The Equipment Design Process
369
Prevention and Cold Water Treatment and Supply Systems provide several examples of how such tests are performed and evaluated.
For smaller water utility plants (up to 1 million gallons per day [MGD]),
phosphate feed solutions can be made up easily by batch as needed. A maximum phosphate solution concentration of 10 wt% or 0.834 lb/gal is normally
recommended. For a phosphate dose of 3 mg/L and a flow of a or 1 MGD, the
volume of phosphate solution fed can be calculated as follows:
1 MGD 3 mg/L
8.34 lb/Mgal
mg/L
1 gal
0.834 lb
=
30
×
×
×
g gal
day
The equipment needed to feed phosphates to the water includes a 55-gallon solution feed tank, a drum mixer, a chemical feed metering pump, and
assorted piping, feed lines, valves, and drains. The capital expenditure
required is usually relatively small and is therefore within the means of
most small water utilities.
TabLE 11.5
Corrosion Properties of Frequently Used Materials in Water Distribution
Systems
Distribution
Material
Corrosion Resistance
Associated Potential
Contaminants
Copper
Good overall corrosion resistance
Subject to corrosive attack from high
velocities, soft water, chlorine,
dissolved oxygen, and low pH
Copper and possibly iron, zinc,
tin, arsenic, cadmium, and lead
from associated pipes and
solder
Lead
Corrodes in soft water with low pH
Lead (can be well above MCl a ),
arsenic, and cadmium
Mild steel
Subject to uniform corrosion
Affected primarily by high dissolved
oxygen levels.
Iron, resulting in turbidity and
red-water complaints
Cast or ductile
iron
Can be subject to surface erosion by
aggressive waters
Iron resulting in turbidity and
red water complaints
Galvanized iron Subject to galvanic corrosion of zinc by
aggressive waters
Corrosion is accelerated by contact
with copper materials and at higher
temperatures as in hot water systems
Zinc and iron; cadmium and lead
(impurities in galvanizing
process may exceed primary
MCl a )
Asbestoscement
Good corrosion resistance
Immune to electrolysis
Aggressive waters can leach calcium
from cement
Asbestos fibers
Plastic
Resistant to corrosion
a MCl = Maximum contaminant levels.
369
Prevention and Cold Water Treatment and Supply Systems provide several examples of how such tests are performed and evaluated.
For smaller water utility plants (up to 1 million gallons per day [MGD]),
phosphate feed solutions can be made up easily by batch as needed. A maximum phosphate solution concentration of 10 wt% or 0.834 lb/gal is normally
recommended. For a phosphate dose of 3 mg/L and a flow of a or 1 MGD, the
volume of phosphate solution fed can be calculated as follows:
1 MGD 3 mg/L
8.34 lb/Mgal
mg/L
1 gal
0.834 lb
=
30
×
×
×
g gal
day
The equipment needed to feed phosphates to the water includes a 55-gallon solution feed tank, a drum mixer, a chemical feed metering pump, and
assorted piping, feed lines, valves, and drains. The capital expenditure
required is usually relatively small and is therefore within the means of
most small water utilities.
TabLE 11.5
Corrosion Properties of Frequently Used Materials in Water Distribution
Systems
Distribution
Material
Corrosion Resistance
Associated Potential
Contaminants
Copper
Good overall corrosion resistance
Subject to corrosive attack from high
velocities, soft water, chlorine,
dissolved oxygen, and low pH
Copper and possibly iron, zinc,
tin, arsenic, cadmium, and lead
from associated pipes and
solder
Lead
Corrodes in soft water with low pH
Lead (can be well above MCl a ),
arsenic, and cadmium
Mild steel
Subject to uniform corrosion
Affected primarily by high dissolved
oxygen levels.
Iron, resulting in turbidity and
red-water complaints
Cast or ductile
iron
Can be subject to surface erosion by
aggressive waters
Iron resulting in turbidity and
red water complaints
Galvanized iron Subject to galvanic corrosion of zinc by
aggressive waters
Corrosion is accelerated by contact
with copper materials and at higher
temperatures as in hot water systems
Zinc and iron; cadmium and lead
(impurities in galvanizing
process may exceed primary
MCl a )
Asbestoscement
Good corrosion resistance
Immune to electrolysis
Aggressive waters can leach calcium
from cement
Asbestos fibers
Plastic
Resistant to corrosion
a MCl = Maximum contaminant levels.