Environmental Engineering Reference
In-Depth Information
In the statement above, Hauser made it clear that flow measure-
ment is not only important but also routine in water/wastewater opera-
tions. Routine, yes, but also the most important variable measured in
a treatment plant. Hauser provided several reasons to measure flow in
a treatment plant, and the American Water Works Association (1995)
listed several more reasons to measure flow:
The
flow rate through the treatment processes must be controlled
so it matches distribution system use.
It is important to determine the proper
feed rate of chemicals added
in the processes.
The
detention times through the treatment processes must be calcu-
lated. This is particularly applicable to surface water plants that must
meet CxT values required by the Surface Water Treatment Rule.
Flow measurement allows operators to maintain a record of water
furnished to the distribution system for periodic comparison with
the total water metered to customers. This provides a measure
of “water accounted for,” or conversely (as pointed out earlier by
Hauser), the amount of water wasted, leaked, or otherwise not paid
for—that is, lost water.
Flow measurement allows operators to determine the efficiency of
pumps (pumps are covered in detail in Chapter 3). Pumps that are
not delivering their designed flow rate are probably not operating at
maximum efficiency, so power is being wasted.
For
• well systems, it is very important to maintain records of the vol-
ume of water pumped and the hours of operation for each well. The
periodic computation of well pumping rates can identify problems
such as worn pump impellers and blocked well screens.
Reports that must be furnished to the state by most water systems
must include records of raw and finished water pumpage.
Wastewater generated by a treatment system must also be mea-
sured and recorded.
Individual
meters are often required for proper operation of individual
pieces of equipment; for example, makeup water to a fluoride satura-
tor is always metered to assist in tracking the fluoride feed rate.
Note: Simply put, measurement of flow is essential for operation, process
control, and recordkeeping of water and wastewater treatment plants.
All of the uses just discussed create the need, obviously, for a num-
ber of flow measuring devices, often with different capabilities. In this
section, we discuss many of the major flow measuring devices currently
used in wastewater operations.
2.13.1 flow Measurement: The old-fashioned Way
An approximate but very simple method to determine open channel
flow has been used for many years. The procedure involves measuring
the velocity of a floating object moving in a straight uniform reach of the
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