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Abstract

This paper depicts the fluoride removal from drinking water can be accomplished by different methods, for example, coagulation-precipitation, membrane separation process, ion exchange, adsorption techniques and so on. Among these procedures, membrane and ion exchange processes are not extremely regular because of its high establishment and support price. Other two tecniques are extremely regular in India. Nalgonda procedure is one of the well known strategies generally utilized for defluoridation of water as a part of developing nations, for example, India, Kenya, Senegal and Tanzania. Among different tecniques utilized for defluoridation of water, the adsorption procedure is broadly utilized and offers acceptable results and is by all accounts more appealing technique for the removal of fluoride regarding expense, straightforwardness of outline and operation. It is apparent from the literature study that different methods have indicated novel potential for the removal of fluoride. Be that as it may, in any case there is a need to figure out the reasonable utility of such developed procedures on a business scale, prompting the change of contamination control.
IJISET - International Journal of Innovative Science, Engineering & Technology, Vol. 2 Issue 9, September 2015.
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ISSN 2348 7968
Fluoride Removal from Water by various techniques: Review
Sanghratna S. Waghmare1 and Tanvir Arfin2
1Senior Scientist, Environmental Materials Division, National Environmental Engineering Research Institute (CSIR), Nehru Marg,
Nagpur-440020, India
2Scientist, Environmental Materials Division, National Environmental Engineering Research Institute (CSIR), Nehru Marg, Nagpur-
440020, India
Abstract
This paper depicts the fluoride removal from drinking water can
be accomplished by different methods, for example,
coagulation-precipitation, membrane separation process, ion
exchange, adsorption techniques and so on. Among these
procedures, membrane and ion exchange processes are not
extremely regular because of its high establishment and support
price. Other two tecniques are extremely regular in India .
Nalgonda procedure is one of the well known strategies
generally utilized for defluoridation of water as a part of
developing nations, for example, India, Kenya, Senegal and
Tanzania. Among different tecniques utilized for defluoridation
of water, the adsorption procedure is broadly utilized and offers
acceptable results and is by all accounts more appealing
technique for the removal of fluoride regarding expense,
straightforwardness of outline and operation. It is apparent from
the literature study that different methods have indicated novel
potential for the removal of fluoride. Be that as it may, in any
case there is a need to figure out the reasonable utility of such
developed procedures on a business scale, prompting the change
of contamination control.
Keywords: water treatment, fluoride removal, adsorption, ion
exchange, review
1. Introduction
Nature of drinking water is a major task in advanced days
because of expansion in pollution of water bodies [1].
Fluoride is one such pollutant that undermines living life
forms, specifically people [2]. Fluoride is an vital in little
amount for mineralization of bone and assurance against
dental caries, higher intake reasons decay of teeth enmel
called fluorosis. Fluoride enters aqueous environment by
weathering of fluoride rich minerals and as through
anthropogenic actions, for example, industrial drains [3].
The issue of fluoride in water bodies is serious for tropical
nations, for example, such as India, Kenya, Senegal and
Tanzania. The best way to pypass this issue is
defluoridation. Various methods are accessible for the
removal of fluoride from water, for example,
precipitation-coagulation, membrane-based processes, ion
exchange and adsorption process. The precipitation-
coagulation method makes vast amount of sludge and may
include leaching of undesirable components; membrane
procedure are lavish and fouling is an inescapable issue.
Adsorption procedure have their own particular poimts of
interest, for example, ease and minimized water disposal.
In this review, a widespread list of procedures literature
has been assembled. It is apparent from a literature study
of around 200 latest papers that minimal effort methods
have exhibited extraordinary removal capacities for
fluoride.
2. METHODS FOR DEFLUORODATION OF
WATER
To conquer the hazardous wellbeing impact of fluorosis,
different approaches for defluoridations are exists like
coagulation precipitation, membrane separation
processes, ion exchange, adsorption techniques and others
(electro-dialysis and electrochemical). Each approaches
have their advantages and limitations and worked
productively under ideal condition to remove fluoride to
more noteworthy range. All the above approaches are
examined briefly with their advantages and limitations.
2.1. COAGULATION AND PRECIPITATION
METHOD
Lime and alum are the most usually utilized coagulants for
Nalgonda technique for defluoridation of water.
Expansion of lime prompts precipitation of fluoride as
insoluble calcium fluoride and raises the pH value upto 11
12. As the lime leaves a leftover of 8.0 mg F-/l, it is
constantly connected with alum treatment to guarantee the
best possible fluoride removal. As a first step,
precipitation happens by lime dosing which is trailed by a
second step in which alum is added to bring about
coagulation. At the point when alum is added to water,
basically two reactions happen. In the first reaction, alum
reacts with an alkalinity’s portion to deliver insoluble
aluminium hydroxide [Al(OH)3]. In the second reaction,
alum reacts with fluoride ions in the water. Best fluoride
removal is proficient at pH range of 5.5 7.5 [4].
Nalgonda technique created by NEERI is coagulation
precipitation method includes an expansion of aluminium
salt, lime and bleaching powder took after by quick
mixing, flocculation, sedimentation and filtration.
Aluminum salt is utilized to remove fluoride from water.
The dosage of fluoride relies on upon the concentration of
fluoride proportionately. The dosage of lime is by and
large 1/20th of the dose of alum. Lime serves to shape
bigger and denser flocs for fast settling. Bleaching powder
is included for cleansing at the rate of 3 mg/l [5]. It is the
most generally utilized defluoridation method especially at
community level [6-8]. The bucket defluoridation system
based Naldonda technique has also been developed for
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household utilize [9]. The process is suitable for 20 litres
of water for one day utilization. The process produces
water with leftover fluoride somewhere around 1 and 1.5
mg/l [10]. Fill and draw type defluoridation system based
on Nalgonda technique has also been account for [9].
Nevertheless, co-precipitation methods in view of
aluminium salts have a few point of interest and restriction:
Interest
1. Generally utilized technique.
2. Technique is more practical when contrasted with
other defluoridation technique.
3. Technique is easy to understant.
Restriction
1. Required chemical dosages are high (Al(OH)3
upto 700 1200 mg/l).
2. Sludge transfer issue.
3. Cannot accomplish the passable furthest reaches
of fluoride.
4. Prerequisite of talented labor
5. Release of aluminium in treated water which may
bring about Alzheimer’s syndrome.
6. Final concentration of fluoride in the treated
water significantly relies on upon dissolvability
of precipitated fluoride and calcium and
aluminium salt.
7. The utilization of aluminium sulfate as coagulant
expands the sulfate ion concentration greatly
which prompting catharatic impacts in human
Nalgonda technique, disregarding introductory
achievement, did not take off in light of some intrinsic
issues as depicted previously. A contact precipitation
defluoridation technique utilizing bone char combined
with sodium dihydrogen phosphate and calcium chloride
has been account for [10]. Narthasarthy et al.
contemplated the joined utilization of calcium salts and
polymeric aluminium hydroxide for the defluoridation
work. Chang and Liu examined coagulation –flocculation
of calcium fluoride precipitates in combination with
polyaluminium chloride and polyacrylic acid at lower
dosage. To beat the restriction of chemical precipitation,
granular calcite is utilized to catch fluoride present in
water as calcium fluoride in a fluidized bed reactor by
Aldaco et al. [31].
2.2. MEMBRANE PROCESS
The membrane separation process is more well known
from industrial viewpoints for defluoridation of
groundwater, wastewater treatment and sea water
desalination [12]. In a membrane separation process,
particles are isolated on the premise of their molecular size
and shape with the utilization of extraordinarily composed
semi-permeable membrane. The semi-permeable
membrane is frequently a thin, nonporous or porous
polymeric film, ceramic, or metal material or even a liquid
or gas. The membrane must not dissolve, disintegrate or
break [13]. The most normally utilized membrane
separation processes for removal of fluoride are reverse
osmosis, nano-filtration, Donnan-dialysis and
electrodialysis.
2.2.1 REVERSE OSMOSIS (RO)
RO is a physical process in which the anions are removed
by applying pressure on the feed water to direct it through
the semi permeable membrane. RO works at higher
pressure with more prominent rejection of dissolved solids.
