CHAPTER ONE
INTRODUCTION
1.1 Back ground of Study
From the ancient times to the present, water filters evolved out of necessity, first to remove materials that affect appearance, then to improve bad tastes and further to remove contaminants that can cause disease and illness (The Water Exchange, 2012). From the boiling of water to improve taste and then filtering through a cloth bag to the cartridge for removing bacteria from water and the ceramic pot filter developed by Dr. Fernado Mazariegos of the Central American Industrial Research Institute (ICAITI) in Guatemala, to make bacterially contaminated water safe for drinking (Doulton, 1997). Ceramic filters were popularly used for centralized water treatment but in recent times they are being manufactured for point of use application (NAS, 2008) and the World Health Organization encourages it’s use as household water treatment systems (HWTS) for effective treatment of drinking water. Clean water is one of the most important public health measures in providing major controls against infectious diseases apart from Safe food and up-to-date medical care. Estimates suggest that 1.5 billion people out of the world over 6.8 billion lack safe drinking water (Zimmerman et al., 2008). In developing countries, 90 percent of all diseases, which kill millions of children every year, are attributed to dirty water (Norman, 2007). Waterborne diseases (such as cholera, and typhoid fever), kill an estimated 5 million to 10 million people worldwide each year (Marquis et al., 2008).
Though many factors contribute to water contamination, climate change, poor infrastructures, and failed aid projects continue to exacerbate the problem. Climate change often stresses water supplies in area that are already water scarce, forcing residents to use unsanitary sources (Predis, 2011). In most African countries, recent foreign infrastructure efforts have had a failure rate of well over 50% amounting to several hundred million dollars of lost (Without accounting for the damage to local livelihoods) (UNICEF, 2012).
Conventional piped water has decade away in much of the developing world, as many of the poorest people must collect water outside the home (Sobsey, 2002). The importance and need for improvement of safe drinking water is highlighted by its presence in the United Nations list of Millennium Development Goals (WHO/UNICEF, 2005).
1.2 Statement of Problem
The water crisis affects millions worldwide and it is expected to worsen over the coming years and decades. Children as said earlier are the most affected by ingestion of contaminated water. 15% of deaths in children under 5 years old are associated with the nearly 2.5 billion case of diarrhea each year (Marquis, 2008). This means that every year 3.4 million children die as a result of diarrhea caused by waterborne microbes, making it the second leading cause of death of children, especially in low- and middle- income countries (Onda et al., 2012). The continued lack of sanitation infrastructure in many countries also leads to contamination of drinking water and affects health and development in the areas (Prussi-ustum et al., 2008). Indeed much of the water used in developing countries shows evidence of fecal contamination. This systematic problems limit progress in many worldwide development goals, such as improving life expectancy, child health and economic productivity (Wolf, 2007). Despite the effort of many non-governmental organisation (NGOs) and world governments, water infrastructure projects such as dams, treatment facilities, and piped-water networks have thus far failed to remedy these major health problems. Since assistance by the world bank first began in 1961, top-down development have been sincerely hampered by lack of political stability and public funding in many of the areas that are most affected by the water crisis (Nairobi, 2007; Bredie et al., 1998).
Several water filtration technologies have been started by educational initiatives and non-governmental organisations recently to resolve potable water scarcity (Sobsey et al., 2008). Chlorination with safe storage, chemical coagulant such as water maker(control chemical, Alexandra, VA), PUR (Proctor and Gamble, Cincinnati, OH), Sodium hypochlorite (SFH/ Nigeria), nut/seed organic medicinal materials, sunlight exposure techniques such as SODIS, SOLAIR, UV radiation technique, filtration techniques such as nano-membrane filtration, reverse osmosis technique, pureit (HLL. Ltd, UNILEVER Inc. India), Organic additive based ceramic filters, Kanchan MIT arsenic filter and bio-sand filters are the most studied and survey techniques used around the globe for water purification (Brown et al.,2007; CDC,2008; Clasen et al.2006a; Clasen et al.2007 Hillie et al.2009; Duke et al.2006; Ngai et al.2006, plapally et al. 2010, Sobsey et al. 2008). Among many options for household water treatment methods, ceramic filter candles are one of the promising techniques for the developing countries (Clasen, 2005). The fact is that ceramic filter candles can be manufactured by local ceramists using locally available materials that not only make it affordable but also make it an attractive point of use treatment technology.
1.3 Aim and Objectives of Study
The aim of this study is to produce a low cost filtration system (ceramic filter candle) using locally sourced materials for household water treatment.
The objectives are:
i. To design a low cost and easily manufactured water filtration System
ii. To determine the effectiveness of kaolin clay from Delta State and rice husk in developing a ceramic filter
iii. To investigate the effect of the proportion of kaolin and rice husk on the porosity of ceramic filter
iv. To investigate the dependence of the rate of percolation of water on the porosity of the filters
v. To determine the effectiveness of the produced ceramic filter candle in water treatment.
vi. To compare the results obtained with that of commercial filter.
1.4 Justification of Study
Majority of studies on ceramic filtration are carried out in developing countries such as Nigeria due to its affordability. Hence, this study is aimed at producing a ceramic filter from locally sourced materials for household water treatment system. It is expected that the results of this study will assist in acquiring more information on the effectiveness of ceramic filter in water treatment.
1.5 Scope of Study
The scope of the study involves;
The collection of kaolin samples from a Kaolin deposit at Ozanogogo Community, Delta State.
Collection of rice husk which will serve as a burnt-out material at new market, Enugu.
Evaluating the physical properties of the compounded clay such as apparent porosity, modulus of rupture, apparent density, and bulk density.
Producing the Ceramic filter candle with varying quantities of Kaolin and rice husk.
Disinfecting the filter Candle with Silver Nitrate or solar
Filtration of Water Sample.
Comparing the flow rates of the filter produced with that of commercially produced one.
Water analysis before and after treatment.
1.6 Significance of Study
The research carried out on filter candle showed that
Increasing the ratio of the rice husk in the filter candle increased the flow rate of the filter candle.
The colloidal silver that was added to the filter candle was able to remove bacteria present in the water sample.
It will serve as an effective method of treating water.
CHAPTER TWO
LITERATURE REVIEW
2.1 Water Filtration
Water filtration is a process of removing suspended and colloidal particles in water. It is principally concerned with the removal of insoluble impurities, biological or physical (George, 1992).
