1311WATER TREATMENT
INTRODUCTIONWater, of course, is used for many purposes associated with
human activity. In its natural state it occurs in and on the
ground in subsurface and surface reservoirs. The quality and
reliability of a source of water will vary considerably, both
in time and space. This means that characteristics (chemical,
physical, and biological) will differ greatly depending upon
the location and type of source. It also means that a given
source may vary over the seasons of the year.
Thus, in the selection of a water source, consideration is
usually given to the use to which the water will ultimately be
put so as to minimize the cost of treatment. Simultaneously
consideration must be given to the reliability of the source
to provide an accurate and constant source of supply. It will
be seen later in this section that a groundwater supply may
enjoy the benefit of requiring little or no treatment, while
a surface supply such as a river, pond or lake may require
considerable and perhaps seasonally varying treatment.
However, a surface supply is visible and therefore more reli-
able whereas a groundwater supply may just disappear with
no warning or notice.
In certain areas, freshwater is so scarce that the source
must be accepted and choices are not available. The history
of water treatment dates back to the early Egyptian civiliza-
tions where the murky waters of the Nile River were held in
large open basins to allow the mud to settle out. The earliest
archeological records of a piped water supply and waste-
water disposal system date back some five thousand years to
Nippur of Sumaria.^1 In the Nippur ruins there exists an arched
drain with an extensive system of drainage from palaces and
residences to convey wastes to the outskirts of the city. Water
was drawn through a similar system from wells and cisterns.
The earliest records of water treatment appear in the
Sanskrit medical lore and Egyptian wall inscriptions.^2
Writings from about 2000 BC describe how to purify “foul
water” by boiling in copper vessels, exposing to sunlight,
filtering through charcoal and cooling in an earthenware
vessel. There is little concerning water treatment in the
Old Testament, but Elisha under instruction from the Lord
“healed” certain waters so that “there shall not be from
thence any more death or barren land.” This “healing” was
accomplished when Elisha “went forth unto the spring of the
waters and cast salt in there ...” It is not clear if this “salt”
was a fertilizer to help grow crops or if it was some chemical
to render the water safe.Settling was first introduced as a modification of decant-
ing apparatus used for water or wine. This apparatus was
pictured on the walls of the tombs of Amenhotep II and
Rameses II in the 15th and 13th Centuries BC. An engineer-
ing report on water supply was written by the then water
commissioner for Rome in AD 98. He described an aqueduct
with a settling basin.
In 1627 the experiments of Sir Francis Bacon were pub-
lished just after his death, and were the first to describe coag-
ulation as well as sedimentation and filtration as a means
of treating drinking water. The first filtered supply of water
for an entire town was built in Paisley, Scotland in 1804.
Starting with a carted supply, a piped distribution system
was added in 1807.^2
However it was not until 1854, in London, that it was
demonstrated that certain diseases could be transmitted by
water. Dr. John Snow suggested that a cholera outbreak in a
certain area in London resulted directly from the use of the
Broad Street pump, and was in fact the source of infection in
the parish of St. James. Dr. Snow recommended that the use
of the pump should be discontinued and the vestrymen of the
parish agreeing, the disease subsequently abated in that area.
The discovery was all the more incredible as the germ
theory of disease, defined by Pasteur and subsequently postu-
lated by Koch, had not at that time been clarified. Subsequently
disinfection of water by addition of chlorine was introduced
on a municipal scale. This step, together with an adequate and
sanitary distribution system, probably did more to reduce the
deaths due to typhoid and cholera and any other single item.
In 1854, cholera claimed a mortality of 10,675 people in
London, England. In 1910, the death rate from typhoid fever
in the City of Toronto, Canada, was 40.8 per 100,000. By
1931 it had fallen to 0.5 per 100,000. These improvements
all related to the extensive water purification and steriliza-
tion techniques which are being introduced to municipal
water treatment systems during that period.^3
In general, the treatment processes of water can be sub-
divided into three groups: physical, chemical, and biological
processes. The biological processes are generally reserved
for waters grossly contaminated with organic (putrescible)
carbon such as sewage or industrial waste waters. These
waters are not normally considered as suitable for drinking
supplies, but undoubtedly as demand for water increases all
available sources will have to be examined. However, for the
present purposes we will consider that the biological stabiliza-
tion of originally polluted waters will be dealt with under theC023_006_r03.indd 1311C023_006_r03.indd 1311 11/18/2005 1:32:33 PM11/18/2005 1:32:33 PM