Point-of-Use Water Treatment Options Today

1. Global Water Crisis, and Interventions

Approximately 1.1 billion people do not have access to improved sources of drinking water (WHO, Water Sanitation Health, 2013). Even so, these current estimates are probably not as high as they should be. This is because the assumptions about the safety or quality of water is based on its source (lakes, rivers, ground), and does not take into account recontamination during its distribution for use (Sobsey, 2002). Many communities have protected water supplies and treated water that is microbiologically safe when collected or when it leaves a centralized treatment system. However, substandard water distribution systems, and illegal connections to the distribution system often lead to contaminated water (Sobsey, 2002). A further compounding problem is that water collected for domestic use often becomes re-contaminated or further contaminated by unsafe consumer storage and handling practices at the household level.

Clean water is often an access issue to a large portion of the population, and many waterborne diseases can bring considerable death. Water and hygiene related diseases like diarrhea claim 2 million lives each year, and also create 4 billions cases of illness (United Nations Water Report, 2012). This justifies the claim that no single type of intervention has greater overall impact on national development and public health than the allocation of resources for safe drinking water (Water and Sanitation, 1996). There has fortunately been some progress made since this statement was issued. The Joint Monitoring Programme for Water Supply and Sanitation announced recently that the Millennium Development Goals drinking-water target was achieved in 2010. They reported that the proportion of people without access to improved drinking water resources had decreased from 24% to 11% since 1990. However, the progress report also noted that these percentages did not reflect evenly throughout the world (United Nations Water Report, 2012). While much has successfully been monitored and achieved over the years, many more people need help all around the world. 

Through review of water, sanitation and hygiene interventions it has been found that improvements to household drinking water at the point-of-use (POU) stage, to reduce diarrheal disease risks, has been drastically underestimated. Most recent reviews estimate that 30-40% reductions of diarrheal disease can be found by improving household drinking water at the POU, rather than treatments at the source (Clasen2007). This information suggests a new strategy for ultimate purification, by pretreating water at the source and then completing a retreatment or prevention of contamination at the household level.

Throughout sub-Saharan Africa there has been limited progress in addressing drinking water concerns for the poorest in this region (United Nations Water Report, 2012). In Ghana, it is generally observed that water resources are relatively abundant when compared to other countries near the Sahel. Some regions of the country even have a high water table, very accessible for human use. However, even though there is abundant water, resources are often contaminated by animal and human activities. Ghana currently has a stable government with little to no political or civilian strife, making water resource remediation an achievable goal. Community Water Solutions (CWS), based out of Boston, has started their drinking water initiatives in the northern city of Tamale, Ghana, for these reasons.

 

2. Community Water Solutions History

Kate Clopeck, a scientist specifically interested in drinking water development work in Central Africa, founded CWS in 2008 to create an effective platform for sustainable water business specifically in Ghana. She wanted to create water filtration systems in the developing world that were run by the people drinking the produced water, as well as empowering women to the run the filtration centers. The bottom line was to develop a system that was effective in bringing clean drinking water to locals but also one that created economic growth by keeping the villagers healthy and continually in the work force. 

CWS can now proudly say that they have launched water treatment centers in 49 villages in Ghana, helping to give a healthier life to 28,130 people (Community Water Solutions, 2013). Through specific follow up monitoring of Escherichia coli (E.coli) and system functionality by weekly water testing, incubation and counting of colonies, CWS can say that 100% of systems are still operating and providing clean water with no colonies of E.coli contamination in each village’s central water source. The company has been established for five years and plans to keep expanding to new villages and areas of Africa beyond Ghana, such as the Ivory Coast and Togo. 

    

3. Water Treatment Overview

To reiterate what was stated above, POU interventions are becoming more vital than ever since scientists realized that source water treatment could sometimes be inconsistent in its effectiveness due to distribution recontamination. There is increasing evidence and awareness for this fact. Dunne et al. (2001) found that in the Ivory Coast, there were mostly negative effects on water quality when comparing water from point of treatment with that water stored at the household level. They found that E.coli was detected in 41% of stored water samples (n=87) but only in 1% of point of treatment water samples (n=108) (Dunne et al, 2001). 

