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Solar Water Pasteurization

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Presentation on theme: "Solar Water Pasteurization"— Presentation transcript:

1 Solar Water Pasteurization
Dale Andreatta, Frank Husson, Robert Metcalf October 16, 2013 Water and Health Conference Chapel Hill, North Carolina

2 Presenters Dale Andreatta, Ph.D. in mechanical engineering, designer of pasteurizers, Columbus, Ohio. (Presenter) Frank Husson, president of Solar Solutions, designer of pasteurizers, San Diego, California. (Present today) Robert Metcalf, Ph.D. in microbiology, promoter of water pasteurization and solar cooking, Sacramento, California. (Currently in Africa)

3 Bob Metcalf is in Kenya at a water conference

4 Basics of Pasteurization
Pasteurization: A heat process that kills all disease-causing microbes (pathogens) including cryptosporidium. First discovered by Louis Pasteur 150 years ago. Hepatitis A is the most heat resistant pathogen, but is killed by a few minutes at 65° C. Not necessary to boil the water, as many believe. Process is not affected by turbidity or acidity of water. World Health Organization now says “thermal processing”, rather than “boiling”. Thermal processing (boiling or pasteurization) is identified as the most effective method of biological pathogen eradication in the 2012 Household Water Treatment handbook from WHO. Heat denatures the proteins, similar to cooking an egg white (which can also be done at 65° C.

5 To demonstrate that 65°C is hot, egg white is added to 65°C water.

6 Egg white starting to cook at 31 seconds.

7 Egg white cooked in 1 minute at 65°C
Egg white cooked in 1 minute at 65°C. This is a demonstration that proteins are denatured quickly at 65°C. The proteins of bacteria (enzymes) are destroyed at this temperature, as are the proteins that surround the nucleic acid of viruses. Boiling is not needed to denature proteins.

8 D values (90% reduction times) bacteria in water
seconds at Bacterium 55°C 60°C 65°C E.coli 0157:H Shigella sonnei Salmonella tyhpimurium <2 Ref: A. Spinks, Water Research (2006)

9 Just as with milk pasteurization, temperatures well below boiling will kill microbes in water.

10 Why is Boiling the Standard Treatment?
Until 1992 there was no practical way to know whether the pasteurization temperature has been achieved. In 1992, the first Water Pasteurization Indicator (WAPI) or “Indicator” was designed. Several other indicators have since been developed.

11 Pasteurization This talk is primarily about solar pasteurization, but we also include fuel-based pasteurization. Indicators work in all sizes and shapes of water vessels. Typically, solar heating is very slow, so you get a 6 log reduction ( %) in all pathogens by the time you reach 65° C.

12 Two Types of Indicators
Petroleum Wax Initial position Melts at 65 C If found here later, 65 C was reached

13 Water Pasteurization Indicators Also known as WAPIs or Indicators
This is an indicator, not a thermometer. Even if the water has cooled down, it still indicates that the water attained the required temperature. Only tells whether required temperature was reached. Indicator sits in the bottom of the water, where the coolest water is located. Inexpensive and reusable.

14 Pasteurization vs. Boiling
With the necessary temperature of 65° C, about ½ the energy can be saved compared to boiling. Indicator alone saves 50% of energy. Solar plus indicator saves 100% of fuel. Much easier to achieve 65° C than boiling temperature, so simple solar devices are viable. Solar on sunny days, fuel heat on cloudy days (or chlorine).

15 Real Purpose of This Talk
To provide information, yes, but…… The real purpose is to stimulate your thinking. Where, how, under what conditions can pasteurization be used? What niche(s) does pasteurization fill?

16 How to Pasteurize Water-Part 1
Batch Pasteurizers Indicator is required

17 The Aqua Pak The Aqua Pak is a dedicated batch pasteurizer, made of inexpensive plastic. Can pasteurize 4-5 liters at a time. Small glass indicator built into the cap. Cost is about $2 if made in the developing world. Currently available, made in San Diego. The plan is for independent entrepreneurs to set up a series of factories, copying the product and the process of making it.

18 Aqua Pak in Use

19 Aqua Pak is multi-function
The Aqua Pak is intended as a pasteurizer, but also as a transport, storage, and anti-recontamination (with its small opening) vessel. Pasteurization can be achieved while on the move, as long as sunlight is hitting the transparent top. Aqua Pak comes with chlorine tablets for cloudy days, and a filter for filtering the water.

20 The Solar Puddle, A Large Batch Pasteurizer
Basic Solar Puddle, built into the ground. Horizontal dimensions compressed for clarity.

21 The Solar Puddle The solar puddle has been tested and studied extensively. Over 80° C can be achieved with thin water layers (25 mm). Pasteurization temperatures can be achieved with up to 75 mm water depth. This is 75 liters of water for a 1 square meter puddle. Many variations possible. Basic version is built into the ground, but benchtop puddle is also possible with wooden sides. Basic version has 4 or 5 plastic layers, but bubble wrap can be substituted.

