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Clay minerals are the characteristic minerals of the earths near surface
environments. They form in soils and sediments, and by digenetic and hydrothermal
alteration of rocks. Water is essential for clay mineral formation and most clay
minerals are described as hydrous alumino silicates. Structurally, the clay minerals
are composed of planes of cations, arranged in sheets, which may be tetrahedrally or
octahedrally coordinated (with oxygen), which in turn are arranged into layers often
described as 2:1 if they involve units composed of two tetrahedral and one octahedral
sheet or 1:1 if they involve units of alternating tetrahedral and octahedral
sheets. Additionally some 2:1 clay minerals have interlayers sites between successive
2:1 units which may be occupied by interlayer cations, which are often hydrated. The
planar structure of clay minerals give rise to characteristic platy habit of many and to
perfect cleavage, as seen for example in larger hand specimens of micas.
Clay Minerals are Phyllosilicates
All have layers ofSi tetrahedraand layers of Al, Fe, Mg octahedra, similar to gibbsite or
The kaolinite clays are 1:1 phyllosilicates
The montmorillonite and illite clays are 2:1 phyllosilicates
The classification of the phyllosilicate clay minerals is based collectively, on the
features of layer type (1:1 or 2:1), the dioctahedral or trioctahedral character of the
octahedral sheets (i.e. 2 out of 3 or 3 out of 3 sites occupied), the magnitude of any net
negative layer charge due to atomic substitutions, and the nature of the interlayer
The basis on which clay minerals are classified is shown below; see Hillier (2003) for
a more detailed introduction to clay mineralogy.
Some types of clay minerals such as mixed-layered clay minerals can only be
identified precisely by techniques such as XRD. Although it is not unusual to have to
use a variety of techniques such asXRD, infrared spectroscopy, and electron
microscopy to characterize and more fully understand types of clay minerals present
in a sample. We have extensive experience of the identification of clay minerals in
both soils and rocks. Our XRD work is based is backed up by our ability to compare
clay mineral diffraction data with calculated diffraction data. This is a particularly
important technique for the precise identification of mixed-layer clay minerals. Our
track record in the Reynolds Cup round robin on quantitative clay mineral analysis is
testimony to the quality of our work on the identification and quantification of clay
minerals. We also have wide experience of the use of electron microscopy to study the
texture and petrographic relationships of clay minerals. A useful gallery of clay
mineral images, showing some of the different morphologies in which clay minerals
can occur can be found
The importance of clays and clay minerals inthe drilling industry is evident from
twodifferent viewpoints. First, commerciallymined clays are added to drilling fluids
tobuild viscosity, control fluid loss, etc. Theseclays include bentonite, attapulgite
andsepiolite. Second, one or more clay mineralsare present in nearly all sedimentary
rocksand their reaction to the drilling process canproduce major problems, such as
holeenlargement, sloughing, shale hydration andthe gumbo phenomenon. The
magnitude ofthese potential problems can be seen if oneconsiders that argillaceous
rocks (shales,siltstones, mudstones, etc.) comprise morethan half of sedimentary
rocks and arecomposed of more than 50% clay minerals.
In addition, many sandstones have as muchas 20-30% clay minerals and
evenlimestones can have small amounts of clayminerals.
The clay minerals are hydrous aluminumsilicates of a layer type lattice structure with
Magnesium, iron and potassium eitherbetween the layers or substituted within the
Lattice. The exception to this is theattapulgite-sepiolite minerals which have achain
The basic structural components are silicatetrahedrons and alumina octahedrons,
Figures 1 and 2, arranged in a sheet structureand bound together by shared oxygens
between the sheets, resulting in the layertype lattice.
A crystal structural classification of the layertype lattice clay minerals divides them
intothree major categories based on thearrangement of the structural units.
The first and most abundant type is referred to as the 2:1 clay minerals and includes
illite and smectite. The structure is constructed of an alumina sheet between two
The second is the 1:1 clay minerals which includes kaolinite and has one silica sheet
and one alumina sheet.
The third category is the 2:1:1 clay minerals which includes chlorite.
The structure consists of a 2:1 lattice with a layer of magnesium hydroxide in the
Illite is by far the most abundant claymineral type found in sediments. It is asegment
of a complex 2:1 structural series ofthe mica family (Figure 3).
