Download Aquafers

SODIS
SOLAR DISINFECTION
Team Aquafers
Scott Weeks, Stephen Russo, James Berg & Jamison Hill
Procedure
© Fundacion SODIS Uniersidad Mayor de San Simon Casilla, 5783, Cochabamba, Bolivia
[email protected], [email protected]
Exposure Times
Environment
Exposure time
< 50% cloudy
6 hr
50% - 100% cloudy
2 consecutive days
Rainy
If water reaches 50°C
(122°F)
SODIS not effective
1 hr
Turbidity

To be effective turbidity
must be below 30 NTU
•
Turbidity test
•In the shade place filled 2 Ltr bottle on
SODIS logo. Look down through the top to
the bottom
•If you can read the letters, less then 30 NTU
•If you can see the sun rays, less then 20
NTU
Bottle Type

2 Ltr bottles usually made of PVC or PET
– PET transmits UV rays more effectively
PVC bottles usually have a bluish gleam
 If burnt PVC smoke smells pungent, PET
smoke smells sweet
 Glass bottles can also be used
 Should not use containers greater then 10
cm (4 in) deep

SODIS Science
Solar energy provides two mechanisms
of treatment:


Thermal (Pasteurization)
UV Radiation
Can work independently, but studies
indicate synergistic effects when
applied together
Thermal Effects
Temperatures at which the most common
waterborne pathogens are rapidly killed,
resulting in 90 percent of the microbes
becoming inactivated in one minute at the
given temperature.
Microbe
Worms, Protozoa cysts (Giardia,
Cryptosporidium, Entamoeba)
Bacteria (V. cholerae, E. coli,
Shigella, Salmonella typhi),
Rotavirus
Hepatitis A virus
Killed Rapidly At
55°C (131°F)
60°C (140°F)
65°C (149°F)
Source: http://solarcooking.org/newsletters/scrnov02.htm#water
UV Radiation
Damages living cells
(i.e. sunburns)
 Causes fundamental
changes in nucleic
acids/DNA
(by producing thyminedimers)
 Excessive radiation can
also change enzymes
and other fundamental
structures

Types of UV Radiation

The inactivation rate of micro-organisms
increases with decreasing wavelength:
Visible light -> UV-A -> UV-B ->UV-C (260
nm)

The maximum DNA absorption corresponds
to the wavelength of UV-C (but sunlight
mostly provides UV-A radiation
Synergistic Effects
1997 EAWAG Study examined effects
of radiation and temperature
Conclusions:
• Between 12 and 40° C, inactivation of bacteria is
mostly due to irradiation
•Inactivation in dark control at is due to heat
•Inactivation in transparent tubes at 50° C show a
combined effect of thermal and radiation
Coliphage f2 Bacteria Results
Rotavirus Results
Limitations of SODIS
Weather Conditions need to be right
 Only feasible for small volumes of water
 Bottle restrictions
 Not effective against all types of
waterborne disease
 Turbidity is a problem
 Possibilities for misuse

Climate

2 days exposure
for 50-100% cover

Doesn’t work when
there is rain

Central regions
more favorable
Can SODIS provide enough clean
water for a household?

Would require 10 2-liter bottles of clean
water per day

How would you prepare for rainy days if
you don’t know when they are coming?

Is it wise to rely on the weather?
Water Depth in Bottle

Water depth should be as low as possible for maximum
radiation and heating.

Should not exceed
10 cm

SODIS bags
Bottle Aging

Aging of PET bottles leads to a reduction
of U.V transmittance
-Scratches
-Photochemical
reactions
What is UV treatment effective
against?

Bacteria: E. coli, Vibrio cholerae,
Salmonella paratyphi, and others

Viruses: Bacteriophages, rotavirus
Not Effective Against:

Chemically contaminated waters

Spore and cyst forming organisms such as
protozoa
– Giardia and Cryptosporidium
Possibilities for Misuse
Bottles exposed to sun in morning, but in
the shade after a couple of hours
 Some users put the bottles on chairs, not
considering that the back of the chair
casts a shadow
 Bottles placed with painted side up
 Partially filled bottles
 Recontamination!

Implementing SODIS
in
Uzbekistan
JDA International, Inc.
Background
Climate and Topography



In April 2001, JDA (Joint Development Associates)
started the SODIS pilot project in the Ferghana valley
near the city of Kokand in Uzbekistan.
Uzbekistan lies on the 41st parallel in Central Asia. The
country is characterized by deserts, semiarid steppes,
vast plains. The climate in the valley can be described as
arid. The winters are cold and summers are hot.
Between April and September there is virtually no
precipitation or cloud coverage (300 days sunshine/year)
and abundant solar radiation (averaging 200 kW/m2
between May to September).
Uzbekistan seems to be a prime location to implement
SODIS
Background
Social History


Economical Status
Post-Soviet Union economic system
–
–
–
–

Collective farms were privatized
Government took care of people’s needs. Individual initiative
and responsibility were neither asked for nor encouraged.
Little experience in decentralized decision making
The water system
– Aging and leaking
– Depended on external Soviet bureaucracy for maintenance
– Who built quite an advanced system for the time: deep wells, water
towers, piping
– Lack of training and funding for proper maintenance and operation by
local Uzbek staff. Currently maintained on the village scale.
– Has contamination issues (backflow, intermittency, and leakage).
– Little capital available because of lack of usage fees.
– Need for low-cost disinfection
Background
Social History cont…

Cold water problem
– Because of history of waterbourne diseases
with water supply, most people boil water or
drink tea. Cold water associated with disease.
– In summertime, people sometimes drink
contaminated water straight from the tap to
cool off and get reinforcing the perception.
– Thus SODIS was called “sun-boiled water”
What was done

Promoters
– 10 local people were trained in the SODIS method. Encouraged to drink
SODIS water. Employed by JDA to promote its use to others. Divided
into 3 teams. 15 villages were targeted for the SODIS campaign
– Approaches used:
 Mystical approach: SODIS – a type of healing water!
 rational approach: Emphasized strongly that drinking SODIS water prevents
disease saves healthcare costs. Money!
– The relational approach: emphasized good relationships with decisionmakers and key people who they introduced the method to.

Marketing schemes
– SODIS game, poster, brochures (highly efficient due to high literacy
rates)

Never promoted as cold water but as “sun boiled water” to keep in
line with cultural preferences.
Results

SODIS promotion project appears to be
effective. Most people introduced will
continue to use it
Source: “Bottles in the Sun”, JDA report: 2001.
http://www.sodis.ch/files/MaterialsJDA/Report_2001_e.pdf
Results 2003 I

Impact of SODIS on health
Results 2003 II
Conclusion: Most villages saw a decrease 2/3 decrease in disease
incidence after SODIS implementation.
Resources
http://www.sodis.ch
 http://www.jdainternational.org/
 Weglin M. et al. Solar water disinfection: scope of the process and analysis
of radiation experiments. J Water SRT-Aqua. Vol. 43 No. 3. 1994.


http://www.grilink.org/ibsrepor.htm
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=348911
http://www.wpi.edu/Pubs/ETD/Available/etd-0423103124244/unrestricted/rojko.pdf
http://www.cdc.gov/safewater/manual/alt_water.htm

http://solarcooking.org/sunandwater.htm
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