2.1.1 Types of Water Filtration Technique
Water filtration techniques include:
2.1.1.1 Solar Desinfection
Solar desinfection based on the principle of desinfection by solar radiation. The procedure is straight forward; an unscratched and uncoloured PET or glass bottle is filled with water and exposed to direct sunlight for a minimum of 6 hour (Heinsbroek and Peters, 2014).
2.1.1.2 Biosand filter
Biosand filter consist of a concrete or plastic frame filled with crushed rock (sand) filter media of 0.15-0.35mm particle (Murphy et al., 2010b). Two filter mechanisms govern the removal principle of biosand filters: physical removal if organic matter and turbidity (Sobsey et al., 2008) and biological removal of colloidal particles and harmful pathogens (Duke et al., 2006; Hunters, 2009; Weber-Shirk and Dick, 1997).
2.2 Ceramic Water Filter
The ceramic filter is based on the following principle: a porous medium of fired clay that retains microbes by size exclusion and high tortuous properties (Hunter,2009; Sobsey et al.,2008; Van der laan et al.,2014).The contaminants are physically prevented from moving through the filter either by screening them out with very small pores and/or, in the case of carbon filters, by trapping them within the filter matrix by attracting them to the surface of carbon particles (the process of adsorption). According to Randy (2005), a filter that removes particle down to 5 microns will produce fairly clean-looking water, but most of the water parasites, bacteria, crystoporidia, gladaria etc. will pass through the pores therefore, a filter must trap particles one micron or smaller to be effective at removing cryptosporidia, or giardia cysts. Viruses cannot be effectively removed by any filtration method. Randy (2005), further said that contaminant reduction can be by physical removal or contaminants are attracted to and held on the surface). The adsorption process depends on the following factors:
1. Physical properties such as pore size distribution and surface area
2. The chemical nature of the source, or the amount of oxygen and hydrogen associated with it.
3. Chemical composition and concentration of the contaminants
4. The temperature and the pH of the water
5. The flow rate or time exposure of water.
Ceramic Water filtration is therefore defined as an instrument or material, which removes something from whatever passes through it. Therefore, ceramic water filtration as defined by Brown, sobsey, porum (2007), is the process that makes use of porous ceramic (fired clay) medium to filter microbes or other contaminants from water. The pore size of the ceramic medium is sometimes small enough to trap anything bigger than a water molecule.
Ceramic water filtration for drinking water treatment has a long pedigree, having been used in various forms since ancient times. Modern historical references to ceramic water "drip filters with safe storage elements suggest that they have been used widely for over 100 years in Latin America and ceramic filters have been produced in Britain at least since 1850 (Brow et. al., 2008). Today pore sizes can be made small enough to remove virtually all bacteria and protozoa by size exclusion down to 0.2 micro meter in the range referred to as microfiltration. Ceramic filters are also often enhanced with a variety of silver containing microbiocidal amendments that are either painted onto the surface, impregnated into the ceramic matrix before or after firing, or applied to filter elements in other ways. Colloidal silver contains positively charged free ions and negatively charged particles. Free silver ions have a toxic effect on micro-organisms even their presence are relatively low in concentrations. Silver reacts with the thiol groups in both functional and structural proteins of the bacteria cell and inhibit glucose, succinate and lactate oxidation (Lantagne, 2001). The three main mechanism of colloidal silver are inhibiting the enzymatic activities, corroding the bacteria cell membranes and negatively interacting with nucleic acid (Russell et al., 1994). Despite knowing the importance of colloidal silver inhibiting and/or controlling microbial growth, ceramic filter without colloidal silver coating has been widely used. Ceramic filters are manufactured in a variety of shapes and sizes which include hollow candle filters, disk filters, and pot filters (matteiletea, 2006) and can be composed of a variety of materials, such as clay, or diatomaceous earth. Clay is a powdery material that forms from the wearing down of rocks containing aluminous compounds (Dies Dictionary, 2005). Clay also contains many chemical impurities which give it certain characteristics. For example, white kaolin is composed mainly of aluminium and silicate, while iron (III) oxide gives red clay its colour.
The advantages of locally produced ceramic filters are that they are portable, light in weight, affordable, and require low maintenance. Filters provide for removal of microorganisms from water by gravity filtration through porous ceramic, with typical flow rates of 1-3l/hr. Unlike chemical or thermal desinfection, ceramic filters do not significantly change water taste or temperature or reduce turbidity (clasen et al., 2004). They have a potentially long useful life of 5 years and above (Campbell, 2005) with proper care and maintenance, although manufacturers may recommend regular replacement of the filter element every 1-2years. The ceramic filter surface is regenerated through periodic scrubbing to reduce surface deposit that slow down filtration rates. The useful life of a ceramic filter may be limited by the frequency of cleaning, and thus the quality of water being treated and the thickness, since repeated cleaning will eventually degrade the filter element. Filter breakage, however, is more commonly cited as the primary source for filter discontinuity. The main drawback for ceramic filtration is its limitation in removal of viruses, heavy metals and pesticides. Also,
Water can become re- contaminated as there is no residual protection.
Initial price can be relatively high
Ceramic membrane is fragile and taps may leak
Ceramic filter can be formed by various ceramic fabrication route such as slip casting, solid casting, gel-casting, pressing, extrusion and hand forming technique (Reed, 1995). Filters have been shown to be provided in low income communities. Ceramic filters are effective if the micro pores which are formed when the combustible or burnt out material is burnt off during firing and can sometimes achieve turbidity levels below WHO standards of 1NTU (Nephelometric Turbidity Unit) or slightly above it (Mcallister, 2005). To increase the effectiveness, some manufacturers add colloidal silver, which its anti-bactericidal activities have been known since the ancient times (silver, 2003). Ceramic filtration technology may be broadly divided into two categories: the relatively advanced technology of those filters made in more developed countries, which are made to exact specifications with considerable quality control and commensurate cost, and those made in developing countries, where there is some variation in the effectiveness but which often employ local materials and expertise, producing a product that is relatively inexpensive and locally available. The principal example of the latter is the Filt`ron project undertaken by potter for peace, an NGO that promotes the technology (lantagne, 2001a, 2001b). The filters have been the focus of increasing research during the 1990s and 2000s through partner organisations of the WHO International network to promote household water treatment and safe storage. Low cost ceramic filtration for drinking water treatment in developing countries is diverse , varying by overall design, production method, clay and other materials, quality assurance and quality control procedures, burntout materials, firing temperatures and methods, chemical (e.g colloidal silver) amendments, and other characteristics (Lantagne 2001; Sobsey 2002; Cheesman 2003; Dies 2003). Because the design and available materials and methods vary widely from region to region, few generalisations can be made about low cost ceramic filters as a whole. Ceramic water filters are recognised as one of the most promising and accessible technologies for treating water at the household level (Clasen et al., 2004). These filters can be made from locally available materials and are relatively inexpensive. Ceramic water filters act by physically removing particles from solution. Many have the ability to remove disease causing bacteria and parasites from contaminated water. For these reasons, ceramic water filtration appears to be a viable method of point-of-use water treatment.
