Disinfection - Wastewater Operators - page 357

significant amounts of ozone or hydrogen peroxide. The lamps must
also meet technical specifications for intensity, output, and arc length.
If the UV light tubes are submerged in the wastestream, they must be
contained within quartz tubes, which not only protect the lights but also
make cleaning and replacement easier.

Contact tanks must be used with UV disinfection. They are designed
with the banks of UV lights in a horizontal position, either parallel or
perpendicular to the flow, or with banks of lights placed in a vertical
position perpendicular to the flow.

Note: The contact tank must provide, at a minimum, a 10-second expo-
sure time.

Key Point: Ultraviolet light is extremely hazardous
to the eyes. Never look directly into the ultraviolet
light, and never enter an area without proper eye
protection where UV lights are in operation.

We stated earlier that turbidity has
been a problem for UV wastewater treat-
ment; however, if turbidity is its Achilles'
heel, then the need for increased main-
tenance (as compared to other disinfection alternatives) is the toe of
the same foot. UV maintenance requires that the tubes be cleaned on
a regular basis or as needed. In addition, periodic acid washing is also
required to remove chemical buildup. Routine monitoring of UV disin-
fection systems is required. Checking for bulb burnout, buildup of sol-
ids on quartz tubes, and UV light intensity is required.

9.4 ozonaTion

Ozone is a strong oxidizing gas that reacts with most organic and
many inorganic molecules. It is produced when oxygen molecules sepa-
rate, collide with other oxygen atoms, and form a molecule consisting of
three oxygen atoms. For high-quality effluents, ozone is a very effective
disinfectant. Current regulations for domestic treatment systems limit
the use of ozonation to filtered effluents unless the effectiveness of the
system can be demonstrated prior to installation.

Note: Effluent quality is the key performance factor for ozonation.

Key Point: Ozone is an extremely toxic
substance. Concentrations in air should not
exceed 0.1 ppm. It also has the potential to
create an explosive atmosphere. Sufficient
ventilation and purging capabilities should
be provided.

For ozonation of wastewater, the facility
must have the capability to generate pure oxy-
gen along with an ozone generator. A contact
tank with ≥10-minute contact time at design
average daily flow is required. Off-gas moni-
toring for process control is also required.
In addition, safety equipment capable of monitoring ozone in the atmo-
sphere and a ventilation system to prevent ozone levels exceeding 0.1
ppm are necessary. The actual operation of the ozonation process con-
sists of monitoring and adjusting the ozone generator and monitoring
the control system to maintain the required ozone concentration in the
off-gas. The process must also be evaluated periodically using biological
testing to assess its effectiveness.