BIPOLAR MEMBRANE ELECTRODIALYSIS FOR THE INTEGRATED
REMEDIATION OF SODIUM SULPHATE WASTEWATER
A. B.Sc. PROJECT
BY
NWOKEJI, UDOCHUKWU CLEMENT
18CC024703
JUNE, 2022
BIPOLAR MEMBRANE ELECTRODIALYSIS FOR THE INTEGRATED
REMEDIATION OF SODIUM SULPHATE WASTEWATER
A. B.Sc. PROJECT
BY
NWOKEJI, UDOCHUKWU CLEMENT
18CC024703
A PROJECT REPORT SUBMITTED TO THE DEPARTMENT OF CHEMISTRY,
COLLEGE OF SCIENCE AND TECHNOLOGY, IN PARTIAL FULFILMENT OF
THE REQUIREMENTS FOR THE AWARD OF THE DEGREE OF BACHELOR
OF SCIENCE (B.Sc.) IN INDUSTRIAL CHEMISTRY, COVENANT UNIVERSITY
i
DEDICATION
This project is dedicated to the advancement of Chemistry and to God, Almighty.
ii
ABSTRACT
Bipolar membrane electrodialysis (BMED) is a technology that dissociates water into
hydrogen ions (H+) and hydroxide ions (OH-) and salt into cations and anions without the
formation of any gas. This study used bipolar membrane electrodialysis to convert sodium
sulphate wastewater into sulphuric acid and sodium hydroxide. The salt conversion
process made use of a three-chamber membrane stack configuration. The effect of
different current density investigated. It was observed that current density of 0.7A was
more effective than 0.3A and 0.5A by 12% and 18% respectively, in the dissociation of
sodium and sulphate ions. The effect volume on total dissociation of the salt ions as 1.5L
salt, 0.5L base and 0.5L acid were 3% better than the other volume ratio. It was observed
that as the salt concentration increased, the levels of co-ions transition across the
membrane also increased resulting in high levels of impurities in the final output of acid
and base. However, the total desalination of the sodium sulphate wastewater was higher
than at lower concentration. In addition to high yield desalination, BMED process made
the production of sodium hydroxide and sulfuric acid possible from the sodium sulphate
wastewater.
iii
CHAPTER 1: INTRODUCTION
1.1 Background to the Study
Freshwater scarcity is one of the world’s most critical challenges of our time, and a series
of significant concerns have been emerging, including a slowing economy, polluted water,
and unhealthy ecosystems (Herrero et al., 2020).The release of high salinity effluents such
as sodium sulphate wastewater from the rayon manufacture, flue gas desulfurization,
spend battery processing pharmaceuticals, food, and agriculture industries have affected
the environment. Also, various inorganic compounds such as hydrochloric acid and
sulphuric acid are usually used in metal processing such as acid, pickling, electroplating,
steel making, mining, and other metallurgy processes (Jaime et al., 2008). The failure of
the industry to fully reuse and reclaim minerals (acids and bases) from wastewater from
the 18th century till the 21st century has harmed the environment, such as an increase in
the pH of the surrounding water leading to unfavorable conditions for aquatic creatures
as fish and plant. The presence of pollutants in the water body also leads to an increase in
biological oxygen demand, chemical oxygen demand, total dissolved solids, total
suspended solids, and contamination of the water body, leading to the spread of disease
among humans to this adverse effect of effluent from industry on the environment, it has
been considered by the industry to explore a sustainable technique for proper recovery of
minerals and zero discharge effluent (Li et al., 2011).
Bipolar membrane electrodialysis is a purification technology that recovers minerals
(acids and bases) from wastewater and makes the water reusable for industrial and local
processes (Yingying et al., 2020). Over the past few years, the bipolar membrane for
the remediation of sodium sulphate wastewater has been effective, economical, and
environmentally friendly. The fundamental aspect of electrodialysis with the bipolar
Membrane (EDBM) is the combination of salt separation with Electrodialysis water
dissociation for the conversion of salt into corresponding acid and base. The bipolar
membrane enhances the dissociation of water into protons and hydroxide ions (Li et al.,
2011). A bipolar membrane is a particular type of layered ion exchange membrane. They
are composed of two polymer layers that carry the charge, one is only permeable for
anions and the other is only permeable for cations(Knežević et al., 2022)
1
A When an electrical current is applied, the deprotonation reaction of water molecules into
hydroxide ion and proton, and salt into anion at the monopolar anion exchange membrane
and cation at the monopolar cation exchange membrane occurs, resulting in the production
of acid and base, respectively (Parnamae et al., 2020). Using this same principle, when
sodium wastewater passes through the BMED, the anions get separated (Wilhelm et al.,
2001). The sodium ion bond with the hydroxide ions to produce sodium hydroxide, and
sulphate ions bond with the hydrogen ions to produce sulfuric acid(Gao et al., 2021). This is
done without the addition of any other chemical and leaves no waste product once the
electrodialysis is over. This is why the BMED is a good environmental technology approach
for the remediation of sodium sulphate wastewater(Jiang et al., 2021).
1.2 Statement of the Problem
The increase in the salinity in wastewater from the use of sodium sulphate compounds for
various industrial processes in the environment has been on the rise and, this has had negative
impacts on the environment, such as elevated biological oxygen demand, chemical oxygen
demand, total dissolved solids, and total suspended solids, and this has affected the aquatic
ecosystem.
1.3 Research Question
Can the use of bipolar membrane effectively recover sodium sulphate from wastewater
through the recovery of sodium hydroxide and sulphuric acid to meet industrial concentration
standards without further purification?
1.4 Aim and Objectives of the Study
1.4.1 Aim
This research aims to make use of the bipolar membrane electrodialysis for the effective
recovery of sodium sulphate ions from wastewater in form of acid (H 2SO4) and base (NaOH).
1.4.2 Objectives
The specific objectives of this study were to:
i. Recover the sodium and sulphate ions from the wastewater.
ii. Investigate the effects of parameters such as current density, volume ratio, concentration,
and filtration on the recovery of sodium and sulphate ions.
2
1.5 Justification for the Study
Sodium sulphate is one of the significant contaminants in wastewater with high salinity
dicharged into the aquatic environment after industrial and domestic usage. This affects
aquatic creatures making
it unfavourable for them to survive. The sodium sulphate
wastewater is converted into a valuable resource using bipolar membrane electrodialysis into
sodium hydroxide and sulfuric acid. It can be recycled back for industrial purposes or
domestic purposes. The use of the bipolar membrane electrodialysis for the remediation of
sodium sulphate wastewater has been economically friendly and environment friendly as no
other source of pollution is generated in the environment. This makes it sustainable and very
effective. Applying the principles of circular economy to the recycling of sodium sulphate
wastewater will lead to a green economy since it can reduce the environmental pollution of
the ecosystem.
1.6 Scope of the Study
The are several ways the remediation of sodium wastewater can be achieved. However, this
study made use of the bipolar membrane electrodialysis for the remediation of sodium sulphate
wastewater for recovery of the sodium and sulphate ions.
