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EVOLUTION OF WATER PURIFICATION
VED PRAKASH
27th May, 2010
INTRODUCTION
Water is one of the basic requirements of life. About 70% of human body is composed
of water. Other than this, it is also required in our day to day life such as cleaning, washing,
food processing, irrigation & so on. It also has uncountable other applications in industries &
laboratories. We cannot imagine life without water. But most of the water present in free form
is contaminated with minerals & microbes which make it unfit for use. So, it needs to be
processed & purified before use. Drinking water or potable water is defined as water of
sufficiently high quality that it can be consumed or used without risk of immediate or long term
harm.
Parameters for drinking water quality typically fall under two categories:
1. Chemical/physical parameters include heavy metals, trace organic compounds, total
suspended solids (TSS), and turbidity. Chemical parameters tend to pose more of a
chronic health risk through buildup of heavy metals although some components like
nitrates/nitrites and arsenic may have a more immediate impact. Physical parameters
affect the aesthetics and taste of the drinking water and may complicate the removal of
microbial pathogens.
2. Microbiological parameters include Coliform bacteria, E. coli, and specific pathogenic
species of bacteria (such as cholera-causing Vibrio cholerae), viruses, and protozoan
parasites. Additional contaminants include protozoan oocysts such
as Cryptosporidium sp., Giardia lamblia, Legionella, and viruses (enteric). Microbial
pathogenic parameters are typically of greatest concern because of their immediate
health risk.
History of water purification:
The purification techniques date back to time when humans first started civilizing. It is
speculated that this “quest” for pure water must have begun in prehistoric times. But the
earliest water treatment records come from Sanskrit writings and Egyptian inscriptions. May it
be the Harappan Culture or be it the Egyptian, all used some basic techniques of water
purification so that the water they consume would taste better. Subsequently, civilizations
emerging in different parts of world tried to find out better & more efficient methods for water
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purification. Even though they were all developing almost independent from each other, yet a
few techniques like sedimentation were common to most of them.
Different methods of purification gradually picked up. Before 1000 A.D., evidence shows
that some civilizations used naturally occurring minerals to purify water. Some civilizations even
started distilling water.
In
India,
sand & gravels were used for removing suspended particles from water
before boiling it. Evidences also state that some herbs were used for water treatment. These
include amla (which has very high vitamin C content), khus (cooling agent, blood purifier &
tonic), seeds of the nirmali (Strychnos potatorum) & lily roots (ref. Susruta Samhita, 2000 B.C.).
Further, some of the Sanskrit writings state that people used to place hot metal instruments in
water & then pass it through crude charcoal filters in order to make water taste better. (ref.
Baker & Taras, 1981). Other purification methods included the use of a kind of stone, known as
“Gomedakam,” and the seed of Strychnos potatorum.
Another Sanskrit manuscript Ousruta Sanghita (2000 B.C.) states that “It is good to keep
water in copper vessels, to expose it to sunlight, and filter through charcoal.”
In
Egypt (15 to 13th century B.C.), iron sulfate or aluminium sulfate or a mixture of
both of them was used in order to load the suspended particle & enhance the sedimentation
speed. After sedimentation has been completed, wick siphons
were used to collect the clean water in another container.
Image Caption: This ancient Egyptian clarifying device was found pictured on
the wall of the tomb of Amenophis II at Thebes. The inscription was carved in 1450 B.C.
th
Reprinted from The Quest for Pure Water. The history of 20 Century. Copyright 1981,
American Water Works Association.
Ancient
Greeks & Romans
used large reservoirs
to facilitate sedimentation of suspended particles in water. With time, people at Greece started
using Hippocrates Sleeve, a fabric bag through which water can be passed in order to filter it. It
traps sediments which makes water to taste or smell bad. Some others, for example, Diophanes
of the first century B.C. advised putting macerated laurel [4] into rainwater. Later, in the first
century A.D., Paxamus proposed that bruised coral or pounded barley, in a bag, be immersed in
bad tasting water
Early holy
Bible records (9th century B.C.) that Moses used a tree to sweeten bitter
water at Marah. The text says that Moses, as per the direction of God threw a piece of wood
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into the bitter water. The water turned sweet & drinkable. This is no miracle as a type of
barberry grows in the desert which has herbal property of sweetening brackish water.[2]
Ancient civilizations assumed water to be suitable for drinking if it was colorless,
tasteless & odorless. They did not know about the tasteless & colorless harmful substances
(minerals & microbes) present in water. There were no methods to detect & clean them off.