The membrane rejects the ions taking into account the size
and electrical charge. RO membrane process is the reverse
of natural osmosis as a consequence of applied hydraulic
pressure to the high concentration side of the solution, it
forces solvent filter through the membrane, against a
pressure gradient into the lower-concentration solution. In
RO, utilizing a mechanical pump, pressure is applied to a
solution via one side of the semi-permeable membrane to
overcome inalienable osmotic pressure. The process
likewise removes soluble and particulate matter,
incorporating salt from seawater in desalination [14]. In
the 80’s, RO membrane separation technique was
effectively connected for the treatment of industrial
wastewater particularly for the removal and recovery of
fluoride from its effluents. More than 90% of fluoride can
be removed regardless of initial fluoride concentration
using RO membrane separation process [15].
Ndiaye et al. was utilized RO separation process for
defluoridation of industrial wastewater observed that the
rejection of fluoride ion was regularly higher than 98%,
considering that the RO membrane was completely
recovered after every arrangement of analyses [15].
Berhanu Assefa et al. concentrated the fluoride retention
of RO membranes of Ethiopian Rift Region were in the
range of 94 to 99 % [16]. Diawara et al. utilized low
pressure reverse osmosis for removing fluoride and
salinity of brackish ground water of Senegal village where
97 to 98.9% of fluoride rejection happened [17]. Gedam et
al. study uncovered that 95 to 98 % of fluoride was
removed from ground water of Moradgaon village of
Chandrapur district by using Polyamide RO membrane
[18]. Schoeman had used RO for defluoridation of some
provincial territories of South Africa expressed that
fluoride can be removed with low pressure RO in the feed
water concentration range from 10 to 17 mg/l to more or
less 0.2 mg/l in the RO permeate and with high pressure
RO from roughly 17 mg/l in the feed water to
approximately 0.2 mg/l in the RO permeate [19]. Briao et
al. used reverse osmosis for desalination of water from
the Guarani Aquifer System for drinking purpose in
southern Brazil. The rejection of 100% of fluoride, 97% of
total dissolved solids (TDS) and 94% of sulphate ions was
achieved by RO at 2MPa pressure and 1.61 m/s of cross-
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section flow velocity. The recovery rate of 93% of
drinking water was obtained by blended water created by
mixing groundwater with permeate [20].
The point of interest and restriction of the RO
membrane separation are given below:
Interest
1. Technique is profoundly compelling for fluoride
removal.
2. RO membrane was completely recovered after
every arrangement of examination.
3. This strategy can remove fluoride more than 90%
regardless of initial concentration.
4. This strategy gives the synchronous removal of
other dissolved solids.
5. It efforts under wide pH range.
6. No obstruction by different ions
7. No chemical oblige, least labor prerequisite and
least operational expense.
8. The process allows the treatment and purification
of water in one stage.
9. It guarantee steady water quality
Restriction
1. Non-attainable for rural regions.
2. Expensive technique.
3. Remove valuable minerals which are basically
require for fitting development, remineralization
is require after treatment.
4. Lot of water get squandered as saline solution
and expendable of salt water is an issue
5. The water gets to be acidic and need pH
improvement.
2.2.2 NANO FILTRATION MEMBRANE PROCESS
Nanofiltration (NF) is the later innovation among all the
membrane processes utilized for defluoridation of water.
The essential contrast in the middle of NF and RO
membrane separation is that NF has somewhat bigger
pores than those utilized for reverse osmosis and offer less
resistance to entry of both solvent and of solute. As a
outcome, pressures needed are much lower, energy
prerequisites are less, removal of solute is substantially
less thorought, and flow are faster [21]. Nanofiltration
membrane removes essentially the larger dissolved solids
when contrasted the RO making the process more prudent.
Notwithstanding over, the permeability of nanofiltration
membrane is higher than RO membrane, making the
performance of NF in desalination more best for some
brackish water [22]. In RO membrane separation 99% of
salt present in water was rejected prompting the disposal
of all the fluoride ion while NF membrane separation
process give incomplete defluoridation of water and
optimal fluoride concentration in water can be
accomplished by changing the operation conditions.
Diawara et al. observed that NF membrane has given
a fluorine retention rate differing somewhere around
63.3% and 71% in certain regions in Senegal [16]. Tahaikt
et al. observed the attractive execution of two modules
(NF90 and NF400) for fluoride concentration under 6 mg/l
in single pass while double pass was important for higher
fluoride concentration to convey down as far as possible
[23]. Pontie et al. used NF90 for acceptable removing
fluoride from brackish ground water of South of Morocco
( Tan Tan City) [24]. Bejaoui et al. used nanofiltration
(NF-90) and reverse osmosis (RO-SG) to lessened fluoride
ions and total salinity of a metal packaging industrial
effluent. The retention of fluoride was more than 90% by
both the membranes. The Spiegler-Kedem model was to
determine reflection coefficient of membrane (r) and
solute permeability coefficient of ions (Ps) [25].
The point of interest and restriction of the NF
membrane process are given below:
Interest
1. High productivity.
2. No chemicals are needed.
3. It lives up to expectations under wide pH range.
4. Interference because of the presence of other ion
is not observed.
5. This process gives an effective barrier to
suspended solids, all inorganic toxin, organic
micro pollutants, pesticides and microorganism.
Restriction
1. Highly expensive technique when contrasted with
other defluoridation techniques.
2. Prone to fouling, scaling or membrane
degradation.
3. It removes all the ions present in water some of
which are key for the ordinary development and
henceforth remineralization of treated water is
needed.
2.2.3 DIALYSIS
Dialysis separates solutes by transport of the solutes
through a membrane instead of utilizing a membrane to
hold the solutes while water goes through it as in reverse
osmosis and nanofiltration. The membrane pores are a
great deal less prohibitive than those for nanofiltration,
and the solute can be driven through by either the Donnan
effect or a connected electric field [26]. Donnan dialysis
is otherwise called diffusion dialysis, is similar to ion
exchange membrane however unique in relation to electro-
membrane process in which the driving force is not an
electric current, but rather basically a distinction in
chemical potential. Concentration difference is the most
obvious driving force for ion transport in Donnan dialysis.
A negative ion can be driven out of a feed solution
through Donnan dialysis is equipped with anion exchange
membrane by utilizing a second alkaline stream. The
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concentration difference of hydroxide ion between the two
solutions compels the hydroxide ion to diffuse into feed
solution. This makes an oppositely directed electrical field
driving an extraction of negative ions from the feed
solution [27]. Hichour et al. examined the Donnan dialysis
process in a counter current system in which the anion-
exchange membrane was loaded with sodium chloride and
the feed was 0.001M NaF together with other sodium salts.
Fluoride migrated into the receiver as other ions migrated
into the feed. This technique was later used to defluoridate
solutions made to rectreate high fluoride Africa
groundwater (>30mg/l fluoride) and whatever other ions
were present the fluoride in the feed could be brought
below 1.5 mg/l [27]. Grames et al. used hybrid method of
adsorption on aluminium oxide and zirconium oxide and
Donnan dialysis with Neosepta-ACS anion exchanger to
treat fluoride water of 4mg/l from phosphate mining in
Morocco and bring it to desirable level (i.e. 1.5mg/l) for
drinking purpose [28]. Durmaz et al. studied the removal
of fluoride from diluted solution with Neosepta AHA
anion exchanger by Donnan dialysis. Neosepta AHA
anion exchanger membrane was used for the removal of
fluoride and the flux of fluoride with respect to the
concentration, pH, and accompanying anions were
obtained between 34 136.10-7 (m.mol.cm-2.s-1). The
transport efficiencies of the membrane were found to be
Neosepta AFN>Neosepta AHA>Polysulfone SB-6407.
Alkan et al. used plasma modified and Prinstine and AFX
anion exchange membrane by Donnan dialysis for
removal of fluoride. The flux values and recovery factors
for plasma modified AFX membrane were higher than that
of Prinstine membrane which was clarified on the premise
of progress of wettability and morphology in the plasma
modified membrane [29]. Boubakri et al. studied the
fluoride removal from dilute solutions by Donnan dialysis
using full factorial design [30].
