CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
Man’s primary need is to have access to a clean and sufficient supply of water because water essentially serves a vital need in domestic, agricultural, and industrial activities. Elimelech and Phillip (2011) reported that consistent access to clean water is considered a core function of countries as they usher in public health, national security, and economic vitality. Despite the fact that three-fourths of the world is covered with water, the world now still considers freshwater shortage as one of the major global concerns that have to be solved. There is a major demand for low-saline water in industrial development and for supplies of safe drinking water, but present natural resources are not sufficient to address this need. This high demand for water and its decreasing supply birthed multiple solutions and alleviation plans like water conservation, water dam construction, among others. However, these solutions and plans proved to be insufficient for such a growing need; this current situation was taken into consideration in water treatment – a focus on the discovery and the development of new ways and techniques to get clean water from the abundant ever-present seawater is done.
Desalination as a water source is very potent and could be a major solution to this global dilemma, however, desalination technologies are very expensive and could cause mounting energy requirements for a given country where they are located (Cohen et al., 2018). One appropriate method for desalination is Electrodialysis (ED), it is one of the most important membrane filtration technologies these days. This process has been widely used in desalination as it removes electrically-charged particles in a given solution by utilizing ion-exchange membranes. More researches are focused on reducing operation cost of desalination plants and have been directed towards development of cost-effective
membrane filtration: feed concentration (McGovern et al., 2014; Sadrzadeh &
Mohammadi, 2008), fouling and scaling (Bahadori, 2016; Gray et al., 2011), membrane composition (Largier et al., 2017), membrane stacking (Kim et al, 2021; Pawlowski et al., 2014) and the use of cheaper alternative energy sources: photovoltaic (Wright &
Winter, 2014), solar-powered (Charcoset, 2009; Khawaji et al., 2008).
Recent advances on ion-exchange membranes (IEM) were done as these are applied broadly to many industrial applications. The preparations for IEMs proved to be challenging since desirable IEMs should possess high conductivity or low resistance, high-ion exchange capacity, permselectivity, among others. Although a lot of studies have been done before, high-ion exchange capacity is still very much interesting for the present study as one of the primary properties in the removal of sodium ions that is very important in desalination. A research on membranes was made using locally produced concrete as permeable membrane. The said project used a recyclable concrete for membrane filtration and utilized renewable solar energy. The study’s result showed that dissolved ions from water can move through concrete if there is a pressure gradient, or by diffusion due to a concentration gradient if pressure head is absent. With the aid of an electrical field, ion diffusion become accelerated, such as chloride into concrete. The diffusion rate of Cl- ions is dependent on the applied voltage and the thickness of the concrete membrane. However, sodium ions were found to be less efficient (Abulencia et al., 2012; Mindness et al., 2003). Further study needs to be conducted to improve the concrete membrane using natural ion-exchange materials such as zeolites.
Zeolites are used in membrane-based filtration technologies (Drobek et al. 2012;
Kazemimoghadam, 2010; Lee et al. 2011; Zhua et al. 2013). Zeolites act as adsorbents that allow ion exchanges (He et al. 2013; Ma et al. 2012; Qin et al. 2010; Swenson et al.
2012; Wanga and Peng, 2010; Zhua et al. 2013). These can be natural or synthetic. Many of the known synthetic zeolites used and studied are from agricultural waste by-products like burnt rice husk ash (RHA) (Ali et al. 2011; Bhavornthanayod and Rungrojchaipon, 2009; Bohra et al. 2014; Chareonpanich et al. 2004; Cheng et al. 2012; Dey et al. 2013;
Katsuki and Komarneni, 2009; Kordatos et al. 2008; Mohamed et al. 2015; Panpa and Jinawath, 2009; Petkowicz et al. 2008), and sugarcane bagasse ash (SCBA) (Moises et al. 2013; Purnomo et al. 2012), etc.
Several research were made using agricultural waste materials for zeolite synthesis but there are no investigations done to further reveal the potent utilization of corn stover ash to synthesize zeolite A. This research investigated a novel potential alternative IEM with synthesized zeolite A from corn stover ash to the conventional ion- exchange membranes, as an inexpensive and environmentally sustainable membrane for ED desalination system used in the removal of sodium ion.
1.2 Problem Statement
Desalination technologies are widely used water treatment process that are generally considered expensive and complex because it requires large operating cost, high energy supply and electrical expenditure, quality standard materials and equipment for membrane maintenance and technical skilled manpower. In addition, the disposal of waste products such as plastics and polymer membranes are drawbacks because of their negative environmental impacts.
In the research project done utilizing a novel ion exchange membrane for desalination method that used locally produced concrete slabs as permeable membrane, they were able to give solution on the abovementioned problems on operation cost and energy supply. It was a system that was designed to be environmental-friendly, inexpensive, and easy to produce, assemble, operate, and maintain. It utilized recyclable concrete slabs for membrane and renewable solar energy. This project was successful in removing chloride (Cl-) ions from salt water. However, sodium (Na+) ions were less efficiently removed. The challenge now is how to enhance Na+ ion diffusion effectively.
Given the fact that zeolites are considered ion-exchange enhancers, which contribute a significant role in membrane filtration technologies and many of the well-studied synthesized zeolites come from agricultural by-products such as rice husk ash, and
sugarcane bagasse ash, the researcher endeavors to use another potent zeolite source which is corn stover ash.
