.
Modication of
such a membrane, i.e. by iron oxides, can remove the trace con-
taminant by adsorption onto the secondary membrane, while
the primary membrane achieves high overall water quality by l-
tering out suspended particles.
The DM lter with diverse separating functions can be devel-
oped by opting suitable pre-depositing materials. The DM lter
made on loosened support materials such as MF and mesh has
an advantage over traditional membranes of operating under
gravity-driven mode.
A driving force by means of a 10 cm water
head was sufcient during DM ltration of secondary wastewater
efuent to achieve 200 L m
when a nylon mesh with an cor-
responding aperture of 25 μm was applied as a DM support mate-
Furthermore, once the DM lter is fouled or exhausted, the
deposited cake layer can be displaced by backwashing either with
water or air,
and a new cake layer of depositing material can be
readily redeposited. The use of water has proved to be an effec-
tive cleaning approach for the exhausted DM lter. More than
90% of the primary membrane permeability could be restored
after four ltration cycles.
DM lters are categorized into two main types: self-forming DM
lters and pre-deposited DM lters. In the rst case, the feed con-
stituents are those which form the DM lter, whereas the pre-
deposited DM lter are developed as a result of deposition of par-
ticles other than the feed solution at the top surface of the pri-
mary membrane prior to the inow of the polluted water.
The pre-deposited DM lter offers the exibility of selecting
appropriate and affordable materials which might be used to
develop the membrane lter. Irrespective of DM lter category,
the DM either: (a) expands the capability of the primary mem-
brane to remove contaminants that otherwise would not be
removed; (b) enhances the overall performance of the conven-
tional primary membrane; or (c) conserves the primary membrane
from fouling.
According to the formation mechanism, DM lters can be classi-
ed into two classes. Class I DM lters are those whereby the pore
size of the primary membrane is really small, to completely retain
the DM lter-forming material. In this case, the dominant mecha-
nism that governs DM formation is the concentration polariza-
When the primary membrane's pore diameter is
signicantly larger than the size of the particles (e.g. dust or bac-
teria) to be deposited, these types of DM lters are referred to
as class II DM lters. The depositing materials can form a bridge-
like structure over the pores and may build occulation centers.
The pore constriction and cake ltration are membrane-forming
mechanisms that are involved in the formation of class II DM l-
Generally, in DM ltration technology a cake layer of specic
thickness is explicitly formed as more and more particles are
deposited on the surface of the primary membrane. As a result,
resistance might not be as badly affected during the formation
of class I DM lters compared to class II DM lters.
class I DM lters have recently gained popularity in water treat-
ment for removal of organics.
The most popular materials used in DM ltration technology are
polymers, hydrous Zr(IV) oxide polymer, metal oxides, soil-based
materials such as kaolin and diatomite, PAC and nanoparticles.
Among these materials, PAC and oxides of iron, aluminum and
titanium were the rst to be applied, whereas nanoparticles are
gaining popularity and are now widely accepted as DM-forming
Iron oxide-based adsorbents (e.g. Fe
) have been
used as pre-depositing material not only for fouling mitigation
of the primary membrane in UF applications
but also for puri-
cation purposes.
ADMlter formed by pre-depositing PAC
particles onto a primary membrane showed excellent efciency
in adsorbing organic pollutants from diluted textile wastewater.
Soil-based materials have also been tested as DM lter-forming
materials, examples of which are clay in treating domestic waste-
clay for color removal
and arsenic removal
On a global scale, arsenic is considered to be a main environ-
mental issue because of its presence in the groundwater and sur-
face water sources; this is of great relevance to environmentalists
because of its toxicity and carcinogenicity, and the number of
affected people worldwide.
It enters the food chain either
through drinking water or by consuming arsenic-containing food,
e.g. rice.
Arsenic in polluted environments primarily exists as
arsenite and arsenate, abbreviated as As(III) and As(V), respec-
tively. Arsenic naturally occurs in over 200 different mineral forms,
of which approximately 60% are arsenates, 20% suldes and sul-
fosalts and the remaining 20% include arsenides, arsenites,
oxides, silicates and elemental arsenic.
As(V) anions prevail in
oxygenated water, whereas As(III) anions occur in moderately
reduced environments (e.g. anoxic groundwater). Under oxidizing
conditions, H
is the more stable species between pH 2 and
7, whereas H
is the more stable species above pH 7 in nat-
ural waters.
Several treatment technologies for arsenic
removal from drinking water have been applied worldwide,
and the most commonly used are chemical coagulation using
metal (iron) salts,
sorption on activated alumina,
oxides and iron oxyhydroxides,
electrocoagulation with Fe/
Al electrodes,
preliminary arsenic oxidation by ozonation or bio-
logical oxidation,
ion exchange using polymer resins
and pres-
sure-driven membrane processes, such as nanoltration
reverse osmosis.
Among the several existing arsenic removal
technologies, chemical precipitation by ferric coagulation fol-
lowed by ltration and adsorption onto iron oxides and iron oxy-
hydroxides appear to be cost effective for large-scale arsenic
treatment plants to comply with established WHO guideline value
of 10 μgL
Chemical precipitation by ferric coagulation
has signicantly higher arsenic removal efciencies compared to
iron-based adsorbent materials, including iron oxyhydroxides.
However, the efforts required for handling the wastes from coag-
ulationltration prevent its application when the treatable vol-
ume of product water corresponds to the one produced for a
small town.
Adsorption technology using iron oxyhydroxides
is considered to be an economical and effective technique for
arsenic removal because of its lower cost and availability of suit-
able commercial adsorbents and their regeneration.
It is gen-
erally believed that arsenic adsorption by porous iron hydroxides
takes place not only due to Coulombic and/or Lewis acidbase
interactions but also because of formation of monodentate and
bidentate inner-sphere complexes.
It is widely acknowledged
that the porous character of iron (oxy)hydroxides adsorbs As(V) at
internal iron complexation sites.
In the present work, the main objective was to create a pre-
deposited DM lter based on the utilization of micro-sized pow-
dered fractions of iron oxide-based adsorbents, namely micro- M Usman et al. © 2021 The Authors.
Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).
J Chem Technol Biotechnol 2021
sized granular ferric hydroxide (μGFH) and micro-sized tetravalent
manganese feroxyhyte (μTMF). μGFH comprises the by-products
(waste) of the industrial production process of the commercially
available granular GFH and which is currently discarded, whereas
μTMF is generated during the production of TMF at the laboratory
scale. Both adsorbent materials are excellent arsenic adsorbents
and exhibit remarkable adsorption afnity towards As(V). A previ-
ous study of our group indicated that the adsorption capacities of
μGFH at an equilibrium arsenic concentration of 10 μgL
pH 8 were found to be 6.9 μg As(V) mg
and 3.5 μgAs
(III) mg
, respectively; whereas for μTMF the adsorption capaci-
ties were 5.5 μg As(V) mg
and 4.8 μg As(III) mg
under the
same experimental conditions.
Further, a recent study of our
group has shown that side-products of iron oxide-based adsor-
bents might be employed in an adsorptionMF hybrid system
wherein the adsorption take place in a slurry reactor simulating
a completely mixed stirred tank reactor. This study also concluded
that the powdered-sized fractions of the studied adsorbents have
an overwhelming inuence on As(V) adsorption rate compared to
larger-sized fractions (>63 μm).
Accordingly, the micro-sized
powdered fractions of iron (oxy)hydroxides might be applied as
pre-depositing materials for in situ preparation of DM lters. In
the present study, we moved forward the research by applying
the powdered-sized fractions of iron oxide-based adsorbents as
DM lter-forming materials and a novel modeling approach to
describe in more detail the efciency of As(V) removal and the
parameters that inuence the effectiveness of the process. We
applied a mass transfer model to describe As(V) removal in the
permeate of the pre-deposited DM adsorber. Furthermore, this
study aims at identifying the best operating conditions for opti-
mum As(V) removal from groundwaters. Application of the
modeling approach will support the optimization and facilitate
the application of DM ltration technology in real arsenic treat-
ment systems.
Until now, all reported pre-deposited DM lters were focused on
factors affecting the formation and mechanisms by which the DM
lters are formed. In the present work, we investigated for the rst
time the performance potential of two powdered-sized conven-
tional iron hydroxides (μGFH and μTMF) as pre-depositing mate-
rials of DM lter to remove As(V) from water in the MF process
and proposed a mathematical model to describe the overall per-
formance of the presented process.