2.2.4 ELECTRO DIALYSIS
Electro-dialysis is the removal of ionic components from
aqueous solutions through ion exchange membranes under
the driving force of an electric. Electro-dialysis is like
reverse osmosis, except current, rather than pressure, to
separate ionic contaminants from water. In any case,
electro-dialysis is not suitable for rural because of use of
electricity. Adhikary et al. have treated defluoridation of
brackish water having fluoride upto 10 ppm with TDS
upto 5000 ppm with an energy necessity of < 1 KWh/Kg
of salt removed and brought it to reasonable firthest
reaches of 600 ppm TDS and 1.5 ppm fluoride [31]. Amor
et al. used electrodialysis process to produce drinkable
water from defluoridates brackish water containing 3000
ppm of total dissolved solids (TDS) and 3 ppm of fluoride
[32]. Annouar et al. studied the fluoride removal of
synthetic water and groundwater of the city of Youssoufla
on chitosan took after by electrodialysis with the help of
the CMX-ACS membranes and compares them to brought
water inside WHO permissible limit [33]. Sahli et al. also
used chitosan and electrodialysis for defluoridation of
brackish underground water of Morocco city and by
coupling these two procedures; they were treated
defluoridated water with 3000 mg/l of total dissolved
solids and 3 mg/l fluoride [34]. Kabay et al. studied the
removal of fluoride from aqueous solution by
electrodialysis under different operating parameters
including applied voltage, feed flow rate, fluoride
concentration and effects of sulphate and chloride ions. It
was observed that the separation performance increases
with initial fluoride concentration in feed solution
increased and fluoride removal increased as applied
potential increased. On the other hand, the performance
was not affected by change in feed flow rate. A chloride
ion impacts the performance of separation of fluoride
while unaffected by sulphate ions [35]. Ergun et al. used
electrodialysis with SB-6407 anion exchanger membrane
for removal of fluoride from water having 20.6 mg/l of
fluoride and decrease it to 0.8 mg/l suitable for drinking
purpose in spite of the presence of chloride and sulphate
ions [36]. Lahnid et al. have made economical assessment
of fluoride removal by electrodialysis. The capital coast of
€ 833,207 with operating cost of € 0.154/m3 was evaluated
for an industrial plant with a capacity of 2200 m3/d water
consumption for 50,000 per capita according to Moroccan
standards for rural areas [37].
The point of interest and restriction of the electro-
dialysis are given below:
Interest
1. Inexpensive pre and post treatment
2. Flexible (seasonal operation)
3. Low chemical request
4. High water recovery
Restriction
1. Only separation of Ionic components
2. Potential formation of H2 in the electrode rinse
3. Specific power consumption for Pumping
4. Necessity of concentrate treatment
2.3 ION-EXCHANGE PROCESS
Fluoride can be removed from water supplies with a
strongly fundamental anion-exchange resin containing
quaternary ammonium functional groups. The removal
takes place according to the following reaction:
The fluoride ions substitute the chloride ions of the resin.
This process proceeds until every one of the sites on the
resin are possessed. The resin is then backwashed with
water that is supersaturated with dissolved sodium
chloride salt. New chloride ions then substitute the
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fluoride ions promping recharge of the resin and
beginning the process once more. The driving force for the
substitution of chloride ions from the resin is the stronger
electronegativity of the fluoride ions. Chikuma et al.
studied the removal of fluoride by utilizing anion
exchange resin and modified anion exchange resin with
lanthanum complex of Alizarian Fluorine Blue in batch
and column mode [38]. Chikuma and Nishimura studied
the fluoride removal by a chloride loaded anion exchanger,
Amberlite IRA-400. The chloride ions held on the surface
of this resin were exchanged for fluoride ions in aqueous
solution [39]. Castel et al. have likewise studied the
removal of fluoride by a two way ion exchange cyclic
process [40]. Ho et al. had enhanced the ion exchange
capacity by titanium oxohydroxide arranged by using
dodecylamine as format. Zirconia and silica have been
presented in the mesoporous titanium oxohydroxide to
improve the ion exchange capacity because of its smallest
particle size with high uniformity among the mesoporous
materials prepared. Process is costly and membrane
fouling problems was happened [41]. Chubar et al. have
studied the removal of different anions like fluoride,
chloride, bromide and bromate from instantaneous
solutions on a novel ion exchanger taking into account
twofold hydrous oxide (Fe2O3.Al2O3.x H2O) [42].
Meenakshi et al. have studied the defluoridation capacity
of a chelating resin, to be specific Indion FR 10 (IND) and
Ceralite IRA 400 (CER). An anion exchange resin was
looked at under various equilibrating conditions for the
distinguishing proof of selective sorbent. The outcomes
demonstrated that chelating resin is more selective than an
anion exchange resin for fluoride removal [43]. Sundaram
et al. used organic inorganic type of ion exchangers for
fluoride removal. The ion exchanger polyacrylamide was
modified with Ce(SO4)2•4H2O , Al(NO3)3•9H2O and
ZrOCl2•8H2O. Ce-Ex has somewhat higher defluoridation
capacity than others (i.e. 2290 mg F-/kg). Likewise it was
used for field trials to reduce level of fluoride
concentration from 1.96 mg/l to the attractive level using
0.25 g of exchangers for 50ml of samples for 30 min of
time of contact [44]. Ku et al. have studied the fluoride
removal of water using aluminium loaded Duolite C-467
resin. The removal of fluoride from aqueous solution was
found to be relatively steady over entire solution pH [45].
The point of interest and restriction of ion-exchange
technique are given below:
Interest
1. High productivity (90-95 % fluoride removal).
2. Retains the superiority of water.
Restriction
1. Technique is exceptionally costly.
2. pH of treated water is low and contains high
concentration of chloride.
3. Interference because of the presence of other
anions like sulphate, carbonate, phosphate and
alkalinity.
4. Regeneration of resin is a an issue on the grounds
that it prompts fluoride rich waste, which must
dealt with before last disposal.
5. It requires longer reaction period.
2.4 ELECTRO-COAGULATION (EC) PROCESS
Electrocoagulation is a technique for applying direct
current to sacrificial electrodes that are submerged in an
aqueous solution [46]. Electro-coagulation is a
straightforward and efficient technique to remove the
flocculating agent produced by electro-oxidation of a
sacrificial anode and generally made of iron or aluminum.
In this process, the treatment is performed without
including any chemical coagulant or flocculants. In this
way, diminishing the amount of sludge which must be
disposed. Then again, electrocoagulation is in view of the
in situ development of the coagulant as the sacrificial
anode corrodes because of an applied current, while the
concurrent advancement of hydrogen at the cathode takes
into consideration contamination removal by flotation.
This technique consolidates three fundamental associated
processes, operating synergistically to remove pollutants:
electrochemistry, coagulation and hydrodynamics. An
examination of the chemical reactions happening in the
electrocoagulation process demonstrates that the main
reactions occurring at the electrodes (aluminum and iron
electrodes) are:
Moreover, Al3+ and OH- ions produced at electrode
surfaces react in the bulk wastewater to form aluminum
hydroxide:
Also the same chemical reactions occurring in the
electrocoagulation process using iron electrodes:
The aluminum and iron hydroxide flocs for the most part
go about as adsorbents and/or traps for metal ions. Thusly,
they would remove with them from the solution. The core
purpose of this investigation was to research of the
electrocoagulation process productivity for fluoride
removal from aqueous environments with iron and
aluminum electrodes and determination of the impacts of
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voltage, pH, initial concentration of fluoride and reaction
time on the removal efficiency [47].