To further show that distribution and subsequent household storage is a major cause of waterborne illnesses in developing countries, a similar result was also found in Southern India. The study site obtained its drinking water from a surface lake and samples were monitored throughout their delivery process until the water was used. It was found that all samples of the treated municipal water were contaminated after being distributed and reaching the household storage point. Furthermore, 67% showed increased contamination during storage periods from 1 to 9 days (Brick, 2004). This study shows that no matter the extent of contamination in a water source, distribution and handling practices often make water even more contaminated. Through these studies and various others, it is clear that POU disinfection is an important missing step that represents a very good opportunity for intervention. Safe household storage practices are now believed to be vital for developing countries and water purification contingency plans. 

 

4. Point-of-Use Water Treatment Systems

Numerous water treatment systems exist today. They all have various advantages and disadvantages based on pathogen inactivation effectiveness, ease of setup and use, availability based on region, and economic practicality. Sobsey (2002) has identified nine water treatment systems that are up to the effective task of alleviating contamination of drinking water around the world in developing countries. They will all be outlined and compared below. These are:

  • Boiling
  • Solar Disinfection Through UV and Heat
  • UV Disinfection with Lamps
  • Chemical Pre-Treatments
  • Chlorination
  • Combined System of Coagulation-Filtration and Chlorination
  • Slow Sand Filters & Diatomaceous Earth filters
  • Aeration
  • Colloidal Silver

 

Boiling

Boiling water to a temperature of 60 C, or a rolling boil, for 5-10 minutes with fuel has been used to disinfect household water since ancient times. It is effective in destroying all types of waterborne pathogens including viruses, bacteria, fungi and protozoans, and can be effectively applied to all types of water, including those with high turbidity. The price of this technique is relatively expensive compared to chemical disinfectants because of the cost associated with a fuel source as well as the time needed to undergo treatment (Sobsey, 2002). This is one of the most simple treatment systems to use besides using solar disinfection, and should be considered when there are no alternatives.

 

Solar disinfection through UV and heat

Although some authorities recommend boiling, using solar radiation is a more accessible, economical and technologically feasible option than heating with fuel because fuel can often be hard to come by (Sobsey, 2002). Solar disinfection materials usually include polyethylene terephthalate (PET) plastic bottles, which are the most accessible types of bottles around the world. Different techniques can be used with these bottles to heat water inside of them. They are usually placed in full sun locations like rooftops and can also be painted black on one side or surrounded by reflective material to increase the suns heat. These are considered passive, low impact systems, which can be very accessible to people in all types of living conditions with strong sunshine. However, if these systems are used over the long term, they could leach chemicals into drinking water for long-term health effects. Westerhoff (2008) found that the chemical antimony was commonly leached from PET bottles, which could, in quantities over 6ppb bring acute and chronic health effects. The research team analyzed how rapid this would happen and found that PET bottles could leach 6ppb in a bottle at 65°C heat after 38 days of exposure. At 70°C this leaching limit would occur in 28 days and at 75°C in 12 days. This is of concern because rooftop temperatures can often reach these limits, and bottles may not be replaced within these time frames.

Pathogen Inactivation Times By Heat and Duration (SEAWAG, 2002).

This type of treatment is still of interest because solar UV and heat can inactivate microbes very effectively. They both work in tandem with heat being more effective against vegetative bacteria, and protozoans than against bacteria spores and helminth ova and UV radiation being more effective against vegetative bacteria and protozoans. It is also possible to achieve high water temperatures very quickly. For example, if the bottles are black, or metal they can reach temperatures above 60°C and inactivate pathogens after a single hour (Sobsey, 2002). A complete table of microorganisms and their inactivation times based on heat and duration is provided here.

Overall, the results of both microbiological and epidemiological studies indicate that solar disinfection of household water has the ability to beneficially improve its microbial count and to reduce household diarrheal disease of consumers (Conroy et al., 1996; 1999 and Wegelin, 1994). Using clear vessels that allows for a combined pathogen inactivation effect by both UV radiation and heat also has been developed, evaluated and put into the field with high success (Managing Water in the Home, 2013). This type of system has very low overhead costs because sunshine is free and bottles are abundant throughout the world. Black paint and storage places for the system are the only small costs associated with solar UV disinfection.