In the present work, the pre-deposited layer of applied adsor-
bents on the primary MF membrane was made by powdered-
sized fractions (163 μm) of GFH and TMF. The chosen pollutant
was As(V), as iron-based adsorbents such as GFH and TMF are cus-
tomarily applied to the treatment of arsenic-polluted waters in a
natural environment. Flat sheet PES-based MF membranes (DUR-
APES200) with a nominal size of 0.2 μm used a primary membrane
were purchased from Membrana GmbH (Wuppertal, Germany).
The industrial-scale production of μGFH (GEH Wasserchemie
GmbH & Co., Osnabrück, Germany) involves the neutralization of
an FeCl
solution and precipitation with NaOH. It mainly com-
prises of akagenéite mineral.
The lab-scale synthesis of μTMF
includes co-precipitation of FeSO
and KMnO
. It is identied as
The important physicochemical properties of the
applied adsorbents were determined in our former studies
and are reported in Table 1. Table 1 lists the specic surface area
which were estimated according to Brunauere-Emmette-Teller
(BET) model and details on BET surface area measurements can
be found in our previous work.
A sieve having a mesh size of 63 μm was applied to separate
powdered-sized μGFH (163 μm) from air-dried μGFH (1
250 μm). The same sieve was applied to acquire powdered-sized
μTMF (163 μm) from μTMF (1250 μm). The individual particle
size of the majority (>98%) of μGFH (163 μm) particles was smal-
ler than 5 μm, while 100% particles of μTMF (163 μm) were smal-
ler than 5 μm. Consequently, the mean particle size of the
powdered-sized μGFH and μTMF materials was 3.5 and 2.8 μm,
respectively. The particle size distribution of powdered-sized μGFH
and μTMF is provided in Supporting Information Figs S1 and S2).
Arsenic-polluted water was obtained by spiking an appropriate
aliquot of As(V) standard solution (Merck Chemicals GmbH, Ger-
many) in deionized (DI) water. A buffer (N,N-bis(2-hydroxyethyl)-
2-aminoethanesulfonic acid (BES; 2 mmol L
) was carefully sup-
plemented to prepare As(V)-polluted water (Carl Roth GmbH +
Co. KG, Germany) to promote pH control for longer periods.
Before continuous feeding tests, a target pH of 8 ±0.1 was set
by addition of either NaOH or HCl.
Experimental setup
Each dead-end DM ltration experiment was divided into three
stages: preparation of primary MF membrane as a porous support
material, pre-deposition of adsorbent particles (DM lter forma-
tion) and ltration experiments employing pre-deposited DM
To prepare for the employment of the primary MF membrane as
porous support material for the deposition of powdered-sized
iron oxide-based adsorbents, the primary MF membrane was rst
rinsed with at least 1 L of pure water to remove residual sub-
stances. An Amicon® 8200 ltration cell constructed by Millipore
(USA) was used for the formation of the pre-deposited MD lter
as well as for the continuous dead-end ltration experiments.
The top-end piece of ltration cell contains the feed inlet, while
the bottom of the cell contains a porous insert that holds a mem-
brane with an active surface of 28.7 cm
AμGFH and μTMF pre-deposited DM adsorber was formed
according to the following procedure: the suspension formed
from mixing powdered-sized fractions of applied adsorbents
(300 or 400 mg in 150 mL pure water) was transferred to a ltra-
tion cell housing the primary MF membrane. The cell was then
sealed with an upper cap and O-ring. The pure water (~0.5 L)
was ltered at 0.5 bar applied ltration pressure through each
membrane and a new membrane was applied to all experiments.
A uniform thin cake layer of adsorbent particles was formed at the
surface of the primary MF membrane by permeation drag, which
is the convective force dragging the particles towards the primary
Once the DM adsorber was formed by pre-depositing the pow-
dered-sized fractions of applied adsorbents at the primary mem-
brane surface, feed solution containing different concentration
levels of As(V) (either 190 or 380 μgL
) at room temperature
(20 ±2°C) was introduced using a peristaltic pump from a solu-
tion reservoir through the membrane ltration cell (Fig. 1). Exper-
iments using constant ux ltration, which is mainly used in plant
practice ltration, rather than constant pressure, were carried out
by keeping the water ux constant while changes in the operating
ltration pressure were continuously monitored. A signal-condi-
tioned pressure gauge (Sensortechnics GmbH, Germany) col-
lected the operating pressure data automatically. As(V)
Pre-deposited dynamic membrane adsorber
J Chem Technol Biotechnol 2021 © 2021 The Authors.
Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).
concentration levels in the efuent of a pre-deposited DM
adsorber were monitored by collecting samples at different time
intervals. The performance pre-deposited DM adsorber was eval-
uated under different operating conditions. The recorded As(V)
removal rates were then modeled using a mathematical model
based on a mass transfer model called the homogeneous surface
diffusion model (HSDM).
Arsenic analysis
Collected permeate samples were measured for total arsenic at
pH 2 using HCl. Measurement of arsenic concentration in the feed
and permeate samples was carried out by graphite furnace
atomic absorption spectrophotometry (GFAAS; 4110 ZL instru-
ment, PerkinElmer, Germany). GFAAS was operated with a graph-
ite furnace tube atomizer. The arsenic samples were atomized
using argon gas. GFAAS was set up with a lamp current of
380 mA, wavelength 193.7 nm for arsenic detection, and a slit
width of 0.7 nm. The peak area was selected as a measurement
mode. The arsenic limit of detection of this method was 0.5 μg
. The maximum standard deviation of the analysis was 5%.
Mathematical modeling of permeate As(V) concentration
A mathematical model incorporating the HSDM has been applied
to describe the concentration proles of arsenic adsorption sys-
These studies have demonstrated that the HSDM
allows the simulation of the dynamic behavior of a variety of
adsorbates (phosphate, arsenic, chloroform and vanadium) onto
porous adsorbents (e.g. activated carbon, GFH and μGFH), as long
as the mass transfer from the solution to the adsorption sites
within the adsorbent particles is constrained by mass transfer
resistances such as surface diffusion and external lm mass trans-
fer, as depicted in Fig. 2.
The HSDM model assumes that the adsorbate (e.g. As(V)) dif-
fuses through a stagnant liquid lm layer developed around an
adsorbent particle into a homogeneous adsorbent sphere. The
Table 1. Physicochemical properties of applied iron oxide-based adsorbents
54, 57
Mean particle
diameter (μm)
content (%)
BET surface
area (m
(mL g
(g cm
μGFH 60 3.5 ~50 283 ±3 0.28 2.6 7.8 ±0.2 1.550
μTMF 44 2.8 <5 178 ±8 0.35 3.2 7.2 ±0.1 0.642
Figure 1. Schematic representation of the laboratory installations for dead-end ltration. Inset demonstrates the pre-deposited cake layer of applied iron
oxide-based adsorbent material.
Figure 2. Schematic diagram of arsenic ion mass transport from the bulk
solution into a particle of porous iron oxide. M Usman et al. © 2021 The Authors.
Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).
J Chem Technol Biotechnol 2021
surface diffusion and the external lm diffusion are the mass
transfer resistances incorporated into the HSDM controlling arse-
nic adsorption.
The mass transfer resistance arises from surface
diffusion (D
) and the external lm diffusion (k
The HSDM is an adsorption model that comprises two partial
differential equations. Equation (1) (referred to as the lter mass
balance equation) describes the mass transport through the
adsorbent layer, whereas the mass transfer into the adsorbent
particle is represented by Eqn (2) (intra-particle mass transfer
equation). The assumptions made in the HSDM are: (i) plugow
conditions in the deposited cake layer; (ii) the adsorbent particles
are spherical; (iii) local adsorption equilibrium occurs within the
adsorbent particle; (iv) instantaneous adsorption takes place on
active adsorption sites; (v) intra-particle surface diffusion is pre-
dominately mass transfer resistance; (vi) solid-phase mass transfer
owing to surface diffusion remains constant for an adsorbent. A
detailed description of the model has been reported elsewhere.
The As(V) mass balance over the pre-deposited DM lter in lin-
ear coordinates (z)is
here tis time, v
is lter velocity, ε
is cake layer porosity, Ris par-
ticle radius, k
is mass transfer coefcient due to the external lm
diffusion, and Cand C
are adsorbate liquid-phase concentration
in the pre-deposited iron oxyhydroxides layer and at the solidliq-
uid interface, respectively.