Electrocoagulation includes electrolytic oxidation of a
proper anode material. Electro-coagulation reactor is
comprised of an electrolytic cell with one anode and one
cathode [48]. Yang et al. studied the electrochemical
removal of fluoride by delivering aluminium sorbent in a
parallel-plate electrochemical reactor. Defluoridation was
done by anodic dissolution of aluminium electrodes in a
dilute sodium chloride (NaCl) aqueous solution. The NaCl
in the solution adequately diminished the power utilization
and advanced the sorbent generation by depasivating the
aluminum–water electrochemical system. The freshly
created Al-sorbent had the capacity diminish fluoride
concentration from 16 to 2 mg/l in 2 min. The final
concentration was further lessened to 0.1 mg/l by partial
neutralization of the mixture to pH 6.3. The sorbent
generation and fluoride adsorption was incorporated into a
solitary electrochemical reactor. The system had the
capacity decrease the fluoride concentration from 16 to 6
mg/l in 2 min of treatment and to around 2 mg/l in 4 min.
The effluent from the electrochemical system needs pH
alteration to bring the fluoride concentration down to less
than 1 mg/l. Feng Shen et al. studied consolidated
procedure of electrocoagulation and electro-flotation for
defluoridation of industrial water. By this process, the
influent fluoride concentration of 15 mg/l, a value after
lime precipitation, reduces to 2 mg/l in an effluent when
the pH in the coagulation cell is around 6, charge loading
is at 4.97 F/m3 water, and the residence time is 20 min.
Indeed, even lower effluent concentration can be
accomplished if 50 mg/l of Fe3+ or Mg2+ are included into
the coagulation unit. The anions for the most part decrease
the fluoride removal efficiency aside from Cl- whose
corrosion pitting of the electrode can bring about 130%
present efficiency. The weakly acidic condition is
satisfactory in the treatment, while too high or too low pH
can influence the development of the Al(OH)3 flocs [49].
Hu et al. studied a continuous bipolar electrocoagulation
flotation (ECF) system for the treatment of the high
fluoride content wastewater following calcium
precipitation with addition of addition of an anodic
surfactant, sodium dodecyl sulfate (SDS). The dose of
SDS in a continuous ECF system was higher than that in
the batch system demonstrating the SDS acted not only as
frother, but also as collector in the consistent system. The
removal of suspended solids (SS) in the consistent system
was not as much as that in the batch system in light of the
fact that the scum was distributed by the flow of
wastewater in the flotation tank [50]. Ghosh et al.
examined the treatment of fluoride containing drinking
water with concentration 2 to 10 mg/l by
electrocoagulation using mono-polar and bipolar electrode
connections. It was observed that the removal of fluoride
was preferred for bipolar connection than for mono-polar
connection. The final recommendable breaking point of
fluoride (1 mg/l) was obtained in 30 min at 625 A m2
using bipolar connection. The operational costs of mono-
polar and bipolar connections were 0.38 and 0.62 US
$ m3 respectively [51]. Drouiche et al. was completed the
treatment of synthetic fluoride containing solutions by
electrocoagulation method using aluminium electrodes for
the treatment of wastewater from photovoltaic wafer
production industry. EC was investigated for applied
potential (10-30V), electrolysis time and supporting
electrolyte (NaCl) concentration (0100 mg/l). Our results
showed that with increasing applied potential and
electrolysis time, the Al+3 dosage increases too, and
thereby favouring the fluoride ions removal. It was also
observed that defluoridation is dependent on the
concentration of supporting electrolyte. Un et al. studied
the removal of fluoride from synthetic water made by NaF
using iron cylindrical reactor as anode and a mechanical
stirrer with two blades as cathode. Sodium sulphate
(Na2SO4) was added to the aqueous solution to increase
conductivity. It was observed that the most effective
fluoride removal was occurred at pH is 6.0. The most
noteworthy treatment efficiency was acquired for the
largest current density and higher concentration of sodium
sulphate. The initial fluoride concentration of 5 mg/l was
reduced to the 0.70 mg/l with the removal efficiency of
85.9% at 3 mA/cm2 [52]. Bennajah et al. studied the
fluoride removal of synthetic solution using
electrocoagulation electro flotation method in two
electrocoagulation cells (i.e. Stirred tank reactor and airlift
reactor) of 20 litre capacity with aluminium electrodes.
The air lift reactor is advantageous for carrying out the
defluoridation removal process based on energy
consumption. A variable order kinetic (VOK) derived
from the Langmuir-Freundlich equation was created to
simulate the kinetics of the defluoridation with EC using
bipolar aluminium electrodes in the airlift reactor. The
outcomes indicated good agreement between the
predictive equation and the experimental data. The
external-loop reactor is affirmed as a productive tool to
accomplish complete flotation using only
electrochemically-generated bubbles without the need for
surfactants or compressed air to induce overall liquid
circulation. Another favorable position for the external-
loop reactor is the instantaneous recovery of the floc,
contrasted with the instance of the stirred reactor where
the recovery of the floc obtained by the EC needs quite a
while or an additional secondary treatment (like filtration
or sedimentation) [53]. Khatibikamal et al. studied the
fluoride removal from industrial wastewater started from
steel industry by electrocoagulation using aluminium
electrode. The impact of different operating conditions
such as temperature, pH, voltage, hydraulic retention time
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(HRT), and number of electrodes between anode and
cathode plates on removal of fluoride were studied. The
outcome demonstrated that the fluoride concentration can
be lessened from 4 to 6 mg/l to lower than 0.5 mg/l with
the HRT of 5 minutes. They likewise examined the
kinetics of fluoride removal, which complies the second-
order kinetic model [54]. Vasudevan et al. studied the
impact of alternating and direct current in
electrocoagulation process on the removal of fluoride from
water using an aluminium alloy as anode and cathode. It
was observed that the utilization of direct current makes
issue of formation of impermeable oxide layer on the
cathode and corrosion of anode happened because of
oxidation. Which lessened the efficiency of the
elctrocoagulation process as the current transfer between
the anode and cathode was not productive. This
disadvantage was overcome by utilizing alternating
current. The removal efficiencies of 93 and 91.5% with
energy consumption of 1.883 and 2.541 kWh kL1 was
accomplished at a current density of 1.0 A dm2 and pH
7.0 using an aluminum alloy as electrodes using AC and
DC, respectively. Langmuir adsorption isother was fitted
and second order kinetics was taken after for both
alternating and direct current. Temperature studies
demonstrated that adsorption was exothermic and
spontaneous in nature [55]. Emamjomeh et al. utilized a
monopolar batch ECF reactor with aluminium as
sacrificial electrode that was submerged in aqueous
solution for removal of fluoride. Dissolving aluminum
(Al3+) is overwhelming in the acidic condition and
aluminium hydroxide has propensity soluble. The
defluoridation process was observed to be efficient for a
pH ranging from 6 to 8. The residual fluoride may happen
in different dissolved forms (F, AlF2+, AlF4−) or finely
formed to solid (cryolite, Al(OH)3−xFx). The mechanism
of the fluoride removal was affirmed to be not just the
aggressive adsorption between OH and F additionally
the development of solid cryolite in the last pH range of
5–8 [46]. Bazrafshan et al. utilized aluminium and iron
electrodes for removal of fluoride by elecrtrocoagulation
method. The outcome uncovered that the most extreme
productivity of fluoride removal was acquired in steady
electrolysis voltage of 40 V and reaction time of 60 minute
[47].Cui et al. studied the executive poly (aniline-co-o-
aminophenol) (PAOA) modified carbon felt electrode
reactor for fluoride removal in constant mode. This reactor
was worked under a more extensive pH range due to
coating with a copolymer PAOA ion exchange film.
Electrode made up of porous carbon felt gave great
electro-conductivity and subsequently acquired upgraded
contaminants mass transfer from bulk solution to the
electrode surface. Fluoride maintenance expanded as the
terminal potential expanded from 0.8 to 1.2 V, and
diminished as inlet flow rate and initial fluoride
concentration expanded. Optimal removal was seen at
around 1.2 V, and the total amount of fluoride removal
reached 10.5 mg/g at pH 7.2 with an initial fluoride
concentration of 10 mg/L. The reactor was utilized upto
seven cycles with back to back recovery [56]. Mumtaz et
al. studied the performance of electrolytic defluoridation
of synthetic solution of sodium fluoride by nonstop
process with aluminium electrodes using direct current.