 

UV Disinfection with Lamps

Lamps can also be used to emit UV light and thus treat water in the same way as a solar UV system. These lamps are usually made with elemental mercury and an inert gas such as argon in a UV-transmitting tube made of quartz. Most modern lamps in this way transmit UV from 200 to 320 nm (the optimal absorption is 254 nm for nucleic acids) (Sobsey, 2002). Older, low-pressure lamps only emit 254 nm UV light, which is ideal for water purification because they provide the best type of inactivation light and are also much cheaper. These lights can emit UV radiation doses of 50-150 mJ/cm2 in high quality water. With this dosage they can effectively eliminate all waterborne pathogens (Sobsey, 2002). However, suspended matter in the water can slow this process by deflecting UV light away from pathogens in the water, so this always needs to be taken into consideration. The inactivation process can take just a few minutes when water is clear but much longer depending on the extent of turbidity. This can be a good solution to purifying small amounts of water because it does not add chemicals, tastes or odors to the water.

The negative impact of this treatment is that this system can give uncertain UV dosage to the water being treated, thus falsely treating it sometimes. There is also no residual chemical in the water, which is generally a good thing, but can also be a negative since it does not prevent contamination further along the distribution chain of the water.

The hindrance for this treatment option is that it is more expensive that other alternatives. Lamps need to be replaced every year or two and electricity needs to be provided at about the same rate as having an incandescent light bulb and using it every day  at 10-30 watts per day (Sobsey, 2002). At a community UV disinfection level 1000 liters of water can be treated at $0.02, or $1.00 per household per year. At the household level it would cost $10-100 per year (Sobsey, 2002). Lamps usually cost between $20 and $60 and need to be replaced every 1 to 3 years for $10 to $50. When taking the machinery costs aside, energy costs of UV disinfection are also considerably less than the costs of disinfecting water by boiling it with fuels like wood or charcoal (Sobsey, 2002). This is a valuable option of economic resources are sufficient.

 

Chemical Pre-Treatments

Chemical pre-treatments like coagulation or precipitation can be effective in causing microbial reductions since many organisms can be attached to sediment in the water. Alum, or aluminum sulfate, is commonly used and is a good simple technology solution for coagulation. It requires proper use and training but equipment can never break because its material is just dissolved into solution (Sobsey, 2002). Once dissolved into solution it creates a precipitate, which traps suspended materials when they fall through the water. It generally has a very low cost, but also depends on the region. It has also been commonly used around the world for coagulation for centuries. Many rural villages throughout Africa also have local knowledge of this material.

Iron salts such as ferric chloride or ferric sulfate are alternatives similar to alum and work in the same way. Lime and soda ash are also alternatives as well as softeners, but are not applicable to many waters because they lack the calcium, magnesium, iron and manganese, which these compounds precipitate.

Natural polymers such as carbohydrates from seeds, nuts, or beans can also be a good alternative to these coagulants in developing counties, however they are rare and location dependent. Training and skill is required to harvest and prepare these natural materials for coagulation uses, but this practice can be very valuable if there is already a known history of use in the region.

While these processes are effective in removing pathogens from sediment materials, the chemical disinfection processes highlighted next are specifically intended to inactivate most pathogens in water (Sobsey, 2002). This type of treatment is especially desirable when dealing with extremely turbid waters.

Chlorine Values for 3-log Inactivation of Giardia Cysts by Free Chlorine (EPA Guidance Manual, 2003).

Chlorine

Of the drinking water disinfectants, free chlorine is the most widely used, the most easily used and most affordable. Free chlorine is highly effective against nearly all waterborne pathogens, with notable exceptions being Cryptosporidium parvum oocysts and Mycobacteria species (Sobsey, 1989). At doses of a few mg/l and contact time of about 30 minutes, free chlorine generally inactivates >4 log10 (>99.99%) of present bacteria and viruses (Sobsey, 2002). A chlorine inactivation table showing the amount of chlorine needed to inactivate common giardia cysts is provided here. 

Point of use chlorination is becoming a more important way to improve microbial quality and reduce diarrheal illness in the developing world. It has been found to be quite effective and a simple solution for many community problems when used in sodium hypochlorite form. Reller et al (2001) found that free chlorine in a hypochlorite solution, Sûr'Eau, was effective in removing 90% of cholera cases in rural establishments in Madagascar. They also found a significant microbe decrease, with E.Coli counts dropping from 13 to 0 Coliform Forming Units/100 ml.