2.3 Types of Ceramic Water Filters
2.3.1 Disk Filter
Ceramic disk filter systems consist of an upper and lower container with a ceramic disk inserted between the two containers. Water is poured into the upper container and then allowed to filter through the disk into the lower collection vessel. A spigot is placed in the bottom container for dispensing the treated water.
2.3.2 Pot Filter
The potters for peace (PFP) Filtron system is a silver-coated, flower-shaped pot of 17 litres in capacity and the storage tank of 7.5-20litres (potters for peace, 2003). The potter for peace filter uses cement to attach the disk to container and then it can eliminate possible leakage along the interface between the disk and the container. Potter for peace filtron gives the flow rate at 1.0-1.75L/hr.
2.3.3 Candle Filters
A candle filter consists of two containers, an upper one which contains one or more ceramic candles inside and the lower one to store filtered water. According to Sagara (2000), candle filters have low flow rates (300-849ml/hr/candle) therefore, two or three candles are used to treat water.
2.4 Basic Raw Materials for Ceramic Water Filter
The basic raw materials use to make ceramic water filters include ball clay minerals, and burnt out materials. The ball- clay mineral are preferred because it exhibits high plasticity to hold the filter particles together and it has a greater dry mechanical strength when fired (Prajapati, 2002). There are two types of clay, namely primary and secondary clays. Primary clays are also called residual clays. They are found in the same vicinity as the parent rock which they decomposed. Primary clay is basically of one type, the Kaolin. Kaolin is extremely refactory clay with a melting point of over 1260°C. Secondary clays are those that have been moved from the site of the parent rock by the forces of water, wind or glacial action.
2.4.1 Kaolin Clay
Kaolin is a dioctahedral 1:1 layered clay mineral that contains 10-95% of the mineral kaolinite. In addition to kaolinite, kaolin usually contains quartz and mica also, less frequently, feldspar, illite, montmorillonite, illmenite, anatase, haematite, bauxite, zircon, rutile, kyanite, silliminate, graphite, attapulgite and halloysite. The structure of the kaolinite is tetrahedral silica sheet alternating with octahedral alumina sheet. These sheets are arranged so that the tips of the silica tetrahedrons and the adjacent layers of the octahedral sheet form a common layer (Zoltan et al., 2005). In the layer common to the octahedral and tetrahedral groups, two-third of the oxygen atoms are shared by the silicon and aluminium, and then they become O instead of OH. The charges within the structural unit are balanced. Analysis of many samples of kaolinite mineral has shown that there is very little substitution in the lattice (Zoltan et al., 2005). The molecular formula that is common for kaolinite group (Kaolinite, Nacrite, and Dickite) is Al 2 Si 2 O 5 (OH) 4 (Christopher et al., 2002).
Kaolinite, the main constituent of kaolin is formed by rock weathering. It is white, greyish-white, or slightly coloured. It is made up of tiny, thin, pseudo hexagonal, flexible sheets of triclinic crystal with a diameter of 0.2-12micro meter. It has a density of 2.1-2.6g/CM3. The cation exchange capacity (CEC) of kaolinite is considerably less than that of montmorillonite, in the order of 2-10meq/100mg, depending on the particle size, but the rate of the exchange reaction is rapid, almost instantaneous (Zoltan et al., 2005). Upon heating, kaolinite starts to lose water at approximately 400°C, and the dehydration approaches completeness at approximately 525°C (Velde, 1992). The dehydration depends on particle size and crystallinity. The most deliterious impurities in kaolin are iron minerals which impact colour to the white kaolin. Iron exists as oxides, hydroxides, oxyhydroxide, sulphides and carbonates along with iron stained quartz/anatase and mica in kaolin (Ramaswamy, 2011). Kaolin essentially find applications in porcelain, nuclear waste treatment, pottery, paper, pigment, and filler manufacturing (Hosseini et al., 2007, Ryu et al., 1995, Mandal et al.,2004) as well as for catalyst and adsorbent production (Lenarda et al., 2004, Atta et al., 2007, Lussier, 1991). Kaolinite adsorbs small molecular substances such as proteins, polyacrylonitrile, bacteria and also viruses (Adamis et al., 2005). The adsorbed material can easily be removed from the particles because adsorption is limited to the surface of the particles (planes, edges) unlike the case with montmorillonite, where the adsorbed molecules are also bound between the layers (Weber et al., 1965).
2.4.2 Burnt out Materials
Burnt out materials are added to the clay to increase the porosity by creating pores in the ceramic material. The most used materials are combustible materials. When the mass is fired, the combustible material burns out leaving corresponding pore spaces. The porosity of the fired mass is roughly proportional to the volume of the combustible matter added. The main combustible material are hardwood sawdust, cork seeds, naphthalene and occassionally fine ground coke, flour, corn husks, starch and rice husks (kabagambe, 2007). Petroleum waste products may also be used however, they burn out at higher temperatures than wooden sawdust (Kabagambe, 2007). Hard wood sawdust is preferred to soft wood sawdust because according to (Mcallister, 2005), hardwood sawdust will not bloat as much as sawdust from other woods resulting in more uniform pores and fewer defects in the filters. When organic burntout material is exposed to the high temperature of the kiln, the burnt out material combust leaving a large cavities in the fired clay. Water moves easily in the cavities compared with the pores in the clay. Therefore the presence of the cavities decrease the distance water needs to travel through the clay substrate, and therefore increases the overall flow rate of the filter. It is thought that if the burnt out cavities were actually joined up creating passage ways through the filter, the flow rate would be well above the established tolerance zone (Lantagne, 2001a) and would be rejected during the manufacture process. Synchrinton data also suggest that there are not clear linkages between cavities created by rice husks (Sampson, 2009).