The intra-particle mass transfer equation indicates adsorbate
transfer in the adsorbent particle in radial coordinates (r) in pro-
portion to Fick's second law of diffusion:
where qis adsorbate solid-phase concentration and D
is mass
transfer caused by surface diffusion. The initial condition and
boundary conditions of the Eqn (2) can be found in the Support-
ing Information.
For model solution, desktop software (FAST 2.1) developed by
Sperlich et al.
was applied. The parameters to solve Eqns (1)
and (2) include readily measurable mass- and volume-related
parameters, i.e. mass of adsorbent applied, mean particle diame-
ter, particle density, cake layer density, inuent adsorbate concen-
tration) and indirectly quantiable parameters such as adsorption
equilibrium and kinetic parameters. It has been proven that the
mathematical model based on the HSDM has the capacity to
describe the impact of water chemistry (e.g. pH and water matrix)
on adsorbate dynamic behavior if the adsorption equilibrium and
kinetic parameters under changed water quality conditions are
available (have been derived).
This software (FAST 2.1) pro-
vides a numerical solution of Eqns (1) and (2) to simulate the con-
centration prole of anions over time of a xed-bed adsorption
lter packed with an adsorbent used in water treatment.
Pre-deposited DM adsorber for As(V) removal
Figure 3 shows the normalized As(V) concentration with respect
to feed As(V) concentration in the permeate of primary MF mem-
brane and pre-deposited DM adsorber as a function of the specic
throughput volume, expressed as volume of treated water per
unit area of primary membrane, for the two applied adsorbents
applied as DM lter-forming materials at pH 8 ±0.1.
The results demonstrate that the primary MF membrane did not
lead to a reduction in normalized As(V) permeate concentration
(Fig. 3) because the nominal pore size of the primary MF mem-
brane is 0.2 nm, which is one order of magnitude larger than
the dominant As(V) species at pH 8 (ionic radius of HAsO
0.397 nm
). Additionally, the PES-based membrane is negatively
charged at pH 8,
and consequently the As(V) removal by elec-
trostatic attractive forces is not imaginable. On the other hand,
at constant water ux of 125 L m
and adsorbent dosage
), expressed as amount of As(V) adsorptive material pre-depos-
ited per unit area of primary MF membrane, of 10.4 mg cm
, the
pre-deposited DM adsorber results in an immediate decrease in
normalized As(V) permeate concentration, with the As(V) concen-
tration reaching a minimum value. The DM adsorber achieved
very high As(V) removal efciency (90%, which corresponds to
=0.1) for the rst 0.15 L cm
specic throughput volume.
Subsequently, the normalized As(V) permeate concentration
started to increase as the volume of treated water was increasing
further (Fig. 3). This was due to the saturation of the deposited
adsorbent layer caused by the continuous inow of As(V)-contam-
inated feed solution. In the case of μTMF pre-deposited DM
adsorber, the rise in normalized As(V) permeate concentration
was slower than when using the μGFH deposited layer, even
though the achieved As(V) adsorption capacity of μTMF (15.4 μg
) was lower than that achieved by using the μGFH (22.4 μg
) at 380 μgL
and at pH 8.
This is most likely due to the
smaller particle size of μTMF, even though the BET surface area
and isoelectric point of μTMF is lower than μGFH (Table 1). The
second explanation might be the large pore diameter of μTMF,
which is causing a more rapid As(V) diffusion inside the adsorptive
material. A similar trend of As(V) removal rates by μTMF and μGFH
was observed during As(V) batch adsorption tests carried out in
the slurry reactor setup.
As the volume of treated water
increased, the normalized As(V) permeate concentration started
to increase. Interestingly, an increase in normalized As(V) concen-
tration was rapid in the case of the μTMF pre-deposited layer after
0.8 L cm
specic throughput volume (Fig. 3). This can be
ascribed to the fact that the adsorption process is restricted to
Figure 3. Normalized permeate concentrations of As(V) as a function of
specic throughput volume by primary MF membrane and pre-deposited
DM adsorber formed of μGFH and μTMF at 125 L m
, amount of
adsorbent at 10.4 mg cm
, feed As(V) concentration =380 μgL
and pH 8.
Pre-deposited dynamic membrane adsorber
J Chem Technol Biotechnol 2021 © 2021 The Authors.
Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).
the number of available active sites on the adsorbent surface. As
the process continues, the more active sites are more rapidly con-
sumed in the case of μTMF as compared to μGFH and thus, at the
nal stage of the process, remaining active sites of μTMF were
consumed by As(V) at a faster rate than μGFH. Moreover, the
adsorption capacity of μTMF is smaller than μGFH, due to which
recorded normalized concentration of As(V) 1 has occurred at
the end of the experiment (~0.9 in the case of μGFH) when spe-
cic throughput volume was 1.25 L cm
. Moreover, the repro-
ducibility of the pre-deposited DMs was also tested in order to
increase the acceptability of these lters in water treatment, and
the As(V) removal rates for the two developed DM adsorbers were
nearly identical under the same operating conditions (Supporting
Information Fig. S4).
The presented results indicate that the lifetime of the pre-
deposited DM adsorber largely depends on the type of pre-
depositing material, micro-pores and particle size of the depos-
ited material as well as on the specic surface area, which deter-
mines the number of active energy sites and the accessibility of
the pollutant to the adsorbent material.
Mathematical modeling of As(V) removal rates in a
dynamic membrane adsorber
The Freundlich constants (K
and n) and D
values are based on
our previous batch adsorption experiments.
Freundlich parame-
ters were derived from batch adsorption equilibrium, whereas D
values were determined by tting the kinetic data derived from
batch adsorption kinetic experiments in the slurry reactor setup
with model solution. The values of Freundlich parameters for
μGFH adsorption are K
=4.5 μgmg
and n=0.268. In the case
of μTMF adsorption, the values of K
and nare 3.5 μgmg
n=0.249, respectively. At an applied As(V) concentration
380 μgL
and pH 8, adsorption loadings determined through
batch isotherm equilibrium tests in deionized water were found
to be 22.4 and 15.4 μgmg
for μGFH and μTMF, respectively.
The values of adsorption equilibrium parameters and D
are used
as inputs to mathematically model As(V) removal rates.
The optimum k
values are evaluated through a constant opti-
mization procedure until the sum of square of error (SSE,
Eqn (3)) is minimized. The SSE reects the bias between the
experimental and the simulated results. An SSE value close to
zero describes the low bias, whereas larger values indicate rela-
tively higher bias between the experimental data and model
Sum of square of error=
Cmodel iðÞCexperiment iðÞ
Figure 4 shows permeate As(V) concentration proles along
with the model predictions expressed as C/C
over the ltration
time. This gure shows the model t to the experimental data,
which is considered to be satisfactory, evidenced from the high
correlation (R
) values and SSE values <1 (Table 2).
The measured model parameters at varying operating condi-
tions are provided in Table 2. Using the D
values determined at
an As(V) concentration of 380 μgL
and the same pH in deio-
nized water, it is evident that the model can accurately predict
the As(V) removal rates at varying amounts of adsorbent material
pre-deposited per unit area of primary membrane and membrane
uxes, which determine the contact time between the adsorbent
pre-deposited layer and feed water. This is most likely due to the
same concentration of As(V) applied in batch and continuous
mode experiments. However, at a lower feed As(V) concentration
of 190 μgL
, the model simulations slightly over-predict the As
Figure 4. Experiments versus model prediction of As(V) removal rates
representing inuence of (A) amount of μTMF and μGFH pre-deposited
per unit area of primary membrane at water ux =125 L m
, feed
As(V) concentration =380 μgL
and pH =8; (B) membrane water
ux for μGFH pre-deposited DM adsorber at adsorbent dose (M
10.4 mg cm
, feed As(V) concentration =380 μgL
and pH =8; (C) feed
As(V) concentration onto μTMF pre-deposited DM adsorber at adsorbent
dose (M
)=10.4 mg cm
, water ux =125 L m
and pH 8. Solid
symbols reect experimental data points, whereas model predictions are
represented by solid lines under corresponding operating conditions. M Usman et al. © 2021 The Authors.
Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).
J Chem Technol Biotechnol 2021
(V) removal rates, as evidenced by low correlation coefcient (R
and high SSE values.