Sobsey (2003) found that in a controlled setting in India, if hypochlorite was applied to stored household water, 24% (P = <0.03) of observed diarrhea would be preventable using the intervention. Quick et al (1999) also found significant diarrhea reduction in cases in Bolivia through chlorination. Their study found that by using free chlorine they reduced diarrhea cases by 44% and E.Coli Coliform Forming Units from 94% to 22%. Through this data, it is believed that simply using chlorine for water treatment could drastically reduce the global burden of waterborne disease.

The costs of chlorine are also very reasonable. A hypochlorite generator usually costs around $8 for associated hardware and bulk storage of materials and annual operating costs are usually about $3 (Sobsey, 2002). Although this treatment method is very effective at inactivating pathogens in drinking water sources there are also negative aspects. Chlorine can cause a new taste in the water, however it may be better than the original taste. Chlorine is also known to create trihalomethanes, which have controversial health side effects. Many researchers have studied them and have no conclusive evidence showing health effects when ingested in small amounts. However, many organizations advise that ingesting large amounts of this compound would be undesirable. With this uncertainty in mind, drinking water experts still believe that using chlorine creates more benefits than harm (Drinking Water Chlorination, 2013).

There has been inconclusive evidence for chlorine effects on humans but there are strong signs those chlorine residuals and forms that get into water environments can be very damaging. Emmanual et al (2004) found that sodium hypochlorite can react with organic compounds in wastewater to create halogenated organic compounds which persist in the environment and are harmful to a whole suite of organisms including D. magna and V. fischeri photobacteria. These residuals could be impactful for many more water organisms but this has yet to be studied. This should be kept in mind when using chlorine near sensitive ecosystems.

The combined application of chemical coagulation-flocculation, filtration and chlorine disinfection is also widely practiced for community water treatment in developed countries and should be seen as a sound solution that addresses many pressing needs.

 

Chloramine

Disinfection of water with the use of chloramines is widely practices as a solution for community water supplies in order to give long-lasting disinfectant to the water but also to reduce odor and taste issues commonly found in the water. Chloramine is a combination of chlorine and ammonia, but is actually less effective (2,000 to 100,000 times) at inactivating E. Coli and rotaviruses in water when compared to free chlorine (WHO, Seminar Pack For Drinking-Water Quality, 2013). It is difficult to use this method as a primary treatment because a controlled amount of chloramine as well as ammonia is needed for effectiveness (Sobsey, 2002). For this reason the chemical is often used as secondary treatment to try to eliminate recontamination. One benefit of chloramination is that it reduces the formation of free chlorine byproducts including trihalomethanes, which have controversial health side effects as listed above. However it is more expensive than free chlorine alone and slower acting, therefore giving it a much smaller role in water treatment applications worldwide (Sobsey, 2002).

 

Slow Sand Filters & Diatomaceous Earth Filters

Slow sand filtration of drinking water has been practiced since the early 19th Century and various sizes of slow sand filters have been used to treat water at the community and household level (Palmateer, 1999). Diatomaceous earth and other fine granular media can be used to remove particulates and microbial contaminants from water by gravity fed filtration. Such filters have achieved high removal efficiencies of a wide range of waterborne microbial contaminants without chemical pre-treatment of the water, but it can be a slow process (Palmateer, 1999). Since contaminants are prevented from passing through most filtration medium, there is a buildup, which can happen quickly if the filter is used often. The filter then needs cleaning and an addition of new medium, which can be difficult or expensive to get. This is one reason why these systems lag behind other options for water treatment (Sobsey, 2002). Filters can be made with sand, fiber or membrane materials, as well as fine particulate material, which can cause respiratory problems (Sobsey, 2002). These sand filters are often more expensive and require more maintenance than alternative treatments.

 

Aeration

Aeration of water alone is a simple procedure, which can also be practical and affordable for many households and water treatment centers. Aeration of water as been practiced since ancient times and was believed to improve water quality by sweetening, removing some distinct tastes, as well as softening, which would removes calcium and other metals from the water (Baker, 1949). It is now known that aeration of water can oxidize and precipitate iron, manganese and sulfur, as well as strip volatile organic compounds, and some taste and odor compounds. However, there is no evidence that aeration for brief time periods has a direct pathogen inactivation effect (Sobsey, 2002). This treatment can be seen as something to add to the water treatment phase, which is affordable and possibly beneficial even for general reasons listed above.

