SP.721 (D-Lab) Fall 2004 Session #7 notes
Water Treatment Systems
Guest speaker: Daniele Lantagne, P.E., U.S. Centers for Disease Control and Prevention (CDC). This lecture will focus on three topics: • • • Review current need for safe water Demonstrate options for safe water Talk about research possibilities
Defining “safe” is the place to begin. Depending on their background, their perspective, their interests, people have different definitions of safe water. Engineers tend to think if what is safe when it leaves the treatment plant, it is safe. However, if water causes disease when it is drunk, it is not safe. Links between engineers and epidemiologists need to be improved, especially in the developing world where technology improvements should play a important role in improving access to safe water. The Global Burden of Unsafe Water “An estimated 1.1 billion persons worldwide have no access to improved water sources, relying on unsafe surface sources such as ponds, streams, and shallow wells like these children are using for their water needs. In addition, hundreds of millions more collect their drinking water from “improved sources”, such as the poorly functioning municipal water system this woman has accessed, that deliver un-chlorinated water contaminated with human and animal fecal waste, and with the bacteria that cause cholera, dysentery, typhoid fever and so many other waterborne diseases. Please note that whether the source is improved or unimproved, in both photos and in hundreds of millions of families across the globe, water is collected outside and often far from the home, primarily by women and children, and that it is then carried, often in open plastic pails or buckets back to the house where it is stored, and used for drinking, washing, cooking, and bathing until another trip to the source is required.” [Source: Daniele Lantagne’s slide notes] “Improved” sources are what many organizations like the U.N. track. Unfortunately this doesn’t necessarily lead to safe water. Improved simply
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means anything connected human-made infrastructure (pipes, reservoirs, etc), as opposed to an open natural water source such as a stream. The toll from unsafe water is staggering. Again, quoting from Daniele’s notes pages: “Each year, an estimated 1.7 to 2.2 million persons die from waterborne diseases. Most of these deaths are due to diarrheal diseases, and most occur in children and other vulnerable populations. More bluntly put, approximately 5,000 children die every day from diarrhea acquired from unsafe drinking water. The total burden of morbidity due to unsafe drinking water is difficult to estimate, but over 1 billion episodes of gastroenteritis and other infections annually are attributed to it each year.” [Source: Daniele Lantagne’s slide notes] Nevertheless, the U.N. Millenium Development goals do not address “safe” water, only expanding access to “improved sources.” A report from early this fall estimates that we’re on track to meet the goal of cutting those without improved water sources in half by 2015. Where does fresh water come from? In the global water cycle, fresh water moves among groundwater, surfacewater, vapor and rainwater. Processes affecting the water supply include evaporation, precipitation, surface runoff and subsurface percolation. Water scarcity is an increasingly worrisome issue, projected to be a source of major conflicts in coming decades. On this map, “Economic water scarcity” signifies economic forces like import/export agriculture competing with the residents’ own water needs. “Physical water scarcity” means one may have to walk many kilometers simply to get water. Bacteria, viruses and parasites (protozoa and helminthes (worms)) are the most significant causes of unsafe water. (Of course there are other causes, i.e. chemical pollution, but the microbes are by far the largest and most direct sources of concern for human health).
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Bacteria • • Cholera can cause the body to lose up to 10 liters of water per day, causing death by dehydration. Bacteria are easily inactivated by chlorine, and are also filterable, as they are 1 micron in size. Cryptosporidia is currently untreatable. With a healthy immune system, it gradually goes away; but it’s a big problem for those with HIV/AIDS. In some places, 80% of kids may carry giardia, although it may not be the cause of bouts of severe diarrhea (dormant or asymptomatic). Protozoa are large and thus easily filtered. They are resistant to chlorine, however. Viruses’ role in unsafe water is less well understood because viruses can’t be cultured. In the U.S., most cases of diarrhea are viral, and pass in 24-36 hours. Because of their small size (most <0.2 micron), viruses can only be filtered today using very expensive industrial products; the handmade ceramic and cloth filters practical for use in developing countries are ineffective. Some viruses are not killed by chlorine.
