Wastewater Conveyance - Wastewater Operators - page 153

4.5 MainTaining fluid floW in PiPing sysTeMs
The primary purpose of any piping system is to maintain free and
smooth flow of fluids through the system. Another purpose is to ensure
that the fluids being conveyed are kept in good condition (i.e., free of
contamination). Piping systems are purposely designed to ensure free
and smooth flow of fluids throughout the system, but additional sys-
tem components are often included to ensure that fluid quality is main-
tained. Piping system filters are one example, and strainers and traps
are two others.
It is extremely important to maintain free and smooth flow and
fluid quality in piping systems, especially those that feed vital pieces of
equipment or machinery. Consider the internal combustion engine, for
example. Impurities such as dirt and metal particles can damage inter-
nal components and cause excessive wear and eventual breakdown.
To help prevent such wear, the oil is run continuously through a filter
designed to trap and filter out the impurities.
Other piping systems require the same type of protection that the
internal combustion engine does, which is why most piping systems
include filters, strainers, and traps. These filtering components may pre-
vent damage to valves, fittings, the pipe itself, and downstream equip-
ment or machinery. Chemicals, various types of waste products, paint,
and pressurized steam are good examples of potentially damaging flu-
ids. Filters and strainers play an important role in piping systems—
protecting both the piping system and the equipment that the piping
system serves.
4.5.1 scaling
Because sodium and calcium hypochlorite are widely used in
wastewater treatment operations, problems common in piping systems
feeding this chemical are of special concern. In this section, we dis-
cuss scaling problems that can occur in piping systems that convey
hypochlorite solution. To maintain the chlorine in solution (used pri-
marily as a disinfectant), sodium hydroxide (caustic) is used to raise the
pH of the hypochlorite; the excess caustic raises the shelf life. A high pH
caustic solution raises the pH of the dilution water to over pH 9.0 after
it is diluted. The calcium in the dilution water reacts with dissolved CO 2
and forms calcium carbonate. Experience has shown that 2-inch pipes
can turn into 3/4-inch pipes due to scale buildup. The scale deposition is
greatest in areas of turbulence such as pumps, valves, rotameters, and
backpressure devices.
If lime (calcium oxide) is added for alkalinity, plant water used as
dilution water will have higher calcium levels and generate more scale.
Although it is true that softened water will not generate scale, it is also
true that it is expensive in large quantities. Many facilities use softened
water on hypochlorite mist odor scrubbers only.