This ignorance led to downfall of many civilizations, most commonly due to water borne
diseases like cholera, typhoid, dysentery, hepatitis B, tuberculosis, meningitis, tricomoniasis,
and cholera, glaucoma, gastrointestinal pain, salmonella, poliovirus, and diarrhea etc.
After the downfall of the Greek & roman civilizations, the Dark Age (5th century to 14th
century) began which led to decline in advancement of science & technology. Some notable
advancement came into picture in 1627 when Sir Francis Bacon began experimenting with salt
water purification. He tried to remove salt from water using sand filters. He believed that as
sand particles are heavier than salt particles, sand would obstruct the movement of salt when
salt water passes through it (other resources [3] state that he used the idea that salt particles
are heavier than water & would be left behind if salt water is passed vertically upwards through
sand). On a micron-to-micron comparison, sand filters remove the least amount of dirt
(depending on the sand particle size) – particles as small as 20 to 25 microns. He tried this
experiment by digging a hole at the sea-shore. Although he failed, but he had restarted the
search for better techniques for water purification.
In 1746, a fellow Frenchman Joseph Army was granted the first patent for a filter
design. The filters consisted primarily of sponges and sand in a variety of configurations.
Toward the end of the century, filtered water was sold on a small scale, but no large
commercial plants were built. Also, British architect James Peacock patented a three-tank,
upward-flow backwash filter in 1791.
In mid 19th century, Anton van Leeuwenhoek used a simple microscope to view tiny
material particles present water which was assumed to be clean. This was a great
breakthrough. This explained why even after drinking clean water, people were suffering from
diseases like cholera. John Snow, a British scientist, further confirmed it by linking it to a leaking
sewer near to the pump house. Water coming from the pump house seemed to be good in
taste & quality but microscopic observations proved the presence of tiny cholera bacteria. This
instance proved once more that the taste and visual clarity of water does not necessarily
indicate purity.
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John Snow traced cholera deaths to a single pump on Broad Street in Soho, England.
The British government made the installation of sand water filters mandatory in the
whole city. This was the first step in which government was involved in public (municipal) water
systems. In 1804, the first citywide, municipal water treatment plant was installed in Paisley,
Scotland. This system was based upon slow sand filters designed by Robert Thom. It provided
filtered & pathogen free water to the whole city. In 1852, the Metropolis Water Act was passed
which enforced that all the water to be supplied to London should be treated with slow sand
water
filters.
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But these slow sand filters had a few demerits like they were very large & required
frequent & extensive cleaning. The large area of land required also interfered with land needs
for city growth. Because of growing needs of filtered water, American scientists developed
rapid sand filters which were easier to clean & had much more capacity & efficiency. This
system required pretreatments like coagulation & sedimentation in order to reduce to filtration
load.
Fig: a typical rapid sand filter
In 1835, John Doulton created a
gravity fed stoneware filter that combined
the technology of a ceramic filter with the artistry of a hand crafted pottery water container.
Henry Doulton, John Doulton's son, introduced the Doulton Manganous Carbon water filter in
1862. Most ceramic filters are now being manufactured for point of use applications. These
devices are typically shaped like a flowerpot or a bowl and are impregnated with tiny, colloidal
silver particles as a disinfectant and to prevent bacterial growth in the filter. The filter sits inside
a 20- to 30-liter plastic or ceramic receptacle with a spigot.
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The advantages of ceramic filters are their ease of use, long life (if not broken), and fairly
low cost. Disadvantages include possible recontamination of stored water since there is no
chlorine residual and a relatively low flow rate-typically one to two liters per hour.