1.7 Limitations of the Study
This study involves the separation of the sodium ion and sulphate ion from the sodium sulphate.
The major limitations encountered were back diffusion-reaction, co-ion transition across the
membrane, and high energy consumption during the electrodialysis process
3
CHAPTER TWO: LITERATURE REVIEW
2.1 Bipolar Electrodialysis Membrane Principle
Bipolar membrane electrodialysis is (BMED) is a membrane technology that dissociates water
into its corresponding hydrogen ion (H+) and hydroxide ion (OH-) through a cation ion
exchange membrane and an anion exchange membrane in the presence of an electrical current
by disproportionation reaction (Friedrich et al., 2001). The bipolar membrane is made up of
two polymeric membranes: the cation exchange membrane that is positively charged and the
anion exchange membrane that is negatively charged. The cation and anion exchange
membrane allows hydrogen ion (H+) and hydroxide ion (OH-) to leave the Membrane (Zhong
et al., 2021) The region of close contact less than 10 mm between the anion ion exchange
membrane and the cation ion exchange membrane is called the bipolar junction, or the
interfacial layer as shown in Figure 2.1 (Parnamae et al., 2020). The dissociation of water
occurs at the bipolar junction without the release of any gas(Wilhelm., 2001). The chemical
equation 2.1 shows the dissociation of water into hydrogen ion and hydroxide ion.
2H2O ←→ H3O+ + OH-
equation (2.1)
Figure 2.1: Bipolar Membrane
The bipolar membrane is a membrane that has both the cation and the anion membrane attached
combined to be known as a heterogeneous membrane(Chen et al., 2021). The anion membrane
in the bipolar membrane are mostly made up of either quaternary ammonium groups, or tertiary
and secondary amine that are encapsulated in a polystyrene matrix (Wilhelm, 2001a). The
functional group of the compound plays a major role during the water dissociation reaction.
The cation membrane in the bipolar membrane is made up of either phosphonic acid or sulfonic
acid. When the bipolar membrane is arranged in a stack with other monopolar membranes
(cation and anion exchange membrane) during electrodialysis and a salt solution is introduced
this will lead to the production of acid and base . The salt solution is made of anions and cations
4
such as sodium sulphate and in the presence of an electrical current, the salt will split into
sodium ion (Na+) the cation, and sulphate ion (SO42-) anion and will pass through the membrane
as shown in figure 2.2 . The hydrogen ion will combine with the sulphate ion to form acid and
flow to the chamber while the hydroxide ion will combine with the sodium ion to form a base
(Li et al., 2011).
Figure 2.2: Bipolar membrane chamber
The generation of hydrogen ions and hydroxide ions at the bipolar junction is assisted by two
major mechanisms (Parnamae et al., 2020).
1. The Wein Effect.
2. The protonation and deprotonation reaction in the presence of a catalyst.
2.1.1 The Wein Effect
The Wein effect is about the application of a high electrical current on the solution during
bipolar membrane electrolysis that will lead to the production of H + and OH- at the bipolar
junction (Parnamae et al., 2020). The arrangement of the bipolar membrane and with other
monopolar membranes plays a huge role during electrodialysis (Friedrich et al., 2001). When
the membrane arrangement is in a configuration where the cation positively exchange
membrane faces the cathode and the anion negatively charge membrane faces the anode this is
5
known as a “reverse bias” but when the cation positively exchange membrane faces the anode
and the anion negatively charge membrane face the cathode this is known a “forward bias”
(Parnamae et al., 2020). The property of the forward bias and the reverse bias shows similar
properties to that of a semiconductor diode. The semiconductor diode is made up of the p-n
junction and has a current-voltage behavior just like water in the bipolar junction. When
electrical current is applied in a forward bias in a semiconductor diode the p-type material gets
attracted to the n-type material leading to a steady current at the junction. When the electrical
current is applied in a reverse bias this will lead to a depletion of the current in the
semiconductor junction leading to no current flow (Parnamae et al., 2020).
Water and a semiconductor operate nearly the same way as shown in figure 2.3 . In the bipolar
membrane during the reverse bias, water is split up into H + and OH- ions. The ion leaves the
bipolar junction and flows through the membrane to their respective chamber. This effect
causes a depletion of the H+ and OH- ions at the junction. The bipolar membrane shows high
membrane resistance initially due to limiting current then, as the production of H + and OH- ions
occurs, there is an increase in the voltage (Parnamae et al., 2020). In the forward bias, there is
an inward movement of the H+ and OH- ion from the solution into the bipolar junction as shown
in figure 2.4.,During this process, the bipolar membrane has low resistance due to the
accumulation of the H+ and OH- ions in the bipolar junction (Li et al., 2011).
Figure 2.3: P-N semiconductor
6
.
Figure 2.3: Reverse Bias (a) and Forward Bias (b)
2.1.2 The Protonation and Deprotonation with the Addition of a Catalyst
One of the key processes that aid in the splitting of water into H+ and OH- at the bipolar
junction is the reversible protonation and deprotonation process with the presence of a catalyst,
Graphene oxide (GOx), in the water dissociation into H+ and OH- (Yan et al., 2018). The
catalyst at the bipolar junction enhances the water dissociation. The protonation and
deprotonation reaction can be explained by two major chemical equations (Yingying et al.,
2020). Firstly, in the condition of a weak acid (AH)
AH + H2O
+
k1 ⇄ k-1 A + H3O
(2.2)
A- + H2O k2 ⇄ k-2 AH + OH-
(2.3)
A- is the catalytic centre in the bipolar membrane.
Secondly in the condition of a weak base (B)
B- + H2O k1 ⇄ k-1 BH + OH-
(2.4)
BH+ + H2O
(2.5)
k2
⇄k-2 B + H3O+
BH+ is the catalytic center.
k1 and k2 indicate the forward rate constant in the bipolar membrane.
k-1 and k-2 indicate the backward rate constant in the bipolar membrane.
The sum of the four equations gives
2H2O ⇄H3O+ + OH-
(2.6)
Research has shown that water is not the only solvent that dissociates in the bipolar membrane
junction. It has also been discovered that low molecular weight alcohols (methanol, ethanol,
and propanol) are also dissociated to produce acid and alkoxide (Li et al., 2011).
MX+ROH→MOR + HX
(2.7)
ROH refers to alcohol and MOR alkoxide or Akali
7
HX for acid
2.2 Sodium Sulphate
Sodium Sulphate is a significant sodium compound. It is a white crystalline solid with the
formula Na2SO4(aq) when it is anhydrous(Gao et al., 2021).
Glauber's salt is a decahydrate with the formula Na2SO4•10H2O as shown in figure 2.5 , Most
types are white powders which are very water soluble.
Figure 2.5: Sodium sulphate
.
In addition to detergents, soaps, kraft pulping, textiles, glass, carpet cleaners, and other Others
(Food preservatives, Oil recovery, etc.) are made using sodium sulfate. Sodium decahydrate is
a major commodity chemical product, with a 6 million metric tons yearly manufacturing
capacity. Anhydrous sodium sulfate, also referred to as the scarce mineral thenardite, is a
drying agent in organic synthesis that is employed as a drying agent(Salih et al., 2011).
