Hard Water, Soft Solutions
The USDA has determined
that some 65% of the water in the USA is “hard” with a pH>7.2. The problem
seems to be worst in the West where the Colorado River (the lifeblood of
Arizona, Nevada and parts of California) is pH=8.3 to 8.5.
If hard water is used for
farming or ornamental vegetation, the salts in the water are left in the soil.
The Agricultural Salinity Assessment and Management, Manual 71, 1991, of the
American Society of Civil Engineers, defines the Sodium Adsorption Ratio as a
maximum of 15%. Above that level nothing will grow; growers should be aware that
parts of Arizona have reached that limit and have been
abandoned.
Another problem with hard
water is that underground irrigation cannot be used because the small tubes are
easily plugged by salt compounds. Some attempt has been made to use hard water
underground and then to flush the tubes with dilute sulfuric acid. This may
clean the tubes, but the hard water with its load of salts is still left in the
soil.
The last question that
might be asked is “What pH do plants prefer? Plants generally prefer neutral or slightly acidic
water.
Solutions
to the Problem
Reverse
Osmosis
At present the most common
technique is reverse osmosis. This
system is expensive to build and maintain. The purified water is satisfactory
for household use, but is too expensive for agriculture.
Reducing the pH With Dilute
Acids
1)
The use of CO2 or other
dilute acid has a number of advantages. The CO2 dissolves rapidly in the hard
water. The salts in solution become solidified and can be removed by a filtering
system.
2)
The water is now softened
and underground irrigation can be used.
Experience in Arizona is that underground irrigation requires approximately 50%
of the water used for spray or ditch irrigation.
3)
The use of soft water
gradually changes the ground from the normal alkaline condition (in the West) to
a more acid state which helps the plants grow
4)
One last factor is that
the use of CO2 is a natural part of the anaerobic digestion process used for
disposal of garbage and waste water. The City of San Francisco disposes of its
garbage using anaerobic digestion.
As a result, it generates CO2 and methane (which is sold to some 30,000
homes for heating) and the solids are sold to the public for
fertilizer.
5)
The cost, assuming that
CO2 is purchased commercially, is 49 cents per thousand gallons of
water
Conclusions
The use of CO2 for water softening is low cost, rapid,
simple, and good for plants; the resulting solid salts are easily disposed of by
burial. The CO2 is permanently removed from the atmosphere.
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July 28, 2008
Hard Water, Soft Solutions
The USDA has determined
that some 65% of the water in the USA is “hard” with a pH>7.2. The problem
seems to be worst in the West where the Colorado River (the lifeblood of
Arizona, Nevada and parts of California) is pH=8.3 to 8.5.
If hard water is used for
farming or ornamental vegetation, the salts in the water are left in the soil.
The Agricultural Salinity Assessment and Management, Manual 71, 1991, of the
American Society of Civil Engineers, defines the Sodium Adsorption Ratio as a
maximum of 15%. Above that level nothing will grow; growers should be aware that
parts of Arizona have reached that limit and have been
abandoned.
Another problem with hard
water is that underground irrigation cannot be used because the small tubes are
easily plugged by salt compounds. Some attempt has been made to use hard water
underground and then to flush the tubes with dilute sulfuric acid. This may
clean the tubes, but the hard water with its load of salts is still left in the
soil.
The last question that
might be asked is “What pH do plants prefer? Plants generally prefer neutral or slightly acidic
water.
Solutions
to the Problem
Reverse
Osmosis
At present the most common
technique is reverse osmosis. This
system is expensive to build and maintain. The purified water is satisfactory
for household use, but is too expensive for agriculture.
Reducing the pH With Dilute
Acids
1)
The use of CO2 or other
dilute acid has a number of advantages. The CO2 dissolves rapidly in the hard
water. The salts in solution become solidified and can be removed by a filtering
system.
2)
The water is now softened
and underground irrigation can be used.
Experience in Arizona is that underground irrigation requires approximately 50%
of the water used for spray or ditch irrigation.
3)
The use of soft water
gradually changes the ground from the normal alkaline condition (in the West) to
a more acid state which helps the plants grow
4)
One last factor is that
the use of CO2 is a natural part of the anaerobic digestion process used for
disposal of garbage and waste water. The City of San Francisco disposes of its
garbage using anaerobic digestion.
As a result, it generates CO2 and methane (which is sold to some 30,000
homes for heating) and the solids are sold to the public for
fertilizer.
5)
The cost, assuming that
CO2 is purchased commercially, is 49 cents per thousand gallons of
water
Conclusions
The use of CO2 for water softening is low cost, rapid,
simple, and good for plants; the resulting solid salts are easily disposed of by
burial. The CO2 is permanently removed from the atmosphere.