Ultraviolet Light Disinfection

Nature’s Way
Since the beginning of time, sunlight has acted as a natural disinfectant.
The ultraviolet (UV) rays, in a concentrated dose, can destroy a wide range of micro organisms by altering the genetic material (DNA) in cells so that bacteria, viruses and other micro organisms can no longer reproduce.
In UV disinfection systems, UV light is produced by germicidal lamps that are submerged in an open channel. As the wastewater flows past the UV lamps, the micro organisms are exposed to a lethal dose of UV energy. UV dose is measured as the product of the UV light intensity times the exposure time within the UV lamp array.

After solids removal, the clear effluent is exposed to Trojan UV disinfection system, where any remaining bacteria are killed by ultraviolet radiation.

 

UV Treatment (left) Post Aeration Ditch (right)

The UV Advantage
In the UV System, low-intensity lamps (similar in construction to fluorescent lamps) are set in an open channel. Ultraviolet rays (UV-light) with a wavelength of 254 nm has the effect of killing bacteria, viral and parasites in effluents from WWTP. The process makes no side products, and makes no risk for the health. UV-light is an alternative to chloride treatment.

Ultraviolet Plant

Ultraviolet Plant

Ultraviolet Plant Components

Ultraviolet Plant Illustration

1. UV Modules
Each UV module consists of a stainless-steel frame, 2 to 8 lamps enclosed in outer quartz sleeves, and an extruded aluminium enclosure holding the electronic ballasts. Individual lamp status is provided on top of each module. The UV modules can be simply set into place in their respective channels.
No mounting is necessary. A “light lock” on the UV module frame prevents any UV energy from escaping outside the channel.
With these UV modules, maintenance is extremely easy. Individual modules can be shut down and lifted out of the open channel for service, without interrupting the performance of the other UV modules.
UV modules are powered through a weatherproof, industrial-quality cable with a durable moulded PVC connector.

2. UV Lamps
UV lamps are mounted on modules installed in open channels. The lamps are enclosed in quartz sleeves, and positioned horizontally and parallel to water flow. A bank is made up of multiple modules placed in parallel positions. All ballast, lamp and sensor wiring runs inside the module frame.
Depending upon your requirements, the instant-start lamps have a 30" or 58" effective arc length and can be assembled in modules with two, four, eight or sixteen lamps each.
Expected lamp life is from 10,000 to 15,000 hours, depending upon site-specific conditions such as on/off lamp cycles, quality of effluent and frequency of cleaning.

3. Quartz Sleeves
The UV lamps are sealed inside the quartz sleeves by multiple seals, effectively maintaining a watertight barrier around the internal wiring while individually isolating
each lamp.

4. Electronic Ballasts
At the heart of the UV System is the electronic ballast. The electronic ballast weighs less than 30 percent of an electromagnetic ballast yet it generates more UV output and significantly less heat. With these improvements in ballast design, Trojan engineers were able to mount the ballast within an enclosure on the module frame.
In the Trojan System design there is no need for mechanical cooling, since normal convection cooling is adequate.

5. Power Distribution Centre
The Power Distribution Centre (PDC) enclosure is constructed of fibreglass and is mounted above the channel. The PDC consists of a termination board, a bus bar
distribution system and relay boards.
The bus bar distribution system receives incoming power from the plant power supply.
The power is distributed through the bus bar and feeds the individual relay boards.
The relay boards transmit power to the UV modules and sends UV module monitoring data to the termination board.
The termination board is the heart of the PDC. It selects signals to be sent out through
the relay board to the UV modules. All the control commands are sent from the System
Control Centre (SCC) to the PDC via this link.

6. System Control Centre
The System Control Centre (SCC) provides monitoring and control of all UV functions.
The Trojan System can be flow paced to turn off or on banks of UV lamps in response to changes in the flow rate.
This conserves power and prolongs lamp life.

7. UV Detection System
A submersible, stainless-steel UV detection probe (one provided for each UV bank)
transmits a measurement of the ultraviolet intensity. The UV probe monitors fouling of
the quartz sleeves, and long-term decrease in UV output from the lamps.

8. Automatic Level Controller

To ensure optimum disinfection, the Trojan designed Automatic Level Controller (ALC)
keeps the level of effluent in the channel constant, within one inch of optimum,
irrespective of flow rate. The weir, or automatic level control gate (ALC), is required in the channel to maintain the appropriate water level over the lamps.

9. Cleaning Systems
The system has been designed to facilitate easy cleaning of the UV modules.
Individual modules can be removed from service and cleaned manually or in a
custom-made cleaning tank.

Maintenance
With no moving parts and just one-third of the wiring and electrical connections of other UV systems, the Trojan System requires very little maintenance.
Regular cleaning of the quartz sleeves helps to maintain efficiency of operation.
Suspended matter, such as algae, plastics, etc., can easily be hosed off with water while the system remains in operation.
Replacing lamps is easy to do, requires no tools and takes less than two hours for a 50-lamp system.