This paper’s main challenge is to investigate the potential use of corn stover ash as zeolites for ion exchange membranes and to determine its feasibility to efficiently remove Na+ ions in the ED desalination method. Moreover, this study focused on the optimization of variable parameters such as calcination temperature, alkalinity and curing time in synthesizing zeolite, particularly zeolite A; and binder ratio, applied voltage, and the number of cell pairs required to achieve the desired freshwater quality in the ED desalination system.
1.3 Objective of the Study 1.3.1 General Objective
This study aims to develop an electrodialysis (ED) desalination system using cement mortar-structured zeolite membrane (CMSZ) with natural ion-exchanging material such as zeolite A from corn (Zea Mays) stover ash.
1.3.2 Specific Objectives
In order to achieve the general objective of the study, the following specific objectives were carried out:
1. prepare zeolite A from corn stover ash using the hydrothermal synthesis method;
2. investigate the effects of the different parameters (calcination temperature, alkalinity, and curing time) in synthesizing zeolite A in terms of percentage yield;
3. characterize the synthesized zeolite A in terms of physicochemical, morphology, and phase identification;
4. convert zeolite NaA to zeolite HA and determine the cation exchange capacity (CEC) of zeolite HA;
5. determine the optimum parameters (calcination temperature, alkalinity, and curing time) in the hydrothermal synthesis of zeolite A using corn stover ash for the % yield and CEC;
6. investigate the effects of binder ratio and voltage in the ED desalination system using cement mortar-structured zeolite membrane; and,
7. determine the optimum parameters (binder ratio, voltage, and cell pairs) in the ED desalination system for sodium ion removal.
1.4 Significance of the Study
Corn is the second-leading Philippine agricultural yield next to rice. It is said to be one major staple substitute for rice and a primary source of animal feed. Corn could therefore create mounting agricultural residues, possibly producing a ton of corn cobs annually. This study will significantly impact the waste utilization of corn by-products to eliminate this rising problem in some agricultural areas of the country. The use of environmentally friendly material for synthesizing zeolite A from corn stover ash helps reduce waste generation.
This study also furthers technology application as it has primarily designed to develop a new potential alternative ion exchange membrane made from cementitious mortar with synthesized zeolite from corn stover ash, for ED desalination system that is simple, readily available, and economical for rural communities to gain access to clean and fresh water.
1.5 Scope and Limitation
This current paper aimed to improve the efficiency of the water filtration system by removing additional contaminants, particularly sodium ions, using a new potential
alternative ion exchange membrane incorporating cementitious mortar and synthesized zeolite A derived from agricultural by-products, specifically corn stover ash.
The researcher conducted the following detailed processes:
Zeolite A was synthesized from carbonized corn stover ash under hydrothermal process. These were characterized using X-ray fluorescence spectroscopy (XRF), Brunauer-Emmett-Teller (BET) Surface Area Analysis, Thermogravimetry and differential thermal analysis (TG-DTA), Fourier transform infrared spectrometry (FT- IR), X-ray powder diffraction analysis (XRD), and scanning electron microscopy (SEM) at the Hinode Laboratory, Tokyo Institute of Technology in Tokyo, Japan.
In the hydrothermal synthesis of zeolite A, one factor at a time was used to investigate factors such as calcination temperature (300, 400, 500, 600, 700oC), alkalinity through fusion ratios (0.5, 1.0, 1.5, 2.0 ratios), and curing time (6, 9, 12, 24 hours). These were utilized to investigate the influence of these factors on the percentage yield and cation exchange capacity of zeolite A synthesized (CEC). Additionally, they served as the basis for optimizing the percent yield and CEC utilizing the response surface methodology with the central composite design through the multi-response surface method with desirability function of Design Expert® Software V.13.
Cement mortar-structured zeolite (CMSZ) membranes were made using a binder ratio (w/w) combination of Portland cement (CEMEX Type IP) and zeolite synthesized from corn stover ash in varied ratios of 95:5, 90:10, and 85:15. All mixes were made using a 4:1 mass ratio of fine aggregates to binder (F/B) and a 0.35 mass ratio of water to binder (W/B). None of the specimens were cured in water. There was no investigation of the CMSZ membranes’ physical and mechanical qualities, such as void content, compressive strength, or permeability.
Finally, the efficiency of the electrodialysis (ED) desalination system was determined. This system consists of an ED cell unit with a cell size of 110 x 110mm2, an
active membrane area of 64cm2 per membrane, and Pt/Ir MMO coated electrodes (supplied by PCA GmBH, Germany); liquid pumps; a DC power supply; and containers for electrode rinse, concentrate, and diluate. The ED system was constructed using cement mortar-structured, as an anodic membrane and cement mortar-structured zeolite as a cathodic membrane in different binder ratios and was operated continuously during the trials and at room temperature. For two (2) hours, prepared salt solution (0.5 M NaCl) was recirculated throughout the concentrate and diluate streams. The electrode rinsing solution was 0.5 M sodium sulfate (Na2SO4). The ED cell was supplied with concentrated, diluate, and electrode rinse solutions at a flow rate of 0.3 mL/s. The concentration of sodium ion was determined by Inductively Couple Plasma-Atomic Emission Spectroscopy (ICP-AES) method using SPS 7800 (SII). Different voltages of 5, 10, and 15V were utilized to determine the sodium ion removal percentage.
Additionally, this served as the foundation for optimizing sodium ion removal conditions utilizing response surface methodology with central composite design of Design Expert®
Software V.13.
