Trojan Technologies Aquafine TrojanUVLogic Series, Installation & Operation Manual

Page: 36 / 186

Introduction to UV Theory
Trojan ogic
TM
Operations & Maintenance
1-2
UV L
1.3 Disinfection vs. Sterilization
Sterilization implies the total elimination of
pathogens or disease carrying microorganisms.
In contrast, disinfection is a reduction in the
concentration of pathogens to non-infectious
levels.
1.4 Applications of UV Light
Disinfection : The most common application of
UV light is disinfection. 254 Nm UV energy
penetrates the cell membrane of
microorganisms and alters the genetic material
of the cell (DNA) destroying its
ability to
reproduce. In this application, UV is commonly
used as an alternate disinfectant to chlorine and
other chemical oxidants and also as a
protection for other technologies in a complete
water treatment system.
Ozone Destruction : Ozone is typically used in
high purity water systems to oxidize trace
chemicals and to disinfect stored water. Often
ozone cannot be tolerated in the final product
water and therefore any residual must be
removed. 254 Nm UV energy is absorbed by
ozone, causing it to break down into dissolved
oxygen.
TOC Reduction : In high purity water systems,
UV is often used in conjunction with ion
exchange equipment for the reduction of trace
organics, referred to as TOC (Total Organic
Carbon). High-energy UV lamps, emitting UV
energy below 200 Nm, are used to trigger the
photolysis of water, producing very powerful
hydroxyl free radicals (OH). These hydroxyl
free radicals attack organic compounds,
breaking them down into carbon dioxide and
water when fully oxidized. Some organic
materials are broken down into weakly ionized
acid-based groups which are then easily
removed by polishing mixed bed ion exchange
equipment.
Chlorine/Chloramines Destruction : UV can
replace sodium meta-bisulfite and carbon
technologies to remove chlorine/chloramines
from source water used in industrial
applications. The addition of 254 Nm UV light
produces OH radicals that can break
chlorine/chloramine compounds down to their
lowest constituents.
1.5 Factors Affecting UV Disinfection
Ultraviolet light kills bacteria, protozoa and
viruses, by destroying their genetic material.
The performance of a TrojanUVLogicTM to
disinfect water is expressed in terms of
reduction of bacteria, or "kill". Each system is
designed to reduce microorganism counts to a
certain allowable level, which depends on the
requirements of the specific application or
regulatory requirements. The dose of UV light
available to kill bacteria is measured in
millijoules / centimeter2, which is equivalent to
the product of the light intensity and the
duration of exposure, or retention time. Any
factor that affects light intensity or retention time
will affect performance.
Dose = Intensity (mW/cm
2
) x Retention Time
(sec)
The Trojan UV Logic
TM
is designed to deliver a
dose that takes into account lamp aging.