Transcript School of CBEE Sponsors: Paul Berg and Jeff Nason

Process Testing for Household Water Treatment Invention
Megan N. Heinze, Thomas D. Jacroux, Richard P. Oleksak
College of Chemical, Biological, and Environmental Engineering
Sponsors: Paul Berg and Jeff Nason
BACKGROUND
• One billion people in developing countries lack access to
safe drinking water.
UMPQUA
Research Company
METHODS
OBJECTIVES
•Synthetic water was dechlorinated
and the transmittance adjusted to
correspond to conditions in
developing countries.
•Coliphage was added to give a final concentration of 106
coliphage/mL. Batches were exposed to UV light.
•Samples were sent to UMPQUA Research Company to determine
the final concentration of coliphage.
•It was desired to determine the capability of the prototype device
by performing an experiment to measure the log reduction of MS2
coliphage depending on the following variables:
•Exposure time
•Water depth
•% Transmittance of water sample
•Use of hand-crank vs. constant maximum lamp
output (DC power supply)
NEW GENERATION DESIGN
RESULTS
•A low-cost household treatment device could significantly
reduce this number.
•A variety of UV lamps are available for water treatment.
The best choice for here is a low pressure germicidal UV
lamp because:
•A spectral peak at 254 nm, close to optimum
•High UV efficiency
•Long lifetime
•Low power requirement
3.0
•UV treatment effectiveness is measured by “log reduction”
of microorganisms.
•The EPA requires a log reduction of 4 for UV treatment
(99.99 % removal) of most viruses.
•MS2 coliphage (used during testing) is a parasite that
viruses use as a host to replicate. It is chosen for water
disinfection because it is the most resistant to UV radiation
and the results are reproducible. Because of its resistance to
UV disinfection a log reduction of 2.3 corresponds to the
EPA required disinfection above.
Figure 4: An empirical model was developed relating the required
depths to achieve desired log reductions with different treatment
times. The equation shown is for a 2.3 log reduction.
2.5
Log Reduction
• Ultraviolet light (100-400 nm) disrupts viral and bacterial
DNA, making them unable to reproduce. The optimal
wavelength for disruption is 265 nm.
Effect of Stirred Reservoir Depth
EPA Standard for
disinfection = 2.3
2.0
1.5
1.0
Depth = 7.4 cm
Depth = 3.8 cm
0.5
0.0
0
20
40
60
Treatment Time (seconds)
Effect of Liquid Transmittance
•How does UV compare with other potential forms of
disinfection for household treatment?
3
Log Reduction
Figure 2: Log reduction versus time is plotted for samples of 75%
transmittance at depths of 7.4 and 3.8 cm . This shows the effect of
depth on log reduction for different exposure times. There is a direct
relationship between log reduction and exposure time.
75% Transmittance/cm
60% Transmittance/cm
2.5
EPA Standard for
disinfection = 2.3
2
80
Effect of Hand Crank versus
DC Power Supply (Replicates)
1.5
3.0
1
2.5
Hand Crank 1
0
•Transmittance (T), absorbance (A), and intensity (I)
describe the way light passes through a medium. A larger
transmittance value (smaller absorbance) means more light
reaches the same depth. Transmittance values are measured
using a spectrometer.
20
40
60
Treatment Time (seconds)
80
Figure 1: Log reduction of MS2 coliphage is plotted for different
exposure times. A DC power supply was used to maintain constant
UV output. Liquid levels were constant at a depth of 7.4 cm
(corresponding to a 5 L batch) with a transmittance of either 60 or
75% per cm. As expected, lower transmittance resulted in smaller
log reduction. At zero exposure time the notable log reduction is
thought to have been caused by residual chlorine in the prototype.
Log Reduction
0
2.0
New Design
Proposed Improvements
•Narrow the length to that of the bulb for better intensity
distribution.
•Incorporate reflective surfaces to realize more of the lamp
output.
•Incorporate a mixing device (such as an impeller) to better
expose microorganisms to UV light.
Hand Crank 2
Based on Figure 4 and estimates of the effects from the
above improvements, a proposed device to treat 4 L of
water in 40 seconds to a log reduction of 2.3 would need a
depth of 13 cm.
Stir 1
0.5
Original Prototype
Stir 2
1.5
ACKNOWLEDGEMENTS
1.0
•We would like to acknowledge:
• Paul Berg for designing the prototype and giving feedback.
• CH2M Hill for funding the project.
• Dr. Nason for his continual guidance.
• UMPQUA Research Company for their timely results.
• BIOVIR Laboratories for providing MS2 coliphage.
• Dr. Yokochi for providing essential equipment.
• Andy Brickman for help with electrical work.
• Nick Au Yeung for help with UV Vis.
• Tim Maloney for his expertise in water disinfection.
• Dr. Harding for organizing the project.
0.5
0.0
Trials
Figure 3: Comparison of the log reductions with stirring/DC
power supply versus hand crank/no stirring. The liquid level was
maintained at 7.4 cm with an exposure time of 40 seconds. Trials
with stirring produced higher log reduction.