Civil Engineering Reference
In-Depth Information
Minimal personnel exposure to UV
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Modular design for installation simplicity
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Figure 19-16 shows a conventional closed-vessel UV reactor. This reactor is typ-
ically used to treat flows up to 600 gallons per minute.
Additional design features for conventional UV disinfection systems include:
UV sensors to detect any drop in UV lamp output intensity
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Alarms and shutdown systems
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Automatic or manual cleaning cycles
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Telemetry systems for remote installations
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Hydraulic Design Considerations
The major elements that should be considered
in the hydraulic design of a UV closed-vessel reactor are: dispersion, turbulence, ef-
fective volume, residence time distribution, and flow rate.
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Poor geometry within the UV contactor (which creates spacing between lamps) can
leave dead areas where inadequate disinfection occurs.
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A key consideration to im-
proving disinfection is to minimize the amount of dead spaces where limited UV
exposure can occur. Plug flow conditions should be maintained in the contactor; how-
ever, some turbulence should be created between the lamps to provide radial mixing
of flow. In this manner, flow can be uniformly distributed through the varying regions
of UV intensity, allowing exposure to the full range of available UV radiation.
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UV systems typically provide contact times on the order of seconds. Therefore, it
is extremely important that the system configuration limit the extent of short circuiting.
Dispersion.
Dispersion is the characteristic of water elements to scatter spatially. The
ideal UV reactor is plug flow, where water particles are assumed to discharge from
the reactor in the same sequence they entered and each element of water passing
through the reactor resides in the reactor for the same period of time. An ideal plug
flow reactor has no dispersion and is approximated by a long tank with high length-
to-width ratio in which dispersion is minimal.
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Fig. 19-16.
Closed vessel UV reactor (Courtesy of Trojan Technologies Inc.)
