Article from Water Environment & Technology magazine
Excerpt from the June 1998 issue of the Water Environment & Technology
magazine (page 40-44)
Emerging Disinfection Technologies
Medium-pressure ultraviolet lamps and other systems are considered for wastewater application
by Gary L. Hunter, Walter J. O'Brien, Robert A. Hulsey, Keith E. Carns, and Ray Ehrhard
As interest in ultraviolet (UV) disinfection for wastewater treatment
has grown, so have the technology options. In addition to low-pressure
UV systems, which have a proven track record, and medium-pressure UV
systems, such technologies as broad-band pulsed xenon, narrow-band
excimer, and pulsed electric fields now are being studied and tested
for possible use in disinfecting wastewater, stormwater, and combined
sewer overflows.
Low-pressure Systems
A low-pressure UV systems consists of a power supply, ballasts, lamps,
a reactor, cleaning equipment, and controls and instrumentation. The
lamps operate at a temperature between 38 degrees Celsius and 49
degrees Celsius (100 degrees Fahrenheit and 120 degrees Fahrenheit) to
produce a near monochromatic radiation of 253.7 nm, which is near
optimum for microbial inactivation.
A "rule of thumb" for low-pressure systems is to use 40 to 60 lamps
per million gallons per day (mgd) of wastewater. The power required
per lamp will range from 65 to 80 W, depending on the type of ballast
(magnetic core or electronic), the desired output of the lamp, and the
lamp's operating temperature. At 80 W per lamp, this amounts to 3.2 to
4.8 kW per mgd.
A recent advancement in disinfecting municipal wastewater is the use of low-pressure, high-intensity lamps. These systems emit a
broader band of light than the monochromatic emission of the
traditional low-pressure systems. Low-pressure, high-intensity lamps
such as those manufactured by UV Systems UltraGuard of Burnaby,
British Columbia, Canada and WEDECO Ltd of Urmston, Manchester,
England, significantly reduce the number of lamps required per million
gallons per day treatment capacity (from between 40 and 60 to
between 4 and 6 lamps) and may be installed directly into an existing
UV reactor if a vertical alignment was used previously. |