The tted k
values decreased signicantly with decreasing
membrane ux for both adsorbent materials. Since the lter
velocity has a direct inuence on the boundary layer thickness,
the lm diffusion rate was reduced with decreasing membrane
ux. Moreover, the k
values were found to be higher for μGFH
than μTMF under the same operating conditions. Large tted k
values for μGFH might be due to its higher adsorption loading
towards As(V) than μTMF. These ndings are consistent with pre-
vious studies,
in which larger k
values for adsorbents were
achieved with higher adsorbent capacity, during adsorption of
nitrate onto commercially available and laboratory-prepared
anion exchange resins in an adsorptionmembrane hybrid pro-
cess. A higher mass transfer at the external surface of the material
provides a higher degree of adsorption for the target pollutant.
For the lower feed As(V) concentration of 190 μgL
, data in
Table 2 show that the SSE value was 0.142 for μGFH and 0.169
for μTMF, demonstrating that the mathematical model is fairly
consistent with the experimental data but unable to describe
accurately the experimentally determined As(V) removal rates.
The possible reason for higher SSE values between experimental
and model results at different feed As(V) concentrations could
be that the D
value applied in the modeling approach was deter-
mined at the higher As(V) concentration of 380 μgL
in batch
mode experiments. When optimum values of D
and k
are applied
in the modeling approach, a strong agreement was observed, as
indicated by improved goodness-of-t parameters (R
=0. 99
and SSE =0.043 for μGFH pre-deposited DM adsorber and
=0.996 and SSE =0.028 for μTMF pre-deposited DM adsorber).
Several model simulations are shown in Fig. 5 employing values of
up to an order of magnitude lower. As can be clearly seen,
model simulations captured the experimental data points much
better when the tted values of D
were decreased from
2.26 ×10
to 1 ×10
and from 1.09 ×10
0.9 ×10
for μTMF and μGFH, respectively. The variation
in D
values might be due to dependence on the surface loadings.
dependence may exist for energetically heterogeneous adsor-
bents such as μGFH and μTMF, and could be explicated by the
reduced adsorption energy with increasing surface loading that
results in increased adsorbate mobility.
In summary, the presented results indicate that a pre-deposited
DM adsorber can be developed by pre-deposition of variable
amounts of the powdered-sized fractions of applied adsorbents
Table 2. Measured model parameters under varying operational conditions
Water ux
(L m
(mg cm
Volume of
treated (L)
Final As(V)
concentration C/
μGFH 31 10.4 380 9 0.15 1.09 0.3 0.963 0.016
62.5 10.4 380 18 0.67 1.09 1.0 0.995 0.042
125 10.4 380 36 0.87 1.09 1.7 0.998 0.031
125 14.0 380 36 0.83 1.09 1.6 0.993 0.027
125 10.4 190 36 0.77 1.09 1.0 0.977 0.142
μTMF 31 10.4 380 9 0.21 2.26 0.07 0.980 0.019
62.5 10.4 380 18 0.85 2.26 0.2 0.995 0.046
125 10.4 380 36 0.98 2.26 1.0 0.998 0.029
125 14.0 380 36 0.95 2.26 1.0 0.994 0.054
125 10.4 190 36 0.90 2.26 0.3 0.974 0.169
is the amount of pre-deposited adsorbent material per unit area of the primary membrane.
Figure 5. Model simulations of normalized As(V) concentrations employ-
ing different values of D
for (A) μTMF pre-deposited DM adsorber;
(B) μGFH pre-deposited DM adsorber at adsorbent dose (M
10.4 mg cm
, water ux =125 L m
and pH 8.
Pre-deposited dynamic membrane adsorber
J Chem Technol Biotechnol 2021 © 2021 The Authors.
Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).
on the primary membrane surface, which reveals that it is possible
to regulate the thickness of the DM lter to treat the arsenic-pol-
luted waters and achieve an As(V) removal efciency of >90%,
which corresponds to C/C
=0.1, as long as the best operating
conditions such as lowermost membrane ux of 31 L m
and higher amount of pre-deposited adsorbent per unit area of
primary membrane (14 mg cm
) were provided. Further, a
higher ux governing shorter contact time has signicantly
improved the As(V) ux through the stagnant boundary layer sur-
rounding an adsorbent particle, as indicated by large k
values. A
respective increase of one and two orders of magnitude for μGFH
and μTMF pre-deposited DM adsorber was computed when
membrane ux was increased from 31 to 125 L m
. Hence it
can be concluded that k
is related directly to the membrane
water ux (contact time). Conversely, the surface diffusion coef-
cient (D
) value is unique and not a function of membrane water
ux and amount of adsorbent applied for DM lter formation,
but is a function of feed As(V) concentration. We therefore pro-
pose investigating the effect of As(V) concentration on the D
values to derive the relationship between As(V) concentration
and D
values to increase the acceptability of the applied mathe-
matical model in the real water treatment system.
In this work, the size of individual adsorbent particle-forming
DM adsorbers are signicantly larger (one order of magnitude)
than the primary membrane pores. Therefore, the pore size of
the primary membrane is not anticipated to have a substantial
inuence on formation of the pre-deposited DM lter. However,
more investigations are proposed to study the effect of the
depositing particles on the surface morphology and strength of
the primary membrane. These investigations would provide more
insights into the repeating use of the primary membrane for for-
mation and deformation of the DM lter.
Operating pressure
Long-term variations in operating pressure were monitored using
a signal-conditioned pressure gauge. A stable operating pressure
was recorded for 100 h constant ux dead-end ow experiments
(data not shown here). This was possibly due to ltration of
organic-free feed water. The operating pressure was in the range
of 618 mbar for μTMF pre-deposited DM adsorber at
=10.4 mg cm
, while for μGFH pre-deposited DM adsorber
the range of operating pressure was 410.5 mbar (Figure 6). The
operating pressure was higher for the higher water ux. This trend
was attributed to the compression of deposited adsorbent cake
layer on the membrane surface at higher membrane ux.
trend was almost linear to the permeate water ux. At a higher
of 14 mg cm
, the operating pressure was 20 and 12 mbar
for μTMF and μGFH pre-deposited DM adsorber, respectively. This
is explained by a large volume of deposited cake layer on the sur-
face of the primary MF membrane, which offers greater resistance
to water owing through the cake layer.
The operating pressures recorded for μGFH pre-deposited DM
adsorber at all water uxes were low when compared to μGFH
pre-deposited DM adsorber possibly due to a lower volume of
adsorbent cake layer (0.2 mL μGFH vs. 0.7 mL μTMF at
=10.4 mg cm
Performance comparison of pre-deposited DM adsorber
The adsorption capacity of the powdered-sized adsorbents
applied as pre-depositing materials for the formation of DM
adsorber was calculated by integrating the breakthrough curve
until C/C
=1 (referred to as Q
) at a water ux of
125 L m
and adsorbent dosage of 10.4 mg cm
. The calcu-
lated Q
value of μGFH recorded through continuous-ow pre-
deposited DM adsorber is 22.8 μg As(V) mg
, while the Q
of μTMF is 15.8 μg As(V) mg
. Similar Q
values of μGFH and
μTMF for As(V) were calculated when As(V) adsorption onto pow-
dered-sized μGFH and μTMF in a slurry reactor was combined with
MF at the same pH 8 (Fig. 7).
In our previous study, the As(V) adsorption capacities of pow-
dered-sized μGFH and μTMF were estimated to be 22.4 μgAs
(V) mg
and 15.4 μg As(V) mg
, respectively, which were deter-
mined through batch adsorption equilibrium experiments at a
residual concentration of 380 μgL
and at pH 8. It can be con-
cluded that adsorption capacities of powdered-sized μGFH and
μTMF are the same when applied in three different experimental
setups (Fig. 7).
For the applied iron oxide-based adsorptive materials, the As(V)
adsorption capacities and bed volume treated (equivalent to a
volume of water treated) the different water uxes studied and
Figure 7. As(V) adsorption capacities achieved through pre-deposited
DM adsorber compared to the adsorption capacities by the Freundlich iso-
therm model (obtained through batch adsorption experiments) and
adsorption of As(V) onto micro-sized iron oxide-based adsorbents (μGFH
and μTMF) in the slurry reactor of adsorptionMF hybrid system at
=380 μgL
and pH 8.
Figure 6. Operating pressure for the μGFH and μTMF pre-deposited DM
lter at M
=10.4 mg cm
. M Usman et al. © 2021 The Authors.
Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).
J Chem Technol Biotechnol 2021
amount adsorbed applied to develop a DM adsorber are summa-
rized in Table 3. The results demonstrate increasing As(V) adsorp-
tion capacities and bed volumes treated at decreasing water ux,
which is explained by increasing contact time between adsorbent
cake layer and As(V) species. Similarly, improved As(V) adsorption
capacities were estimated at larger adsorbent dosages, which is
attributed to a large number of available adsorption sites at
higher M
=14 mg cm
relative to M
=10.4 mg cm
. These
observations lead to the conclusion that implementing lower-
most water ux (31 L m
) and large amounts of adsorptive
materials (M
=14 mg cm
) to form pre-deposited DM adsorber
are benecial in treating As(V)-contaminated waters.