2.4.2.1 Rice Husks
Rice husks are the hard protecting coverings of grains of rice. The abundant rice husk naturally have high content of silica and the silica has a high reactivity (Sun and Gong, 2001). The silica is porous and has abundant hydrophillic Si-OH groups, therefore adsorping much moisture.
Rice husk is unusually high in ash compared to other biomass fuels in the range of 10-20%, highly porous and light weight with a high external surface area.
2.5 Factors Affecting Filter Performance
Several factors can affect filter performance. These factors can be properties of the filter, such as porosity, filter thickness, or filter surface area. Factors affecting filter performance can also be characteristics of the water being filtered, such as height of water above the filter element or water quality. Additionally, filter additives, such as activated carbon and silver, can affect filter performance.
2.5.1 Porosity
Porosity is a critical factor affecting filter performance. Porosity is a measure of the volume of empty space, or pores, in a medium. Total porosity of a solid is defined as the volume of voids divided by the total volume of the solid (Harvey notes, 2004). Porosity in a ceramic water filter allows for water to flow through the element. Filters with a greater porosity will allow more water to flow through the filter. The sizes of the pores are also important in determining the level of water purification achieved. Many ceramic water filters have pores ranging in size from 0.1 to 10 microns. Filters with large pores will not be as effective at straining/removing turbidity or microbiological contamination from a water sample. However, the flow rate of these filters will typically be greater since there is more space for water to flow through. Conversely, filters with small pores will be better at reducing turbidity and microbiological contamination, but may have very slow flow rates.
2.5.2 Filter Thickness
The thickness of the ceramic water filter will also affect the flow of water through the element. Filters with thin shells will allow water to flow through the element faster (greater flow rate). However, thin filters may not be as effective as thick filters at removing turbidity and microbiological contamination. Thick filters have more opportunities for particles to become trapped.
2.5.3 Filter Surface Area
Filter surface area is also an important factor affecting filter performance. Filter surface area is directly proportional to flow rate. Filters with a larger surface area will have greater flow rate, as there is more space for water to flow through. Conversely, filters with small surface area will have slower flow rates. One way to increase surface area without modification works particularly well with ceramic candle filters. Rather than placing only one ceramic candle filter in a container, two, three or even four candles could be placed in a bucket to increase the volume of water filtered in a given time period.
2.5.4 Water Elevation
In addition to filter properties, characteristics of the water will also affect the flow through the filter element. Height of water above the filter element, also known as fluid pressure or hydraulic head, will affect the flow rate. The greater the height/volume of water, the more pressure on the filter element, and thus the more flow through the pores in a given time period. As the water level declines over time (i.e water is filtered) the flow rate will concomitantly decrease. For this reason, the water level should be maintained as high above the filter as possible, the top bucket containing the filter should be filled continuously (Franz, 2004).
2.5.5 Water Quality
Water quality will also affect the flow of water through a ceramic water filter. Water possessing many suspended particles (high turbidity) and/or high organic content will not flow through the filter as quickly as cleaner water, resulting in a smaller volume of water filtered over a given time period. Polluted water will often times clog the filter, resulting in the need for more frequent cleaning of the filter element. For highly turbid water, sedimentation or coagulation can be used pre-filtration to remove large particles, thus allowing for an increase in the flow rate.
2.5.6 Activated Carbon
In addition to evaluating flow through a ceramic water filter, other filter performance characteristics should be considered, such as the filters ability to reduce chemical content or improve taste and/or odour (Ceramic Water Filter Technologies, 2004). To improve performance, activated carbon is often added to the filter's interior. Activated carbon is made from a variety of carbonaceous materials, which are heated slowly in the absence of air to produce an extremely porous chemically active material (Viessmañet.al. 2005).
2.5.7 Silver
Many ceramic water filters also possess loose silver, colloidal silver or silver nitrate on the interior or exterior of the filter element. Silver is purported to have bactericidal properties. It has been used throughout history for maintaining water cleanliness (Silver, 2005). Silver acts by disrupting the cell membrane, causing it to disintegrate. Additionally, bacteria do not develop resistance to silver, as they do for antibiotics (Pan American, 2005).
2.6 Characterization Technique
2.6.1 X-ray Diffraction
X-ray diffraction is a method used for identification of crystalline materials such as clay. The theory is based on applying elastic scattering of x-rays on structures to acquire information on the unit cell parameters of the product (Kulprathipanja, 2010). By measuring the angles and intensities of these diffracted x-ray beams, x-ray diffractometer can produce a pictorial view of the density of electrons within the crystal. The two dimensional image can be converted into a three dimensional model of the density of electrons within the crystal using the mathematical method of fourier transform. X-ray diffraction is produced as a reflection at well-defined angles. Every crystalline phase has its own diffraction images. The diffraction image contains a small number if maximum points that is not all the families of crystallographic planes given maximum diffraction points.
X-rays are produced when the wavelength of the scattered x-rays interfere constructively i.e. forming a diffraction pattern for constructive interference, the difference in the travel path must be equal to integer multiples of the wavelength. When this constructive interference occurs, a diffracted beam of x-rays would leave the crystal at an angle equal to that of the incident beam. The general relationship between the wavelengths of incidence x-rays, angle of incidence and spacing between the crystal lattice planes of atoms is known as Bragg's law.
n.λ= 2d.sinθ
When n= order of reflection
λ= wavelength of the incident rays
d= inter-planar spacing of the crystals
2.6.2 X-ray Fluorescence
Electromagnetic radiation having wavelength in the range of 0.01 to 10nm, corresponding to frequencies in the range 30 pentahertz to 30 hexahertz and energies in the range 100eV to 100KeV are known as x-rays. When atoms of any chemical element are irradiated with x-rays they emit energy in the form of fluorescent x-rays; the energy is characteristic of each element involved (Ohrman, 2000). The intensity of each fluorescent line varies according to the quantity of element present in the investigated sample. The term "Fluorescence" is applied to a phenomenon in which the absorption of radiation of a specific energy results in the re- emission of radiation of a different energy (generally lower).
Ionization of a material component atom may take place when the material is exposed to short wavelength x-rays or to gamma rays. Ionization consists of the ejection of one or more electrons from the atom, and may occur if the atom is exposed to radiation with energy greater than its ionization potential. X rays and gamma rays can be energetic to expel tightly held electrons from the inner orbital of the atom. The removal of an electron in this way makes the electronic structure of the atom unstable, and electrons in higher orbitals "fall" into the lower orbital to fill the hole left behind. In falling, energy is released in the form of a photon, the energy of which is equal to the energy difference of the two orbitals involved (Robson, 2001).
