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Final Report: Comparative Analysis of Three Sustainable Point of Use Drinking Water Treatment Technologies for Developing Nations

EPA Grant Number: SU832463
Title: Comparative Analysis of Three Sustainable Point of Use Drinking Water Treatment Technologies for Developing Nations
Investigators: Sobsey, Mark D. , Whittington, Dale
Institution: University of North Carolina
EPA Project Officer: Nolt-Helms, Cynthia
Project Period: October 1, 2005 through September 30, 2006
Project Amount: $75,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2005)
Research Category: P3 Challenge Area - Water , Pollution Prevention/Sustainable Development



The purpose of this research is to determine the costs, health and economic benefits, and effectiveness in improving water quality of different POU drinking water treatment technologies intended for the developing world. This project focuses on three distinct POU technologies: coagulation-flocculation-chlorination, ceramic microfiltration, and intermittently operating slow sand filtration (IOSSF), also known as the biosand filter. For this project we performed two major analyses of each system: effectiveness and cost-benefit. The second major analysis in this project, which was begun in Phase I and completed in Phase II, is an analysis of the costs of each technology, including manufacturing, distribution, and time to operate and maintain the POU system, and the relationship of these costs to the benefits of use. The benefits measured will include reduction in diarrheal disease by users as compared to nonusers, and the attendant benefits such as reductions in lost work time and resources spent on health care. We will also measure the benefits of health outcomes in terms of Disability Adjusted Life Years avoided (DALYS). This information will make it possible for people in the developing world who could benefit from POU to identify the technology that is the most appropriate, effective and sustainable for their homes and communities.

Summary/Accomplishments (Outputs/Outcomes):

Parameters investigated during Phase II of the study include (1) flow rate (2) daily volume filtered (3) filter cleaning and (4) media type. Systematic investigation of the mechanisms at work both during active filtration and during the filter’s paused or idle time is continuing. Reductions of bacteria, viruses and turbidity by the IOSSF tend to be lower than those demonstrated for traditional SSF. However, they can increase substantially with increasing retention time of water in the filter bed. The design implication is that the removal of microbes in the IOSSF could be improved by maximizing the residence time of water in the filter. This can be accomplished in several ways: 1) introducing a daily charge volume that is smaller than the filter bed pore volume; 2) constructing a flow rate control device that would reduce the flow rate; 3) providing a longer time interval between the introduction of each charge; or 4) increasing the size of the filter bed. More research under well-controlled conditions is needed to understand the mechanism(s) that are responsible for microbial attenuation in the IOSSF so as to optimize the design and operation of the IOSSF. This research has shown that the idle period is very important and has implications for selection of charge volume, frequency of charge introduction and duration of charge filtration. The increase in microbial attenuation that occurs over repeated charges is related to filter maturation and needs systematic study. Differences in the reductions for different microbes, particularly for viruses, suggest multiple mechanisms of attenuation. The BSF demonstrated the ability to remove >5.76 log10 of Cryptosporidium oocysts. Problems with recovery prevented the demonstration of greater oocyst removal but performance of the filter far exceeded the EPA performance standard of 3-log10 parasite removal for point-of-use drinking water treatment devices

Improvement of water quality by he biosand filter in field use was also evaluated. During the six month sampling period, BSF households had improved drinking water for the entire six month period. Geometric average reductions of E. coli for the entire study were moderate at 80%. However, the average reduction improved with time beginning initially at 50% during the first week of sampling after filter installation and increasing to 92% at 22-weeks after installation. Furthermore, average concentration of E. coli in water treated by the biosand filter was 5 MPN/100mL. Average turbidity reduction during the six-month was 11%. Turbidity reductions improved over the length of the study and were approximately 25% after six months. Average treated water turbidity was < 1 NTU. For the six-month study, biosand filter performance improved as measured by improvements in reductions of E. coli and turbidity. However, these measurements were limited by the quality of the untreated water. Many untreated water samples were free had < 1 E. coli/100mL. The low concentration of E. coli in untreated water made it difficult to measure reductions and influenced the average performance. This is also true for turbidity. While average turbidity reductions were low, average filtered water turbidity was very low. The results from this study suggest that in the field, average reduction may not be a good indicator of performance due to variable water quality. Filtered water quality may be a better indicator of performance in these type of field studies.

Analyses of water quality improvement in the field by ceramic filters were also carried out. Analysis of the effect of time in use on log10 reduction of E. coli over the follow up period (18 weeks) by treatment method yielded a significant result for water treatment by the CWP1 (p < 0.0001) and the use of the CWP2 (p < 0.0001). Plots of the log10 reduction over the study period show wide variation in the performance of the CWP1 and CWP2 during the follow up. Because rainfall is known to be an important determinant of water quality and availability, linear regression was performed to determine whether any association existed between rainfall and E. coli reduction over time. No association was observed. Although the reduction of E. coli by the CWP1 was shown to be significantly greater than either boiling or use of the CWP2, the observed differences in effectiveness were small. And because these results indicate only a marginally greater performance for one treatment method against one bacterial indicator organism, these results do not strongly indicate that one of these methods is more effective overall for the treatment of household drinking water. The reduction of E. coli in household samples for all treatment methods followed a log-normal distribution centered around 99% reduction, with reduction as high as 99.9999% and also negative reductions. Negative log reduction values occurred in 24 sample sets of CWP1 (4.9%), 25 of CWP2 (5.0%), and 23 sample sets of boiled water (8.2%) when comparing E. coli counts in untreated versus treated water, indicating higher levels in the treated water. These results are consistent with several studies showing that recontamination of stored water in the home could significantly impact the quality of potable water used in the household.