Illite has lesssubstitution of aluminum in the silica sheet,less potassium in the
and finer crystal size than muscovite.However, illite is essentially inert tohydration
and is the most common nonswellingcomponent of mixed layer-claysformed by the
diagenetic alteration ofsmectite.
Illite is similar to muscovite and is the most common clay mineral, often composing
morethan 50 percent of the claymineral suite in the deep sea.
They are characteristic of weathering in temperate climates or in high altitudes in the
tropics, and typically reach the ocean via rivers and wind transport.
The Illite clays have a structure similar to that of muscovite, but is typically deficient
in alkalies, with less Al substitution for Si. Thus, the general formula for the illites is:
with 1 < y < 1.5, but always with y < 2.
Because of possible charge imbalance, Ca and Mg can also sometimes substitute for K.
The K, Ca, or Mg interlayer cations prevent the entrance of H2O into the structure.
Thus, theillite clays are non-expanding clays.
Illite type clays are formedfrom weathering of K and Alrich rocks under high pH
conditions. Thus, they form by alteration of minerals like muscovite and feldspar.
Illite clays are the main constituent of shales.
smectite is family of expansible 2:1 phyllosilicate clays having permanent layer
charge because of the isomorphoussubstitution in either the octahedral sheet
(typically from the substitution of lowcharge species such as Mg2+, Fe2+, or Mn2+ for
The most common smectite is Montmorillinite, with a general chemical formula :
Montmorillinite is the main constituent of bentonite, derived by weathering of
volcanicash. Montmorillinite can expand by several times its original volume when it
comes incontact with water. This makes it useful as a drilling mud (to keep drill holes
open), and toplug leaks in soil, rocks, and dams.
Montmorillinite, however, is a dangerous type of clay to encounter if it is found in
tunnelsor road cuts. Because of its expandable nature, it can lead to serious slope or
Smectite is the least stable clay mineral; it isthe most susceptible to hydration
anddiagenetic alteration. It has a 2:1 latticestructure with magnesium and
ironsubstituted for aluminum and one of severalcations in the interlayer region along
withone or more layers of water (Figure 4).
Theinterlayer region is highly susceptible tohydration, although interaction
betweeninterlayer ions and adsorbed water limits thelevel of hydration, depending
on the ionpresent.
When water is abundant, continuedswelling to many tens of layers of water inthe
interlayer region is common for smectitewith sodium as the interlayer ion,
whereascalcium in the interlayer position seems torestrict expansion.
The interlayer in montmorillonite or smectites is not only hydrated, but it is also
expansible; that is, the separation between individual smectite sheets varies with the
amount of water present in the soil. Because of this, they are often referred to as
Soils having high concentrations of smectites can undergo as much as a 30% volume
change due to wetting and drying or these soils have a high shrink/swell potential
and upon drying will form deep cracks.
MIXED LAYER CLAYS
Mixed layer clays are formed either bydegradation by weathering or by
diageneticalteration of clay minerals. Theinterlayering may be considered to occur
(1) regular alternation oflayers in a rational repetitive sequence
(2)a non-rational alternation sequence
where layers are neither regularly repetitivenor are likely to occur in equal
Although any combination of two or moreclay minerals can form a mixed layer
clay,the most common occurrence is a randomsequence of illite type layers and
smectitetype layers. The proportion of swelling tonon-swelling layers determines
theexpandability of these clay minerals.
Kaolinite has a 1:1 structure with one silicasheet and one alumina sheet (Figure 5),
withmost of the oxygen ions in the alumina sheet
being replaced by hydroxyl ions. Thisresults in a neutral composition with nosurface
charges to attract interlayer cationsor water and therefore no possible expansionof
used in the ceramic industry, especially in fine porcelains, because they can be easily
molded, have a fine texture, and are white when fired.
These clays are also used as a filler in making paper.
Chlorite is classified as a 2:1:1 mineral. Itsstructure is identical with the 2:1
mineralsexcept for a layer of magnesium hydroxidefixed in the interlayer region
This magnesium hydroxide layer neutralizesthe surface charge of the 2:1 lattice so
thatthe chlorite structure is non-expandable.
Vermiculite is a high-charge 2:1 phyllosilicate clay mineral.
It is generally regarded as a weathering product of micas.