The optimal defluoridation was happened at conditions of
optimal pH of 6.5, optimal current of 3A and flow rate of
550 ml/min for residual fluoride concentration inside of as
far as possible [57]. Naim et al. used batch
electrocoagulation-floatation procedure for removal of
fluoride from analar (AR) and commercial grade sodium
fluoride solution using bipolar and monopolar ECF.
Complete removal of fluoride was acquired after 5 min for
AR grade (5mg/l) and for commercial grade (4.93 mg/l)
solution without including any added substances.
Monolayer configuration had more powerful removal than
the bipolar one [58]. Babu et al. studied the defluoridation
of distilled and ground water by using electrocoagulation
floatation method with mild steel electrodes. The
maximum fluoride removal efficiency of distilled water
was 84.9% and 79.4% in batch and constant mode
respectively for the highest applied voltage of 25 V and
pH of 6.42 in batch system. Removal efficiency from
ground water was 79.6% and 28.7% in batch and
consistent mode respectively [59]. Andey et al. studied
performance the solar based electrolytic defluoridation
plants by using aluminium plate electrodes with direct
current. It was observed that electrolytic defluoridation
create the treated water with fluoride under 1 mg/l and 90
- 99 % decrease in bacterial load from the raw water with
the fluoride in the range of 2 to 5 mg/l and total coliform
and fecal coliform counts in the range of 120 to 630
CFU/100 ml and 70 to 100 CFU/100 ml respectively in
raw water, Reduction in hardness and nitrate is likewise
seen in treated water. The repeating expanse for the
treatment worked out for electrolytic defluoridation
showing plant is $ 0.4 / m3 of treated water which is
significantly more not exactly the treatment cost by some
other defluoridation system accessible [60]. Tastaban et al.
studied the fluoride removal of synthetic water through
electrocoagulation by utilizing aluminium electrodes at
acidic pH range. It was found that fluoride removal was
more efficient for the pH range between 3 6.5 and
fluoride concentration was get decreases from 5 mg/l to
lower than 1 mg/l. First order kinetic model was fit for this
study. Takdastan et al. studied defluoridation of drinking
water by Electrocoagulation (EC) procedure utilizing iron
and aluminum electrodes. The fluoride removal of 97.86%
was accomplished by aluminum electrodes at optimum
condition (pH of 7.5, applied voltage of 20V and contact
time of 40 min) and discovered more than defluoridation
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by utilizing iron electrodes. The fluoride removal
efficiency was expanded by expansion of voltage, number
of electrodes, reaction time as well as decrease of space
between electrodes. The energy consumption of aluminum
electrodes was not as much as iron electrodes [61].
Sandoval et al., 2014 studied the fluoride removal from
synthetic drinking water (10 mg/l F- in 0.5 g/l Na2SO4 and
1.5 mg/l ClO- at pH 7.7 and conductivity 410 µScm-1) by
electrocoagulation with aluminum as sacrificial anode in a
consistent filter press reactor combined with a flocculator
and clarifier (Sludge settler). The treated water with
fluoride under 1.5 mg/l was observed by
electrocoagulation at optimum conditions (current density
= 5-7 mA/cm2 and linear flow velocity = 0.91-1.82 cm/s)
gave aluminum doses between 19.28-52.67 mg/l. The
fluoride removal from 10 mg/l to 1 mg/l was obtained
along with minimum energy consumption of 0.37 kWh/m3
at current density of 5 mAcm-2 and mean linear flow
velocity of 1.8 cms-1 [62]. Naim et al., 2015 studied the
defluoridation of water by electrocoagulation (EC)
technique by using bipolar aluminum electrodes. The
complete fluoride removal from 6.44 mg/l analar sodium
fluoride solution was accomplished inside of 15 min. The
optimum minimum weight of NaCl for complete
defluoridation from fluoride solution of 10 mg/l was
observed to be 0.5g. The optimum pH and speed of
agitation was 6 and 300 rpm. The defluoridation of water
by EC was more for analar NaF solutions than commercial
NaF solutions [63].
The point of interest and restriction of
electrocoagulation are depicted as takes after [48]:
Interest
1. EC obliges basic equipment, simple to handle and
less support cost.
2. EC treated water is consumable, colourless and
odourless.
3. EC produces low sludge that is promptly settable
and simple to de-water since it essentially content
metallic oxides or hydroxides.
4. EC produces more steady and effectively
separated by filtration.
Restriction
1. The ‘sacrificial electrodes’ are dissolved into
wastewater streams as an after effect of oxidation,
and should be consistently supplanted.
2. The utilization of electricity may be lavish in
numerous spots.
3. An impermeable oxide film may be framed on the
cathode prompting loss of productivity of the EC
unit.
4. High conductivity of the wastewater suspension
is needed.
5. Gelatinous hydroxide may tend to solubilize now
and again.
2.5 ADSORPTION
Adsorption is the bond of molecules species from bulk
solution for a surface of of a solid by physical or chemical
forces. Adsorption procedures include the water’s entry
through a contact bed where fluoride is removed by ion
exchange or surface chemical reaction with the solid bed
matrix. As contrast with different procedures of
defluoridation, adsorption method is prominent because of
its straightforwardness and also accessibility of extensive
variety of adsorbents. Adsorption onto solid surface is
straightforward, flexible and suitable procedure for
treating drinking water systems, particularly for small
groups. Adsorption technique is efficient and can remove
ions over an extensive variety of pH to a lower leftover
concentration than precipitation [64,65]. A few adsorbent
materials have been attempted in the past to check their
possibilities and techno-economic feasibility as
defluoridating specialists. Activated alumina, activated
carbon, activated alumina coated silica gel, calcite,
activated saw dust, activated coconut shell powder,
activated fly ash, groundnut shell, coffee husk, rice husk,
magnesia, serpentine, tri-calcium phosphate, bone
charcoal, activated soil sorbent, defluoron-1, defluoron-2
and so on various adsorbent materials reported in literature
[66-74]. The most regularly utilized adsorbents are
activated alumina and activated carbon. The fluoride
removing efficiency of activated alumina gets influenced
by hardness, pH and surface loading (the ratio of total
fluoride concentration to activated alumina dosage). The
adsorption procedure can remove fluoride up to 90% and
the treatment is exceptionally practical. Regeneration is
needed after at regular intervals of 4–5 months and
viability of adsorbent for fluoride removal reduces after
every regeneration cycle. Mckee and Johnston
investigated the utilization of powdered activated carbon
for fluoride removal and accomplished noble outcomes
[75]. The procedure is pH dependent with noble results
just at pH 3.0 or less. Hence, the utilization of this material
is costly because of need of pH alteration. Activated
alumina method for defluoridation is being prolifereated in
a few villages by the voluntary organizations funded by
UNICEF or different agencies to give safe drinking water.
Sarita Sansthan, Udaypur, Rajasthan is spreading the
method with the viable help of UNICEF by giving a
bucket (approximately 20 L capacity) fitted with a
microfilter at the bottom containing 5 kg of activated
alumina. The point of interest and restriction of adsorption
are given below:
Interest
1. Ease of operation.
2. Adsorption procedure is worthwhile
3. High productivity for fluoride removal and can
remove up to 90% fluoride.
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4. Produce high quality water.
5. Regeneration is conceivable.
Restriction
1. Disposal of depleted adsorbents and concentrated
regenerated makes issue.
2. Interference because of the vicinity of different
anions may bring about competition for active
sites on adsorbent.
3. Drop in removal effectiveness after regeneration
step.
4. Highly pH subordinate.
5. High concentration of total dissolved salts (TDS)
can brings about fouling of the alumina bed.
3. Conclusions and future perspective
This review has endeavored to cover an extensive variety
of procedures which have been utilized so far for the
removal of fluoride from the drinking water and industrial
wastewater. The traditional system of removing fluoride
from drinking water is liming and the attending
precipitation of fluoride. Then again, the weaknesses of
the vast majority of these strategies are high operational
and upkeep costs, auxiliary contamination, for example,
generation of toxic sludge and so on and intricated process
included in the treatment. Distinctive tecnnologies systems,
utilized for defluoridation, were discriminatingly
examined. It was reasoned that coagulation strategies have
by and large been discovered compelling in defluoridation,
however they are unsuccessful in conveying fluoride to
fancied concentration levels. The quest for option and
appropriate fluoride removal methods thusly still stays of
curiosity.