2.2.1 Chemical Properties and Physical Properties
At ambient temperature, Na2SO4(aq) is chemically highly sTable, being relatively inert to most
oxidizing or reducing agents. It can be converted to sodium sulfide at elevated temperatures. It
is a neutral salt that forms pH 7 solvents. The stability of such salt is due to the fact that
Na2SO4(aq) is composed of an acid (sulfuric acid) and a base (acid) (sodium hydroxide).
Na2SO4(aq) + H2SO4(aq) → 2 NaHSO4(aq)
equation (3.1)
Na2SO4 is an ionic sulphate that contains both Na+ and SO4-2 ions. When aqueous solutions are
mixed with Ba2+ or Pb2+ salts, insoluble sulfates is form:
Na2SO4(aq) + BaCl2(aq) → 2 NaCl(aq) + BaSO4( s) equation (3.2)
As illustrated in the gr, sodium sulphate has interesting water solubility
characteristics. Between 0 and 32.4 °C, its solubility is more than tenfold,
reaching a high of 49.7 g Na2SO4 per 100 g of water.
8
Figure 2.6: Thermodynamic behaviour of Na2SO4
2.2.2 Sodium Sulphate Wastewater
The series application of sodium sulphate in the production detergents, soaps, kraft pulping,
textiles, glass, pharmaceutical carpet cleaners, and others (Food preservatives, Oil recovery,
etc.) all have the presence of sodium sulphate in their composition of wastewater(Salih Jawad
et al., 2011), although the presence of sodium sulphate has no a direct threat to the
environment(Salih Jawad et al., 2011) the accumulation of the compound to the environment
from the deposition from wastewater has affect the aquatic life by increasing the pH of water,
cause diarrhea in human health when drank and affect plant growth. Numerous industrial
operations, including as rayon production, flue gas desulphurization, spent battery processing,
and neutralization, generate around one-third of the sodium sulphate (Na2SO4) wastewater
(Mariusz et al ., 2014)
The major depositor of high-rich sodium sulphate is the chemical industry as listed above and
domestic home from laundry service (Zhong et al., 2021).
2.3 The Use of Bipolar Membrane for the Remediation of Sodium Sulphate Wastewater
There have been a lot of conventional processes for the remediation of sodium sulphate
wastewater such as evaporation, crystallization, solvent assistance, cooling, and freezing to
extract sodium sulphate salt from wastewater, but all of these methods non economically and
environmentally friendly and have low concentrations yield (Jiang et al., 2021).
The use of bipolar membrane electrodialysis has gradually been an alternative to the
conventional method of remediation of wastewater (Zhang et al., 2015). The application of the
bipolar membrane has enabled the reuse of wastewater and the recovery of sodium hydroxide
9
and sulfuric acid (Chen et al., 2020). This compound makes up the sodium sulphate
wastewater aside from the impurity presence.
The use of the bipolar membrane for high selective separation of this salt compound without
chemical additive has made the bipolar membrane effective and aims at zero discharge waste
and circular economy (Mariusz et al., 2014).
The production of acid and base from wastewater of sodium sulphate using the bipolar
membrane electrodialysis principle. The splitting of a water molecule into hydrogen ions and
hydroxide ions. Sodium ions bond with hydrogen ions to form sodium hydroxide and sulphate
with hydrogen form sulphuric acid. The bipolar membrane electrodialysis is made up of three
major components for the production of acid and base. The cation exchange layer, anion
exchange layer, and the bipolar Membrane (Mariusz et al., 2014). . The generation of sulfuric
acid and sodium hydroxide comes from these three chambers as shown in the diagram below
The cation exchange membrane, anion exchange membrane, and bipolar membrane are in a
repeating unit as shown in figure 2.7, although there are several configurations for the
arrangement of the membrane for electrodialysis . The salt solution is introduced into the
system and an electric current is applied, sodium ions migrate to the base chamber through the
cation exchange membrane and bond with hydronium ions to form sodium hydroxide and
sulphate goes to the acid chamber through the anion exchange membrane to bond with
hydrogen ion to form sulfuric acid.
Figure 2.7: Extraction of H2SO4 and NaOH from Na2SO4
Before the wastewater is subjected to bipolar membrane electrodialysis, the must have to go
through a series of membrane filtration such as microfiltration to remove microorganisms and
microscopic material that could contaminate the final concentration of the product or cause
membrane blockage, ultrafiltration to remove viruses, bacteria, and unwanted compound,
10
nano filtration to remove mainly calcium and magnesium that cause membrane fouling,
reverse osmosis to have a highly concentrated product. All this method depends on the source
and composition of the wastewater(Wilhelm., 2001).
There are several factors to consider when working with the bipolar membrane to achieve a
good result. These factors are :
Volume ratio: the volume ratio across the three chambers plays a vital role in the purpose of
high ion concentration. When working with a volume ratio of 1:1:1 with simply means equal
volume across each chamber the concentration of the ions in the solution will be good but
when working with a volume ratio of 2:1 that is a double the volume of salt solution to the
volume of acid and base, this gives a higher concentration final product when working with
2:1 although when the ratio becomes too higher such as 3:1, 4:1 this will leads to a rapid
increase in concentration gradient across the membrane quickly and even before the final
concentration is been achieved a neutralization reaction has started to occur (Zhang et al.,
2015).
Temperature: solubility of sodium sulphate in the wastewater high in between is the range
of 0 and 32.4 °C at 49.7 g Na2SO4 per 100g of water. The level of dissociation of the ions
occurs faster in this temperature range (Wilhelm., 2001).
The concentration of the wastewater: The initial concentration of the wastewater after the
series of filtration is also important as the study showed if the initial salt concentration is too
high the level of co-ions transition and back neutralization will occur rapidly as the
concentration gradient builds up speedily and if the concentration of the salt solution is low it
will take time for the achievement of final concentration will take a long time leading to high
energy consumption(Zhou et al., 2016).
Current efficiency: is a critical parameter in the electrodialysis process. According to
Faraday's law, it determines how effective ion transport across ion exchange membranes is for
a given applied charge. In the bipolar membrane electrodialysis is the measure of the
efficiency of the generation of H+ and -OH ion the spitting of water and the rate of resistance
in the solution increase with time due to desalination of the solution the applied voltage has to
be increased to maintain a sTable current during the reaction (Mariusz et al., 2014).
Co-ions and Neutralization reaction: This is also known as co-ions known as salt leakage
when the corresponding ions transfer to another chamber such as sodium ions going to the
sulphate chamber and sulphate ions going to the sodium chamber. This usually occurs at high
concentrations gradient across the membrane and when the ratio has nearly reached the end
11
point also imperfection of the membrane contributes to the characteristic. The neutralization
reaction occurs when the acid and base solution begins to diffuse back into the salt solution
chamber due to the high concentration gradient across each Membrane (Zhou et al., 2016)
12
CHAPTER THREE: MATERIALS AND METHODS
3.1 Materials
3.1.1 Chemial Reagent
The chemicals and reagents used in this study include Na2SO4, H2SO4, HOCl, buffer4 solution,
HCl, NaOH, deionized water, tap water.