Vermiculite is also hydrated and somewhat expansible
though less so than smectite because of its relatively high
Vermiculite possesses the special property of expanding
to between six and twenty times its original volume when
heated to approximately 1,000 degrees Celsius. This
process, called exfoliation, liberates bound water from
between the mica-like layers of the mineral and literally
expands the layers apart at right angles to the cleavage
Vermiculite is used to loosen and aerate soil mixes. Mixed
with soil, it improves water retention and fertilizer release,
making it ideal for starting seeds. Also used as a medium
for winter storage of bulbs and flower tubers.
Contrary to popular usage in our industry,bentonite is not a mineral. Bentonite
is arock, which in most instances would be
classified as a claystone. This rock wasformed by postdepositional alteration
ofvolcanic ash and its composition isdependent on the environment in which
thealteration took place.
Bentonite is composed primarily of smectitealong with varying amounts of
quartz,feldspar, cristobalite, zeolites, gypsum,kaolinite,micas, carbonates and
volcanicglass. Composition of the smectite varies inthe type of lattice substitution and,
moreimportant, the ionic population of theinterlayer region. The outstanding
propertyof smectite which is so important to drillingfluids is its ability to swell to
many times itsvolume when sodium is the interlayer ion.
This type of smectite is predominant in thebentonites found in the Wyoming area
aswell as other bentonites used in drillingfluids.
There are four main groups of clay minerals:
Kaolinite group - includes kaolinite, dickite, nacrite, and halloysite; formedby the decomposition
of orthoclase feldspar (e.g. in granite); kaolin is theprincipal constituent in china clay.
Illite group- also includes hydrous micas, phengite, brammalite, celadonite,and glauconite (a
green clay sand); formed by the decomposition of somemicas and feldspars; predominant in
marine clays and shales.
Smectite group- also includes montmorillonite, bentonite, nontronite,hectorite, saponite and
sauconite; formed by the alteration of mafic igneousrocks rich in Ca and Mg; weak linkage by
cations (e.g. Na+, Ca++) results in
high swelling/shrinking potential
Uses of Clay
1) Oil & Water Drilling
2) Drilling Mud
3) Cooling andcleaning the drill Gushers” used to be common until the use of drilling
mud was implemented
Clay slurrys have effectively been used to remove a range of comtaminants, including
P and heavy metals, and overall water clarification.
Filtering: Clays are used to decolorize, filter, and purify animal, mineral, and
vegetable oils and greases due to their high absorbing properties.
Environmental Sealants: Bentonite is used to establish low permeability liners in
landfills, sewage lagoons, water retention ponds, golf course ponds, and hazardous
Bentonite is used as a binder in tablet manufacturing and in diarrhea medications.
Clays are used as thickeners in a wide variety of cosmetics including facial creams,
lipsticks, shampoos and calamine lotion.
Pelletizing: Bentonite is used to bind tiny particles of iron ore, which are then formed
into pellets for use as feed material for blast furnaces.
Paints: Finely ground clays are used in the paint industry to disperse pigment evenly
throughout the paint. Without clays, it would be extremely difficult to evenly mix the
paint base and color pigment.
Clay Rocks in Egypt
There was clay deposits in Egypt in the following main areas:
The Sinai Peninsula
The South-western part of Central Sinai stored huge heat and rawmaterials the clays. One
of the most important raw materials in the Sinai Peninsula kaolin in the area of Abu
zenima, where Tina alkaolinih in many locations, some of them in the northeastern area of
about 200 km2 limited between 10 am – 16.5 33 East and latitudes 03 29-13.5 29 North,
approximately 15 km from the city of Abu zenima. Others are located in the South-East of
Abu zenima in an area some 150 km 2 are between longitudes 15 33 23 33 East and
latitudes 52.5 28 – 58.5 28 North.
There are layers of kaolin in Abu zenima with thick layers of sandstone, ranging from fish
can be exploited economically between 1, 4.5 meters, thickness ranges from sandstone
layers alternating with 10, 20 m. Tina reserves amount to alkaolinih North and South Abu
zenima about 16.5 million tonnes.
The new deposits are found kaolin in the early 1980s, the plateau wandering, about 25 km
east of Abu zenima, this area is determined by the intersection of a latitude 10.5 29 North
and longitude 15.5 33 East. And reserves that was explored in the plateau of wandering
about 88 million tons.