A naturally mined ore, Pyrolox is a mineral form of manganese dioxide
which has been used in water treatment for more than 75 years. Pyrolox is a
granular filtration media for hydrogen sulfide, iron and manganese reduction.
Pyrolox
functions
as
a
catalyst
&
it
remains
relatively
unchanged.
Pyrolox works on a principle whereby the hydrogen sulfide, iron and
manganese are oxidized and trapped on the media while simple backwashing
cleans the bed. No chemical regeneration is required, nothing is imparted into the
drinking water and Pyrolox has a high capacity for low contaminant concentrations. Chlorine or
other oxidants accelerate the catalytic reaction. Advantages:
1.
2.
3.
4.
Effective reduction of iron, sulfur and manganese
Durable material with long service life and low annual attrition of bed
No chemical regeneration required only periodic backwashing.
Pyrolox is a natural mineral form of manganese dioxide, making it an
environmentally sound means of water filtration.
Present day technologies:
Chlorination: John Snow recognized the disinfecting nature of chlorine & used it
for killing cholera causing bacteria Vibrio cholarae. The municipal corporation of Britain started
chlorinating water in order to eradicate water borne diseases. This resulted in sharp decline in
deaths caused due to diseases like cholera, typhoid & dysentery. It was so successful that Life
magazine named water chlorination as “probably the most significant public health advance of
the millennium”! Presently around 98% of world’s water treatment plants use chlorine to
disinfect water.
* Cryptosporidium - A chlorine-resistant protozoan that makes its way into municipal water
facilities. The protozoan can cause severe gastrointestinal illness.
But chlorine has its own demerits. It is listed as a poison & is harmful to the human
body. When chlorinated water is showered, because chlorine vaporizes much faster as
compared to water, it turns into gas & causes respiratory diseases like asthma. Further, chlorine
can react with organic substances in water producing its chloride derivatives such as chloroform
& dichloromethane. These are quite harmful to the human body.
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To overcome these difficulties,
shower filters
2012
were designed. They can
remove chlorine as well as other harmful chemicals & VOCs. Most shower filters involve a twostep process in which water first flows through a granular copper/zinc media. This stage is
designed to remove chlorine and restore the natural pH balance of the water. In the second
stage of filtration, the water flows through a carbonized, coconut shell medium which
eliminates synthetic chemicals and VOCs. This purification helps in maintaining healthier
respiratory system, skin & hair.
A major achievement in the field of water purification was
Bio-sand Filters. It
was developed by Dr. David Manz in the 1990s at the University of Calgary, Canada. Over
200,000 biosand filters have been implemented in more than 70 countries around the world. A
typical biosand filter consists of a container a little less than a meter tall and perhaps 30 cm in
width and depth, filled with sand. The biologically active layer, which takes a week or two to
fully develop, is maintained by keeping the water level above the top of the sand. As with slow
sand filters, this bioactive layer helps to filter, adsorb, destroy, or inactivate pathogens. A
porous plate is usually located above the sand to prevent disturbance to the bioactive layer
when water is added. Users simply pour water into the top of the apparatus, and collect treated
water from the outlet.
Due to its simple design & great utility, it has become very famous, especially in
developing countries. It has several advantages such as:
1. The apparatus can be built using concrete—a commonly available and relatively
inexpensive material.
2. Internal parts are readily available which makes it ideal for developing countries.
3. Maintenance is fairly simple, usually consisting of agitating the upper surface of the
sand once a month or so and manually collecting the suspended material.
4. The cost of upkeep is quite low, since there are few or no parts to replace.
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fig: Bio-sand filter
Cartridge filters:
They have much larger surface area as compared to sand water filters. They have several
advantages such as:
1.
2.
3.
4.
5.
They are compact
Have longer lifetime
Permit better water flow as they generate lesser reverse pressure.