The adsorption capacities of powdered-sized μGFH and μTMF
acquired through a pre-deposited DM lter can be compared with
similar studies employing highly efcient commercial adsorbents
for As(V) removal from water.
Although these studies
have been executed under different experimental conditions
(e.g. water matrix, inuent As(V) concentration, pH and experi-
mental setup), so the results of these studies cannot be directly
compared. However, when the As(V) adsorption capacities and
bed volumes treated are compared (Table 3), the studied pow-
dered-sized iron oxide-based adsorptive materials are superior
in remediating As(V) contaminated water even at very little con-
tact time (7 and 2 s for μTMF and μGFH, respectively, because of
extremely fast As(V) adsorption kinetics.
In this study, a pre-deposited DM adsorber was developed in situ
at low pressure (0.5 bar) by depositing the powdered-sized frac-
tions of iron oxide-based adsorbents on the primary MF mem-
brane, wherein the adsorbent deposited layer has acted as an
adsorptive ltration barrier to remove As(V) from water applied
in the MF process under varying operating conditions. Experimen-
tally determined As(V) removal rates were described by a mathe-
matical model incorporating surface diffusion and external lm
diffusion. The main ndings are as follows:
(1) Applied adsorbents with individual particle size in the range
of 23μm were pre-deposited on the primary MF membrane
to form a DM adsorber. The developed pre-deposited DM
Table 3. Comparison of adsorption capacities of some adsorbents for As(V) reported in the literature with the adsorption capacities evaluated in this
work (pH is shown in parentheses where reported)
Material Type of experiment Operating conditions Bed volumes treated at C/C
at C/C
=0.1 Reference
GFH Lab-scale column
Arizona groundwater
As(V) =100 μgL
pH =8.6,
Mass of GFH =2.78 g
3 000 at EBCT =0.5 min
8 000 at EBCT =2.5 min
11 000 at EBCT =4.0 min
Westerhoff et
Lab-scale column
As(V) =400 μgL
pH =8.2,
EBCT =1.1 min
1 500 Cui et al.
Lab-scale column
As(V) =100 μgL
pH =7.3,
EBCT =1.2 min,
mass of bayoxide =8g
3.09 Tresintsi et
μTMF Pre-deposited DM
Synthetic water
As(V) =380 μgL
pH =8.0,
=10.4 mg cm
7 560 at 125 L m
(EBCT =7s)
9 050 at 62.5 L m
(EBCT =14 s)
9 900 at 31 L m
(EBCT =28 s)
This work
μTMF Pre-deposited DM
Synthetic water
As(V) =380 μgL
pH =8.0,
=14 mg cm
9 450 at125 L m
(EBCT =7 s) 8.12 This work
μGFH Pre-deposited DM
Synthetic water
As(V) =380 μgL
pH =8.0,
=10.4 mg cm
14 400 at 125 L m
(EBCT =2s)
21 600 at 62.5 L m
(EBCT =4s)
36 450 at 31 L m
(EBCT =8s)
This work
μGF Pre-deposited DM
Synthetic water
As(V) =380 μgL
pH =8.0,
=14 mg cm
22 320 at 125 L m
(EBCT =2 s) 5.19 This work
ECBT is the empty-bed contact time and expressed as adsorbent bed volume to the ow rate.
is the adsorbent dose, expressed as amount of adsorptive material deposited per unit area of the primary MF membrane.
Pre-deposited dynamic membrane adsorber
J Chem Technol Biotechnol 2021 © 2021 The Authors.
Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).
adsorber shows remarkable As(V) removal efciencies (as high
as ~99%) with excellent reproducibility.
(2) μGFH and μTMF proved to be promising as emerging pre-
depositing material for a DM lter and equally good for appli-
cation in water treatment systems targeting As(V) removal.
(3) Parametric study indicates that As(V) removal rates of pre-
deposited DM adsorbers can be controlled by changing the
membrane water ux and amount of pre-depositing material
per unit area of the primary membrane. Longer times of 90%
As(V) removal can be achieved by increasing pre-depositing
material over the primary membrane and lowering mem-
brane water ux.
(4) As(V) removal rates of a pre-deposited DM adsorber can be
accurately predicted using the applied mathematical model
relying on the HSDM.
(5) The surface diffusion parameter of the HSDM can be consid-
ered as independent of membrane water ux and the amount
of applied adsorbents used to form pre-deposited DM
(6) Under the same operating conditions, the magnitude of the
mass transfer due to external lm diffusion was affected by
the type of adsorbent material having different As(V) adsorp-
tion capacities. The k
value was linearly related to the adsorp-
tion capacity of applied adsorbent material towards As(V).
(7) Low-pressure DM ltration technology is a sustainable and
practicable approach that can be applied to remediation of
arsenic-contaminated waters. The DM ltration technology
may be further extended with repeated use of the exhausted
iron oxide-based adsorbent materials to reduce the quantity
of produced waste for environmental sustainability and to
obtain more information on practical applications.
The authors are obliged to the German Academic Exchange
Service (DAAD) for the fellowship of Mr Usman and the Hamburg
University of Technology for resources. Professor Mitrakas,
Department of Chemical Engineering, Aristotle University of Thes-
saloniki, Greece, and GEH Wasserchemie GmbH & Co., Osnabrück,
Germany, are thanked for offering tetravalent manganese feroxy-
hyte and the micro-sized granular ferric hydroxide materials for
the purposes of research. Open access funding enabled and orga-
nized by Projekt DEAL.
The authors declare no conict of interest.
Supporting information may be found in the online version of this
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... However, scientific progress has expanded notice of water contaminant types and reawakened the necessity for comprehensive water treatment. Oxyanions (or oxoanions) (As, V, B, W, and Mo) are formed by a number of redox-sensitive metalloids and metals, including titanium dioxide, iron oxides, manganese dioxide, aluminum oxides, and numerous oxide minerals [14,15]. Due to their toxicity, non-degradability, and movement in aquatic habitats, these species are detrimental to living organisms. ...
... Materials 2022,15, 5392 ...
Full-text available
Water contamination is one of the most urgent concerns confronting the world today. Heavy metal poisoning of aquatic systems has piqued the interest of various researchers due to the high toxicity and carcinogenic consequences it has on living organisms. Due to their exceptional attributes such as strong reactivity, huge surface area, and outstanding mechanical properties, nanomaterials are being produced and employed in water treatment. In this review, recent advances in the use of nanomaterials in nanoadsorptive membrane systems for wastewater treatment and heavy metal removal are extensively discussed. These materials include carbon-based nanostructures, metal nanoparticles, metal oxide nanoparticles, nanocomposites, and layered double hydroxide-based compounds. Furthermore, the relevant properties of the nanostructures and the implications on their performance for water treatment and contamination removal are highlighted. The hydrophilicity, pore size, skin thickness, porosity, and surface roughness of these nanostructures can help the water permeability of the nanoadsorptive membrane. Other properties such as surface charge modification and mechanical strength can improve the metal adsorption effectiveness of nanoadsorptive membranes during wastewater treatment. Various nanocomposite membrane fabrication techniques are also reviewed. This study is important because it gives important information on the roles of nanomaterials and nanostructures in heavy metal removal and wastewater treatment.
... Some of these adsorbents are as follows: an aluminium mining by-product (4.51 mg/g) [37], PBGC-Fe/C (4.83 mg/g) [20], organo-modified natural zeolite materials (6.7 mg/g) [38], biochar-magnetite composite (5.49 mg/g) [14], Chinese red soil (0.936 mg/g) [39], iron-coated seaweeds (7.3 mg/g) [40], goethite-P (AAm) composite (1.22 mg/g) [13], iron-oxide-based adsorbents μGFH (22.4 mg/g) and μTMF (15.4 mg/g) [41], Fe-sericite composite beads (5.78 mg/g) [42], and red mud-modified biochar (5.923 mg/g) [43]. ...
