UV For Developing Countries
A new tool for the disinfection
toolbox?
Prof. Bill Larsen’s
system
First UC Berkeley UV Tube
Next Model
Sri Lankan Neighborhood Scale
Installation
B9 Plastics Better Water Maker
Ultra-Violet Light
UVA (315 – 400 nm): sun tans
UVB (280 – 315 nm): sun burns
UVC* (200 – 280 nm): disinfection
Interferes with DNA
Replication/
Reproduction
(*Nearly 100% filtered by the atmosphere.)
History of UV Drinking Water
Disinfection
•1910 Marseilles, France: UV is first used to treat drinking
water. Abandoned for free chlorine (by-product of soda production)
•1970’s: Disinfection by-products discovered. UV disinfection of
drinking water common in Europe.
•1990’s: Outbreaks in the US lead to concern that chlorine is not
effective against some organisms.
•March 1993: a cryptosporidium outbreak
in Milwaukee leads to 400,000 illnesses and
100+ deaths.
History of UV Water Disinfection
•1999: Town of Ontario, NY becomes the first community in North America to
disinfect surface source drinking water with UV light.
Poly-alum added
Sedimentation
Gravel, sand, and GAC filters
Lake Ontario
Chlorine residual added
Storage
UV
•Currently: there are over 1500 wastewater treatment plants using UV in the US.
UV System Components
• UV Bulbs and Ballast (AC or DC)
– Mercury-argon lamps (an electrical arc ignites the
mercury vapor which emits UV light)
– Hope for LEDs in the future…
• Chamber
• Quartz Sleeve
– passes UV
– maintains bulb temperatures
• Sensor
– to monitor bulb output
• Cleaning Mechanism
Mercury Vapor Bulbs
• Like florescent bulbs except:
– Quartz not glass
– No phosphor coating
• 88% of the output at 253.7 nm
• Lamp is susceptible to cooling
•
by the effluent
Limited Lamp Life—1 year
continuous operation
Determining Dose (Fluence)
Dose (Fluence) = Intensity * Exposure
Time
(J/m2)
(W/m2)
(s)
Function of bulb and
water characteristics
Function of
hydrodynamics
&
Geometry of reactor
Simple Microbial Response
Dose Response Curve for E. Coli (wild type)
(Sommer et al, 1998)
0% inactivated
Log Survival
0
-1
90% inactivated, 10% surviving
-2
99% inactivated, 1% surviving
-3
99.9% inactivated, 0.1% surviving
-4
99.99% inactivated, 0.01% surviving
-5
99.999% inactivated, 0.001% surviving
-6
0
10
20
30
40
50
60
UV Fluence or Dose (J/m2)
70
80
90
100
A More Complicated Response
Explanation of Shoulder
•Threshold of DNA
“hits” to inactivate?
•Reactivation?
?