2.7 Review of Related Works on Ceramic Filters
Previous work has been done to test the effectiveness of ceramic filter in treating water.
Agbo (2015) developed a ceramic filter candle from Nsu clay which he used in treating water. The pH of water sample obtained after filtration was 6.69, which is within the range of the WHO standard for drinking water. He obtained a value of 15mg/l and 0.34mg/l for total dissolved solid and total suspended solid respectively, while the filter average removal efficiencies for these parameters were 76% and 70% respectively. The result showed that flow rate increases with increase in the ratio of sawdust to clay.
Abirigal et al., (2014) performed an experimental study on the effects of double filtration on the rate of water percolation and E. Coliform removal efficiency of ceramic water filters made from mixtures of different ratios of clay powder, fine sawdust and powder of grog. Result obtained showed that for both single and double filtration mechanism, the rate of water percolation is higher for filters with a high proportion of sawdust. This is because more pores are formed when the green bodies of filters with high proportions of sawdust are fired (Clair, 2000 and Dies, 2003). In addition, the percolation rate is lower in double filtration mechanism because the particle laden water has to navigate through intricate maze of labyrinths in two filters instead of one (Crittenden et al., 2005)
The result obtained for turbidity and E. Coli showed that double filtration mechanism lowered the turbidity of the filtered water compared to single filtration mechanism.
Lamichhane et al., (2013) compared the performance of three different types of ceramic filter candles (MCC, Puro and Surya) in treating drinking water. Filter candles performance with or without colloidal silver coating were determined based on flow rate, E. Coliform removal efficiency and total coliform removal efficiency. The E. Coliform removal efficiency of MCC candle was 39% to 60% without CS coating while it was 69% to 77% with CS coating. The result showed that better performance of MCC filter can be achieved after CS coating but could not meet the WHO guideline. E. Coliform removal was observed at first 29minutes without CS coating in puro candle whereas 100% E. Coliform removal was achieved at the same time after coating with CS. Beter E. Coliform and total coliforms removal efficiency of surya candle with the increased water retention time after CS coating was noted. They concluded that significant impact of CS coating in controlling and/or inactivating E. Coliform and total coliforms were noted for all filter candles and among them puro filter candle was found to be the most efficient for eliminating bacteria cells from water. Performance of filter in terms of filtration was not affected by the CS coating as a minimal difference in the water flow rate before and after silver coating was noted.
Isikwue (2010) evaluated the performance of locally made ceramic pot as a water purification system. He observed that the turbidity of the raw water was 49.0 NTU while the turbidity level in all the filtrate ranged from a minimum value of 3.0NTU to a maximum value of 30.0 NTU. The pH level in the raw water was 7.6 while pH from all the filtrates of the ceramic pot filters ranged from 6.6 to 7.2 thus: all the ceramic pot designs met W.H.O's maximum desirable concentration levels for drinking water (6.5-8.5).
Olalekan (2013) developed and evaluate the performance of ceramic filter as a point of use water purifier. In her experiment, four samples of raw water (Well, Rain, River, and Bore hole) were tested for turbidity, hardness, pH, conductivity, Total Dissolved Solid, and Total Suspended Solid). The ceramic filter showed good performance for reducing turbidity, hardness, pH, conductivity, Total Dissolved Solid and Total Suspended Solid.. The turbidity was 0.92 to 19.7 NTU for raw water and 0.77 to 0.55 NTU for filtered water which met the WHO standard (< 1.0 NTU) (WHO, 2004). The hardness of raw water sample ranged from 38-420mg/L. Some of the values for raw water samples where high when compared with WHO standard of <80mg/l for drinking water, but rain has its hardness within the drinking water standard. This was expected , since rain water is typically rated as soft. After filtration, the hardness of the water sample ranged from 6 to 34mg/L and the average hardness removal efficiency was 85.1%.
Olubayode et al., (2013) determined the suitability of five selected clay samples from different part of Nigeria for the production of ceramic filter. Places used in this study included Ibafo in Lagos State, Ondo in Ondo State, Ilesha in Osun State, Ajebo in Ogun State and Kumbuso in Kano State. It was Concluded that Clay from Lagos State is the best for filter Production.
Erhuanga et al., (2013) developed ceramic filter candles for household water treatment in Nigeria. In his production, he made use of Kaolin, laterite, bone char and charcoal. He concluded that all filter samples reduced the fluoride concentration of water in the range of 33.6-75%, and they also gave good microbial treatment result with percentagw reductions in microbial load of up to 78%.
2.8 Gap in Literature
Production of filter candles for household water treatment is not something new, this has been x- rayed by the works of different authors on household water treatment. Although these filter candles have successfully treated water, there has not been any work done to increase the flow rate of the filter candles which is usually slow in water treatment.
Choosing to use kaolin from Ozanogogo community for the production of the filter candle is in a bid to bring the community to lime light because the community has a large deposit of kaolin but attempt has not been made in using it for the production of ceramic filter.
This work therefore, is aimed at producing a filter candle with increased flow rate from materials sourced locally.
CHAPTER THREE
MATERIALS AND METHODS
3.1 Materials
Materials used for the production of ceramic filter candles include:
Clay
Rice husks
Sodium silicate
Water
Mortar and pestle
Weighing scale
30 gauge wire mesh sieve or 600µm mesh
Stirring stools
Plaster of Paris (P.O.P) Mould
Fettling tools
Pottery Oven
Kiln
PVC adhesives
Sand Paper
3.2 Methods
3.2.1 Sample Collection
3.2.1.1 Collection of Kaolin Sample
The Kaolin sample used in this study was collected from a kaolin deposit at ozanogogo community.
3.2.1.2 Study Area of Kaolin Deposit
Ozanogogo is located at about 15km North of Agbor Obi in Ika South Local Government Area of Delta State. It is situated around Latitude 6°05'-6°25' N and Longitude 6°18'-6°20' E.
Plate 3.1 Kaolin Deposit in Ozanogogo community.
Plate 3.2 Map of Delta State Showing all Ethnic Group
3.2.1.3 Purchase of Rice Husk
The rice husk that served as a burnt out material was purchased from New Market, Enugu.