Notes for kaolin described their varying proportion of aluminum oxide from area to 20,
36% and the proportion of impurity mica and iron oxides, and titanium, necessitating the
need for treatment and processing of the raw material to raise the proportion of aluminum
oxide and reduce impurities to meet local market needs in various industries, especially for
alumina refractories and ceramics, export possible export. Kaolin is used currently in the
Sinai produced alumina refractories and ceramic tiles. Refractories industry experts should
address this material, especially since the price of a tonne of kaolin imported
approximately $ 180 while the price of a tonne of kaolin Egyptian about 40 pounds.
And targeted projects in Sinai, depending on availability of TINA kaolin and pure
limestone is white cement production project is being created now Mt. Sadat in Suez with a
production capacity of 250,000 tons per year with an estimated investment cost of around
500 million pounds. This project will provide 600 jobs from various disciplines. There is
currently only one factory for the production of white cement in Minya province card
design 250,000 tons, enough to meet the demand of the local market.
The Aswan region:
After the cessation of the production of kaolin from the Sinai Peninsula following the 1967
aggression was discovered about 16.5 million tons of kaolin in the Kalabsha southwest of
Aswan has been exploited in the manufacturing of refractories. And the proportion of
alumina from 29% to 35%, but production from the region has largely focused on areas of
the Sinai Peninsula after liberation for technical and economic reasons. Kalabsha kaolin
needs further technical evaluation and economic studies of the reserves.
And the exploitation of thermal albolklay mud and Tina from Abu Rish areas before me
and Abu Rish and Abu Virginia North of Aswan, where in large quantities in an area 70
km 2 and a thickness of 2 to 4 m. Take advantage of the Egyptian company for refractories
Tina extracted from its mines in Virginia, Abu refractories, where it is marketed under the
name "Egyptian 32, 30" (numbers indicate percentage of alumina), characterized by raw
materials with low Abu Virginia bug which reflected its impact on refractories production
specifications, and these serve as raw materials for the production of ceramics and
ceramics produced by the company mentioned in the four factories in Helwan and
Alexandria, Aswan and discern how malleable and dry.
There are several albolklay photo Tine were the following:
• Clay loam: alumina up to about 22% and iron up to 19%.
• Green Clay: alumina ratio ranges from between 22, 26% and between 3.9%.
• Clay gray: about 29% alumina and iron 3, 16%.
• Green italics for the Tan clay: the ratio of around 29% alumina and iron about 7%.
Used mud brick industry in albolklay drainage pipes, pottery products. Can then address
this material and access to appropriate use of ferric oxide in the production of refractories
and ceramic tile and porcelain with high plasticity help ease of composition. And treatment
can get varying qualities of excellent and good and to draw all the appropriate production
type so don't outlaw this raw products do not need to type.
Clay minerals are probably the most abundant minerals in sedimentary rocks.
They are also the most unstable minerals.
Their composition and structure determinetheir properties, which to a large
extentgovern the properties of rocks in which theyoccur. Therefore, it is important
tounderstand these minerals in order toproperly assess and predict potential
Bentonite products for water purification
Bentonite products provide versatile applications for waste water treatment and
The existing smectite clay-minerals in the bentonite (i.e. montmorillonite) generate a huge
reactive surface when disperged. The clay minerals´ weak negative charge enables it to
adsorb changeable cationic components.
Fig. 1 shows the structure of smectites exhibiting two tetrahedron-layers and one
octahedron layer. By exchange of ions with higher valence against ions with weaker charge
the silica layers of montmorillonite show a negative charge. This is compensated by
adsorption of counter ions in the interlayers whereby the TOT-layer corpuses are
electrostatically held together. The charge of the layers is but so weak that the interlayer
cations are exchangeable. Furthermore the weak charge effects an expansion of the
interlayers, enabling the counter ions to be integrated with their hydrate shell (inner
Fig 1: crystalline structure of montmorillonite
The original earth alkaline cation compound in the interlayers of the most market common
activated bentonites have been exchanged by Na+-ions during a technical process
(alkaline activation). Calcium bentonites are not activated and exhibit less swelling
They contain smectites with interlayers being predominantly occupied with Ca2+ or
Mg2+-ions. Furthermore there are natural sodium bentonites
(Wyoming-Bentonites, but also in other deposits) comprising smectites that are
predominantly occupied with Na+-ions between their interlayers, often in coexistence with
Ca2+ or Mg2+ -ions in various quantities.