3.1.2 Apparatus/ Instrument
Beaker, pH meter (JUMO GmbH & Co. KG, Fulda, Germany), conductivity meter (JUMO
GmbH & Co. KG, Fulda, Germany), electrodialysis (ED) machine (Unit ED 64004, PCCell
GmbH, Heusweiler, Germany), filtration machine, titration machine, magnetic stirrer,
measuring cylinder, conical flask, reagent bottle, automatic pipette, analytical balance.
3.1.3 Membrane
Bipolar membrane, spacer memebrane, microfiltration membrane, Ultrafiltration
membrane, nanofiltration membrane.
3.2 Methods
3.2.1 Electrodialysis Machine Setup
The ED machine as shown in figure 3.1 consisted of a current generator supplying constant
voltage (0–30 V), a control unit, an online measuring system for pH, temperature, conductivity,
and voltage, three independent storage containers for acid, salt solution, and base connected in
circuits with three magnetically coupled centrifugal pumps NDP 25/4 (ITS-Betzel,
Hatterscheim, Germany).
The electrodialysis machine consists of a commercial heterogeneous polyethylene-based anion
exchange membrane (AEM), cation exchange membrane (CEM), and bipolar membrane (BM)
the configuration is AEM/BM/CEM.
The effective membrane area was 64 cm2 per membrane, with 1 mm of spacing between
membranes. The anode and cathode materials were Pt/Ir-coated titanium and the V4A steel.
They were placed in the polypropylene electrode housing material. Cooling water was
circulated through the outer layer of the double-wall tanks, maintaining the feed temperature
at a constant level (Knežević et al., 2022).
13
Figure 3.1: Electrodialysis Machine
3.2.2 Preparation of the Different Concentrations of 11.8 g, 16.3 g and 18.5 g of Na 2SO4
Different masses of 11.8 g, 18.5 g, and 16.3 g of Na2SO4, were weighed in the analytical
balance and dissolved in 1 liter of deionized water each to prepare various concentrations of
the solution. The preparation was done in triplicates making 3 L of each solution.
The pH of the Na2SO4 solution was taken using the pH probe, conductivity and temperature
using the conductivity meter.
3.2.3 Electrodialysis of Na2SO4 to NaOH and H2SO4
The Electrodialysis of the compound with the bipolar membrane started with the rinsing of the
machine with tap water and then deionized water to remove any contamination. This process
was done more than three times with tap water and deionized until the conductivity was
0mm/ms.
The salt solution was fed into the salt chamber and deionized water into the acid and base
chamber. The initial deionized water and salt solution pH and conductivity were recorded using
an external pH meter and conductivity meter, which also recorded the temperature. The weight
of both deionized water and the salt solution was taken in grams using the weight balance.
14
Once the solution was in its chamber, the height of the solution was recorded, this was done to
monitor the change in volume due to ion flux. A pressure of flow rate of 15 L/h was used on
the three chambers.
3.2.4 Current and Voltage Application on the EDBM
The application of different voltage and current was applied during the bipolar membrane
electrodialysis to know the best optimization for the process.
At the beginning of the experiment, the conductivity of the salt solution was high and does not
require much voltage for the desalination of the solution. As the experiment went on, the ion
contained in the salt solution began to migrate to the acid and base chamber; as a result,
conductivity decreased, and the resistance in the solution became high; for that reason, the
voltage was increased to have sTable currents in the system. The current used in the experiment
were 0.3A, 0.5A, and 0.7A currents. During the experiment, an initial of 12V was applied to
the BMEDmachine. Once the acid and base chamber conductivity chamber pass 0.4mS, the
voltage was then adjusted to meet the current demand till the end of the experiment, once there
was no change in the conductivity of the salt solution anymore.
3.2.5 Volume Application on the BMED
The application of different volumes on the BMEDwas used to check for the best method for
the extraction of NaOH and H2SO4 from Na2SO4 solution in concentration.
0.5L, 1.5L, and 1L were used in this experiment.
The use of 1L was the first used in the experiment. 1L of Na2SO4 solution was used in the salt
chamber and 1L of deionized water in both the acid and base chamber was used. The result of
the experiment was noted
The use of 1.5L and 1L was the second approach in this experiment. A volume of 1.5L Na2SO4
solution was used in the feed chamber and 1L of deionized water both in the acid and base
chamber during the BMEDexperiment.
The use of 1.5L and 0.5L was the last approach that was used in the BMED experiment. A
volume of 1.5L of Na2SO4was used in the feed chamber and a volume of 0.5L of deionized
water was in both the acid and base chamber.
15
Figure 3.2:Sodium Sulphate Wastewater
3.2.6 Pre-Treatment of The Wastewater
A series of filtration processes were done to the wastewater as shown in figure 3.2 before it
was used in the bipolar membrane electrodialysis.
The filtration process where Micro-filtration with was used to remove colloids matter,
microorganisms, and macromolecules ranging from 0.02 µm to 10 µm, Ultrafiltration was used
to improve the quality by removing bacteria, viruses parasite, and divalent ions, Nanofiltration
was used to remove total dissolved solid , organic matter and calcium and magnesium ion. The
filtration machine as shown in figure 3.3 was highly effective in the removal of unwanted
matter before each experiment.
16
Figure 3.3: Filtration Machine
Figure 3.3: filtration machine
3.3 Methods of Statistical Analysis
3.3.1 Titration of the Acid and Base Produce in the BMED
The use of a titration machine and a pH meter as an indicator was used. The titration
commenced with the rinsing of the conical flask with deionized water and calibrating of the
pH probe with a buffer solution. The titration machine was refilled and the volume set to
0.00ml. The pH probe was in deionized water until a sTable reading is of pH 7 was obtained.
The titration for the acid (H2SO4) analyte was done using a volume of 2ml. The use of 0.1M of
NaOH was used as the titrant and was titrated against the analyte which was H 2SO4 that was
produced from the BMED. The titration was stopped once there was a sTable reading of pH 7
on the pH meter.
The titration for the base (NaOH) analyte was done using the volume of 2ml. The use of 0.1M
of HCl was used as the titrant and was titrated against the analyte which is NaOH that was
produced from the BMED. The titration was stopped once there was a sTable reading of the
pH 7 on the pH meter.
3.3.2 Ions Analysis of Acid and Base
The acid and base produce from the Sythesis and wastewater were taken for ion analysis to
know the level of co-ions transition across the membrane into the solution, to know the
dissociation power of each parameter that were tested.
17
CHAPTER FOUR: RESULTS
4.1 The Effect of Different Parameters on the Bipolar Membrane Electrodialysis
Process.
Different parameters were tested during the electrodialysis to see which would give the best
result during the experiment. The parameters tested were volume, concentration, current
density, microfiltration nanofiltration, and ultrafiltration.
Other parameters recorded were initial and final volume, conductivity, weight, temperature,
pH, the mass of acid and base produced, and ion analysis.