22 Two benchtop solar puddles: Bubble wrap top layer on left.
Two-layer top layer, on right, with top layer removed.

23 Pot-based pasteurizers

24 Test Results Limited testing to date, due to issues with latitude and cloudy weather in Ohio. 70° C was achieved on a mostly sunny day at 40° North latitude. About 6.5 liters pasteurized. Larger pots tested, 29 liters, 55° C achieved for 1 hour. The key to performance is that the grass gets hot quickly, transfers heat to the pot by convection and radiation.

25 Other Batch Pasteurizers
Other batch pasteurizers can be made from things including bottles, jugs, and sheets of plastic used to form a pouch. Plain materials can be used, (grass, cheap polyethylene) though cheap plastic degrades in about 3 months because it does not have UV inhibitors added. The polyethylene in the Aqua Pak has 36 months of UV inhibitor added. Any kind of solar cooker can also be a pasteurizer.

26 Simple Solar Cooker Being Used as a Pasteurizer

27 Summary of Batch Pasteurization
Batch pasteurization is simple, effective, and can be very low in initial cost. An indicator is required. Batch pasteurization is limited to modest amounts of water. Will always be in the “Household Water Treatment and Storage” category. Can be combined with filtering, and chlorine to give residual disinfection.

28 How to Pasteurize Water-Part 2
Flow-Through Pasteurizers Thermostatic valve is required

29 Flow-Through Water Pasteurizer Principle
Heater, Solar or Flame Heat Heat Exchanger Dirty Water, 20° C 60° C Heat transfer From hot to cold 80 ° C Clean water Out, 40° C Thermostatic valve

30 Flow-through pasteurizers
Solar or flame heat can be used. Process is automatic. Outlet water is only warm, not hot. You can use a heat exchanger to recycle the heat in the outgoing water, increasing the throughput by 3 times or more, while adding 50% or less to the cost. Many experimental units have been built using solar, but no commercial solar units currently available.

31 InStove Water Pasteurizer
Institutional Stove Solutions, Cottage Grove, Oregon, builds large high quality wood-burning stoves for schools. A new option is a flow-through pasteurizer using the large stove and large pot as the heater. Much larger quantities of water can be pasteurized.





36 400 Liters per hour at 10 grams of wood per liter


38 InStove Water Pasteurizer
100% effective against common harmful microbes in preliminary testing Failsafe design – unpasteurized water cannot leave the system Can produce over 4000L of safe water per day One unit provides drinking water for as many as 1000 people Optimized for use with InStove stoves 20+ times more energy efficient than boiling water over an open fire Uses less than: - 10g of fuel per liter produced - 4kg of fuel per hour Designed for use in refugee camps, institutions (schools, hospitals, etc.), or as a small business Cost is about $1000 for the stove and $1000 for the pasteurizer parts.

39 Limitations of Pasteurization
No residual disinfection, but you can add a little chlorine. Doesn’t improve appearance or taste, but you can add a filter. Somewhat energy intensive. Doesn’t help with chemical or mineral contamination (most places only have biological contamination).

40 Summary Pasteurization is one way of purifying water.
Very safe, very verifiable, low cost. Somewhat energy intensive, so appropriate only for small to modest quantities of water. No residual disinfection (unless coupled with chlorine) and does not improve taste, color, cloudiness (unless coupled with a basic filter). Clearly, pasteurization is not the solution in all situations, but its potential has barely been touched.

41 Additional Information
Contact information Where to get……. Further reading A worldwide energy calculation

42 Contact Information Dale Andreatta, Ph.D., Frank Husson, Robert Metcalf, Ph.D.,

43 Additional contacts, Solar Cookers International
For plastic indicators, Aqua Paks, and solar cookers. st St. Sacramento, California, US 95811 (916)

44 Additional Contacts, Solar Solutions, LLC
For Aqua Paks, glass indicators, petroleum wax. Solar Solutions, LLC Willow Creek Rd. San Diego, California, US (858) extension 4703

45 An Excellent Review of Water Purification Technologies is:
An Overview of Water Disinfection in Developing Countries and the Potential for Solar Thermal Water Pasteurization, by Jay Burch and Karen Thomas Search for NREL/TP

46 Worldwide Energy Consumption to Boil Water
If one billion people boil 4 liters of water per day for drinking, this requires about 4.58E17 Joules of energy. If they boil on wood stoves with 12% efficiency (also accounting for the fuel left unburned when the water reaches boiling) the amount of fuel burned will be 2.4E8 metric tons. This produces about 3.5E8 metric tons of carbon dioxide. This is about 1.2% of the total from fossil fuels, plus carbon monoxide and black carbon. If they boil on propane stoves with 50% efficiency, 1.9E7 metric tons of propane will be consumed, leading to 5.7E7 metric tons of carbon dioxide. This is about 0.2% of the yearly total from fossil fuels. Regardless of the method, the global warming potential is significant, and could be reduced significantly with any of the techniques given here.

47 Papers by the Current Presenters
“The Solar Puddle – A Low-Cost Water Pasteurizer,” Andreatta, Dale; American Solar Energy Society, 2001 “Inexpensive Personal Solar Water Pasteurizer,” Husson, Frank; Andreatta, Dale, American Solar Energy Society, 2003



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