What kind of advantages do S&B Industrial Minerals GmbH bentonites offer for
the waste water industry?
With AQUAMONT S&B Industrial Minerals GmbH offers powdery means for
flocculation precipitation and adsorption based on natural minerals.
We offer diverse products matching special requirements that are determined by the
different consistencies of the waste water.
AQUAMONT based on high swellable and fine dispersable bentonite generates
flocculating colloidal dispersions and effects a strong adsorption due to its high
specificparticle surface and interlayer charge.
By the negative surface charge of the dispersed clay particles positively charged particles
are closely and partly irreversibly bound, agglomerated, flocculated and embedded.
Due to its cation exchange capacity AQUAMONT particularly binds cationic tensides,
softeners based on quaterny ammonium compounds and heavy metals.
AQUAMONT is also applicable as a means for flake enrichment effecting an accelerated
sedimentaion or in combination with appropriate polyelectrolytes as a means for
AQUAMONT being a chemically inert silica mineral does not contribute to any additional
strain of the waste water.
Fabrication and dosage
AQUAMONT optimally develops its effect when added to the waste water in a hydrated
and dispersed condition.
Therefore it is advantageous to prepare AQUAMONT in pure tap water under high
shearing rates to generate a suspension showing a solid concentration of 5 %. Before
use the suspension should be swollen while slightly stirred for at least 1 hour. For
the preparation of the suspension especially powerful mixers or even dispersing units
should be used. At less intense preparation a higher water temperature supports and
accelerates hydratizing, swelling and delamination.
To achieve an optimal effect the AQUAMONT-suspension has to be pured homogeneous
into the waste water by intense mixing or strong turbulences.
If that is not possible lower concentrated suspensions should be applied which can
easily be poured homogeneously into the waste water.
Most appropriate for dosing are piston membrane pumps, eccentric worm pumps
and, if necessary, centrifugal pumps.
Typical proportions are 50 to 150 g AQUAMONT per m3 wate water depending on
The flocculation of AQUAMONT is best initiated by high molecular and weak anionic
Polyacrylamides (molar mass > 107), if not yet being induced by calcium-, aluminum or
Iron salts. The proportion is at 0, 5 to 1 % of the AQUAMONT quantity while the addition
Is to be done in form of a 0,2 to 0,5 % suspension after AQUAMONT has been
added. Laboratory tests have to determine the minimum time between adding
AQUAMONT and polymers. After intense mixing a sufficiently long time should be
kept for a better macro flocculation.
Water purification using clay pot water filters and copper mesh
Lack of clean water for use by rural communities in developing countries is of great
concern globally. Contaminated water causes water-borne diseases such as diarrhea, which
often lead to deaths, children being the most vulnerable. Therefore, the need to intensify
research on point-of-use (POU) water purification techniques cannot be overemphasized.
In this work, clay pot water filters (CPWFs) were fabricated using terracotta clay and
sawdust. The sawdust was ground and sieved using 300, 600 and 900 μm sieves. The clay
and sawdust were mixed in the ratios 1:1 and 1:2, by volume. Pots were then made, dried
and fired in a furnace at 850oC. Raw water collected from nearby rivers was filtered using
the pots. The raw and filtered water samples were then tested for E. coli, total coliforms,
total hardness, turbidity, electrical conductivity, cations and anions. The 600 μm pot had
the capacity to destroy E. coli completely from the raw water, whereas the 900 μm pot
reduced it by 99.4%. The 600 μm and 900 μm pots could reduce the total coliform
concentration by 99.3% and 98.3%, respectively. An attempt was also made to investigate
the germicidal action of copper on the coliforms in raw water, with a view to utilising it in
the CPWFs. Results showed that 10 g of copper, in the form of mesh made of thin wire of
diameter 0.65 mm, had the capacity to completely eliminate E. coli, by immersing it in 300
mℓ of raw water for 5 h, and total coliforms, by immersing it for 10 h. Subsequently,
copper was added to the CPWF by placing the mesh in the receptacle of the CPWF. Tests
showed that copper could destroy any remaining E. coli in the filtered water, rendering the
CPWF a completely viable POU technique for producing clean water. All other critical
parameters such as total hardness, turbidity, electrical conductivity and ions in the filtered
water were also within acceptable levels for drinking water quality. The filtration rate of
the pot was also measured as a function of grain size of the sawdust and height of the water
column in it. The filtration rate was found to increase with grain size and height in all of
Water treatment describes industrial-scale processes that make water more acceptable for
an end-use, which may be drinking, industrial, or medical. Water treatment is unlike small-
scale water sterilization that campers and other people in wilderness areas practice. Water
treatment should remove existing water contaminants or so reduce their concentration that
their water becomes fit for its desired end-use, which may be safely returning used water to
The processes involved in treating water for drinking purpose may be solids separation
using physical processes such as settling and filtration, and chemical processes such
as disinfection and coagulation.