4.2 The Effect of Current Density on 11.8 g of Na2SO4 Solution
Current densities of 0.3A, 0.5A, and 0.7A were applied to 11.8 g of Na2SO4 solution at a
constant volume of one liter of salt, acid, and base. The application of different current densities
played a significant role in the total mass of sodium hydroxide and sulphuric acid produced,
the time of the experiment, pH of the solution, conductivity, and the volume of the acid and
base produced at the end of the experiment.
4.2.1 The Use of 0.3A on 11.8 g of Na2SO4
The use of 0.3A was the first current density applied in the BMED. The value of the initial
parameters as shown in Table 4.1 was recorded, change in volume, conductivity, weight,
temperature, and pH of each of the salt, acid, and base solution. Table 4.1 shows the final result
of the parameters after the BMED process. The values of the mass of acid and base produced
from the BMED is presented in Table 4.1. The acid, base, and salt solutions were taken for
analysis after the BMED to determine the purity level of the acid and base produced. In
addition, the total dissociation of the sodium sulphate into sulphuric acid and sodium hydroxide
is shown in Table 4.1. The total time of the experiment was 207 minutes.
18
Table 4.1: The use of 0.3A on 11.8 g of Na2SO4 solution on the BMED
Initial values
of salt before
BMED
Solution
feed( Na2SO4)
acid
Base
Volume Conductivity
1L
13.82ms/cm
1L
4.8µs/cm
1L
0.34µs7cm
Weight
1001.1g
993.1g
995.2g
Temperature°C
26°C
18.4°C
18.3°C
pH
6.25
7.08
7.13
Final values of
Salt before
BMED
Solution
feed( Na2SO4)
acid
base
Volume Conductivity
925ml 0.967ms/cm
1L
36.7ms/cm
1001L
33.1ms/cm
Weight
912.15g
995.35g
1020.10g
Temperature°C
23.2°C
19.6°C
17.5°C
pH
3.15
1.7
12.43
Ions analysis
and mass base
of acid and
produced
SO42-mol/L ions
0.003039893 salt
0.073665362 acid
0.001311735 base
Na+ mol/L ions
0.00419214 salt
0.007860262 acid
0.132751092 base
Acid Mass
7.655g of SO42
Base Mass
3.598g of Na+
4.2.2 The Use of 0.5A on 11.8 g on Na2SO4
The use of 0.5A was the second current density applied in the BMED. The value of the initial
parameters as shown in Table 4.2 was recorded, change in volume, conductivity, weight,
temperature, and pH of each of the salt, acid, and base solution. Table 4.2 shows the final result
of the parameters after the BMED process. The values of the mass of acid and base produced
from the BMED is presented in Table 4.2. The acid, base and salt solutions were taken for
analysis after the BMED to determine the level of purity of the acid and base produced. In
addition, the total dissociation of the sodium sulphate into sulphuric acid and sodium hydroxide
is shown in Table 4.2. The total time of the experiment was 140 minutes.
19
Table 4.2:The use of 0.5A on 11.8 g of Na2SO4 Solution on the BMED
Initial values
Solution
Volume Conductivity
Weight
of salt before
feed( Na2SO4)
1L
13.84ms/cm 1003.70g
BMED
acid
1L
1.18µs/cm
995.15g
Base
1L
0.34µs7cm
991.55g
Final values of
Salt before
BMED
Solution
feed( Na2SO4)
acid
base
Volume Conductivity
950ml
1148µs/cm
999.95ml 38.0ms/cm
1125ml
31.5ms/cm
Ions analysis
and mass base
of acid and
produced
SO42-mol/L ions
0.00333139 salt
0.085824935 acid
0.001790622 base
Na+ mol/L ions
0.004279476 salt
0.005196507 acid
0.117860262 base
Weight
939.45g
939.45g
1128g
Temperature°C
19°C
23.5°C
20.6°C
pH
6.35
7.53
7.05
Temperature°C
20°C
19°C
18.5°C
pH
3.09
1.65
12.61
Acid Mass
7.54gram of SO42-
Base Mass
4.175gram of Na+-
4.2.3 The Use of 0.7A on 11.8 g on Na2SO4
The use of 0.7A was the third current density applied in the BMED. The value of the initial
parameters as shown in Table 4.3 was recorded, change in volume, conductivity, weight,
temperature, and pH of each of the salt, acid, and base solution. Table 4.3 shows the final result
of the parameters after the BMED process. The values of the mass of acid and base produced
from the BMED is presented in Table 4.3. The acid, base and salt solutions were taken for
analysis after the BMED to determine the level of purity of the acid and base produced. In
addition, the total dissociation of the sodium sulphate into sulphuric acid and sodium hydroxide
is shown in Table 4.3. The total time of the experiment was 105 minutes.
20
Table 4.3:The use of 0.7A on 11.8gram of Na2SO4 Solution on the BMED
Initial values
of salt before
BMED
Solution
feed( Na2SO4)
acid
Base
Volume
1L
1L
1L
Conductivity
13.76ms/cm
0.53µc/ms
0.34µs/cm
Weight
1003g
990.60g
989.35g
Temperature°C
23.7°C
23°C
22.9°C
pH
6.36
6.8
7.29
Final values of
Salt before
BMED
Solution
feed( Na2SO4)
acid
base
Volume
935ml
995ml
1L
Conductivity
898µs/cm
37.1ms/cm
36.2ms/cm
Weight
926g
989g
1002.4g
Temperature°C
25°C
19.2°C
21.8°C
pH
3.13
1.75
12.46
Ions analysis
and mass base
of acid and
produced
SO42-mol/L ions
0.003029483 salt
0.066461231 acid
0.001145165 base
Na+ mol/L ions
0.003406114 salt
0.005633188 acid
0.130524017 base
Acid Mass
8.174g of SO42-
Base Mass
3.959 of Na+
4.3 The Effect of Volume on 11.8 g of Na2SO4 solution at a 0.7A
The application of the various types of volumes was used in this experiment, Using 1.5L of salt
solution and 1L each of acid and base. Use 1L of salt solution and 0.5L each of acid and base.
Then the use of 1.5L of salt solution and 0.5L of acid and base solution.
4.3.1 The effect of volume 1.5L of salt solution and 1L Acid and Base
The use of 1.5L of salt solution and 1L acid, and 1L base was the first volume ratio that was
used in the BMED. The value of the initial parameters, as shown in Table 4.4 was recorded,
change in volume, conductivity, weight, temperature, and pH of each of the salt, acid, and base
solution. Table 4.4 shows the final result of the parameters after the BMED process. The values
of the mass of acid and base produced from the BMED is presented in Table 4.4. The acid,
base and salt solutions were taken for analysis after the BMED to determine the level of purity
of the acid and base produced. In addition, the total dissociation of the sodium sulphate into
sulphuric acid and sodium hydroxide is shown in Table 4.4.
21
Table 4.4:The result of using a current of 0.7A with a concentration of 11.8gram of Na 2SO4
using a 1.5L of salt solution and 1L of acid and base solution.