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AUTHOR BIBLIOGRAPHY
Sanghratna S. Waghmare is a
working as a Senior S
cientist at
Environmental Materials Division,
CSIR-
National Environmental
Engineering Resea
rch Institute
(CSIR-
NEERI), Nagpur. He has
experience in condition assessment
of RCC buildings and bridges using
NDT and PDT techniques also
engaged in development of building
materials from wastes, design and
development of instant houses and
polymer comp
osites from sisal
fibers. Currently, Waghmare has
been involved in defluoridation and
carbon dioxide sequestration.
Tanvir Arfin is currently working
as a Scientist at Environmental
Materials Division, CSIR-National
Environmental Engineering
Research Institute (CSIR-NEERI),
India. Dr. Arfin has been actively
engaged in research related to
various fields of electrochemistry,
defluori
dation, platinum group
materials, polymer science,
membrane, hybrid materials,
graphite oxides and biomass energy.
He has published more than 28
scientific peers reviewed journal
papers and 9 book chapters
.
571
... And also, high fluoride concentrations can lead to induces the necrosis, leaf curl on tender leaves which unwanted by product [5]. Accumulation of fluoride ions in human body over a long period of time can be lead to change the structure of DNA [6]. Due to the elevated levels of fluoride, long term diseases such as dental fluorosis (1.5-4.0 mg/L) and skeletal fluorosis (4-10 mg/L) can be occurred in human body. ...
... The variation of extent of adsorption with concentration of solution has been correlated by the Langmuir and Freundlich adsorption isotherms [6]. The adsorption isotherm was determined by using initial fluoride concentrations of 0.5, 1.0, 1.5 and 2.0 mg/L at 30 C temperature, 100 rpm shaking speed, 0.2 g adsorbent dosage and 45 min contact time. ...
Article
Full-text available
Fluoride is a useful ion for human health and fluoride related health problems can occur due to the deficiency or excess intake. Human intake of fluoride is consumed mainly from drinking water. The removal of fluoride ions from its aqueous solutions and water samples using activated carbon, was conducted in this study. For the preparation of activated carbon dried palmyrah (Borassus flabellifer) nut shells were used as a low cost adsorbent. Activation of dried palmyrah nut shell charcoal was done with concentrated H3PO4 and 25% NaOH separately as activating agents. Characterization of the non-activated carbon (NAC), phosphoric acid activated carbon (PAC) and sodium hydroxide activated carbon (SHAC) was conducted using different parameters. Fluoride removal efficiency of PAC was investigated for a synthesized fluoride solution which was prepared using NaF and deionized water in four different conditions such as contact time, adsorbent dosage, initial fluoride concentration and temperature. Fluoride concentration in samples was measured by SPADNS method. Then seven different field water samples were collected from Nochchiyagama area, Anuradhapura district which is a major fluoride contaminated ground water containing area in Sri Lanka. The physicochemical characteristics of PAC was found to be high compared to NAC and SHAC. Optimum conditions for the highest fluoride removal efficiency of PAC were observed as 45 min contact time, 0.2g adsorbent dosage, 1 mg/L initial fluoride concentration at 30 °C temperature with 61% adsorption efficiency. The pseudo-first order and pseudo second order kinetic models were applied in this experiment. The pseudo second order exhibited the best fit for the kinetics studies that indicates the chemisorption process. The experimental isotherm data were analysed by different models; the adsorption follows the Freundlich model providing better fit for the equilibrium data. PAC from palmyrah nut shells would make an alternative source of activated carbon and low cost adsorbent for the fluoride ions.
... However, RO is affected by various parameters like ionic strength, type of ionic exchange membrane used, pH, presence of co-existing anions and applied potential etc. 47 Nevertheless, RO is not affected by initial concentration in water as up to 90% of fluoride can be removed using reverse osmosis. 48 Nanofiltration is another type of convenient membrane process operating comparatively at lesser pressure and capacity. Nanofilteration membranes have more permeability than RO. ...
... Besides, the pore size of nano-filters is larger as compared to those in membranes of RO and accordingly, less pressure is required for nanofiltration and many essential minerals are retained to some extent. 48 Nasr 2 examined the performance of NF5 and NF9 two commercial nano-filter membranes and these were observed to effectively remove fluoride ions over chloride ions. It was also observed that certain ions act as interference in fluoride removal in groundwater filtration. ...
Article
Full-text available
Fluoride(F-) is the 13thmost abundant chemical element in the Earth's crust which has been widely recognised for its health benefits at low concentration but poses a serious threat to public health at very high doses. The world health organization has set the fluoride guideline limit of 1.5 mg/l in drinking water. Globally, over 260 million people drink water with high fluoride concentrations. Widespread distribution and high fluoride levels in the potablewater in most of the areas of the world has prompted substantial research and mitigation efforts to address the growing public health concerns related to fluoride contamination. With the recent advances in science, various defluoridation methods such as adsorption, ion exchange, precipitation-coagulation, membrane processes, biological defluoridation and even integrated approaches have been developed for the management of fluoride-contaminated aquatic environments. This review provides an up-to-date insight into thedefluoridation techniques developed and implemented throughout the world and highlightsthe advantages and disadvantages of each technique.The literature survey confirms that despite developing so many novel techniques for defluoridation over the years, there is still no effective fluoride removal technique that can achieve the desired results in a cost-effective and sustainable manner. Therefore, development of a commercially practical, economical, and sustainable technique is required to prevent people especially the most vulnerable from poor and developing nations (dependent on untreated water)from the hazards of fluoride contamination.
... Several treatment methods for oil removal have been implemented, including adsorption, froth flotation, membrane filtration, biological treatment, coagulation, and flocculation. Nevertheless, except for adsorption, all of these treatments have drawbacks, such as high operating costs and less ecologically friendly [4]. Biological treatment is indeed environmentally friendly, but biodegradation methods are not always simple because biological processes depend on suitable environmental growth and appropriate levels of nutrients for microorganisms to grow [5]. ...
Article
Treatment of oil pollution remains a challenge due to the growing urbanisation. Thus, there is an increasing number of global studies on exploiting simple and effective methods to remove oil from water. In the present work, spent tea leaves (STL) have been modified using oleic acid (OA) and free fatty acids from waste cooking oil (FFA-WCO). The aim was to enhance the hydrophobicity of the STL so that they can act as an oil adsorbent. The functional groups of the fatty acids within the modified STL were identified using the Fourier Transform Infrared (FTIR) Spectroscopy analysis, while the surface morphology of STL was characterised using a Scanning Electron Microscope (SEM). The performance of the synthesised adsorbents for oil adsorption was tested in batch adsorption experiments. The FTIR results revealed that free fatty acids have been successfully impregnated onto the surface of STL. SEM analyses showed that the surface of the fatty acid-modified STL has smoother surfaces compared to the rougher surface of unmodified STL. From the batch adsorption test, the highest adsorption capacity was observed using 1:10 ratio of STL to WCO, with 120 min of contact time, 1 g of adsorbent dosage, and under the temperature of 45 °C. The adsorption capacity of STL@FFA-WCO at the optimum condition was 1.800 ± 0.15 g/g. For the effect of modification agents, STL that were modified using oleic acid (STL@OA) showed greater adsorption capacity of 2.267 ± 0.21 g/g. These findings proved that the fatty acid-modified STL have the potential of becoming green adsorbents for oil removal.
... These could include monitoring programs for drinking water wells or fluoride removal, e.g. adsorption treatment (Bhatnagar et al., 2011) or membrane separation processes (Waghmare and Arfin, 2015), and improving health management systems. Compared to the previous nationwide representation of fluoride at the sub-tehsil-scale (Khan et al., 2002), the novel maps presented here have a 3-4 order of magnitude higher spatial resolution (250 m), are based on much larger new datasets, and predict the probability of high groundwater fluoride for areas where data are lacking. ...