... Some of these adsorbents are as follows: an aluminium mining by-product (4.51 mg/g) [37], PBGC-Fe/C (4.83 mg/g) [20], organo-modified natural zeolite materials (6.7 mg/g) [38], biochar-magnetite composite (5.49 mg/g) [14], Chinese red soil (0.936 mg/g) [39], ironcoated seaweeds (7.3 mg/g) [40], goethite-P (AAm) composite (1.22 mg/g) [13], iron-oxidebased adsorbents µGFH (22.4 mg/g) and µTMF (15.4 mg/g) [41], Fe-sericite composite beads (5.78 mg/g) [42], and red mud-modified biochar (5.923 mg/g) [43]. ...
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Arsenic (As(V)), a highly toxic metalloid, is known to contaminate wastewater and groundwater and is difficult to degrade in nature. However, the development of highly efficient adsorbents, at a low cost for use in practical applications, remains highly challenging. Thus, to investigate the As(V) adsorption mechanism, a novel porous α-Fe2O3/Fe3O4/C composite (PC-Fe/C-B) was prepared, using bamboo side shoots as a bio-template, and the breakthrough performance of the PC-Fe/C-B composite-packed fixed-bed column in As(V) removal was evaluated, using simulated wastewater. The PC-Fe/C-B material accurately retained the hierarchical porous microstructure of the bamboo bio-templates, and the results demonstrated the great potential of PC-Fe/C-B composite, as an effective adsorbent for removing As(V) from wastewater, under the optimal experimental conditions of: influent flow 5.136 mL/min, pH 3, As(V) concentration 20 mg/L, adsorbent particle size < 0.149 mm, adsorption temperature 35 °C, PC-Fe/C-B dose 0.5 g, and breakthrough time 50 min (184 BV), with qe,exp of 21.0 mg/g in the fixed-bed-column system. The CD-MUSIC model was effectively coupled with the transport model, using PHREEQC software, to simulate the reactive transportation of As(V) in the fixed-bed column and to predict the breakthrough curve for column adsorption.
... Mathematical models have been widely used to estimate the dynamics of the operation of a GAC column. Specifically, Homogeneous Surface Diffusion Model (HSDM), which has been applied in studies with several pollutants providing reliable information that reproduces the operation of a column of Full-scale [31][32][33][34][35][36]. The model considers the adsorption process occurring in two sequential diffusion steps, namely: diffusion through the stationary fluid layer surrounding the adsorbent particle (film diffusion) and diffusion through the internal pores of the adsorbent (surface diffusion). ...
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Climate change and the increase in the availability of nutrients in aquatic environments have increased the occurrence of cyanobacterial blooms which can produce cyanotoxins such as cylindrospermopsin (CYN). Activated carbon adsorption have been proved to be efficient for CYN removal. In the present study, a carbon with high CYN adsorption capacity was identified between two granular activated carbons. For this carbon was estimated the operating time of a full-scale granular activated carbon column under different empty bed contact times (EBCT). The fixed-bed breakthrough was estimated using the Homogeneous Surface Diffusion Model (HSDM). Wood carbon showed greater capacity to remove CYN. The experimental equilibrium data best fitted Langmuir isotherm model, in which wood carbon had a maximum adsorption capacity of 3.67 μg/mg and Langmuir adsorption constant of 0.2791 L/μg. The methodology produced satisfactory results where the HSDM simulated the fixed-bed breakthrough with a coefficient of determination of 0.89, to the film diffusion coefficient (Kf) of 9 × 10−6 m/s and surface diffusion coefficient (Ds) of 3 × 10−16 m2/s. It was observed that the increase in EBCT promotes a reduction in the carbon use rate. The best carbon use rate found was 0.43 kg/m3 for a EBCT of 10 min and breakthrough time of 183.6 h
... 31/2001). Among the 6 adsorbents used with the synthetic solution, this series of tests was conducted using only TiO 2 , A33E and GFH, since they are reported to possess a high removal capability versus arsenic in liquid solutions [21,25,[27][28][29][30][31]. Under real conditions of application, there would be the need to reduce both fluoride and arsenic concentrations below the respective limits. ...
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The fluoride removal capability of six different adsorbents (four commercial, i.e., titanium dioxide-TiO2, ArsenXPnp-A33E, granular activated carbon (GAC) and granular ferric hydroxide (GFH), and two laboratory media, i.e., nano-fine media and nano-granular media) was determined under batch conditions using synthetic and real contaminated water containing arsenic and vanadium. The kinetic and equilibrium characteristics of the adsorption process under different operating conditions (pH value, initial fluoride concentration, adsorbent dosage, water composition) were obtained. Among the tested adsorbents, TiO2 showed the highest adsorption capacity; it was also capable of reducing fluoride concentration below the limit set for drinking water without pH control. TiO2 still remained the best adsorbent in the treatment of real contaminated groundwater, where it was also capable of efficiently removing both arsenic and vanadium. The other adsorbents were capable of achieving the same fluoride reduction, although only for acid pH. The nano-sized laboratory media showed an adsorption removal efficiency below that of TiO2 but superior to that of A33E, GAC and GFH. Among the investigated parameters, the removal efficiency was mainly affected by adsorbent dosage and pH. The pseudo-second order model best fitted the kinetic experimental data of all the media. The maximum adsorption capacity predicted by this model was in the following decreasing order: TiO2 > A33E > GAC > GFH. The removal capability of all the media drastically decreased due to the presence of competitive ions and unfavorable pH conditions. The best isotherm model changed depending on the type of adsorbent and pH conditions.
... The adsorption phenomena of MO can be studied from a kinetic point of view; the experimental data concerning the adsorbed quantity of the pollutant as a function of the contact time variation are important because they provide us additional information on mass transfer resistance. During biosorption, the transfer of adsorbing metal ions takes place from the fluid phase to the active sites of the biosorbents take place in four chronological phases (Worch 2012;Usman et al. 2020bUsman et al. , 2021 as illustrated in Fig. 10. These four chronological phases of adsorption kinetic are a) Transport of metal ion from the solution to the stagnant (boundary) layer enveloping the discrete particle of the biomaterial b) Transfer of metal ions across the boundary layer to the biosorbent's surface. ...
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The increasing demand for using competent and inexpensive methods based on biomaterials, like adsorption and biosorption, has given rise to low-priced alternative biosorbents. In the past few years, Moringa oleifera (MO) has emerged as a green and low-priced biosorbent for the treatment of contaminated waters with heavy metals and dyes, and given its availability, we can create another generation of effective biosorbents based on different parts of this plant. In this review paper, we have briefed on the application of MO as a miraculous biosorbent for water purification. Moreover, the primary and cutting-edge methods for the purification and modification of MO to improve its adsorption are discussed. It was found that MO has abundant availability in the regions where it is grown, and simple chemical treatments increase the effectiveness of this plant in the treatment of some toxic contaminants. The different parts of this miraculous plant’s “seeds, leaves, or even husks” in their natural form also possess appreciable sorption capacities, high efficiency for treating low metal concentrations, and rapid adsorption kinetics. Thus, the advantages and disadvantages of different parts of MO as biosorbent, the conditions favorable to this biosorption, also, the proposal of a logical mechanism, which can justify the high efficiency of this plant, are discussed in this review. Finally, several conclusions have been drawn from some important works and which are examined in this review, and future suggestions are proposed.
... Iron-based oxide/hydroxides [10] and ozone [8] are used by oxidizing agents, and electrocoagulation is a selective method [11] for removing As (III). Particularly, porous membranes, hybrid membranes processes, electrocoagulation, and adsorption assisted membrane systems have proven to be effective for arsenate adsorption in addition to iron oxyhydroxides adsorption [12][13][14][15]. However, due to the additional energy required to filter coagulants rich in As to purify water, it is not practical for use in developing nations [8,9]. ...
Full-text available
In recent decades, the removal of hazardous chemicals that have entered wastewater and groundwater as a result of industrial and consumer activities has become an issue of concern. Specifically, removing arsenic (III) from groundwater is critical and equally crucial in the use of low-cost, efficient adsorbent materials. One purpose of this study was to develop a low-cost hydroxyapatite adsorbent (Ca5(PO4)3OH) by reacting the Ca component of calcined dolomite with phosphorus, and another was to apply the developed adsorbent to remove arsenic (III) from well water in developing countries. In this study, phosphorus adsorption was performed on thermally calcined dolomite, and the adsorption isotherm of the phosphorus study was investigated on selected calcined dolomite. The maximum amount of phosphorus on the selected calcined dolomite was 194.03 mg-P/g, and the Langmuir isotherm model was fitted. Arsenic (III) adsorption was investigated in a wide pH range (pH 2~12) using the new adsorbent. The amount of arsenic (III) adsorbed was 4.3 mg/g. The new absorbent could be effective in removing arsenic (III) and become an affordable material.