Low maintenance -- Easy to clean using a pressurized backwash
Can filter particles up to the range of 5 to 10 microns (our eyes can see particle sizes
up to 35 microns)
Ozone Water Treatment
Probably the oldest method of water purification, ozone treatments are becoming popular
again because of developments that accelerate processing time and increase reliability. Ozone
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is an unstable molecule, a "free radical" of oxygen which readily gives up one atom of oxygen
providing a powerful oxidizing agent which is toxic to most waterborne organisms. It is an
effective method to inactivate harmful protozoa that form cysts. It also works well against
almost all other pathogens. Water is filtered and purified through an injector that produces air
bubbles and destroys not only chemicals, but also pesticides, sulfide compounds, bacteria and
viruses. Ozone treatment plants now require the use of a much smaller ozone generator with
no storage drums. Demerits with this method are that it utilizes electricity & it leaves no
residual disinfection.
Reverse osmosis
In this method, filtered water is passed through a semi-permeable membrane on
application of pressure. Solutes are left behind depending on the pore size of the
membrane. It is capable of removing TDS, heavy metals, fluoride, pesticides & microorganisms. But it has certain disadvantages such as low recovery, brine disposal, high
maintenance (membrane change in 3 years) & volatile organics are not removed. It also
requires pretreatment.
Ultraviolet disinfection
Ultraviolet light is very effective at inactivating cysts. It inactivates microbes by denaturing their
genetic material. The main disadvantage to the use of UV radiation is that, like ozone
treatment, it leaves no residual disinfectant in the water. Another demerit is that it uses
electricity.
Water conditioning:
This is a method of reducing the effects of hard water. Hardness salts are deposited in water
systems subject to heating because the decomposition of bicarbonate ions creates carbonate
ions that crystallize out of the saturated solution of calcium or magnesium carbonate. Water
with high concentrations of hardness salts can be treated with soda ash (sodium carbonate)
which precipitates out the excess salts, through the common-ion effect.
WATTS Scale Prevention Systems transform Calcium ions into Calcium crystals, which
are stable and cannot attach to pipes, surfaces, hardware or heat exchanger components. The
crystals are so small they are easily rinsed away by the water flow. Quality Purolite 100
Softening ion exchange resin may also be used.
Chlorine & VOC removal:
Coconut shell carbon, because it is comprised of predominantly micro porous, structures, is a
superior performing product for the removal of chlorine, chlorinated solvents and VOCs.
Centaur removes both chloramine and hydrogen sulfide from potable water. Centaur is
outstanding in VOC removal, taste and odor control and in operating efficiency when compared
with traditional activated carbons.
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Lead solvency reduction: In areas with naturally acidic waters of low conductivity
(i.e surface rainfall in upland mountains of igneous rocks), the water may be capable of
dissolving lead from any lead pipes that it is carried in. The addition of small quantities
of phosphate ion and increasing the pH slightly both assist in greatly reducing plumbo-solvency
by creating insoluble lead salts on the inner surfaces of the pipes. Calcite may be used for
increasing the pH of water.
Arsenic removal:
Arsenic is removed from water by reducing arsenic (As V and III) using proven granular ferric
oxide replaceable resin cartridge. Aluminium oxide may also be used for the purpose.
Fluoride Removal:
Although fluoride is added to water in many areas, some areas of the world have excessive
levels of natural fluoride in the source water. Excessive levels can be toxic or cause undesirable
cosmetic effects such as staining of teeth. Fluoride is also a known carcinogen. One method of
reducing fluoride levels is through treatment with activated alumina.
Granular Activated Carbon filtering:
A form of activated carbon with a high surface area adsorbs many compounds including many
toxic compounds. Water passing through activated carbon is commonly used in municipal
regions with organic contamination, taste or odors. Many household water filters and fish tanks
use activated carbon filters to further purify the water. Household filters for drinking water
sometimes contain silver as metallic silver nanoparticles. If water is held in the carbon block for
longer period, microorganisms can grow inside which results in fouling and contamination.
Silver nanoparticles are excellent anti-bacterial material and they can decompose toxic haloorganic compounds such as pesticides into non-toxic organic products.
