Final Report: Sun, Bottles and Beeswax: Local Solutions for Clean Water Using Solar Disinfection

EPA Grant Number: SU834742
Title: Sun, Bottles and Beeswax: Local Solutions for Clean Water Using Solar Disinfection
Investigators: Doll, Susan , Raichle, Brian W. , Gay, Ashley , Taubman, Brett , Camp, Brooks , Bowman, Josh , Cavert, Katie , Dodd, Katy , Welsh, Patrick , Tuberty, Shea
Institution: Appalachian State University
EPA Project Officer: Page, Angela
Phase: I
Project Period: August 15, 2010 through August 14, 2011
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2010) RFA Text |  Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Chemical Safety , P3 Challenge Area - Safe and Sustainable Water Resources , P3 Awards , Sustainable and Healthy Communities


Access to clean drinking water is an everyday struggle in the developing world for over two billion people with an overwhelming 2.2 million deaths occurring each year due to preventable water-borne illnesses, with a disproportionate number of deaths among children and infants (World Health Organization [WHO], 2004). The objectives of the Phase I funding were to explore specific aspects of solar pasteurization technology including:

  • Methods for characterizing daily solar profiles and quantifying the “six hour” exposure periods required to achieve pasteurization (solar profiles).
  • Configurations for maximizing thermal gain (bottles and platforms).
  • Indicator for identifying when pasteurization temperatures are reached.
  • Conditions under which microbial load is reduced.
  • When/if toxic compounds are leaching from the plastic bottles.

Because there are no visible indications when water reaches pasteurization temperature, the most critical aspect of the project was the development of a simple, reusable indicator that can be made from locally available materials, specifically beeswax. In addition, a methodology for characterizing daily solar profiles was developed in order to quantify “six hour” exposure periods during clear and cloudy days in Boone, North Carolina, as well as in equatorial Rwanda.

Few development problems can be addressed by a single discipline, and access to clean water is no exception. Technical challenges affecting water quality in the developing world include the technologies and energy sources for treatment, biology and chemistry of water quality that can be affected by treatment, collection and storage containers, and end-user adoption. The Phase I research team integrated multiple disciplines in order to gain a better understanding of the science of solar disinfection as a means to clean water and the end-use container. The chemistry team attempted to determine the effects of heat and ultraviolet (UV) radiation on plastic bottles; the biology team evaluated the efficacy of the treatment method at reducing detrimental microorganisms; the appropriate technology team developed practical treatment and indicator methods; and the sustainability team worked to incorporate the use local resources and consideration of environmental, social, economic, and institutional factors.

In order to integrate these different components, this research comprised an interdisciplinary team of over 25 students and four advising faculty from many departments in Appalachian State University (ASU), as well as interested community members. A goal of Phase I was to involve students in the Departments of Technology (building science and renewable energy programs), Biology, Chemistry, and Sustainable Development and offer educational experiences in the context of a real-world problem. This type of practical research opportunity serves many purposes, including team building, gaining lab experience and project management skills, and understanding how developing a sustainable water treatment technology is multi-faceted and challenging, especially in the developing world.

Summary/Accomplishments (Outputs/Outcomes):

Phase I of this solar water pasteurization research project proved to be a rewarding and challenging educational experience for the students involved. Four task groups were formed, including (1) thermal performance, (2) beeswax, (3) water quality/microbiology, and (4) plastic bottle toxicity. These teams pursued the research goals set out in Phase I by working in groups of 4-5 students recruited by the student lead investigator. Significant results include successful testing of bottle/platform configurations and the creation of a beeswax indicator from recycled materials. A description of the objectives, methodology and results for each are provided below.

Thermal Performance – Solar Profile and Platform/Bottle configuration:

Solar Profile
Objective: Characterize visible and UV components of sunlight at different locations.

Methodology: Data were collected in Boone and Wilkesboro, North Carolina (36 degrees N) and Kigali, Rwanda (2 degrees S) on mostly clear and cloudy days. Cumulative visible and UV light were calculated for all locations and expressed as a percentage of Rwanda “clear” day totals. Values were also calculated subtracting out scattered background light of 15,000 Lux. Solar noon irradiance values were also identified.

Results: Total clear day visible light in Rwanda was 25-35% higher, but only 10-25% higher for the UV component, when compared to clear day exposure in North Carolina (NC) for the same time period. In addition, solar noon values in Rwanda were ~50% higher than in NC and partially cloudy days with intermittent strong sun had values as low as 60% less than clear day. These results indicate that present rules-of-thumb for the amount of time in sunlight that is required to reach pasteurization temperatures may not be adequate for all locations and weather conditions, confirming the critical need for an affordable and accessible temperature indicator.

Platform/Bottle Configuration
Objective: Measure the effect of bottle coloration and platform surface material on temperature rise in plastic water bottles.