Protozoa •
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Viruses • • •
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To highlight the limitations with filtration technology, the class views a graph of microbe sizes (removed due to copyright considerations 1 ). Select data points include: • • • • • Polio virus: 0.03 micron HIV: 0.1 micron E. coli: 1 micron Protozoa: 10-100 micron Reference points: Red blood cell = 6 micron, lower limit of human vision = 40 micron
Water treatment has two primary goals: remove the dirt and debris, and remove the organisms that cause disease. There are many different low and high-tech mechanisms to achieve both these goals.
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Source: Levinson, Warren and Ernest Jawetz. Medical Microbiology & Immunology: Examination & Board Review. Stamford, CT: Appleton & Lange, 1996.
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Chlorine has been a favorite means of disinfecting water in developed countries for many years. It’s become less common in Europe recently over fears that the THM (trihalomethanes) byproduct of chlorination presents too much cancer risk (1 extra cancer in every 100,000 people after 70 years of drinking chlorinated water). The class discusses the relative risks and concerns of the developing world vs. developed world. Cancer only becomes a major concern when life expectancy approaches 60-70 years – not the situation in many countries still combating diarrheal complications. Citizens of developed countries take for granted the benefits of good water treatment. The class views a graph of typhoid incidence in Philadelphia 18851945 (not shown here due to copyright considerations). After reaching nearly 10,000 cases in 1906, filtration and chlorination combined to reduce typhoid cases to just above 100 cases per year by the 1930s. The capital-intensive large infrastructure approach to development may not be the right model for 21st century developing countries. When you’re creating development projects, this becomes an ethical question. For example: instead of a decades-long expensive installation of copper cable landlines and high speed business-oriented networks like that in the U.S., developing countries have switched to cell phone networks; it’s brought service to many more people much sooner than if they’d stuck with landline networks. When over 1.1 billion still lack safe water, is there a lesson to be learned? The U.S. and Europe expect consistently safe water 24/7. If your country isn’t politically or economically stable, this is pretty hard to achieve. Thus smaller scale community based water infrastructure is becoming the norm for developing countries.
Community-based water systems (such as “captage,” top, and sand filtration, bottom) can provide safe water via piped distribution, yet be much lower cost and simpler to maintain than largescale U.S.-style water systems.
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These photos show a past D-Lab project: a chlorine flow control device made with local parts. In Central and South America, many communities are theoretically chlorinating but their existing systems and methods present many practical challenges. This D-lab mechanism helped to reliably chlorinate water over time when it is not possible to have a worker present at all times. (Pictures courtesy of Amy Smith).
Post-Source Water Issues
Transport: “CARE, one of our Safe Water System partners, provided this striking photograph of a child in Mozambique carrying water home to his family. The bucket of water is full and open, and his hands are curled into it around the top to keep it from falling. This unavoidable hand-to-water contact means that even the purest water from the best protected bore hole well will be contaminated with any diseasecausing agents that are on the water- bearer’s hands even before it crosses the threshold of his or her home.” [Source: Daniele Lantagne’s slide notes] Storage: “Inside the home, things only get worse, as illustrated by this photo taken at the height of the cholera epidemic in Peru over a decade ago. In addition to the buckets used for collecting and carrying water, other containers are often used for storing water at home, but they too tend to have wide uncovered mouths. Water is removed by dipping hands and objects in, further contaminating the stored water with the prevalent fecal flora. At the time we took this photo, and in the months that followed, CDC was busy helping the Pan American Health Organization and Ministries of Health throughout the Americas try to control the raging cholera epidemic. Water from many sources was the principle vehicle for cholera transmission in each country. “Boil water” orders were issued, but most persons could not afford to comply with them, and even those who could were at risk for acquiring cholera from contamination that occurred while the boiled water was stored unprotected at home. The longterm cholera fix, extending piped, treated, safe water coverage to the entire population of Latin America, was projected to cost billions of dollars and take many years to complete. So the Safe Water System was initially conceived as an inexpensive, practical alternative that would enable families to protect
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themselves from cholera and other waterborne diseases until more definitive solutions could be implemented.” [Source: Daniele Lantagne’s notes on slide] The International Network to Promote Household Water Treatment and Safe Storage (see http://www.who.int/household_water/en/) is a consortium of universities, NGOs, government and private sector groups. Its goal is “to contribute to a significant reduction in waterborne disease, especially among vulnerable populations, by promoting household water treatment and safe storage as a key component of water, sanitation and hygiene programmes.” Everyone would like to have safe water in the house, from a tap, 24/7; but it’s clear that large infrastructure schemes won’t meet this goal in many places. Point Of Use (POU) water treatment becomes a favored alternative. Some POU schemes are detailed in the slide. The first things to evaluate when considering household POU treatment alternatives are: • • • Test in a controlled lab environment for effectiveness and quality Run field surveys about how people will actually use it and how they feel about it. Based on this knowledge, evaluate whether it will actually have benefits in use (health impact) and whether it can grow beyond the individual villages studied thus far (scalability).