Plate3.3 Unprocessed Rice Husk
3.2.1.4 Water Sampling
The water sample used in this study was collected using 10 liter container from Amirinma Ocha River, Oshimili South, Delta State.
3.2.1.5 Study Area for Water Sampling
Amirinma Ocha is located at 6°18'N, 6°41E, Delta state. The river which the locals depend on for fishing and a source of drinking water is also a place where most of the indigenes pass out fecal waste. During the rainy season the water tend to increase in volume and during dry season, it tends to dry out.
3.2.2 Sample Processing
3.2.2.1 Processing of the Kaolin Sample
The kaolin sample was soaked in water for two days to obtain slurry. The slurry was then sieved to remove foreign and deleterious substances. The sieved slurry was then allowed to settle down for three days after which the clear floating water was decanted. It was left for three days in order to allow the remaining water present to drain out completely. The kaolin clay was dried under the sun and then ground using a mortar and a pestle and this was sieved using 600μm to get a definite particle size.
The rice husks were sieved into a separate bowl using 600μm sieve to get a definite particle size.
Plate 3.4 Processed Kaolin Plate 3.5 Sieved Rice Husk
3.2.3 Procedures for Physical Analysis of the Clay
The collected clay was dispersed in excess water in a pre-treated plastic container and stirred vigorously to ensure proper dissolution. The dissolved clay was then filtered through a 0.425mm mesh sieve to get rid of unwanted particles and plant materials. The filtrate was allowed to settle, after which excess water was decanted off. The clay was then sundried and oven dried at 1000°C for 3hrs, pulverized and passes through a mesh sieve of size 0.18mm. 1.6kg of the clay was weighed and mixed with appropriate amount of water to make it plastic for the moulding process.
2.2.1.3: Adhesive for bonding the plastic container and the filter
PVC adhesive was used for bonding the ceramic filter. The adhesive was purchased from a plumber shop. It was used because according to the specifications of this adhesive it was suitable for household and industries repair and welds, bonds to all metals, plastic, rubber, wood, ceramic, glass and concrete. In this study, the adhesive was used to bind a ceramic and plastic percolator. The adhesive was also not shrinking, waterproof and hardened in less than 3 minutes. These properties were very important for the use of the adhesive in the study.
2.2.2; Preparation of samples
2.2.2.1; Sieve
A 30 gauge wire mesh which is equivalent to 600 µm wire mesh was bought from a hardware shop and a sieve was cutout and fixed in a local wood workshop. The sieve was used to sieve the clay and sawdust powders. This would give powder particles of diameter less than or equal to 600 µm.
2.2.2.3. Plaster of Paris mould
The plaster of Paris mould used in the study was produced from the master mould constructed at Ceramic Section PRODA Enugu.
2.3 Method of Production
1. Material Processing
2. Formulation
3. Casting
4. Drying & Firing
2.3.1 Clay processing
The organic and coarse materials in the clay were removed by hand. The clay was mixed with water until continuous homogeneous colloidal slurry was obtained. The slurry was sieved through a 200μm sieve. Successive decanting was done to obtain a silt of clay. The silt was then poured into a plaster of Paris mould to remove the excess water. The semi-dry cast was left to dry in air. The dried cast was ground by pestle and mortar to fine powder which was then sieved through the 30 mesh sieve, ready for compounding.
2.3.2 The Formulation of the body.
The clay and rice husk were weighed in the proportion of 50:50, 55:45 and 60:40 labeled A, B, and C respectively.
Each sample was poured into basin with 500mls of water to dissolve; the solution was immediately deflocculated with 5mls of sodium silicate which is the one of most vital requirements of a casting –slip, (Slip is the solution of the compounded bodies) It is expected that when the slip is its state of maximum deflocculation, the slip will have its maximum fluidity that possesses a high ratio of water to clay.
2.3.3. The physical analysis of the compounded bodies
Before the production of the water filter candles the physical analysis of the already compounded bodies and the kaolin clay were done to ascertain if the bodies would be feasible in the water filter candle production as well as the strength and the durability of the products.
The physical parameters and method of determination are explained below while the tables and the results are shown at the result and discussion segment
2.3.3.1. Determination of Relative Plasticity
The relative plasticity was determined using the cylindrical test pieces. The original height, Ho of the test pieces were obtained by the use of the venier caliper by taking the average of three sides. Afterwards, a manual plastometer machine was used to deform the test pieces. The deformation height, Hi was recorded taking the average of three sides. The relative plasticity was then calculated (lynne et al, 1980).
Relative Plasticity = Ho/Hi
2.3.3.2 Determination of Modulus of Rupture
Five long rectangular test pieces were made and air dried for 7 days after which they were oven dried at 1050C until a constant weight was obtained .A set of four pieces were fired to temperatures of 900, and another set at temperature of 1000oC in a laboratory kiln (Fulham Pottery). The electrical transversal strength machine was used to determine the breaking load, P (Kg). A vernier caliper was used to determine the distance between supports L (cm) of the transversal machine. The height, H (cm) and the width, B (cm) of the broken pieces were determined and the average value obtained from the two broken parts was recorded. The modulus of rupture was then calculated:
Modulus of Rupture (Kg/cm2) = 3PL
2BH2
2.3.3.3. Shrinkage Determination
Immediately after molding of the rectangular test pieces, a vernier caliper was used to insert a 5m mark on each of them; this was recorded as the original length Lo (cm). The test pieces were then air dried for 7days and then dried in an oven at 1050C until a constant weight was obtained. The shrinkage from the 5cm mark was then determined and recorded as the dried length, Ld (cm). Afterwards, four of the dried samples were fired to their respective temperatures of 900, and another set at temperature of 1000oC, the shrinkage of the test pieces from the 5cm mark were then determined and recorded as the fired length, Lf (cm). The shrinkage was then calculated:
Wet-Dry Shrinkage (%) = 100[Lo - Ld]
Lo
Dry-Fired shrinkage (%) = 100[Ld - Lf]
Ld
Total Shrinkage (%) = 100[Lo – Lf]
Lo
2.3.3.4. Determination of Water of Absorption
The fired test pieces obtained after firing were then weighed and the weight recorded as dry weight, M1 (g). Thereafter, the test pieces were soaked in water for one hour, then removed, cleaned and weighed immediately and recorded as soaked weight, M2 (g). The water of adsorption was then calculated:
Water of Absorption (%) = 100 [M2 – M1]
M1
2.3.3.5. Porosity and Density Determination
After the procedure described above was completed. The suspended weight of the test pieces were then determined by the use of a lever balance and recorded as M3 (g). The apparent porosity, apparent density and bulk density were then calculated:
Apparent Porosity (%) = 100 [M2- M1]
M2 – M3
Apparent Density = M1/[M1 – M3]
Bulk Density = M1/[M2 – M3]
2.3.4: Slip casting
The shaping of articles by casting is extensively used for pottery. Especially for complicated shapes just as molten metal can be cast into the required shape by pouring into mould precisely a plaster mould. Such a mould, being porous, absorbs water is stiffened. After some time, excess slip can be poured away and after a further period, the article in the mould can be removed from the mould.
