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

Shigella
TABLE 6-25
UV DOSAGE FOR SELECTED ORGANISMS
Organism Dosage for 99% Kill at a = 0.0
Salmonella
Poliovirus
IIW sec/cm2
4,000
6,000
6,000
IH Viral Form 8,000
E. Coli
Protozoan
7,000
180-300,OOOa
Fecal Coliform 23,000b
a For 99.9% inactivation.
b Field studies corrected to a = 0; 99.96% inactivation.
Wastewater should be pretreated to a quality such that turbidity is less
than 10 JTU and color is less than 15 mg/l. Intermittent sand filtered
effluent quality will generally not exceed these limits when properly
managed. It would be desirable to provide measurement of UV transmit-
tance in the wastewater on a continuous basis to ensure that sufficient
UV power reaches the organism to be treated. Dosage values should be
conservative until more data are available.
mum UV dose of, 16,000 mw sec/cm2 or kw set/m
points throughout the disinfection chamber. A maximum depth of penetration
should be limited to about 2 in. (5 cm) to allow for variation in
wastewater absorption. The UV lamps should be enclosed in a quartz
glass sleeve and appropriate-automatic cleaning devices should be provided.
A UV intensity meter should be installed at a point of greatest
water depth from the UV tubes,.and an alarm provided to alert the owner
when values fall below on acceptable level.
180
J herefore, a desired mini-
should be applied at all