Industrial water treatment
Two of the main processes of industrial water treatment are boiler water
treatment and cooling water treatment. A lack of proper water treatment can lead to the
reaction of solids and bacteria within pipe work and boiler housing. Steam boilers can
suffer from scale or corrosion when left untreated leading to weak and dangerous
machinery, scale deposits can mean additional fuel is required to heat the same level of
water because of the drop in efficiency. Poor quality dirty water can become a breeding
ground for bacteria such as Legionella causing a risk to public health.
With the proper treatment, a significant proportion of industrial on-site wastewater might
be reusable. This can save money in three ways: lower charges for lower water
consumption, lower charges for the smaller volume of effluent water discharged and lower
energy costs due to the recovery of heat in recycled wastewater.
Corrosion in low pressure boilers can be caused by dissolved oxygen, acidity and excessive
alkalinity. Water treatment therefore should remove the dissolved oxygen and maintain the
boiler water with the appropriate pH and alkalinity levels. Without effective water
treatment, a cooling water system can suffer from scale formation, corrosion and fouling
and may become a breeding ground for harmful bacteria such as those that cause
Legionnaires ' disease. This reduces efficiency, shortens plant life and makes operations
unreliable and unsafe.
Water treatment: Disinfectants and Other
Disinfectants: Ozone, as a very strong oxidant, is one of the main disinfectants when
purifying water. As ozone breaks down in the water, a complex chain reaction mechanism
occurs under the effect of the various solutes in the water or released during purification
treatment. Its ability to inactivate living cells can be extended to the point of provoking
Ultraviolet (UV) radiation is produced using ultraviolet lamps with quartz covers. UV
produces a minimum of by-products when treating the water.
Other: An advanced oxidation process (AOP) is a system to purify water by chemical
oxidation to deactivate residual organic pollutants. AOPs are capable of generating a more
powerful and less selective secondary oxidant in the reaction medium by activating an
available primary oxidant. AOP has been only gradually used in the water treatment
industry. One of the many AOP systems, the combined O3/H2O2, is the most widely used
one especially for the purpose of destroying pesticides in order to produce water for human
Fabrication of porous clay pots
Porous pots were made using terra-cotta clay and sawdust. The sawdust
was ground and sieved using 300 μm, 600 μm and 900 μm sieves. The
clay and sawdust were mixed in the ratios 1:1 and 1:2 to make the pots,
which were then dried for a week and fired in an electric furnace at
850oC. Firing time was 8 h and cooling time was 20 h. For initial tests,
small pots of capacity 1 ℓ and thickness of approximately 1.0 cm were
made. (Throughout this paper, the pots are labelled with grain size of the
sawdust and clay/sawdust ratio. For example, 300 μm (1:2) refers to a pot
made of clay and 300 μm grain size sawdust, in the ratio 1:2).
Schematic diagram of a clay pot water filter (CPWF)
Testing of pots
Raw water, collected from Lobamba and Mtilane Rivers in Swaziland,
was filtered using the pots. Both the raw and filtered water were then
tested for E. coli, total coliform, total hardness, turbidity, electrical
conductivity, cations and anions. Filtration rates of the pots were
measured as a function of the grain size as well as the height of the water
column in the pots.
Germicidal effect of copper
A detailed study was carried out to determine the germicidal effect of
copper in combating coliforms in raw water. This was done by counting
the number of coliform colonies remaining: (i) after immersion of
different masses of copper in a fixed volume (300 mℓ) of raw water, and
(ii) by immersing the same amount (10 g) of copper for different time
intervals. Coliform tests were carried out on both raw water and copper-
treated water samples.