Methodology: Two clear, 500 ml plastic bottles, one of which was painted black on one vertical half, were placed on different material surfaces under heat lamps in a controlled environment to distinguish which configuration would be optimal for heat gain. The tested surfaces included materials that would be locally available in the developing world: metal roofing, metal roofing painted black, semi-opaque white plastic roofing, sand, gravel and dirt. The black metal roofing was also tested with an insulating bed of straw underneath it. Bottles were placed on these surfaces with the black side down for the half-black bottle.

Results: Effects of the platform surfaces were negligible relative to the effect of the black paint on the back of the bottle. Peak water temperatures in the clear bottle were consistently in the 60 – 65°C range, regardless of platform surface, while temperatures in the half-black bottle were consistently in the 65 – 70°C range. The highest observed temperature was achieved with the half-black bottle on the white plastic roofing panel. Based on these findings, it is recommended whenever possible that water bottles be painted on one vertical side to increase solar absorption in the bottle. The volume of the bottles used would necessitate treatment of 2-4 bottles per day for each person. Further testing of larger volume bottles that may be locally available is needed to increase treatment capacity.

Objectives: Determine the feasibility of using beeswax as an effective indicator that water in plastic bottles has reached pasteurization temperatures and develop a prototype indicator. Solar pasteurization completely inactivates water-borne pathogens, and occurs at 65°C. Most parasites and disease-causing bacteria are inactivated at 60°C.

Methodology: Melting characteristics were determined using a Melting Point Apparatus (MPA) for raw beeswax from North Carolina and Rwanda, purchased “purified” beeswax, and other purchased plant waxes including candelilla wax (native to Mexico) and carnauba wax (native to Brazil), both known to have higher melting points than beeswax. Beeswax alone, and percent mixtures of beeswax and plant waxes were tested to determine melting point. The beeswax team also brainstormed materials that might be locally available in the developing world and identified three options to use for a prototype indictor.

Results: Materials that exhibited an effective melting point above 65oC are: candelilla wax by itself and mixtures of 25% carnauba wax with 75% pure or Rwandan beeswax (see Table 1). Three prototypes using beeswax and a portion of a drinking straw, a bic pen, and a portion of a plastic bag inside the cap of the water bottle, were successfully produced and tested. Results show tremendous potential for producing a sustainable, low-cost solar pasteurization temperature indictor from local materials in areas with access to beeswax. The ease of production will provide entrepreneurial opportunities for selling the beeswax, producing the indicator, and potentially reconditioning used indicators.

Table 1: Mean Melting Points of Wax Materials (Note: MP= Melting Point)



Unmixed Materials

Mixtures with beeswax

Pure beeswax


NC raw beeswax

Rwandan raw

Candelilla wax

Carnauba wax


RRB 75%: Carn 25%


PB 75%: Carn 25%

Mean MP (°C)








Water Quality: Microbiology Objective: Determine the effect of temperature, contact time, and UV exposure. Specific objectives of the testing were to identify microbial sensitivity to a range of temperatures, investigate interaction between temperature and contact time, and the potential effects of UV light at levels comparable to natural sunlight. Initial testing revealed that microorganisms were killed at lower temperatures than anticipated, with very short contact times. Protocols have been adjusted and further data are being collected to better encompass appropriate temperature and contact ranges.

Chemistry Objective: Investigate Plastic Bottle Toxicity The purpose of the chemical analysis component was to confirm literature reports that heat and UV exposure do not cause significant leaching of toxic compounds from plastic bottles (Wegelin, 2000 and Schmid et al., 2008). An additional objective was to test plastic bottles brought back from Rwanda that may be produced using different manufacturing practices. No definitive results were available at the writing of this report due to complications with instrumentation and methodology limitations. However, methods have been refined and further results are expected for the DC exhibition.


The purpose of the Phase I funding was to explore specific aspects of solar pasteurization technology. Specifically, we wanted to better understand the impact of solar profiles on sunlight exposure, identify conditions for maximizing thermal gain (bottles and platforms), identify conditions under which microbial load is reduced, and investigate when/if toxic compounds are leaching from the plastic bottles. The most innovative aspect of the project was the successful development of an indicator that can be made from locally available materials, specifically beeswax. We also developed a methodology for characterizing daily solar profiles and quantify “six hour” exposure periods during clear and cloudy days in Boone and equatorial Rwanda that will inform future field studies to determine the solar exposure required to achieve pasteurization temperatures. Results point out the limitations of the solar pasteurization technique during excessively cloudy weather. Under laboratory test conditions, enhanced thermal performance was observed in the half-black bottles when placed on the white plastic roofing material. Further testing is required to confirm Phase I results under field conditions, using locally available materials.

Supplemental Keywords:

global burden of disease, solar disinfection, solar pasteurization, plastic bottles, microbiology, environmental justice, water pasteurization indicator, beeswax temperature indicator, sustainable development, developing world application, appropriate technology, water quality

Relevant Websites:

Technology and Environmental Design Graduate Study Exit