Volume Conductivity
Weight
Temperature°C
Initial values
Solution
feed( Na2SO4)
1.5L
14.03ms/cm
1499.6g
21°C
of salt before
acid
1L
1.3µc/cm
991.45g
21.7°C
BMED
Base
1L
0.13µs/cm
995.8g
19.6°C
Final values of
Salt before
BMED
Solution
feed( Na2SO4)
acid
base
Ions analysis
and mass base
of acid and
produced
SO42-mol/L ions
0.002654701 salt
0.11641126 acid
0.001270092 base
Volume
1.4L
1L
1.01L
Conductivity
0.99ms/cm
56.0ms/cm
52.0ms/cm
Na+ mol/L ions
0.003842795 salr
0.006724891 acid
0.20558952 base
Weight
1415.65g
1001.55g
1012.45g
Temperature°C
23.9°C
19°C
16.4°C
Acid Mass
11.527 g of SO42-
was used in the BMED. The value of the initial parameters as shown in Table 4.5 was recorded,
change in volume, conductivity, weight, temperature, and pH of each of the salt, acid, and base
solution. Table 4.5 shows the final result of the parameters after the BMED process. The values
of the mass of acid and base produced from the BMED are presented in Table 4.5. The acid,
base and salt solutions were taken for analysis after the BMED to determine the level of purity
of the acid and base produced. In addition, the total dissociation of the sodium sulphate into
22
pH
2.98
1.56
12.7
Base Mass
5.5176 g of Na+
4.3.2 The effect of volume 1L of salt solution and 0.5L Acid and Base
The use of 1L of salt solution and 0.5L acid and 0.5L base was the second volume ratio that
sulphuric acid and sodium hydroxide is shown in Table 4.5.
pH
6.66
7.32
7.32
Table 4.5:A volume of 1L salt and 0.5L each for acid and base on 11.8gram of Na2SO4
Volume Conductivity
Weight
Temperature°C
Initial values
Solution
feed( Na2SO4)
1L
13.95ms/cm
1004.3g
24.5°C
of salt before
acid
0.5L
0.51µs/cm
495g
19.5°C
BMED
Base
0.5L
0.49µs/cm
497.55g
21°C
Final values of
Salt before
BMED
Solution
feed( Na2SO4)
acid
base
Ions analysis
and mass base
of acid and
produced
SO42-mol/L ions
0.002925377 salt
0.151505372 acid
0.001530357 base
Volume
970ml
499ml
530ml
Conductivity
120µs/cm
68.2ms/cm
62.4ms/cm
Na+ mol/L ions
0.00371179 salt
0.026375546 acid
0.24069869 base
Weight
954.95g
493.50g
531.30g
Temperature°C
25.3°C
21°C
19°C
Acid Mass
14.89 g of SO42-
The use of 1.5L of salt solution and 1L acid and 1L base was the third volume ratio that was
used in the BMED. The value of the initial parameters, as shown in Table 4.6 was recorded,
change in volume, conductivity, weight, temperature, and pH of each of the salt, acid, and base
solution. Table 4.6 shows the final result of the parameters after the BMED process. The values
of the mass of acid and base produced from the BMED is presented in Table 4.6. The acid,
base and salt solutions were taken for analysis after the BMED to determine the level of purity
of the acid and base produced. In addition, the total dissociation of the sodium sulphate into
23
pH
2.9
1.74
12.49
Base Mass
6.97 g of Na+
4.3.3 The effect of volume 1.5L of salt solution and 0.5 L Acid and Base
sulphuric acid and sodium hydroxide is shown in Table 4.6.
pH
6.72
7.62
7.62
Table 4.6:A volume of 1.5 L salt and 0.5L each for acid and base on 11.8 g of Na2SO4
Initial values
of salt before
BMED
Solution
feed( Na2SO4)
acid
Base
Volume
1.5L
0.5L
0.5L
Conductivity
13.9ms/cm
55.0µs/cm
0.77µs/cm
Weight
1509.1g
495.85g
499.85g
Temperature°C
23.7°C
22.5°C
21.5°C
pH
6.36
7.14
7
Final values of
Salt before
BMED
Solution
feed( Na2SO4)
acid
base
Volume
1.4L
0.678L
0.745L
Conductivity
1084µs/cm
77.1ms/cm
69.3ms/cm
Weight
1423.9g
673.8g
745.8g
Temperature°C
25.3°C
21°C
19°C
pH
3
1.51
12.46
Ions analysis
and mass base
of acid and
produced
SO42-mol/L ions
0.002675523 salt
0.172430665 acid
0.003831099 base
Na+ mol/L ions
0.003537118 salt
0.020480349 acid
0.251266376 base
Acid Mass
16.42 g of SO42-
Base Mass
7.2135 g of Na+
4.4 The Effect of Different Concentrations on 1L of Na2SO4 and 0.5L Acid and Base of
Solution at 0.7A
The application of the various type of concentrations was used in this experiment, The use of
16.3gram and 18.5gram salt concentration solution. The current of 0.7A and volume of 1.5L
of salt and 0.5L were kept constant.
4.4.1 The use of 16.3 g of Na2SO4 on the BMED
The use of 16.3 g of Na2SO4 was the first salt concentration that was used in the BMED. The
value of the initial parameters, as shown in Table 4.7 was recorded, change in volume,
conductivity, weight, temperature, and pH of each of the salt, acid, and base solution. Table
4.7 shows the final result of the parameters after the BMED process. The values of the mass
of acid and base produced from the BMED is presented in Table 4.7. The acid, base and salt
solutions were taken for analysis after the BMED to determine the level of purity of the acid
and base produced. In addition, the total dissociation of the sodium sulphate into sulphuric acid
and sodium hydroxide is shown in Table 4.7.
24
Table 4.7:The result of 16.3 g of Na2SO4 on the BMED
Volume Conductivity
Initial values
Solution
feed( Na2SO4)
1L
18.05ms/cm
of salt before
acid
0.5L
121.5µs/cm
BMED
Base
0.5L
0.82µs/cm
Final values of
Salt before
BMED
Solution
feed( Na2SO4)
acid
base
Ions analysis
and mass base
of acid and
produced
SO42-mol/L ions
0.002842092 salt
0.200143666 acid
0.003164821 base
Volume
0.940L
0.445L
0.565L
Conductivity
1.102ms/cm
87.3ms/cm
76.7ms/cm
Na+ mol/L ions
0.003580786 salt
0.025545852 acid
0.29 base
Weight
1002.1g
499.9g
498.5g
Temperature°C
23.7°C
22.5°C
21.5°C
pH
6.29
7.24
6.93
Weight
928.55g
444.10g
564.9g
Temperature°C
25.3°C
21°C
19°C
pH
2.98
1.6
12.39
Acid Mass
19.39 g of SO42-
Base Mass
22.9 g of Na+
4.4.2 The use of 18.3 g of Na2SO4 on the BMED
The use of 18.3 g of Na2SO4 was the second t salt concentration that was used in the BMED.