Presently, the combination of following processes is used for municipal drinking water
treatment worldwide:

Pre-chlorination - for algae control and arresting any biological growth

Aeration - along with pre-chlorination for removal of dissolved iron and manganese

Coagulation - for flocculation

Coagulant aids also known as polyelectrolytes - to improve coagulation and for thicker floc
formation

Sedimentation - for solids separation, that is, removal of suspended solids trapped in the
floc

Filtration - removing particles from water.

Desalination - Process of removing salt from the water.
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Disinfection - for killing bacteria
Whole house water filters
Most of them use four stage filtration & treatment.
1. Sediment removal in order to prevent filter clogging.
2. Water atomization: conversion of harmful chlorine into harmless zinc chloride.
3. Bituminous activated carbon filter (currently best available filtration technology
available).
4. Coconut shell activated carbon filter. Both are required for removal of pesticides,
remnants of organic matter & other harmful chemicals.
Presently a typical water purification system is composed of:
1.
2.
3.
4.
5.
6.
7.
8.
Particulate Filter
Clarity Cartridge
Pre Active Silver Carbon Cartridge
Electronic Membrane Life Enhancer
RO Membrane
Post Active Silver Carbon Cartridge
Ultra Filtration Cartridge
UV Purification System
UF Technology: A capillary tube-based technology that not only guarantees drinking water
that's pure and safe, but crystal clear and tasty too.
Electronic MLE: Electronic MLE prevents the accumulation of dissolved salts, like calcium and
magnesium thereby, enhancing the life of the membrane and improving water flow.
Some of the expensive techniques are:
1. Gas hydrate crystals centrifuge method. If carbon dioxide gas is mixed with
contaminated water at high pressure and low temperature, gas hydrate crystals will
contain only clean water. This is because the water molecules bind to the gas
molecules at molecule level. The contaminated water is in liquid form. A centrifuge
may be used to separate the crystals and the concentrated contaminated water.
2. Direct contact membrane distillation (DCMD). Applicable to desalination. Heated
seawater is passed along the surface of a hydrophobic polymer membrane.
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Evaporated water passes from the hot side through pores in the membrane into a
stream of cold pure water on the other side. The difference in vapor pressure
between the hot and cold side helps to push water molecules through.
Future of water filtration system:
Due to over industrialization & excessive human use, water resources have become
polluted. “Once we’ve polluted the water—how do we purify it?” This is the main problem
which we will face in near future. Some of the methods to overcome this are listed below:
1. Transformation of water filtration technology from municipal based to whole house
system or combination of both.
2. The whole house systems can be further modified by incorporating nanotechnology
into it. Silver & gold nano-particles have already been used for pesticide removal.
3. Due to its disinfecting effect, UV light treatment is similar to the effect produced by
boiling. It disinfects the water by destroying the genetic material of microbes. It is
more energy efficient as compared to boiling. It is also easier to handle as compared
to chlorination. It does not produce any side-effects as nothing is added to the
system during disinfection. UV disinfection can be done naturally by placing water in
transparent containers in sunlight. It is one of the most cost effective, efficient &
environmental friendly methods of water disinfection. It can either work on electric
power source or on solar power source. For UV treatment of water, may be a short
& strong pulse UV would be a better option as compared to continuous use of UV
light as it provides a much concentrated dose of UV. Disadvantage of this method is
that it utilizes electricity which limits its use. Further, it does not leave any residual
disinfection, so pathogens may grow back.
4. Silver Dihydrogen Citrate (SDC): This technique was developed by U.S. company
Pure Bioscience in order to kill most of the disease causing bacteria & viruses. This
technique uses stabilized silver ion to kill the microbes. It is useful because it is
odorless & safe to consume.
5. Aerobic Granular Sludge Technology: This technology causes all bacteria present in
water to solidify into heavy granules & settle to the bottom of the tank. Small filters
could be produced for home use, while larger tanks would be destined for industrial
use. (Discovered by a team of Dutch scientists from the Delft University of
Technology).
6. Particle-Exclusion Phenomenon Filters: dissolved particles move away from a
hydrophilic or water loving surface, leaving behind pure water. This water can be
extracted & then used.