Explanation of Tailing
and imbedded bacteria
•“Shielding” depends on
particle absorbance
•Imbedded bacteria
•UV resistant bacteria
Water Composition
Turbidity
• Can lead to scattering, reflection, blocking of microorganisms by
•
•
•
•
particles
Considered negligible up to 5 NTU
Theoretically, overall intensity is not reduced, but, energy is lost
through interactions with particulates
Embedded microorganisms present the real limitation
Precede by filtration or flocculation/sedimentation
Absorption Coefficient
• Certain particles absorb at germicidal wavelengths
• Fe, sulfites, aromatic organics, humic acid, dechlorination with Sodium
Thiosulfate
• Presence can greatly increase attenuation
UV Regulatory Standards
US
• 1966: Dept. Health, Education & Welfare – 160
J/m2
• 1999: NY State still required 160 J/m2 when I
started working with UV
• ~2000: WHO Recommends 380 J/m2
• 2002: ANSI/NSF Standard 55 set at 400 J/m2
1 LOG (90%)
2 LOG (99%)
UV Dos e (J /m 2 )
4 LOG (99.99%)
B A CTERIA
B acillus anthracis (6,4)
B acillus s ubtilis (6)
Cory nebacterium diphtheriae
E.coli (1,6,4)
Leg ionella pneumophila (1,4)
Micrococcus s peroides (4)
Proteus v ulg aris (6,4)
Salmonella ty phi (1)
Ps eudomonas aerug inos a (1,4)
Salmonella enteritis (1,4)
Salmonella ty phimurium (6,4)
Shig ella dy s enteriae (1,4)
Shig ella parady s entaeriae (1)
Shig ella flexneri (1)
Shig ella s onnei (1,4)
Staphy lococcus albus (6)
Staphy lococcus aureus (1,4)
Streptococcus hemoly ticus (6,4)
Streptococcus lactis (6,4)
Streptococcus v iridans (6,4)
Vibrio cholerae (1,4)
VIRUSES
Poliov irus 1 (1,3,3,8)
Coliphag e (1,4)
Hepatitis A v irus (1,3,3,10)
Rotav irus SA 11 (1,3,3,10)
A denov irus 40 (8)
A denov irus 41 (8)
PROTOZOA
Giardia muris (1)
A canthamoeba cas tellanii (1)
Cry ptos poridium parv um (9)
0
100 200 300 400 500 600 700 800 900 1000 1100 1200 1300
NSF/ANSI 55 Required Minimum Fluence ...
3 LOG (99.9%)
Estimation of Dose (Fluence)
• Biological Assays with Virus
– Develop dose (fluence) inactivation relationship with
Quasi Collimated Beam Apparatus
– Measure Log inactivation in UV device
UV Bulb
Aluminum
Plate
Bulb
Holders
Collimating Box
Concentric
Apertures
Quasi Collimated UV rays
Manual UV Shutter
Petri Dish with sample
and stir bar
Magnetic Stir Plate
MS2 Colifage response to UV
Log Removal
5/12/2005
5/7/2005
3/25/2005
2/28/2005
2/5/2005
10/27/2004
5/9/2004
4/19/2004
NWRI High
NWRI Low
Linear (Log Removal)
0
1
Log Removal
2
3
4
y = 0.0043x + 0.2918
R2 = 0.9656
5
6
7
0
200
400
600
800
Fluence (Dose) J/m
1000
2
1200
1400
Estimation of Dose
• Chemical Actinometry
–Photochemical reaction rate
•Molecules react with UV photos
•Products of the reaction used to
determine quantity of photons
absorbed (dose)
Dose Estimation:
Point Source Summation
p
RHOi,j
INTENSITYi,j :=
· exp –(sw· R ) ·
R
4 · n · p · RHOi,j2
x
R
RHO
RHO i,j :=
(x – y)2 + R2
σw= abs of water
y
Intensity
•Bulb is considered a line of point sources
distributing light equally in all directions
•Intensity at each point is calculated as the sum
of all point sources
Benefits of UV
• No known byproducts
• Short contact time (sec, instead of min)
• No danger of overdosing
• Ability to inactivate cyst forming organisms
(e.g. Giardia, Cryptosporidium) at doses
used for water treatment
• No transportation of hazardous chemicals
Limitations
• No residual
•
disinfectant
Photoreactivation and
dark repair possible
• Bulb fouling
– Organic constituents,
hardness, algae and
biofilm on quartz
sleeve