Boiling used to be the baseline treatment recommendation, but has fallen out of favor due to its high fuel cost, time-consuming demands (up to 10 minutes to achieve “safety,” and having no benefits regarding storage contamination. Bottled water is too expensive for everyday needs, as well as being poorly regulated in many countries. Q: How long will microbes survive in a dry environment, i.e. what’s a good dishwashing protocol? A: Microbe survivability varies widely, from a few seconds for some viruses to a very long time for some protozoa. Some people have adopted alcoholbased hand gels for dishwashing – rub on and wipe off. Ms. Lantagne mentions it’s “CDC lore” that among a population, 10% are “health nuts” that will follow any health recommendation; 80% will do what’s relatively easy; and 10% will not change ANY habits to improve their health.
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Filtration
Filtration is a common form of water treatment; with widely varying but sometimes quite successful results. Overall considerations are listed in this slide. Next, we’ll consider several particular filtration schemes.
GWI Purifier
The GWI Purifier uses a string filter in the top bucket for turbidity removal, a Granulated Activated Carbon (GAC) filter for chemical removal, and chlorination for disinfection. GWI is Gift of Water, Inc., a Floridabased NGO working in Haiti. Churches in the US sponsor purifiers for a village. GWI hires local technicians to provide training and maintenance services, and currently works in about 10 communities serving ~30,000 people. The effectiveness of the GWI Purifier was studied in an MIT S.M. thesis, with results as described in these 3 slides.
“Correct usage” is necessary to achieve the promised benefits, but it varied widely among different communities.
Among these factors for program success, having the technicians present when and where they’re needed was considered most important.
The purifier is a complex device, requiring technician visits, and causing some units to break within six months. Cost averages $50 per year per house, mostly due to the in-home visits. In summary, the GWI Purifier was seen as capable of delivering safe
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water benefits, but there are also some significant challenges to realizing that potential.
PFP Ceramic Filter
Potters For Peace (PFP) is a Colorado-based NGO promoting a local manufacturing model. Their ceramic filter design impregnates colloidal silver (an antibacterical agent) into the clay and filters impurities down to 0.6 to 3 microns. A lab study, summarized in this slide, found the PFP filter to be effective.
However, a field study found the PFP filter wasn’t so effective in actual use. Turbidity clogs it up, and the buckets tend to collect and regenerate contamination. Once the flow rate drops, it doesn’t support the 10-12 liter/day requirements of most families. Thus, while its local manufacture and low cost are good features, its in-the-field performance did not measure up to expectations.
Filtration – Recap
In summary, the GWI and PFP filters represent fairly typical tradeoffs between sustainability and effectiveness – it’s hard to have both! There are many other filtration systems to consider. For instance, the Biosand filter (by Davnor) is supposed to remove turbidity, protozoa, and 90-96% of bacteria; but the actual health benefits in field use are unknown – to what extent does the remaining bacteria cause problems like diarrhea? Stainless steel filters by Bajaj are another filter worth evaluating.
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Q: How long are these field effectiveness studies? A: They usually last between two and six months, depending on the baseline conditions and expected results.