Design and testing of the clay pot water filter (CPWF)
Finally, for fabrication of clay pot water filter for point-of-use
application, 600 μm (1:1 and 1:2) and 900 μm (1:1 and 1:2) pots were
made. They had a capacity of 2 ℓ and a thickness of approximately 1.5
cm. The pots were suspended inside plastic receptacles with lid and tap,
as shown in Fig. 1. Copper mesh made of thin copper wire of mass 2.5 g
and diameter 0.65 mm was placed at the bottom of the receptacle. Raw
water and filtered water, with and without copper mesh, were tested for
E. coli, total coliform, total hardness, turbidity, electrical conductivity,
cations and anions.
Results and discussion
Table 1 shows the effect of filtering raw water on E. coli, using 300 μm,
600 μm and 900 μm grain size pots. The 300 μm and 600 μm pots had the
capacity to remove E. coli in the raw water completely. The E. coli level
was as high as 9 600 CFU per 100 mℓ. However, the 900 μm pots could
not reduce the E. coli level to zero, even though a decrease from 9 600 to
1 CFU/100 mℓ (~ 99.99%) was achieved. The 1 CFU/100 mℓ of E. coli
that remained in the filtered water may presumably be due to the larger
pore sizes of these pots, which allowed the bacteria to pass through.
The presence of E. coli indicates that the water could have been
contaminated with animal or human waste and could cause waterborne
diseases such as diarrhoea, which often lead to deaths, particularly among
children. Because of the potential disease-causing characteristics of
certain E. coli, removal of E. coli from raw water is a major step in all
water purification systems. It is worth noting that the accepted level for
potable water quality is zero CFU per 100 mℓ for coliforms.
Table 2 shows the effect of grain size on the filtration rate of the pots.
The data show that the larger the grain size, the higher the filtration rate.
Filtration rates of the 600 μm and 900 μm pots were found to be about 2
to 3 times the filtration rate of the 300 μm pot. This is expected because
larger grain size presumably results in larger pore size and hence higher
filtration rate. In comparison with the 300 μm pot, the 600 μm pot would
be ideal for small-scale water filters because of its higher filtration rate.
Even though the 900 μm pot had the highest filtration rate, it had the
disadvantage of not being able to remove the E. coli completely.
Figure 2 shows the variation of filtration rate with the height of the water
column in a typical pot. Being gravity-driven, filtration rate is expected to
increase linearly with height. However, the rate was found to increase
non-linearly with height, as shown. For example, an increase in the height
of the water column by a factor of 5 (from 40 to 200 mm) led to an
increase in the filtration rate by a factor of about 15 (from 70 to 1 100
mℓ/h). This non-linearity can be explained by the fact that water filtration
takes place not only through the base of the pots but also through its
sides. From a practical point of view, it is therefore advisable to design
pots that are as tall as possible in order to get the maximum filtrate.
Figure 3 shows the germicidal effect of copper, in 300 mℓ raw water, as a
function of mass. As seen, the coliform colonies remaining in the water
decreased with the mass of copper added.. For example, 1 g of copper
reduced the total coliform level from an initial count of 2 413 to 1 046
CFU/100 mℓ (~ 56.7%) in 10 h, while 9 g of copper had the capacity to
reduce the level to 18 CFU/100 mℓ (~ 99.3%) within the same time
interval. A similar trend was seen for E. coli.
The germicidal effect of copper as a function of time is shown in Fig. 4. It
is observed that the number of coliforms destroyed increases with time.
For example, 10 g of copper can reduce the E. coli level from 186 to 4
CFU/100 mℓ (~ 98 %) in 1 h and to zero (100%) in 5 h. Total coliform
was reduced to zero after a period of 10 h. A similar decrease in E. coli
concentration in river water isolates, using copper pots, has been reported
(Shrestha et al., 2009). To the knowledge of the authors, no work has
been found in literature on the use of copper in CPWFs for its germicidal
It noted that in both cases (Fig. 3 and Fig. 4) the activity of copper is
much stronger initially. This is because an essential condition for the
inactivation of the bacteria is that they come into contact with the metal.
Hence, the larger the number of coliforms present in the vicinity of the
copper at a particular instant, the greater the chance that the coliforms
will come into contact with it and be killed, since the coliforms move
about randomly in the water.