Pre-deposited dynamic membrane (DM) has been widely applied in filtration processes, yet the microscale quantitative analysis of DM particles deposition and resuspension has not been studied. In this study, the fundamental physics of DM particles deposition and resuspension on the support filter surface in a channel is numerically revealed by a user-defined solver via combining the Discrete Element Method with Lattice Boltzmann Method (LBM-DEM). After comprehensive model validations in terms of a single sphere sedimentation and two spheres sedimentation in water, the effect of particle mass proportion, particle size, and fluid inlet velocity on DM particles deposition on support filter surface is studied. A critical and a threshold particle mass proportion and fluid inlet velocity are identified under the given conditions. Furthermore, the impact of dynamic membrane thickness (L) and backwash velocity (Vf,b) on DM particles resuspension from support filter surface is explored. The time required for DM complete resuspension is correlated as a function of L and Vf,b. The proposed correlation is then verified against the empirical correlations in the open literature, demonstrating its reasonability in predicting DM particles behaviours during the backwashing. The microscale findings guide the design and optimization of dynamic membranes.
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Heavy metal pollution represents an urgent worldwide problem due to the increasing number of its sources; it derives both from industrial, e.g., mining, metallurgical, incineration, etc., and agricultural sources, e.g., pesticide and fertilizer use. Features of membrane technology are the absence of phase change or chemical additives, modularity and easy scale-up, simplicity in concept and operation, energy efficiency, and small process footprint. Therefore, if membrane technology is coupled to adsorption technology, one of the most effective treatment strategies to remove heavy metals, namely, Adsorptive Membrane Technology, many typical disadvantages of traditional processes to remove heavy metals, such as low-quality treated water, excessive toxic sludge production, which requires further treatment, can be overcome. In this review, after a broad introduction on the relevance of heavy metal removal and the methods used, a thorough analysis of adsorptive membrane technology is given in terms of strategies to immobilize the adsorbents onto/into membranes and materials used. Regarding this latter aspect, the impressive number of papers present in the literature on the topic has been categorized into five types of adsorptive membranes, i.e., bio-based, bio-inspired, inorganic, functionalized, and MMMs.
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Biomass waste has known as a new precursor for the production of carbon-based materials due to its carbon richness, low cost, ease to access, ubiquitous, renewable and environmental-friendliness. In this publication, the study on the availability of biomass waste and the carbon-based materials (CBMs) for wastewater treatment application is reviewed and addressed. This paper discussed several types of CBMs such as activated carbon, graphene, carbon nanotubes, biochar, and carbon aerogel. The production of these different CBMs and their modification are given special attention. As harmful organic, dyes, and inorganic pollutants emerging from the wastewater has caused damage to the environment and water supplies, adsorption is the most widely utilised conventional technology for the removal of hazardous pollutants due to its ease of use and relatively cheap in comparison with other emerging methods. This corresponds to the CBMs which mainly works on the adsorption mechanism to perform the wastewater treatment. There are three kinds of biomass waste being explained which are sewage sludge, lignocellulosic, and cotton-based waste. This paper also extensively summarised a multitude of aspects regarding the biomass waste and the CBMs derivation from biomass waste. The challenges on the synthesis of CBMs from biomass was also included. In summary, the conclusion and future direction of the research were also discussed.
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Owing to environmental pollution and increasingly strict regulations, heavy metals have attracted the attention of many researchers in various disciplines. Alginate and chitosan derivatives have gained popularity as biosorbents for water treatment. An increase in the number of publications on modified biosorbents for the biosorption of toxic compounds reveals widespread interest in examining the requirements and positive contribution of each modification type. This paper reviews the advantages and disadvantages of using alginate and chitosan for adsorption. Well-known modifications based on chitosan and alginate, namely, grafting, functionalization, copolymerization and cross-linking, as well as applications in the field of adsorption processes, especially amino acid functionalization, are reviewed. The selection criteria for the best biosorbents and their effectiveness and proposed mechanism of adsorption are discussed critically. In the conclusion, the question of why these adsorbents need modification before use is addressed.
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Threats due to insufficient, inadequate and costlier methods of treating contaminants such as arsenic have emphasized the significance of optimizing and managing the processes adopted. This study was aimed at the complete elimination of arsenic from an aqueous medium with minimum energy consumption using the electrocoagulation process. Arsenic removal around 95% was rapidly attained for optimized conditions having a pH of 7, 0.46 A current intensity, 10 mg/L initial concentration and only 2 min of applied time duration using the energy of 3.1 watt-hour per gram of arsenic removed. Low values of applied current for longer durations resulted in the complete removal of arsenic with low energy consumption. Various hydroxide complexes including ferrous hydroxide and ferric hydroxide assisted in the removal of arsenic by adsorption along with co-precipitation. Surface models obtained were checked and found with a reasonably good fit having high values of coefficient of determination of 0.933 and 0.980 for removal efficiency and energy consumption, respectively. Adsorption was found to follow pseudo-first-order kinetics. Multivariate optimization proved it as a low-cost effective technology having an operational cost of 0.0974 Indian rupees (equivalent to USD 0.0013) per gram removal of arsenic. Overall, the process was well optimized using CCD based on response surface methodology.
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Granular ferric hydroxide (GFH) is often used for fixed bed adsorbent (FBA) columns in groundwater purification units around the world to remove arsenate contaminations. Groundwater can contain also other toxic (e.g., antimonite and vanadate) and non-toxic oxo-anions (phosphate and silicic acid) that are known to affect FBA lifetimes. Therefore, understanding the breakthrough of toxic compounds intended for removal by FBA is essential to their design, and is important to predict accurately breakthrough curves (BTCs) for FBAs in waterworks to plan future operating costs. Rapid small-scale column tests (RSCCT) and pilot-scale FBA were used to simulate vanadate BTCs for complex groundwater chemistries. The BTCs were simulated successfully using a homogeneous surface diffusion model (HSDM) combining equilibrium chemical adsorption and kinetic mass transfer. Adsorption parameters for various groundwater compositions were predicted using the CD-MUSIC surface complexation model, which was set up for the first time for akaganéite-based granular ferric hydroxide with a competitive multi-solute system. The results indicated that V(V) is less prone to competitive adsorption effects, and use of the homogeneous surface diffusion model to predict the BTCs requires then the kinetic mass transfer Biot number to be used as the only fitting parameter. On the other hand, a concentration overshoot could be observed for the two weaker absorbed oxo-anions arsenate and phosphate because of displacement by the vanadate. Results of pilot scale test column BTCs of vanadate for three waterworks with different groundwater compositions could be favorably extrapolated with a unique Freundlich constant kF of 3.2 derived on basis of the multi-solute CD-MUSIC model, and a unique Biot number of 37 fixed for all three different test sites.
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The adsorption of arsenic (V), As(V), on two porous iron oxyhydroxide-based adsorbents, namely, micro-sized tetravalent manganese feroxyhyte (µTMF) and granular ferric hydroxide (µGFH), applied in a submerged microfiltration membrane hybrid system has been investigated and modeled. Batch adsorption tests were carried out to determine adsorption equilibrium and kinetics parameters of As(V) in a bench-scale slurry reactor setup. A mathematical model has been developed to describe the kinetic data as well as to predict the As(V) breakthrough curves in the hybrid system based on the homogeneous surface diffusion model (HSDM) and the corresponding solute mass balance equation. The kinetic parameters describing the mass transfer resistance due to intraparticle surface diffusion (Ds) involved in the HSDM was determined. The fitted Ds values for the smaller (1 - 63 μm) and larger (1 - 250 μm) diameter particles of µGFH and μTMF were estimated to be 1.09 × 10-18 m2/s and 1.53 × 10-16 m2/s, and 2.26 × 10-18 m2/s and 1.01 × 10-16 m2/s, respectively. The estimated values of mass transfer coefficient/ kinetic parameters are then applied in the developed model to predict the As(V) concentration profiles in the effluent of the hybrid membrane system. The predicted results were compared with experimental data for As(V) removal and showed an excellent agreement. After validation at varying adsorbent doses and membrane fluxes, the developed mathematical model was used to predict the influence of different operation conditions on As(V) effluent concentration profile. The model simulations also exhibit that the hybrid system benefits from increasing the amount of adsorbent initially dosed and from decreasing the membrane flux (increasing the contact time).