Chemical Water Treatment
Chemical treatment has different characteristics than filtration. See the slide for a summary. In some cases, the cost ratio of chemical treatment vs. boiling is 1:60! Due to its strengths, robustness and low cost, the CDC has been actively promoting a chemical treatment solution in partnership with other companies and organizations.
The CDC Safe Water System
See http://www.cdc.gov/safewater/. “The Safe Water System is simple. It provides families with the means to treat their drinking water at the point-of-use – by adding dilute sodium hypochlorite bleach – and the means for them to store treated drinking water safely – in a narrow-mouthed, lidded vessel with a spigot that can be used to collect, transport, disinfect and store drinking water in the home. A capful of the locally-produced dilute sodium hypochlorite from the 500 ml CLARO bottle is just the right amount to treat 20 liters of water in the locally-produced CLARO storage vessel. These two items [shown in the slide] were marketed together as part of the first national Safe Water System project in Bolivia in 1996.” [Source: Daniele Lantagne’s notes on slide] “The hypochlorite solution and the storage vessel are the “hardware” of the Safe Water System, but the most critical component is the “software”. By that I mean the messages and the methods used to induce and sustain healthy changes in behavior, including safe water handling, and improvements in hygiene and sanitation, such as handwashing. These printed materials are from Safe Water System programs in Bolivia, Zambia, and Ecuador, but our social marketing and implementation partners also reach people through radio and TV broadcasts, community mobilization campaigns, and interpersonal behavior change techniques such as motivational interviewing. We realized long ago that for the Safe Water System to have impact, it needed to be economically self-sustaining, and hence one function of the “software” is to get people to buy the “hardware”. Fortunately, the bleach solution costs very little to produce, and 10 to 25 cents worth will last a family an entire month. Safe storage vessels cost between 2 and 5 dollars, but are still within the means of many of those who
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can benefit from them. Increasingly, we’ve recognized that the “hardware” also helps to sell the software. In other words, people who purchase and bring into their homes a bottle of hypochlorite for water treatment and a safe water storage vessel are likely to be receptive to messages promoting simple hygiene measures like handwashing - which by the way, is a lot easier to do when your water is kept in a vessel with a spigot. The hardware empowers families to manage their household water and sanitation environment better, and this reinforces their willingness to adopt and maintain new behaviors.” [Source: Daniele Lantagne’s notes on slide] The water treatment solution bottles are sold under different brand names in each country. Shown in the slide, left to right, are bottles from Bolivia, Peru, Zambia, Uganda (in yellow), Kenya, India, and Madagascar. The Safe Water System program employs in-country partners and extensive evaluation.
Results so far have been very promising, with overall reductions in diarrhea rates of about 50%.
“But as good as that makes us feel, when we leave our logarithmic scales behind and examine our progress on a pie chart representing the billion plus persons without safe water, we see immediately how much more needs to be done…We believe that the Safe Water System can help us reach the goal, and have projected a figure of 100 million regular users by 2007 if we can find the resources to support our proposed 20 country expansion.” [Source: Daniele Lantagne’s notes on slide]
Other POU Treatment Technologies
In addition to the filtration and chemical treatment systems discussed so far, several other prospects are worth mentioning. (Briefly, as class time is running out…) Proctor and Gamble has developed the PuR product as a single-use sachet capable of treating 10 liters. It’s noteworthy as an example of private sector
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involvement, and has proven effective in the field. Drawbacks include a process requiring lots of steps and two buckets, and somewhat prohibitive cost. (Class discussion ensues on the sales pattern of single-use sachets, so common now for occasional use consumer products like shampoo. It’s not clear how effective this model is for products designed to reduce disease.) Ultraviolet treatment is noteworthy for its ability to treat large quantities quickly, and also deal with contaminants not treated well by alternatives. It does require some expensive infrastructure, however.
Solar disinfection is shown in the slide using large plastic jugs and a black tarp. It’s among the cheapest of treatment solutions.
In closing: there are tremendous ongoing research opportunities for safe water systems in developing countries. Keep in mind groups like Engineers without Borders, Engineers without Frontiers, Amnesty International, etc., when seeking support and collaboration.
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