2.3.4.1 Procedure for casting
Bind the candle plaster of Paris mould with a rubber band.
Stir the slip with an electrical stirrer so as make the materials in the slip to be in a uniform state.
Pour the slip into the mould as it reduces when the plaster of Paris mould absorbs water from the slip.
When there is a satisfied thickness of the cast, pour out the excess slip to form an orifice.
After about thirty minutes, remove the article that was produced from the mould.
2.3.4.2; Atmospheric and electrical drying of water filter candles
The water filter candles were allowed to undergo atmospheric drying that is to remove the water content which the mould cannot absorb. This process took about seven days .The candles were parked in an electrical dryer and set to a temperature of about 150oC so as to remove moisture content that could not be absorbed by the atmosphere. This took up to three (3) to five (5) hour.
2.3.5. Firing of water filter candles
Filter candles also undergo firing in the kiln. When clay bodies are fired in the kiln, they lose moisture organic matter, sulphur and carbon IV oxide. As the temperature rises, some of the clay particles begin to fuse destroying the original clay structure and binding the mass together
2.3.5.1; Procedure for firing water candles
-Fettle the candles to remove the outline of the mould that appeared on the candle.
Pack them into the kiln and fire to temperature 1000oC-1100oC
2.3.6; Fitting the filter sample in a PVC Percolator
The filter was fitted in the PVC percolator as follows: a filter candle was fixed into the PVC percolator tightly round the filter, to ensure that the fitting was water-tight, PVC adhesive was used to seal around the percolator and the candle contact. Fig.2.14 shows the percolator with a filter fitted.
The candles are usually hollow ceramic cylinders that are fitted with plastic end caps attached using epoxy. The epoxy, or other, appropriate sealant, is necessary to prevent contaminated water from short‐circuiting the filtering process. The bottom end cap contains a threaded fitting that is then attached to the bucket using a gasket and a nylon nut. Figure 2.13 show the ceramic filter element (inverted to show the threaded fitting). In Indonesia, cement end caps are currently being used.
2.3.7 Percolation rate of water
The volume of water through the filter for a given time was measured using a measuring cylinder. The percolation rate of water through the filter was calculated using the equation
Q = Vf/AtE
Where Vf, is volume filtered A, the area of the filter and tE, is the time of filtration. The surface area of the filters was calculated from equation.
A = πd2/4 Where d, is the diameter of the filter. Percolation rate was reported in ml (hour)-1 cm-2
3.4 Filter Candle Production
3.4.2 Body Formulation
Clay: Rice husk Code
50:50 A
55:45 B
60:40 C
Different ratios of Clay to rice husk were used in the production of filter candles. The formulations used include 50:50 which was produced like the normal conventional filter candle found in the market, 55:45, 60.40 were produced while also taking into consideration the surface area of the filter candle. Clay and rice husk were added to a bowl and subsequently mixed together for five minutes to form a homogenous mixture, water was slowly added until there was even wetting of the dry component, it was mixed continuously for 10 minutes with the hand.
3.4.3 Shaping of the Filter Candle
The formulated body was transferred to a table and underwent kneading process to remove air from it that can cause cracks during firing. These were later transferred and pressed to a male and female mould so as to take the shape of the mould. The already formed candle shape was Left in the mould for 20 minutes and was then demoulded and air dried for 5days to remove the excess water that can cause expansion and cracks during firing. The already air dried candles were fired for 5hrs at a temperature of 1000°C. These candles were allowed to cool to room temperature. The filter candles produced were smoothened using sand paper.
3.4.5 Application of Silver Nitrate (AgNO3 )
A measuring Cylinder was used in measuring 500ml of water into a bowl,2 gram of silver nitrate was added and continuously stirred untill it was dissolved. It was allowed to stand for 30 minutes before it was applied to the inner and outer surface of the filter candle using a brush. The Silver coated was allowed to dry for two days before use.
3.5 Filter Set Up
The filter candle is made up of the upper and lower bucket, ceramic candle, plastic tap, and percolator. The filter candles was fixed to a percolator using pvc adhesive and then screwed to the lower bucket through the holes made in the upper bucket and the lid of the lower bucket. Raw water is poured in the upper bucket, the water passes through the pores in the candle and is collected in the lower container.
Plate 3.6 Filter Set Up
3.6 Flow rate Test
The flow rate of the produced filter candles and that of a commercial one were determined using a measuring cylinder to directly measure the total volume of water that passed through the filter in an hour.
Flow rate= Volume of filtrate/time cm 3 /s
3.7 Physiochemical and Microbial Analysis of the Water Samples
Physiochemical and microbial analysis were also carried out to test the quality of the raw water and the water filtrate with the produced filter candle of interest. Parameters tested for includes Total Dissolved solid, Total suspended solid, pH, Hardness, Alkalinity,Turbidity, E. Coliform and Total Coliform.
3.7.1 PH Determination
Method: pH was measured by Electrometric Method Using Laboratory pH Meter Hanna Model HI991300 (APHA; 1998)
Procedure
The electrodes were rinsed with distilled water and blot dry
The pH electrodes was then rinsed in a small beaker with a portion of the sample
Sufficient amount of the sample was poured into a beaker to allow the tips of the electrodes to be immersed to a depth of about 2cm. The electrode was at least 1cm away from the sides and bottom of the beaker.
The temperature of the adjustment dial was adjusted accordingly
The pH meter was turned on and the pH of the sample recorded
3.7.2 Determination of Total Dissolved Solid
Method: It was determined using APHA 2510 A TDS 139 tester (APHA; 1998)
Procedure.