The value of the initial parameters, as shown in Table 4.8 was recorded, change in volume,
conductivity, weight, temperature, and pH of each of the salt, acid, and base solution. Table
4.8 shows the final result of the parameters after the BMED process. The values of the mass
of acid and base produced from the BMED is presented in Table 4.8. The acid, base and salt
solutions were taken for analysis after the BMED to determine the level of purity of the acid
and base produced. In addition, the total dissociation of the sodium sulphate into sulphuric acid
and sodium hydroxide is shown in Table 4.8
25
Table 4.8:The result of 18.3 g of Na2SO4 before the BMED
Volume Conductivity
Initial values
Solution
feed(
Na
SO
)
1L
20.12ms/cm
of salt before
2
4
acid
0.5L
0.67µs/cm
BMED
Base
0.5L
o.76µs/ms
Final values of
Salt before
BMED
Solution
feed( Na2SO4)
acid
base
Ions analysis
and mass base
of acid and
produced
SO42-mol/L ions
0.002894145 salt
0.293849421 acid
0.004424502 base
Volume
0.925L
0.490L
0.535L
Conductivity
1.053µs/cm
98.3ms/cm
86.1ms/cm
Na+ mol/L ions
0.006462882 salt
0.031659389 acid
0.329650655 base
Weight
1006.8g
499.9g
498.5g
Temperature°C
24.3°C
18°C
18°C
pH
6.45
7.05
6.88
Weight
909.63g
493.3g
551.40g
Temperature°C
25.3°C
21°C
19°C
pH
2.99
1.67
12.58
Acid Mass
21.13 g of S042-
Base Mass
9.686 g of Na+
4.5 The Use of Real Wastewater
The use of this parameter was used in this experiment 0.7A, 1L of wastewater, 0.5L of acid,
and base solution of deionized water.
This is made use of different filtration before the bipolar membrane electrodialysis which was,
microfiltration, ultrafiltration, and nanofiltration.
Observation was made on the effect of microfiltration, ultrafiltration and nanofiltration verse
microfiltration and ultrafiltration.
4.5.1 Microfiltration, Ultrafiltration and Nanofiltration Wastewater
The use of microfiltration, ultrafiltration, and nanofiltration of the wastewater was the first
filtration processed wastewater that was used in the BMED. The value of the initial parameters,
as shown in Table 4.9 was recorded, change in volume, conductivity, weight, temperature, and
pH of each of the salt, acid, and base solution. Table 4.9 shows the final result of the parameters
after the BMED process. The values of the mass of acid and base produced from the BMED is
presented in Table 4.9. The acid, base and salt solutions were taken for analysis after the BMED
to determine the level of purity of the acid and base produced. In addition, the total dissociation
of the sodium sulphate into sulphuric acid and sodium hydroxide is shown in Table 4.9.
26
Table 4.9:The BMED of Microfiltration, Ultrafiltration and Nanofiltration Wastewater
Volume Conductivity
Weight Temperature°C
Initial values
Solution
feed( Na2SO4)
1L
13.01 ms/cm
1000.6 g
24.3°C
of salt before
acid
0.5L
0.46 µs/cm
495.45 g
18°C
BMED
Base
0.5L
0.54 µs/cm
496.55 g
18°C
Final values of
Salt before
BMED
Solution
feed( Na2SO4)
acid
base
Ions analysis
and mass base
of acid and
produced
SO42-mol/L ions
0.00229 salt(final)
0.138555 acid
0.001374 base
0.063546
salt(initial)
Volume
0.925 L
0.49 L
0.47 L
Conductivity
1.099 µs/cm
45.7 ms/cm
21.32 ms/cm
Na+ mol/L ions
0.003624salt(final)
0.004017acid
0.064192base
Final salt solution
Acid
Base
Initial salt solution
Final salt solution
Acid
Base
Initial salt solution
Temperature°C
25.3°C
21°C
19°C
pH
2.97
1.67
12.46
Acid Mass
103.02 g of S042-
Base Mass
4.46 g of Na+
PO4-P mol/L
0.002208
0.000956
0
0.003338
NH4-N mol/L
0.001084
0.050132
0.056086
0.082437
K mol/L
0.000102
0
0.003913
0.002865
Ca mol/L
0
0.000125
0.000324
0.000125
0.022838 salt(intial)
DOC mg/L
ion analysis
of other
compound
present
in the
wastewater
Weight
958.67 g
489.75 g
468.15 g
pH
3.01
6.56
6.15
8.3
13.8
Cl mol/L
0.000649
0.00488
0.000677
0.002764
4.5.2Microfiltration and Ultrafiltration Wastewater
The use of microfiltration, ultrafiltration, and nanofiltration of the wastewater was the first
filtration processed wastewater that was used in the BMED. The value of the initial parameters,
as shown in Table 4.10 was recorded, change in volume, conductivity, weight, temperature,
and pH of each of the salt, acid, and base solution. Table 4.10 shows the final result of the
parameters after the BMED process. The values of the mass of acid and base produced from
the BMED is presented in Table 4.10. The acid, base and salt solutions were taken for analysis
after the BMED to determine the level of purity of the acid and base produced. In addition, the
27
total dissociation of the sodium sulphate into sulphuric acid and sodium hydroxide is shown in
table 4.10
Table 4.10:The use of real wastewater that has pass-through microfiltration, and ultrafiltration
on the BMED
Volume Conductivity Weight Temperature°C
Initial values
Solution
feed( Na2SO4)
1L
25.1 ms/cm
984.5 g
22.9 °C
of salt before
acid
0.5L
0.0167 µs/cm 501.6 g
19.4 °C
BMED
Base
0.5L
0.0167 µs/cm 500.5 g
19.4 °C
Final values of
Salt before
BMED
Solution
feed( Na2SO4)
acid
base
Ions analysis
and mass base
of acid and
produced
SO42-mol/L ions
Na+ mol/L ions
0.17368 salt(final)
0.230407 acid
0.003665 base
0.002405 salt(intial)
0.063886 salt(final)
0.230407 acid
0.117729 base
0.005328 salt(initial)
Volume
0.95L
0.55L
0.53L
Conductivity
1.33 µs/cm
66.8 ms/cm
38.7 ms/cm
TOC mg/L
ion anaysis
of other
compound
present
in the
wastewater
Weight Temperature°C
988.95g
2.8°C
556.9 g
1.49°C
527.25 g
12.6°C
pH
0.95
0.55
0.53
Acid Mass
157.66g of S042-
Base Mass
11.84 g of Na+
NH4-N mol/L
0.208981
0.161576
0.101178
0.001152
Ca mol/L
0.000125
0.000299
0.000848
0.000125
final salt solution
Acid
Base
initial salt solution
7.5
21.6
168
PO4-P mol/L
0.008142
0.002383
0
0.004901
final salt solution
Acid
Base
initial salt solution
Cl mol/L
0.005416
0.013089
0.003385
0.000733
K mol/L
0.007008
0.001432
0.009259
0.000102
28
pH
2.65
6.78
6.78
CHAPTER FIVE: DISCUSSION
The primary purpose of this work was to use the BMED for remediation of sodium sulphate
wastewater to produce sodium hydroxide and sulphuric acid. Different parameters were tested
and optimized during the experiment to obtain the best possible recovery rate of the ions from
the wastewater. The parameters considered were current density, volume, the concentration of
the salt solution, and the filtration method.