 

Silver Treatment

There is now a new movement to make ceramic water cisterns, which have been impregnated with silver to kill bacteria (Lantagne, 2001). One company that excels in this is Potters for Peace (PFP). They are an independent, non-profit, international network of potters concerned with peace and justice issues who also tackle water problems at its core. PFP aims to train potters around the world to make this technology more well known.

Silver has an inherent and extreme effectiveness for inactivating bacteria in water. There are three main ways in which silver achieves this inactivation. Silver reacts with sulphydral groups in the bacteria destroying their cells functioning capabilities. It also binds with bacterial cell membranes, creating outer cell layers to have abnormalities resulting in cell lysis and death. Finally, it reacts with nucleic acids, in which Ag+ binds with DNA base pairs and prevents DNA replication (Russell, 1994). A general cost analysis found that silver treatment is approximately $25 per household for filter, plus an additional $5 for annual replacement, making it relatively comparable to UV lamp treatment (Sobsey, 2002).

When examining this type of treatment it is also important to see how silver comes in contact with humans naturally and how it affects them. WHO has concluded and recommends for no one to consume more than 10 grams of silver per lifetime. While most silver can be found naturally in ground and surface water at 5 ug/L, it can be harmful if large amounts are put into the body and subsequently stored in the skin and liver. Argyria is the only known human health effect of silver, and is a condition in which silver is deposed on skin and hair (Lantagne, 2001). WHO has established an additional guideline value for when silver is used to maintain quality of drinking water. This guideline says that higher levels of silver, up to 0.1 mg/L, could be tolerated in such cases without risk to health. Therefore, the guideline and proper measurement of PFP filters is 0.1 mg/L in the finished filtered water (Lantagne, 2001). With this new emerging technology based in ceramic filters, it will be interesting to see how its price can be reduced as production of the technology expands.

 

5. CWS Choice

There is now evidence in the water treatment field that has found simple, low-cost interventions at the household and community level to be quite effective at inactivating pathogens. The field consensus is that these types of interventions dramatically improve microbial quality at the household stored water level, reducing risks of diarrheal disease and death in the population (Sobsey, 2002).

When considering a drinking water treatment system for rural Ghanaian villages there are several things to take into consideration. Portability, ease of use, durability, and cleaning access are key for surviving this countryside. Low technical maintenance is important, and chemical materials need to be accessible and affordable, otherwise the system ceases to function very quickly.

Kate and the CWS team thought addressing these issues through technically simple water treatment systems would prove most effective to communities in northern Ghana. With little access to markets and certain filtration items only a few approaches listed previously would be available. She also wanted to avoid the common approach through large centralized machinery, because it simply doesn’t make sense for villages this dispersed. Piping would be expensive and a waste of resources. For these reasons a simple low tech implementation was chosen.

The final decision was to use a chlorine-based approach with alum as a coagulant to remove turbidity. This treatment would remove bacteria through the settling out of sediments but also with the chlorine acting as a disinfectant. Household contamination was also addressed in this strategy. All families were given hygiene training as well as household containers, equipped with drip nozzles preventing contamination of the water while in the family home.

The system also uses low-cost locally sourced materials for water treatment, and is sized to properly accommodate the the community partners needs. CWS believes small scale will ensure better quality and maintenance of the water treatment system. They also speak with stakeholders in the community, along with the chief elders and women to establish a sense of ownership over this system once it is built. The key with this effort is to create sustained use of such systems and to develop a sense of caring for the system, which is usually lacking in most government led efforts.

 

6. Business Sustainability

Community Water Solutions wants their water treatment systems and implementation protocol to be sustainable. The model for Community Water Solutions is for each fellow to fundraise $3,000 for building supplies, system chemicals and maintenance, their room and board, and translator fees, prior to the project start date. This makes it possible to rapidly build and operate these water treatment systems within a few weeks after starting the process.

The long term management of each system is especially important. A group of elders in each village designate two well-respected women who they believe would be suitable in running their water treatment center. Once these women are chosen, they become the managers of this water business, often selling buckets of water to each family daily. These manager collect profits from this business, and put aside 30% for future system supplies. This type of business arrangement encourages the local managers to have their systems operating at the highest level possible. They are also encouraged to be flexible with their water pricing scheme, so as to be competitive in the local water market, and so that community members purchase locally rather than from a regional treatment center. This Low tech solution has now worked in dozens of villages throughout northern Ghana, and continues to function as intended.

 

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