,
74
The Last Resource
the basic raw material than salt and water—a fact which We shall
see can cause some serious diiculties in the design and economical
operation of desalination plant.
In many countries the public water supplies are governed by
strict regulations which cover_…an10ng- other things the permissible
)
levels of dissolVed salts. The United States Public Health Service,
‘
for example, states that the total salt content of drinking water
*
should not exceed 500 ppm. but must not exceed 1,000 ppm. The
various dissolved constituents are also tightly controlled. Nevertheless, sometimes
arises where such restrictions are n0t
‘
possible. How much higher can the salinity rise? Experiments
“
during the Second World War on survival kits for emergency life—
rafts showed that—subject to the concentrations of common salt,
‘
sùlphate and magnesium being within certain limits—water with
up to 1,500 p.p.m. total dissolved solids was acceptable.
‘
Unfortunately the amount of water consumed directly«by man is
very small cof>ared to the vast quantities used in agriculture …and
'
industry, both of which are rather less adaptable when it comes to
they—matter of salinity. Although some salt—resistant plants are being
'
bi‘ed‘ on experimental stations, most cr0ps are-very
to
brackish water. The… presence of dissolv‘èdsallts
'
can ilead>-_ to increased costs from corrosion and impaired
efciency, for example by formirtg & hard
on heat‘exchanging surfaces: Praatically all industrial users
Water… would
prefer tohave-æWater —… completely free of dissolved salts. ln many
cases this*could save»theadditional —eätens€
water
supplies to ensutethät dissolved impri‘r‘ities remain in solution br,
morerrarely,
completely.
,,
f‘Ï
,
:,
Methods of desdiiâtäoñ*
In the past, two processes,—edistlatibn
been commercially
m
Of these only,: distil—
lation has been used enemiväy m sweeten
"
has been conned largely to the treatment of brackishànd) similar
waters. However, there may
processes to choôse—îfr—omin
the future; atleast a dozennewer ones are being investigated: As
research progr6Sses and morecritical evaluation, becomes—necessary,
some processes have come to the f0re but so far
fully challenged the two mentioned above. The storÿîof#êthè search
for cheaper, more efcient desalting
74
The Last Resource
the basic raw material than salt and water—a fact which We shall
see can cause some serious diiculties in the design and economical
operation of desalination plant.
In many countries the public water supplies are governed by
strict regulations which cover_…an10ng- other things the permissible
)
levels of dissolVed salts. The United States Public Health Service,
‘
for example, states that the total salt content of drinking water
*
should not exceed 500 ppm. but must not exceed 1,000 ppm. The
various dissolved constituents are also tightly controlled. Nevertheless, sometimes
arises where such restrictions are n0t
‘
possible. How much higher can the salinity rise? Experiments
“
during the Second World War on survival kits for emergency life—
rafts showed that—subject to the concentrations of common salt,
‘
sùlphate and magnesium being within certain limits—water with
up to 1,500 p.p.m. total dissolved solids was acceptable.
‘
Unfortunately the amount of water consumed directly«by man is
very small cof>ared to the vast quantities used in agriculture …and
'
industry, both of which are rather less adaptable when it comes to
they—matter of salinity. Although some salt—resistant plants are being
'
bi‘ed‘ on experimental stations, most cr0ps are-very
to
brackish water. The… presence of dissolv‘èdsallts
'
can ilead>-_ to increased costs from corrosion and impaired
efciency, for example by formirtg & hard
on heat‘exchanging surfaces: Praatically all industrial users
Water… would
prefer tohave-æWater —… completely free of dissolved salts. ln many
cases this*could save»theadditional —eätens€
water
supplies to ensutethät dissolved impri‘r‘ities remain in solution br,
morerrarely,
completely.
,,
f‘Ï
,
:,
Methods of desdiiâtäoñ*
In the past, two processes,—edistlatibn
been commercially
m
Of these only,: distil—
lation has been used enemiväy m sweeten
"
has been conned largely to the treatment of brackishànd) similar
waters. However, there may
processes to choôse—îfr—omin
the future; atleast a dozennewer ones are being investigated: As
research progr6Sses and morecritical evaluation, becomes—necessary,
some processes have come to the f0re but so far
fully challenged the two mentioned above. The storÿîof#êthè search
for cheaper, more efcient desalting