5.1 The Effect of Current Density
The current density played a vital role during the experiment. The current density is the driving
force for splitting ions that lead to the formation of acid and base (Chen et al., 2020).
The lab-scale current used in this experiment was 0.3A, 0.5A, and 0.7A on a concentration of
11.8gram of sodium sulfate, a volume of 1L of salt solution chamber, and 1L of acid and base
solution chamber.
When 0.7A of current was used, it produced a mass of sulphate of 8.174 g and sodium ion of
3.959 g as indicated in Table 4.3. The mass of the acid produced by 0.7A current was higher
by 7.7% compared to 0.5A (Table 4.3) and 6.3% compared to 0.3A (Table 4.3). The mass of
base from 0.7A was 3.959 g which was lower by 5.17% when compared to 0.5A which
produced a total mass of 4.175 g.
The overall performance of the dissociation of sodium ion and sulphate ion from the
wastewater by 0.7A was 12% effective compared to 0.3A and 18% better when compared to
0.5A.
When the current density is not sufficient, it will take a longer time for the dissociation from
the salt solution, which will lead to the building up of concentration gradient across the
membrane. The concentration gradient will lead to the back neutralization of the solution, co
ion transfer across the membrane and increase in energy consumption (Mariusz et al., 2014).
The current density of 0.7A showed a better dissociation of the ion when compared to 0.3A
and 0.5A using 1L of solution and 11.8 g. Although the use of 0.5A gave a better result in the
minimization of ion transfer across the membrane, as shown in Table 4.2.
5.2 The Effect of Volume
The effect of the volume ratio used in this experiment were 1L, 1.5L, and 0.5L. The use of 1L
of the acid, 1L base, 1L salt (Table 4.3), the use of 1.5L salt, 1L acid, 1L base (Table 4.4), the
use of 1.5 L salt solution, 0.5 L base, 0.5 L acid (Table 4.6) and 1L salt solution,0.5L acid, and
0.5L base (Table 4.5).
29
The constant parameter during the volume ratio experiment was 11.8 g of sodium sulphate
solution and 0.7A current. The volume ratio used was 3:1, which was 1.5L salt, 0.5 L acid,
and 0.5L base solution, ratio 2:1, which was 1L of the acid, 1L base, and 1L salt, and lastly
ratio 1:5:1, which was 1.5L salt, 1L acid, 1L base solution.
The different volume ratios used showed the ratio with good concentration, minimize co-ions
transfer, and minimum energy consumption. The volume ratio of 3:1 produced a mass of
sulphate of 16.42 g and 7.2135 g of sodium which were higher by 9% and 3% when compared
to a 1L salt solution,0.5L acid, and 0.5L base.
The volume ratio of 3:1 was 29% higher in sulphate mass and 25% in sodium mass compared
tolume ratio 1.5L salt, 1L acid, 1L base. Lastly, when compared to 1L of the acid, 1L base, and
1L salt, it was 50% higher in the mass of acid produced and 45% in the mass of base produced.
The ion analysis results in the Table 4.4 showed that 1.5L salt, 0.5 L acid, and 0.5L gave the
highest compound dissociation of the ion from the salt solution by the percentage of 3% and
had the highest level of co-ion transfer across the membrane due to high concentration gradient
across the membrane.
5.3 The Effect of Concentration
The initial concentration of the salt solution plays a huge role during the electrodialysis process.
The high concentration of salt solution produces a good mass of acid and base concentration,
but the level of co-ion movement across the membrane was high when Table 4.32 compared
to Tables 4.28 and 4.17. This is due to the rapid increase of the concentration gradient across
the membrane.
5.4 The Sample Wastewater
During the fermentation process sulphuric acid was used to control the pH value of the medium.
There are microorganisms called Sulfolobus acidocaldarius, which have shown potential in the
production of pharmaceuticals. For the organism to be used in the fermentation process, the pH
value of the medium has to be maintained at pH 3.0. Sodium sulphate was to simulate the
wastewater for the fermentation.
5.5 Filtration Process
Three major filtrations were carried out; microfiltration, ultrafiltration, and nanofiltration.
The effect of the filtration was observed on the amount of acid and base produced. The main
reason filtration was done was to increase the purity of the final solution of acid and base, avoid
30
the scaling of the bipolar membrane by calcium and magnesium, and reduce the production
time.
5.6 Microfiltration
Microfiltration membrane removed microscopic particles and organisms that could damage the
bipolar membrane during electrodialysis.
5.7 Ultrafiltration
Ultra-filtration was used for the removal of bacteria, viruses and parasites on a microscopic
level from the wastewater because the organisms reduces the operating performance of the
electrodialysis process, and the final output of the process.
5.8 Nanofiltration
Nanofiltration was used to remove divalent ions such as calcium and magnesium present in the
wastewater. The Mg2+ and Ca2+ cause membrane fouling as deposition of this compound on
the membrane during the electrodialysis process. The use of the nanofiltration had side effects
on the total mass of acid and base produced. It was observed the use of the nanofiltration
removed some of the sodium sulphate salt from the waste water when compared with another
filtration method that was just done with microfiltration and ultrafiltration. The total acid and
base production without the use of nanofiltration was 34.7% higher in acid and 42% higher in
base production.
The concentration of the final acid and base produced when the nanofiltration was applied was
of a good result, but it had the highest level of co-ion transferred across the membrane. The
level of ion transfer across the membrane was 76.2% on the transfer of sodium ion to the
sulphate ion chamber and 62% higher on the transfer of sulphate to the sodium ion chamber
see Tables 4.9.
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CHAPTER SIX: CONCLUSION AND RECOMMENDATION
6.1 Conclusions
Bipolar membrane electrodialysis was investigated as an innovative separation technique for
the reclamation of sodium hydroxide and sulfuric acid in sodium sulphate wastewater in this
study. In this study, evaluation criteria and operating variable controlling the finished product
was defined and used to show the suitability of the BMED technology. Overall experimental
findings indicated that BMED is an effective separation technique. The BMED technology, in
coupled with high efficiency desalination, enables for the generation of sodium hydroxide and
sulfuric acid using sodium sulphate effluent.
Once all variables were evaluated, the overall desalination percentage surpasses 70%, as well
as the salt-based acid and base conversion percentages ,vary around 60% and 80%. The BMED
method enables for desalination as well as acid and base extraction even without the formation
of additional waste. Furthermore, due to the obvious co-ion transition, reverse diffusion, and
electro-osmosis, energy consumption is a key limitation of BMED.
6.2 Recommendations
The major limitation were co-ion transition, and back diffusion, can be reduced
by the structural improvement of ion exchange membranes. Thus, both energy efficiency and
product yield can be increased. The use of bipolar membrane electrodialysis can be used to
recover acid and base from high salinity wastewater solution from the environment and this
helps to achieve a sustainable technology for the reduction of pollution in the environment.
32
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