The studies carried out in Phase II show that the biosand filter could achieve a 42% reduction in diarrheal disease in communities in the Dominican Republic, and ceramic filters could achieve a 49% reduction in diarrheal disease in communities in Cambodia. Previously done studies of the coagulation-flocculation-chlorination system show that it could reduce diarrheal disease by 40% in rural Guatemalan communities.

All three technologies can reduce diarrheal disease, but the cost-benefit relationships of each may differ. The coagulation-flocculation chlorination system is the most expensive per disability-adjusted life year avoided, at $490/DALY. It is a consumable technology, requiring households to have financial resources for repeated purchasing of the product over time. The biosand filter ranged from $1 to approximately $120 per DALY avoided. The cost of this technology is lowered because it is a durable good requiring a one-time purchase. The cost-benefit ratio can be improved both by reducing the cost of the filter to the consumer (by subsidies or other means), but also by extending the useful life of the filter, driving down the cost per DALY as the filter is in longer use in households. The ceramic water filter has the lowest cost per DALY avoided. However, ceramic filters are less durable and more susceptible to breakage than biosand filters. The need to replace broken filters may drive up the cost/DALY. Like the biosand filter, improving technology to extend the useful life of the filter may drive down the cost per DALY avoided from diarrhea.


The findings from Phase 2 studies can greatly enhance the ability of communities, NGOs, and other implementers of POU technologies to choose an appropriate technology for a specific setting and user population. People using POU technologies range from the world’s poorest people, living on less than $1/day with no access to infrastructure, to the emerging middle classes in developing nations, who have poor quality or unreliable infrastructure. Each of the POU technologies evaluated has demonstrated health benefits, and some communities may be willing to bear higher costs for those health benefits if a particular technology suits their needs for convenience, portability, durability, water quantity produced, or other factors.

Journal Articles on this Report : 5 Displayed | Download in RIS Format

Other project views: All 20 publications 6 publications in selected types All 5 journal articles

Type Citation Project Document Sources
Journal Article Brown JM, Proum S, Sobsey MD. Escherichia coli in household drinking water and diarrheal disease risk: evidence from Cambodia. Water Science & Technology 2008;58(4):757-763. SU832463 (Final)
  • Abstract from PubMed
  • Full-text: IWA Publishing-PDF
  • Abstract: IWA Publishing-Abstract
  • Journal Article Brown J, Sobsey MD, Loomis D. Local drinking water filters reduce diarrheal disease in Cambodia: a randomized, controlled trial of the ceramic water purifier. American Journal of Tropical Medicine and Hygiene 2008;79(3):394-400. SU832463 (Final)
  • Abstract from PubMed
  • Full-text: American Journal of Tropical Medicine and Hygiene-HTML
  • Abstract: American Journal of Tropical Medicine and Hygiene-Abstract
  • Other: American Journal of Tropical Medicine and Hygiene-PDF
  • Journal Article Elliott MA, Stauber CE, Koksal F, DiGiano FA, Sobsey MD. Reductions of E. coli, echovirus type 12 and bacteriophages in an intermittently operated household-scale slow sand filter. Water Research 2008;42(10-11):2662-2670. SU832463 (Final)
  • Abstract from PubMed
  • Full-text: ScienceDirect
  • Abstract: ScienceDirect
  • Other: ScienceDirect PDF
  • Journal Article Stauber CE, Elliott MA, Koksal F, Ortiz GM, DiGiano FA, Sobsey MD. Characterisation of the biosand filter for E. coli reductions from household drinking water under controlled laboratory and field use conditions. Water Science & Technology 2006;54(3):1-7. SU832463 (Final)
  • Abstract from PubMed
  • Full-text: Hydraid PDF
  • Abstract: IWA Online
  • Journal Article Stauber CE, Ortiz GM, Loomis DP, Sobsey MD. A randomized controlled trial of the concrete biosand filter and its impact on diarrheal disease in Bonao, Dominican Republic. American Journal of Tropical Medicine and Hygiene 2009;80(2):286-293. SU832463 (Final)
  • Abstract from PubMed
  • Full-text: American Journal of Tropical Medicine and Hygiene-Full Text HTML
  • Abstract: American Journal of Tropical Medicine and Hygiene-Abstract
  • Other: American Journal of Tropical Medicine and Hygiene-PDF
  • Supplemental Keywords:

    drinking water, treatment, health effects, cost-benefit, point of use technology, RFA, Scientific Discipline, Water, Chemical Engineering, Environmental Chemistry, Microbiology, Drinking Water, Environmental Engineering, alternative disinfection methods, sustainable development, waterborne disease, ceramic filters, comparative analysis, fecal contamination, disinfection of waters, Other - risk management, microbial risk management, point of use, water disinfection, biosand filtration, drinking water contaminants, human health, water treatment

    Relevant Websites:

    http://www.cawst.org/index.php?id=128 Exit EPA Disclaimer
    http://www.samaritanspurse.uk.com/projects/water.asp Exit EPA Disclaimer
    http://www.biosandfilter.org/Exit EPA Disclaimer>
    http://www.potpaz.org/ Exit EPA Disclaimer
    http://www.rdic.org/ Exit EPA Disclaimer
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    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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