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. 31 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 REFERNCES Akhter, M., Habib, G., & Qamar, S. U. (2018). Application of electrodialysis in waste water treatment and impact of fouling on process performance. Journal of Membrane Science & Technology, 8(02). Balster, J., Stamatialis, D. F., & Wessling, M. (2004). Electro-catalytic membrane reactors and the development of bipolar membrane technology. Chemical engineering and processing: process intensification, 43(9), 1115-1127. Chen, Q. B., Wang, J., Liu, Y., Zhao, J., Li, P. F., & Xu, Y. (2021). Sustainable disposal of seawater brine by novel hybrid electrodialysis system: Fine utilization of mixed salts. Water Research, 201, 117335. Chen, X., Ruan, X., Kentish, S. E., Li, G. K., Xu, T., & Chen, G. Q. (2021). Production of lithium hydroxide by electrodialysis with bipolar membranes. Separation and Purification Technology, 274, 119026. Chen, Y., Wrubel, J. A., Klein, W. E., Kabir, S., Smith, W. A., Neyerlin, K. C., & Deutsch, T. G. (2020). High-performance bipolar membrane development for improved water dissociation. ACS Applied Polymer Materials, 2(11), 4559-4569. De Kler, R.C.F., Legrand, L., Schaetzle, O. Hamelers, H. V. M. (2018). Solvent-Free CO2 Capture Using Membrane Capacitive Deionization. Environmental Science & Technology 52 (16), 9478-9485. Friedric.,G.W.,(2001). Bipolar Membrane Electrodialysis –Membrane Development and Transport Characteristics. Twente University Press (TUP). Frederik, W., Luis, F., Stephanie, O., Xavier, D., Johann G., Jean, L., (2021). Recovery approaches for sulfuric acid from the concentrated acid hydrolysis of lignocellulosic feedstocks: A mini-review. Energy Conversion and Management: X, (10) 1000074. Fu, L., Gao, X., Yang, Y., Aiyong, F., Hao, H., & Gao, C. (2014). Preparation of succinic acid using bipolar membrane electrodialysis. Separation and Purification Technology, 127, 212-218. Gawaad, R. S., Sharma, S. K., & Sambi, S. S. (2011). Sodium sulphate recovery from industrial wastewater using nano-membranes: A review. International Review of Chemical Engineering, 3(3), 392-398. Giesbrecht, P. K., & Freund, M. S. (2020). Recent advances in bipolar membrane design and applications. Chemistry of Materials, 32(19), 8060-8090. Jan, Kroupa., Jan, Kincl., Jiril, C., (2014). Recovery of H 2SO4 and NaOH from Na2SO4 by electrodialysis with heterogeneous bipolar membrane. Desalination and Water Treatment 56(12),3238-3246. 33 Jian, C., Yu, X., Ru, Y., Meng, W.,(2021). An electrodialysis-based coupling technique for simultaneous reclamation of waste acid and cleaner production of organic acid. Journal of Membrane Science 638, 119683. Katarina, K., Daniela,R., Michael, H., Jorg, k., Norbert, K., (2021). Assessment of Graphical Methods for Determination of the Limiting Current Density in Complex Electrodialysis-FeedSolutions. Membranes 12(2),241. Kujawski, W., Yaroshchuk, A., Zholkovskiy, E., Koter, I., & Koter, S. (2020). Analysis of membrane transport equations for reverse electrodialysis (RED) using irreversible thermodynamics. International Journal of Molecular Sciences, 21(17), 6325. Li, Y., Shi, S., Cao, H., Wu, X., Zhao, Z., & Wang, L. (2016). Bipolar membrane electrodialysis for generation of hydrochloric acid and ammonia from simulated ammonium chloride wastewater. Water research, 89, 201-209. Nowak, M., Jaroszek, H., & Turkowska, M. (2014). Conversion of waste sodium sulfate with bipolar membrane electrodialysis. Membranes and Membrane Processes in Environmental Protection, 119(June), 337-349. Pärnamäe, R., Mareev, S., Nikonenko, V., Melnikov, S., Sheldeshov, N., Zabolotskii, V., ... & Tedesco, M. (2021). Bipolar membranes: A review on principles, latest developments, and applications. Journal of Membrane Science, 617, 118538. Peng, S., Xu, X., Lu, S., Sui, P. C., Djilali, N., & Xiang, Y. (2015). A self-humidifying acidic– alkaline bipolar membrane fuel cell. Journal of Power Sources, 299, 273-279. Pourcelly, G. (2002). Electrodialysis with bipolar membranes: principles, optimization, and applications. Russian Journal of Electrochemistry, 38(8), 919-926. Shen, C., Wycisk, R., & Pintauro, P. N. (2017). High performance electrospun bipolar membrane with a 3D junction. Energy & Environmental Science, 10(6), 1435-1442. Tuovinen, T., Tynjälä, P., Vielma, T., & Lassi, U. (2021). Utilization of waste sodium sulfate from battery chemical production in neutral electrolytic pickling. Journal of Cleaner Production, 324, 129237. Wen-Qiong, W., Yun-Chao, W., Xiao-Feng, Z., Rui-Xia, G., & Mao-Lin, L. (2019). Whey protein membrane processing methods and membrane fouling mechanism analysis. Food Chemistry, 289, 468-481. Wang, M., Wang, K. K., Jia, Y. X., & Ren, Q. C. (2014). The reclamation of brine generated from desalination process by bipolar membrane electrodialysis. Journal of membrane science, 452, 54-61. Wilhelm, F. G. (2001). Bipolar membrane electrodialysis. University of Twente. Yan, Z., Zhu, L., Li, Y. C., Wycisk, R. J., Pintauro, P. N., Hickner, M. A., & Mallouk, T. E. (2018). The balance of electric field and interfacial catalysis in promoting water 34 dissociation in bipolar membranes. Energy & Environmental Science, 11(8), 22352245. Zhang, Y., & Angelidaki, I. (2015). Recovery of ammonia and sulfate from waste streams and bioenergy production via bipolar bioelectrodialysis. Water research, 85, 177-184. 35