Article
Full-text available
Concentrations of naturally occurring fluoride in groundwater exceeding the WHO guideline of 1.5 mg/L have been detected in many parts of Pakistan. This may lead to dental or skeletal fluorosis and thereby poses a potential threat to public health. Utilizing a total of 5483 fluoride concentrations, comprising 2160 of new measurements as well as those from other sources, we have applied machine learning techniques to predict the probability of fluoride in groundwater in Pakistan exceeding 1.5 mg/L at a 250 m spatial resolution. Climate, soil, lithology, topography, and land cover parameters were identified as effective predictors of high fluoride concentrations in groundwater. Excellent model performance was observed in a random forest model that achieved an Area Under the Curve (AUC) of 0.92 on test data that were not used in modeling. The highest probabilities of high fluoride concentrations in groundwater are predicted in the Thar Desert, Sargodha Division, and scattered along the Sulaiman Mountains. Applying the model predictions to the population density and accounting for groundwater usage in both rural and urban areas, we estimate that about 13 million people may be at risk of fluorosis due to consuming groundwater with fluoride concentrations >1.5 mg/L in Pakistan, which corresponds to ~6% of the total population. Both the fluoride prediction map and the health risk map can be used as important decision-making tools for authorities and water resource managers in the identification and mitigation of groundwater fluoride contamination.
... Managing industrial wastewater treatment especially fluoride removal is practiced via ion-exchange and/or reverse osmosis and adsorption for drinking water. These technologies are suitable only for low concentration of fluorides due to their high cost (Waghmare and Arfin 2015). ...
Article
Full-text available
Background The main object of the present study is the industrial wastewater effluent treatment resulting from a solar cell manufacturing process, which is a Joint Egyptian Chinese Renewable Energy laboratory, in Sohag Governorate. Fluoric and hydrochloric acids are the main pollutants causing a pH of 1 to 3. The effluent is neutralized by the addition of both potassium hydroxide and calcium hydroxide to permit the precipitation of the resulting sparingly soluble calcium fluoride. The chlorides are partially precipitated as calcium chloride, and the further addition of hydrated aluminum sulfate is used to precipitate the remaining extra chloride as an insoluble complex to reach the allowable chloride concentration in the treated effluent. Set of experiments at bench and pilot scales were run to achieve the optimum conditions for defluorination and dichlorination taking into consideration not exceeding the allowable ranges of pollutants as soluble salts in the final effluent. Results Experimental results showed that the performance of a pilot scale was satisfactory in fluorides, chlorides, and dissolved solids by 97.64, 78.85, and 79.4% removal, respectively. Based on these results a full-scale industrial treatment unit was designed for construction and operation as a treatment unit for industrial wastewater contaminated with fluorides as main pollutant. Conclusions The recommended treatment procedure succeeded in the removal of fluorides and chlorides as main contaminants in the effluent which permit the use of treated water in the irrigation of non-edible plants, according to Egyptian Code No. (501/2015).
... Several methods, such as adsorption [35,36], precipitation [37,38], and membrane separation [39], have been applied to remove fluoride from water. Notably, each method has its own advantages and disadvantages [40,41]. Therefore, an appropriate method should be selected depending on the unique situation. ...
Article
Seeking a technically reliable disposal platform for milk sludge has drawn particular concern considering its hazardous potential to our environment. Milk sludge from the dissolved air flotation process has abundant calcium because of the naturally available calcium in milk and lime addition as a coagulant. No previous study on its ability to remove fluoride based on its abundant calcium has been reported. As a strategic measure to minimize the environmental impacts, milk sludge was pyrolyzed. Milk sludge biochar was used as an adsorbent to remove fluoride from water. To delineate the close relationships between the fluoride removal capacity and the physico-chemical properties of biochar, milk sludge biochar was fabricated at the temperature range from 500 to 800 ˚C. In an effort to align the experimental/theoretical data, adsorption kinetics, isotherms, column studies, and equilibrium modelling using visual MINTEQ 3.1 were conducted. In addition, milk sludge biochar was characterized using field-emission scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Biochar fabricated at 800 °C (MS800) exhibited the highest fluoride removal capacity of 485.9 mg/g. Only MS800 mainly composed highly soluble Ca(OH)2 while the other temperature-prepared biochar mainly composed of less soluble CaCO3. Consequently, MS800 is providing more Ca²⁺ to the system. At the equilibrium, MS800 releases Ca²⁺ ∼200 mg/g into water within 24 hours. X-ray diffraction of the spent biochar shows that fluoride was removed by forming a CaF2 precipitation. All experimental findings of this study confirmed that milk sludge converted into a value-added, efficient environmental media to remediate fluoride-contaminated wastewater.
... Ion exchange has high efficiency (90-95%) but the presence of carbonate, sulfate, and phosphate ions affects its efficiency. This is a costly technique and fluoride loaded resins and their regeneration is a problem (Waghmare and Arfin 2015). Adsorption is considered a good method because of its cost-effectiveness and comfortable operation (Ghosal et al. 2015;Mei et al. 2020). ...
Article
Full-text available
In the present work, pond clay was modified with lanthanum and applied for fluoride uptake from an aqueous environment. The clay soil was treated with a 0.1 M solution of lanthanum oxide and heated at 500 ℃ for 90 min in a muffle furnace. The modified clay was characterized by the following techniques: particle size analysis, zeta potential, Fourier-transform infrared, scanning electron microscopy, transmission electron microscopy, pH at the zero point of charge, X-ray diffraction, Brunauer–Emmett–Teller, and X-ray photoelectron spectroscopy. The adsorption experiments revealed that modified clay soil was very effective in removing fluoride with an adsorption capacity of 1.96 mg/g. The fluoride removal was followed well with Langmuir isotherm (R² = 0.999), pseudo-second-order kinetics (R² = 1), and the adsorption was an exothermic process. The performance of lanthanum-modified clay (LMC) in a fixed bed column was evaluated using different models, including the Thomas, Adams–Bohart, Yoon–Nelson, and Clark models. A regeneration study was compared with NaOH and NaHCO3 and successfully performed for four adsorption cycles. A probable mechanism is proposed including ligand exchange, electrostatic attraction, and inner complexation for fluoride adsorption on the LMC. The developed adsorbent was also tested for the treatment of natural groundwater.
Article
The high prevalence of dental fluorosis and bone mineralization deficiency as a result of exposure to fluorides has increased in Kenya over the years due to consumption of water with elevated levels of fluoride. The World Health Organization (WHO) provides a guideline of 1.5 mg/L level of fluoride in drinking water. However, majority of studies carried out in Kenya over the last 40 plus years have indicated very high levels of fluoride in drinking water in various regions, with a prevalence in dental fluorosis observed in children and adults living in Rift valley and central regions due to basaltic and volcanic rocks. Unfortunately, this trend of fluoride-induced enamel changes has been observed in other regions such as Nairobi and Machakos which were originally presumed to contain low fluoride levels. This study sought to analyse the applicability of Maerua subcordata root powder (MSRP) in the removal of fluorides in borehole drinking water. Fresh Maerua subcordata roots were peeled to obtain the white flesh, chopped into small pieces, dried and ground into powder. The process parameters varied were; fluoride ion concentration [F−] (0–12 mg/L), adsorbent dosage (0–200 g/L) and equilibration time (30–240 min) [F−] were hence analysed before and after treatment using ion selective electrode (ISE) fluoride meter. Results indicated that MSRP is a viable plant in fluoride treatment with approximately 68% fluoride ion removal efficiency. An MSRP dosage of 200 g/L was found optimal in [F−] reduction while a 2 mg/L [F−] concentration recorded the highest reduction of [F−]. The optimal equilibration time was found to be 30 min. The results can be used to develop a low-cost column for treatment of high fluoride waters in rural areas using MSRP. Borehole samples were treated with MSRP using the optimized conditions; however their reduction levels were lower than the [F−] standards used. It is envisaged that with further modification and/or doping with zero-valent iron nanoparticles, it’s efficiency will be improved.