Table 3 shows the coliform counts in raw and filtered water samples
using 600 μm and 900 μm pots. The initial count for total coliforms and
E. coli in the raw water was 5 475 and 697 CFU per 100 mℓ, respectively.
The 600 μm pot reduced the total coliform count to 38 CFU per 100 mℓ
(nearly 99.3%) and the E. coli count to zero. Incorporation of copper in
the receptacle reduced the total coliforms to zero as well. The 900 μm pot
reduced the total coliform and E. coli levels by 99.3% and 99.4%,
respectively, and addition of copper in the receptacle reduced their
concentrations by 99.98% and 100%. These results suggest that use of
copper in the CPWF is an effective means to eliminate coliforms in raw
water. Thus, there are two mechanisms responsible for the removal of
impurities from contaminated water – the physical process, using the
pores in the structure of the pot, and the biological process, through the
germicidal effect of copper. Silver is another metal known to have
germicidal action on microorganisms (Blanc et al., 2005; Landeen et al.,
1989; Lin et al., 1996; Jayesh et al., 2008), and has been effectively used
in CPWFs in colloidal form and as nanoparticles (Hwang et al., 2007;
Halem et al., 2007). However, fabrication of such silver-impregnated
filters can be cumbersome if it is to be carried out by a rural community,
as compared to using copper mesh. Moreover, silver is expensive and not
Table 4 shows the effect of filtering raw water samples on total hardness,
turbidity and electrical conductivity of the filtrate, using a 600 μm pot.
Total hardness in the raw and filtered water was within the RSA standard
for potable water. Filtration could reduce it by nearly 55%. Total
hardness in the range 0–200 mg/ℓ CaCO3 has no adverse health effects
(RSA guidelines: WRC, 1999; John and Trollip, 2009).
Turbidity in the raw water was much higher than the RSA and WHO
limits. Filtration reduced it from 8.31 to 1.13 NTU (~ 86%), which is an
acceptable level for potable water. Turbidity does not have any direct
adverse health effects.
However, it provides information about the presence of suspended solids,
and is a measure of the cloudiness of water.
Electrical conductivity of the raw and filtered water was found to be
within the RSA standard. Filtering reduced it from 51.78 to 35.05 μS/cm
(~ 32%). Electrical conductivity has no adverse health effects below 700
μS/cm, but indicates the total dissolved salt content in water.
Table 5 shows the effect of filtering raw water samples, using a 600 μm
pot filter, on the concentration of various anions. The sulphate ions were
reduced to 21.84 mg/ℓ (~ 44%) whilst the chloride ions decreased to 1.25
mg/ℓ (~ 54%). The rest of the anions, namely, ammonia, nitrite, nitrate,
fluoride and phosphate ions, showed an increase in concentration after
filtering. This could be a result of leaching as water passed through the
pot. Even though the concentration of these anions increased, their levels
in the filtered samples were still within acceptable limits for potable
Table 6 shows the effect of filtering raw water, on the concentration of
various cations. Calcium, iron and magnesium ions were reduced, while
the concentration of nickel and vanadium ions increased, presumably
because of the presence of these ions in the clay. There was no noticeable
change in the concentration of the other cations.
Porous pots were made from terracotta clay and sawdust. The clay and
sawdust, ground and sieved using 300 μm, 600 μm and 900 μm sieves,
were mixed in the ratios 1:1 and 1:2 to make the pots. They were then
dried and fired in an electric furnace at 850oC. The pots were suspended
inside plastic receptacles to make clay pot water filters (CPWFs) for
point-of-use (POU) application. The filters were tested for their ability to
purify raw water obtained from local rivers. The 600 μm filter yielded
water that was completely free of E. coli, and reduced the total coliform
concentration by 99.3%. The 900 μm filter could reduce the E. coli levels
by only 99.4% and the total coliform levels by 98.3%, but had the
advantage of having a higher filtration rate compared to the 600 μm filter.
Tests showed that copper is a suitable antibacterial agent to combat
coliforms in contaminated water. Copper mesh made of thin wire of
diameter 0.65 mm was placed inside the receptacles of the filters. This
resulted in the 600 μm filter being able to eliminate the total coliform
completely from the filtered water, whilst the 900 μm filter reduced it by
99.9% and eliminated the E. coli completely. The use of copper as an
antibacterial agent in the CPWF is therefore an effective and reliable
means for producing clean water for domestic use. The filtration rate was
found to increase with the grain size of the sawdust and height of the
water column in the pot. These factors need to be taken into account
when designing pot filters for practical use.
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