• Requires electricity
Add chlorine residual
Shield from visible light
for 1-2 hrs
 Overdose
Clean sleeve
Suspend bulb
Design: ss-PVC
Side View
(transparent)
65 cm
G-8 germicidal UV bulb
water level
water
outlet
Ferro Cement UV-Tube
Figure 1: Cross Section and Side View of the
Ferro Cement UV-Tube
Cable
Nut and Bolt
Ballast
Ferro cement
cover
Metal Cover
Bulb
Inlet
Ferro cement
trough
Water
Outlet
Laboratory Testing
All UV-Tube Designs
• Microbial Testing
• Hydrodynamic Tracer
•
Constant
Head Tank
Tests
Materials Degradation
Testing
Bulb Studies
• Cycling
• Warm-Up Time
Flowmeter
UV-Tube
Mixing Tank with
Pump
MS2
Challenge
Test
MS2 Microbial Testing
MS2 Fluence Response Curve
MS2 Challenge of the UVTube
Log Removal
5/12/2005
5/7/2005
3/25/2005
2/28/2005
2/5/2005
10/27/2004
5/9/2004
4/19/2004
NWRI High
NWRI Low
Linear (Log Removal)
0
1
Avg: 4.38
95% CI: 2.98 – 5.77
-1
2
-2
Log Removal
Log Survival
0
-3
-4
3
4
-5
y = 0.0043x + 0.2918
R2 = 0.9656
5
-6
0
1
2
Test
3
4
5
6
643
967
1292
7
0
200
400
600
800
Fluence (Dose) J/m
1000
2
1200
1400
Rhodamine Tracer Testing
Tracer Test, ss-PVC UV-Tube at 5 L/min
0.05
4/25/2005
0.04
% of Dye Exiting
4/29/2005
5/5/2005
0.03
5/7/2005 New Design
0.02
0.01
0
0
• Pulse input with syringe
• Samples every 3
•
seconds
Measure on
spectrophotometer 555
nm
50
100
Time (s)
Date
4/25/
2005
4/29/
2005
5/05/
2005
5/7/2005 New Design
q
35.2
36.5
35.8
36.4
tbar
36.1
7
35.5
34.5
35.7
q/tbar
0.97
1.03
1.04
1.03
Materials Degradation
Interactions of UV-Tube Materials with UV in
the presence of water…
– Flow through, minimal flow.
– Overnight test, 16 hours.
– Vacation test, 8 days.
– Total Evaporation, 35 days.
Test for volatile organic compounds and metals.
Materials Degradation Results
• PVC alone  carcinogenic volatile organics
• ABS alone  Benzene!
• Galvanized steel  High zinc levels (taste)
• Lined PVC  low levels of vocs, acceptable
• Stainless with PVC endcaps  low levels,
acceptable
• Copper and aluminum have not been
tested.
Bulb Studies
Cycling Study
• One cycle daily: 12
hours on, 12 hours off
• Four cycles daily: 3
hours on, 3 hours off
• Twelve cycles daily: 1
hour on, 1 hour off
Warm up Study
Bulb Covers
Cycling Timers
UV Issues/Challenges
•
•
•
•
•
Electricity requirements
Safety: UV exposure and electric shock
Material interactions with UV
Water depth and hydraulics (UV dose)
Water Characteristics
– Embedded Bacteria
– Fe, sulfites, aromatic organics, humic acid, &
dechlorination with sodium thiosulfate absorb UV
• Safe storage (no residual disinfectant)
• Bulb life
• *****Dissemination *****
Important Facts:
• UV is bad for your eyes, skin
• Turbidity, chemicals affect UV
transmittance
• Bulb life is limited
• Water depth and hydraulics are important
• No residual disinfectant
Materials and UV-C
• Blocks UV:
– Glass
– Plexiglass
• Transmits UV:
– Quartz
– Teflon
• Reflects UV:
– Aluminum
• Reacts with UV:
– PVC
– ABS
– Other plastics?
Design Features:
• Effective
– Eliminate microorganisms
• Portable or built in place
– Size, weight
– Construction
• Simple
– Local materials
– Simple tools
Design Features:
• Reliable
– Easy operation
– Little maintenance required
– Long term use
• Cheap!
• Fast (2 lpm or more)
• Safe
– NO UV Exposure
– Visual cue telling if light is on or not
Challenges
• Compatible with 15 W (G15T8) or 30 W
(G30T8) UV bulb
• 12 V DC or 110 V AC ballast
• Flow regulation
• Filtration
• Uniform and optimal UV exposure
The Biggest Challenge:
Final production price:
< $100 US