On-Site Wastewater Treatment and Disposal Systems - Forced ...

Cleaning of quartz glass enclosures is of paramount importance since UV
transmittance is severely impaired by the accumulation of slimes on the
enclosures. Cleaning is required at least 3 to 4 times per year at a
minimum, and more often for systems employing intermittent flow. If
automatic wipers are employed, the frequency of manual cleaning may be
reduced to twice per year. Expected lives of lamps are variable, nor-
mally ranging from 7,000 to 12,500 hours. It is good practice, however,
to replace lamps every 10 months, or when metered UV intensity falls be-
low acceptable values. A complete cleaning of quartz glass enclosures
with alcohol is required during lamp replacement. Based on limited
operational experience, it is estimated that 10 to 12 man-hr per yr are
required to maintain the UV system. Power requirements for the UV
system for design flow rates up to 4 gpm (0.25 l/ set) are approximately
1.5 kWh/day.
6.5.4 Ozonation
6.5.4.1 Description
Ozone, 0 , a pale blue gas with pungent odor, is a powerful oxidizing
agent. 1 t is only slightly soluble in water, depending upon temperature,
and is highly unstable. Because of its instability, ozone must be
generated on site.
Ozone is produced by the dissociation of molecular oxygen into atomic
oxygen with subsequent formation of 0 . It is produced commercially by
passing an oxygen-containing feed gas ?I etween electrodes separated by an
insulating material (54)(55). In the presence of a high-voltage, highfrequencygapdischarge,
ozone is generated from oxygen in the electrode
Ozone is a powerful disinfectant against virus, protozoan cysts, and
vegetative bacteria (54)(55)(56)(57). It is normally sparged into the
water to be treated by means of a variety of mixing and contact devices.
Because of its great reactivity, ozone will interact with a variety of
materials in the water, resulting in an ozone demand. The short half-
life of ozone also results in the rapid disappearance of an ozone resid-
ual in the treated water.
6.5.4.2 Applicability
Ozone is currently used to disinfect water supplies in the United States
and Europe, and is considered an excellent candidate as an alternate
wastewater disinfectant (54)(55)(56)(57). The major drawback to its
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