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Groundwater contaminated with geogenic arsenic (As) is frequently used as drinking water in Burkina Faso, despite adverse health effects. This study focused on testing low-cost filter systems based on zero-valent iron (ZVI), which have not yet been explored in West Africa for As removal. The active ZVI bed was constructed using small-sized iron nails, embedded between sand layers. Household filters were tested for nine months in a remote village relying on tube well water with As concentrations of 400–1350 μg/L. Daily filtered volumes were 40–60 L, with flow rates of ~10 L/h. In parallel, downscaled laboratory filter columns were run to find the best set-up for optimal As removal, with special attention given to the influence of input pH, flow rate and water/nail contact time. Arsenic removal efficiencies in the field were 60–80% in the first six months of operation. The laboratory experiments revealed that trapped air in the nail layer greatly lowered As removal due to preferential flow and decreased water/nail contact time. Measures taken to avoid trapped air led to a partial improvement in the field filters, but effluent As remained >50 μg/L. Similar structural modifications were however very successful in the laboratory columns, where As removal efficiencies were consistently >95% and effluent concentrations frequently <10 μg/L, despite inflow As >1000 μg/L. A constantly saturated nail bed and careful flow control is necessary for optimal As removal. Slow flow and longer pauses between filtrations are important for sufficient contact times and for transformation of brown amorphous Fe-hydroxides to dense magnetite with incorporated As(V). This preliminary study has shown that nail-based filters have the potential to achieve As removal >90% in a field context if conditions (filter bed saturation, flow rate, pauses between filtrations) are well controlled.
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Arsenic is among the major drinking water contaminants affecting populations in many countries because it causes serious health problems on long-term exposure. Two low-cost micro-sized iron oxyhydroxide-based adsorbents (which are by-products of the industrial production process of granular adsorbents), namely, micro granular ferric hydroxide (μGFH) and micro tetravalent manganese feroxyhyte (μTMF), were applied in batch adsorption kinetic tests and submerged microfiltration membrane adsorption hybrid system (SMAHS) to remove pentavalent arsenic (As(V)) from modeled drinking water. The adsorbents media were characterized in terms of iron content, BET surface area, pore volume, and particle size. The results of adsorption kinetics show that initial adsorption rate of As(V) by μTMF is faster than μGFH. The SMAHS results revealed that hydraulic residence time of As(V) in the slurry reactor plays a critical role. At longer residence time, the achieved adsorption capacities at As(V) permeate concentration of 10 μg/L (WHO guideline value) are 0.95 and 1.04 μg/mg for μGFH and μTMF, respectively. At shorter residence time of ~ 3 h, μTMF was able to treat 1.4 times more volumes of arsenic-polluted water than μGFH under the optimized experimental conditions due to its fast kinetic behavior. The outcomes of this study confirm that micro-sized iron oyxhydroxides, by-products of conventional adsorbent production processes, can successfully be employed in the proposed hybrid water treatment system to achieve drinking water guideline value for arsenic, without considerable fouling of the porous membrane. Graphical abstract
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Next to the pore size distribution, surface charge is considered to be one main factor in the separation performance of ultrafiltration (UF) membranes. By applying an external surface potential onto an electro-conductive UF membrane, electrostatic induced rejection was investigated. This study introduces in a first part a relatively simple but yet not reported technology of membrane modification with direct current sputter deposition of ultrathin (15 nm) highly conductive gold layers. In a second part, characterization of the gold-coated UF flat sheet membrane with a molecular weight cut-off (MWCO) of 150 kDa is presented. Membrane parameters as contact angle (hydrophobicity), pure water permeability, MWCO, scanning electron microscopy imaging, zeta potential, surface conductivity and cyclic voltammetry of the virgin and the modified membrane are compared. Due to the coating, a high surface conductivity of 107 S m−1 was realized. Permeability of the modified membrane decreased by 40% but MWCO and contact angle remained almost unchanged. In a third part, cross-flow filtration experiments with negative charged Suwannee River Natural Organic Matter (SRNOM) are conducted at different cathodic and anodic applied potentials, different pH values (pH 4, 7, 10) and ionic strengths (0, 1, 10 mmol L−1). SRNOM rejection of not externally charged membrane was 28% in cross-flow and 5% in dead-end mode. Externally negative charged membrane (−1.5 V vs. Ag/AgCl) reached rejection of 64% which was close to the performance of commercial UF membrane with MWCO of 5 kDa. High ionic strengths or low pH of feed reduced the effect of electrostatic rejection.
Adsorption processes have played a central role in water treatment for many years but their importance is on the rise with the continuous discoveries of new micropollutants in the water cycle (pharmaceuticals for example). In addition to the classical application in drinking water treatment, other application fields are attracting increasing interest, such as wastewater treatment, groundwater remediation, treatment of landfill leachate, and so on. Based on the author's long-term experience in adsorption research, the scientific monograph treats the theoretical fundamentals of adsorption technology for water treatment from a practical perspective. It presents all the basics needed for experimental adsorption studies as well as for process modelling and adsorber design. Topics discussed in the monograph include: introduction into basic concepts and practical applications of adsorption processes; adsorbents and their characterisation, single and multi-solute adsorption equilibria, adsorption kinetics, adsorption dynamics in fixed-bed adsorbers and fixed-bed adsorber design, regeneration and reactivation of adsorbents, introduction into geosorption processes in bank filtration and groundwater recharge. According to the increasing importance of micropollutants in the water cycle, particular attention is paid to their competitive adsorption in presence of background organic matter. Clear illustrations, extensive literature references and a useful index make this work indispensible for both scientists and technicians involved in water treatment. © 2021 Walter de Gruyter GmbH, Berlin/Boston. All rights reserved.
Arsenic contamination has been widely recognized as one of the most consequential environmental pollutants due to its anthropogenic activities. Arsenic toxicity and remediation have become the focus of many institutions, including industries, environmental groups, and the general public. The treatment of arsenic contamination is of irrefutable significance to lower floras and faunas, humanity, and their living ecosystem. This review comprehensively examines different arsenic toxicities to the environment and their associated removal techniques. To begin with, the appraisal focuses on the general background of arsenic occurrences in the environment, its related health hazards, and measurement techniques. In addition, it also provides a comprehensive discussion of how arsenic impurities can be removed from the environment using diverse established and advanced technologies like adsorption, ion exchanges, electrokinetic processes, electrocoagulation, chemical precipitation, phytoremediation, nano phytoremediation, membrane technology, and phytobial remediation. Finally, the pros and cons of the remediation/removal methods are enumerated, as well as their principal ongoing accomplishments. The simplicity, low cost, and easy operational procedure of adsorption technique and use of novel functional materials such as graphite oxides, metal organic frameworks, carbon nanotubes and other new forms of functional materials are better future alternatives for arsenic removal.
Dowsing for danger Arsenic is a metabolic poison that is present in minute quantities in most rock materials and, under certain natural conditions, can accumulate in aquifers and cause adverse health effects. Podgorski and Berg used measurements of arsenic in groundwater from ∼80 previous studies to train a machine-learning model with globally continuous predictor variables, including climate, soil, and topography (see the Perspective by Zheng). The output global map reveals the potential for hazard from arsenic contamination in groundwater, even in many places where there are sparse or no reported measurements. The highest-risk regions include areas of southern and central Asia and South America. Understanding arsenic hazard is especially essential in areas facing current or future water insecurity. Science , this issue p. 845 ; see also p. 818
A dynamic membrane (DM) is a layer of particles deposited via permeation drag onto a conventional membrane, such that the deposited particles act as a secondary membrane that minimizes fouling of the primary membrane to lower transmembrane pressures (TMP) and enable higher permeate fluxes. Since the first DM was created in 1966 at the Oak Ridge National Laboratory, numerous studies have reported synthesis of DMs using various materials and explored their abilities to perform reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF) and microfiltration (MF). DMs are classified into two categories, namely, (i) self-formed, whereby the feed constituents form the DM; and (ii) pre-deposited, whereby the DM is formed by a layer of particles other than the feed prior to introduction of the feed. This paper endeavors to present a comprehensive review of the state-of-the-art on the latter. Key materials used as DMs, their formation and various factors influencing it, regeneration of DMs and modifications to DM systems for performance enhancement are discussed. The role of DMs in preventing fouling in the primary membrane (PM) is explained. The applications of DMs in four major areas, namely, salt and organic solute rejection, treatment of industrial effluents, treatment of water and wastewater, and oily-wastewater treatment are reviewed. Furthermore, technical and economic advantages of DMs over conventional processes are considered, and challenges in current DM research are discussed. Finally, directions for future research are suggested.