D.O.E.
tested
D.O.E.
Test Report on 8 Watt Stainless Steel UV
As
carried out by the University of East London
14th December 1992
Environment & Industry Research Unit
Report on the Effect of Ultraviolet light on Bacteria
The aim of the project was to determine the efficiency of the 8 Watt
Ultraviolet light units against a range of specific bacteria, as shown
below, and at two flow rates of domestic tap water.
Method
20 litres of tap water, from a drinking water source, was inoculated
with 20 ml of a suspension, in sterile distilled water, of the organism
under test. The organism was mixed thoroughly with the water by passing
air through the mixture for several minutes.
A sample of the water was taken and the number of viable bacteria
determined before treatment. The ultraviolet light was switched on
and allowed to reach peak emission for 10 minutes. The water was then
allowed to flow through the UV unit and a sample was taken from the
downstream side using a sterile hypodermic syringe through a serum
cap. The number of viable bacteria were determined after exposure
to the Ultraviolet light.
The water was run to waste into another reservoir, hence the system
was isolated from the atmosphere. This provided a safe working environment
and protection from contamination.
Initially, gravity was used to provide the motive force for the water,
but some inconsistent results suggested that the method could be improved.
Finally a high rate peristaltic pump was used to pass the water through
the UV-unit at full and half speed; the flow rates were determined
in a separate experiment.
Conclusions
In any biological system there is a great deal of variability
and the method used was refined during the course of the project to
eliminate as many variables as possible. The final apparatus gave
fairly consistent results, but in many cases experiments had to be
repeated.
The Ultraviolet sterilising unit performed well under fairly exacting
conditions. The numbers of bacteria passed through the unit were very
much higher than would be found under normal conditions in this country.
Also many of these organisms would not normally be found in water,
except under extreme conditions of contamination.
The results indicate that at very high flow rates the lethal activity
of the unit deteriorates. A value of 99.9% reduction is the ideal
level obtained and this was generally found at a flow rate of 0.9
litres per minute.
In conjunction with previous studies with the unit, it is clear
that under the conditions of the test, the Ultraviolet sterilising
units should be able to destroy harmful bacteria in domestic water
supplies.
Results
Table 1. Reduction in numbers of various bacteria by a continuous
flow Ultraviolet sterilising unit.
|
Organism
|
Percentage Reduction
in Numbers
|
| |
at 9.3 1/min |
at 4.8 1/min |
| Escherichia coli |
99.0 |
98.0 |
| Klebsiella pneumoniae |
99.9 |
99.9 |
| Staphylococcus aureus |
91.5 |
99.9 |
| |
at 1.6 1/min |
at 0.9 1/min |
| Clostridium sp. |
99.7 |
99.9 |
| Pseudomonas aerupinosa |
99.9 |
99.9 |
| Chromobacterium lividum |
99.9 |
99.9 |
| Micrococcus sp. |
99.6 |
99.9 |
| Salmonella tvphimurium |
99.9 |
99.9 |
| Streptococcus fecalis |
99.9 |
99.9 |
| Lepionella pneumophila |
99.8 |
99.9 |
| Vibrio cholerae |
99.5 |
99.9 |
These test results refer to the 8 watt unit. We also manufacture
15 watt, 30 watt and 55 watt stainless steel units,
For
more details email us at: uvs@kockneykoi.co.uk
or
fax us on: 08448 000 001 England or +441708 441684 International