The fiber filter disc was prepared by placing it, wrinkled side up, in the filtration apparatus. Vacuum was applied and the disc washed with three successive 20ml washings of distilled water. Continuous suction was applied to remove all traces of water.
ii) A clean evaporating dish was heated to 180 ±2°C in an oven for 1hr, cooled and stored in a desiccator until needed. It was weighed immediately before use
iii) A sample volume was chosen to yield between 2.5 and 200mg dried residue.
iv) 50ml of well mixed sample was filtered through the glass-fibre filter; it was washed with three successive 10ml volumes of distilled water, allowing complete draining between washings. Suction was continually applied for about 3 minutes after filtration is complete.
v) Filtrate was transferred to a weighed evaporating dish and evaporated to dryness on a steam bath.
vi) The evaporating dish was finally dried for at least 1hr in an oven at 180 ± 2°C, cooled in a dessicator to balance temperature and weigh.
Calculation:
TDS= (A-B) ×103 mg/l/ Sample Volume in ml
Where A= Weight of dish+ Solids (mg)
B= weight of dish before use
3.7.3 Turbidity Determination
Procedure:
i) 'EPA 180' was selected as the measurement mode in the turbidimeter
ii) The sample was placed in a clean, dry turbidity vial. Cap securely. Excess liquid and fingerprint was wiped off with a soft cloth. Sample chamber and covered with vial cap.
iii) MEASURE key was pressed. The result was displayed on the instrument.
3.7.4 E.Coliform and Coliform Test
Method: Plating Method
Bacteriological analysis of E. Coliform test was done according to the procedures in the US Food and Drug Administration- Bacteriological Analysis Manual (FDA-BAM).
All media were prepared according to the manufacture's instruction and sterilized using autoclave at 121°C for 15 minutes.
Procedure:
i. 1ml of each of the serial diluted sample were pipette into different petri-dishes, well labelled and sterilized medium (Agar) were poured into each of the petri dishes and swirled for proper homogenation.
ii. The plates were allowed to solidify, inverted and incubated for 24 hours at 37°C. Presumtive E. Coli colonies on CLED Agar appear different colour with or without metallic sheen.
iii. Presumptive E. Coli were picked and streaked onto nutrient agar and incubated at 37°C for 24 hours under aerobic condition for purification to obtain a pure culture
iv. Pure cultures were identified using gram staining, E. Coli latex agglutination test and biochemical tests (indole production, utilization of citrate and lactose production).
CHAPTER FOUR
RESULTS AND DISCUSSION
4.1 RESULTS
4.1.1 Physical Analysis of the Formulated Body
The results for physical analysis of the formulated body is shown in Table 4.
TEMPERATURE
900oC
10000C
11000C
CODE NO
A1 B1 C1 A2 B2 C2 A3 B3 C3
TOTAL SHRINKAGE % 11.89 12.23 13.67 7.00 7.15 8.83 2.892 3.845 4.576
WATER ABSORPTION % 33.15 32.89 30.41 30.19 30.13 27.73 29.98 28.10 25.78
BULK DENSITY g/cm3 1.45 1.50 1.523 1.536 1.59 1.59 1.539 1.549 1.588
APPARENT DENSITY g/cm3 1.88 2.53 3.23 2.87 3.53 3.73 2.86 2.67 2.00
APPARENT POROSITY (%) 47.11 43.45 25.66 46.39 39.12 22.59 46.14 30.00 20.27
MODULUS OF RUPTURE kg/m2 16.06 17.45 19.28 21.10 21.59 22.00 29.09 32.76 33.60
The result for physical analysis shows that apparent porosity and water of absorption increases with increase in rice husk used while total shrinkage, apparent density, bulk density and modulus of rupture decreases with increase in rice husk.
4.1.2 Graphs Showing all Physical Parameters for each Samples against Temperature
Figure 4.3: A graph of Modulus of Rupture against Temperature
Figure 4.6: Apparent Porosity increase or decrease with Temperature
Figure 4.7: A graph of Water of Absorption against Temperature
Table 4.3 Flow rate of the Filter Candles
Filtrate A-50:50
Filtrate B-55:45
Commercial Filter
Filtrate A Filtrate B Commercial Filter
0.278 0.472 0.361
Plate4.4 Performance of Flow rate test on filter candles
Figure 4.9: Chart showing various Filter design and its relationship with
Flow rate
4.2Discussion
4.2.1 Firing Process
Ceramic Filter candles were produced with three recipes of clay to rice husk in percentage ratio of 50:50, 55:45, and 60:40 by Solid Casting Method.
After firing of the filter candles, colour change were observed (from green to white). Of all recipes that were used, Sample from A and B gave the best result for flow rate and hence was used in this study. Cracks that were seen in some filter candles may be due to some unseen tiny particles present in the processed rice husk or clay that was used in the production of filter candles or poor kneading.
4.2.2 Physical Analysis on Formulated Body
Table 4.1 shows the results obtained for the physical analysis done on Clay. The results obtained for physical analysis on the clay shows that water of absorption and apparent porosity increases with increase in rice husk used. The rice husks tend to create more pores during firing and more water is absorbed as the rice husk is increase while the clay is reduced creating thinner walls and hence quicker contact with the filter body.
Total shrinkage, dry fired shrinkage, and wet-dry shrinkage decreased with increased in rice husk. The formulated body with composition of 50:50 had the lowest shrinkage value because it absorbed more water than any other body and hence it will take longer time to shrink compared to others.
The Modulus of rupture, apparent density, bulk density decreased with increase in the proportion of rice husk used.
It is also seen that the modulus of rupture, apparent density, bulk density, dry-fired shrinkage, wet-dry shrinkage and total shrinkage increased with increase in temperature from 1000 to 1100°C for each samples. This may likely be as a result of increased dehydration process, as kaolin tends to lose more water at increased temperature and this can also result in cracks.
Apparent Porosity and Water of Absorption for each sample tend to decrease with increase temperature as the pores tend to become smaller at higher temperature.
4.2.3 Flow rate of Filters
From the result obtained for flow rate for all filter candles, it is observed that the commercial filter used in this study had a flow rate which was less than that of filter B(55:45) The least flow rate was filter A(50:50)
Although filter candle A had a higher proportion of rice husk (50:50), Sample B had a higher flow rate (55:45), this was because of the increased surface area.
Sample B filter Candle with clay to rice husk ratio of 60:40 performed poorly and hence was not used. According to Miller (2010) filter candles with a very poor flow rate should be discarded.
The flow rate of the commercial filter used for this study was slightly above that of Sample A.
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