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Aquaporins: Aquaporins are "the plumbing system for cells". Aquaporins selectively
conduct water molecules in and out of the cell, while preventing the passage
of ions and other solutes. Also known as water channels, aquaporins are integral
membrane pore proteins. The water pores are completely impermeable to charged
species, such as protons, a property critical for the conservation of the
membrane's electrochemical potential. Aquaporin is able to selectively bind water
molecules (hence allowing them through) and prevent other molecules from
entering. Water molecules traverse through the pore of the channel in single file.
Primary market focus includes ultra pure water (UPW) used in extreme applications
such as medico, biotech, in the production of semiconductors and flat panels and
other industrial purposes. Secondary market focus includes desalination of seawater and
pressure retarded osmosis applications.
8. Is it possible to make a living self sustaining water purification system that can be
used on commercial basis?
Point to be noted:
Healthcare professionals warn of too much purification in food and beverages, leading to
compromised immune systems and ultimately more adverse affects on health.
THIS IS ONE OF CHIEF REASONS WHY PEOPLE IN DEVELOPING COUNTRIES LIKE INDIA
HAVE STRONGER IMMUNE SYSTEM AS COMPARED TO THOSE IN DEVELOPED COUNTRIES LIKE
USA & UK.
Search for Clean Water Continues…
References:
1. The Quest for Pure Water: The History of Water Purification, American Water Works
Association’s (AWWA).
2. http://en.wikipedia.org
3. http://www.ehow.com
4. Baker, M.N. and Taras, Michael J. 1981. The Quest for Pure Water: The History of the
Twentieth Century, Volume 1 and 2. Denver: AWWA.
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5. Blake, Nelson M. 1956. Water for the Cities. Syracuse: Syracuse University Press.
Bruce, F.E. 1958. History of Technology, Volume 5. Oxford: Claredon Press.
6. http//:www.youtube.com
Glossary
1. Khus (Andropogan Muricatus)
Widely used in aroma therapy and perfumes, Khus is a cooling agent, tonic, and blood
purifier. It has a very cooling effect on the skin, and is used in treating many skin
disorders. Khus is known to have a calming effect on the nervous system, and therefore
is also used in psychological treatments for anger control, insomnia, and stress relief.
Other medicinal uses of Khus include ringworm, indigestion, and loss of appetite, fever,
gastric irritation, menstrual problems, vomiting, diarrhea, sprains, back pain,
rheumatism, and shooting pains in nerves.
2. VOCs - Volatile Organic Chemicals. VOCs are synthetic chemicals dissolved in water—
such as insecticides or herbicides—which vaporize at low temperatures.
3. Cryptosporidium - A chlorine-resistant protozoan that makes its way into municipal
water facilities. The protozoan can cause severe gastrointestinal illness.
4. Macerated laurel- it is obtained from 4 laurel leaves and an orange peel macerated in 1
liter of water for 4 hours. Laurel is a legendary herb. It is used in therapeutics, for
treating anorexia, flu and common cold, as well as illnesses concerning the nervous
system, digestive problems, and intestinal infections, inflammations of the mouth,
chronic rheumatism, spasms, and stomach agony.
5. BOILING: Heating water in order to kill parasites. 10 to 15 minutes of boiling is enough
to kill almost all the microbes. In order to have good efficiency, increment one minute is
required with every 300 m increase in altitude above sea level.
6. RECOMMENDED LEVEL OF MINERALS IN DRINKING WATER: Recommendations for
magnesium have been put at a minimum of 10 mg/L with 20–30 mg/L optimum; for
calcium a 20 mg/L minimum and a 40–80 mg/L optimum, and a total water
hardness (adding magnesium and calcium) of 2 to 4 mmol/L.
7. WATER FLUORIDATION
In many areas fluoride is added to water with the goal of preventing tooth decay.
Fluoride is usually added after the disinfection process. In the U.S., fluoridation is usually
accomplished by the addition of hexafluorosilicic acid, which decomposes in water,
yielding fluoride ions.
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