Article
Full-text available
Technological and economic development have influenced the amount of post-production waste. Post-industrial waste, generated in the most considerable amount, includes, among others, waste related to the mining, metallurgical, and energy industries. Various non-hazardous or hazardous wastes can be used to produce new construction materials after the “solidification/stabilization” processes. They can be used as admixtures or raw materials. However, the production of construction materials from various non-hazardous or hazardous waste materials is still very limited. In our opinion, special attention should be paid to waste containing fluoride, and the reuse of solid waste containing fluoride is a high priority today. Fluoride is one of the few trace elements that has received much attention due to its harmful effects on the environment and human and animal health. In addition to natural sources, industry, which discharges wastewater containing F− ions into surface waters, also increases fluoride concentration in waters and pollutes the environment. Therefore, developing effective and robust technologies to remove fluoride excess from the aquatic environment is becoming extremely important. This review aims to cover a wide variety of procedures that have been used to remove fluoride from drinking water and industrial wastewater. In addition, the ability to absorb fluoride, among others, by industrial by-products, agricultural waste, and biomass materials were reviewed.
Article
Full-text available
Water is one of the natural resources required for life on earth. Contaminants (natural or manmade) in drinking water affect the human health. Because of the high cost of abstraction and the poor quality of groundwater, the significance of groundwater as an alternative water source is recognized. Unfortunately, groundwater is getting contaminated as a result of a variety of natural and human causes. One of the natural contaminant, fluoride (electronegative element) is present high in rocks as well as deep well/bore well water and causes dental fluorosis. Water samples were collected from selected villages of Dharmapuri and Krishnagiri district and analyzed for physicochemical parameters. The objective of our study is to find out the natural flocculant/coagulant potential of Strychnos potatorum seeds that could readily and easily eliminate chemicals and serves water as a common applicable technique, column adsorption. Total dissolved solids (TDS), Mg²⁺, and Ca²⁺ levels in water were moderately altered on incubation with biocoagulant, Strychnos potatorum seeds. P³⁻, S²⁻, and NO⁻3, SO²⁻4, and Cl⁻ levels were notably altered from the very high level to the permissible level as in soft water. The highlight of purification of water with Strychnos potatorum seeds is the drastic reduction in fluoride content, and the quantity of water was recommendable for drinking purposes as equivalent to soft water. This result significantly reveals soft water obtained after purification is found to be superior to reverse osmosis water with adequate minerals in potable water. Thus, natural biocoagulant sustains the quality of the drinking water and efficiently eliminates toxic fluoride. The present study concludes that natural contaminant fluoride in deep well and deep soil water could be effectively defluoridated by natural biocoagulant Strychnos potatorum seeds without altering physicochemical properties of drinking water.
Article
Full-text available
Fluoride is a vital element, essential for support of dental wellbeing. However, fluoride concentrations in drinking water above 1.5 mg/L may be inconvenient to human wellbeing. Numerous approaches have been established for removing extreme fluorid from drinking water. The current manuscript reviews demonstrate the capability of mixed metal oxide, in a constant flow for removal of fluoride ions from industrial wasterwater and drinking water request to to give helpful data about the distinctive advancements. At the point when conceivably the adsorption capacity of metal oxide under diverse experimental condtions is accounted for to help to think about the fluoride's adequacy removal process.
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Full-text available
Approximately 25% of the world’s population has no access to clean and safe drinking water. Even though freshwater is available in most parts of the world, many of these water sources contaminated by natural means or through human activity. In addition to human consumption, industries need clean water for product development and machinery operation. With the population boom and industry expansion, the demand for potable water is ever increasing, and freshwater supplies are being contaminated and scarce. In addition to human migrations, water contamination in modern farming societies is predominantly attributable to anthropogenic causes, such as the overutilization of subsidized agrochemicals― artificial chemical fertilizers, pesticides, fungicides, and herbicides. The use of such artificial chemicals continue to contaminate many of the precious water resources worldwide. In addition, other areas where the groundwater contaminated with fluorides, arsenic, and radioactive material occur naturally in the soil. Although the human body is able to detoxify and excrete toxic chemicals, once the inherent natural capacity exceeded, the liver or kidneys, or both organs may fail. Following continual consumption of polluted water, when the conditions are unfavourable and the body’s thresholds are exceeded, depending on the type of pollutants and toxin, liver, cardiac, brain, or renal failure may occur. Thus, clean and safe water provided at an affordable price is not only increasingly recognized, but also a human right and exceedingly important. Most of the household filters and methods used for water purification remove only the particulate matter. The traditional methods, including domestic water filters and even some of the newer methods such as ultra-filtration, do not remove most of the heavy metals or toxic chemicals from water than can harm humans. The latter is achieved with the use of reverse osmosis technology and ion exchange methods. Properly designed reverse osmosis methods remove more than 95% of all potential toxic contaminants in a one-step process. This review explains the reverse osmosis method in simple terms and summarizes the usefulness of this technology in specific situations in developing countries.
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Full-text available
The current manuscript reviews show about adequacy of various materials based on calcium for removal regarding fluoride through drinking water and industrial waste water. Fluoride is really a conscientious and non-biodegradable toxin in which aggregates inside the earth, plants, untamed lifestyle and inside people. Like this, understanding regarding it's evacuated, utilizing best strategy together with ideal efficiency is required. For that enlargement regarding attributes, upgrade within the sizes to modify the particular interest regarding reliance for calcium, the primary and fundamental technological improvement are already essential finished through the use of calcium base absorbent for different application inside remedy regarding waste water. On this content, the particular review associated with the latest progress on the modification of calcium based adsorbent to collect in order to enhance the solubility and application. It exhibits the basic factor, for example, type and concentration of initiator, temperature and time are responsible for affecting the calcium based absorbent. The calcium and its subsidiaries have bunches of abilities for the procedure of defloration, so it is likewise anticipated to great hotspot for tossing from water and waste water as too. A recovery strategy was proposed to reuse the adsorbent for better economy of the procedure. In the current review, the different characteristic of calcium based absorbent, for example, preparation, application, kinetic studies impacts have been advanced for further viewing.
Conference Paper
Many borehole waters in rural areas in South Africa are unfit for human consumption because the fluoride (>1,5 mg/ℓ), nitrate-nitrogen (>6 mg/ℓ) and salinity (>1 500 mg/ℓ) concentrations are too high. Ion exchange (IX) and reverse osmosis (RO) technology are available that can be used for defluoridation, denitrification and desalination of water. However, methodology, guidelines and the economics for the use of these technologies in rural areas are not readily available. Therefore, the objectives of this investigation were to develop methodology, guidelines and the economics for the defluoridation, denitrification and desalination of water in rural areas. The capital costs of ion-exchange household defluoridation and denitrification units are estimated at R5 000 each. Operational costs vary from R0,43 to R3,99/kℓ depending on the feed water concentration. The capital cost of a small RO unit to produce approximately 50 ℓ/d defluoridated water is estimated at approximately R3 000. (Operational cost R3,00/kℓ). The capital cost of an RO unit to produce approximately 5 kℓ/d desalinated water is estimated at approximately R20 000. (Operational cost R1,69/kℓ). The capital cost of an RO unit to produce approximately 50 kℓ/d denitrified water is estimated at approximately R150 000. (Operational cost R2,17/kℓ).
Article
Removal of fluoride from model water (distilled water + NaF salt + Na 2SO4) by electrocoagulation using iron electrode was investigated in this study. Experiments were conducted to evaluate the effects of current density (0.5-3 mA/cm2), initial pH (5-9), and supporting electrolyte (Na2SO4) dosage (0.005-0.03M) on the performance of the system. The influent pH value was found to be a very important parameter that affected fluoride removal significantly. Therefore, influent pH value of 6 was determined to be the most proper value for this study. The highest treatment efficiency was obtained for the largest applicable current density. The initial fluoride concentration of 5 mg/L was reduced down to 0.82 mg/L with the removal efficiency of 83.6 % and electrical energy consumption (EEC) of 1.4 kWh/m3 at 1mA/cm2 whereas 1.03 mg/L which is within the range suggested by WHO was reached with the removal efficiency of 79.4% and EEC of 0.2 kWh/m3 at the current density of 0.5 mA/cm2.