Review of Decentralized Water Purification Systems for Use in Developing Countries

Miguel A. Camelo Rosas

MANE 6960H01 Air & Water Pollution Control Engineering Fall 2013

Table of Contents 1.0 Introduction ............................................................................................................................... 3 2.0 Relationship Between Water Quality and Health ..................................................................... 4 3.0 Present Situation of Water Supply in Developing Countries.................................................... 5 4.0 Limited Water Quantity Decentralized Solutions ..................................................................... 6 5.0 Low Cost Decentralized Water Purification Systems ............................................................... 6 7.0 Conclusions ............................................................................................................................. 11 7.0 References ............................................................................................................................... 11

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1.0 Introduction

Access to potable water is a basic necessity for human life. However, it is estimated that one third of the world’s population does not have access to clean water sources. Furthermore, it is expected that by 2025 almost 3.5 billion people, 48% or the world’s population, will have an insufficient water supply (Brown, 2002). Aside the health aspect, another of the main problems with this water scarcity is that is threatening the economic and social growth in rural areas of developing countries. This is more pronounced in rural areas of developing countries since urban areas usually favor the implementation of a centralized potable water solution, with governments being more prone to achieve a successful solution. There are several technologies that allow the purification of water for both microorganism and solid matter. However, they are usually costly and require electricity, something that rural areas of many developing countries don’t have as accessible as urban ones. Therefore, the need for point-of-use purification systems seems like the most viable solution to this problem, with numerous “old” as well as avant-garde technologies coming into play. Some of them don’t require big investments, and some don’t even require the use of electricity. The purpose of this research paper is to examine the water scarcity problem, look at the different lowcost decentralized water purification systems, and propose further research in this field. Future developments in the comparison of the current technologies and in the proposal of implementation plans need to be carried out. An increased education in the benefits of the different types of systems needs to be pursued if these countries are to implement them.

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2.0 Relationship Between Water Quality and Health

One of the primary risks with water quality in developing countries is linked to microbial pollution. Different viruses, protozoa, bacteria, or larvae (such as cholera, dysentery, giardiasis, and typhoid) can cause several illnesses. They are usually because of fecal matter contamination of the water supply, as this acts as a medium for the pathogens to travel. Water quality is associated with about two dozen infectious diseases (Arnal, Fernandez, Verdu, & Garcia, 2001). There are also other sources of water related diseases, usually tied to water’s support of the life cycle of infecting agents or organism that spread them. Mosquitoes and other insects usually living close to water sources spread diseases like malaria, dengue, and yellow fever. The last major health issue associated with poor water quality is due to lack of proper hygiene in water scarce areas. Some of the diseases caused by this could be leprosy, hookworm, conjunctivitis, and ascariasis. Microbial pollutants aside, natural and anthropogenic chemical pollutants are also a concern when dealing with water quality. On the natural component, the most widely know are arsenides and fluoride. A high concentration of these chemicals in drinking water could cause skin diseases, crippling diseases, and cancer. The World Health Organization (WHO) has placed guidelines on the daily intake of these and other pollutants like cadmium, mercury, manganese, lead, copper, and uranium. These can therefore come from natural sources, like arsenic and fluoride, or come from anthropogenic sources, like heavy metals and pesticides. The latter ones are often neglected, but are a major problem in developing countries. They are commonly used without much regulation and end up finding their way into the water sources. It’s estimated that some 3 million people suffer from pesticide poisoning in developing countries (WHO, 1992).

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3.0 Present Situation of Water Supply in Developing Countries

The water supply situation in developing countries can be divided in two, water supply in urban areas and water supply in rural areas. In urban areas, centralized approaches are usually taken by the government for water distribution. Large numbers of people in a concentrated area provides, in theory, a potential for a very efficient water supply system. Nevertheless there are several obstacles due to the imperfect ways in which cities and towns have grown in size. The “urbanization” of the developing countries has created a dynamic of rapidly changing areas and this presents a challenge on infrastructure and service provision. Rapid urban population growth, mainly consisting of the poorest households, gives rise to very big slums/shanty towns where a centralized infrastructure may not be neither economically nor technically feasible to establish (Thomas & Ford, 2005). In rural areas, the population is not in a concentrated region but rather spread out. This is usually a cause for reduced infrastructure and water supply services. If a centralized system is not available, which is the case in a large portion of rural areas in developing countries, water is obtained individually through underground or surface water sources. This poses problems with both the quality and quantity of the water. If a shared solution, like a common spring or well is employed in a small rural community, access is usually an issue. In the “lucky” rural areas where infrastructure for water supply is already in place, the growth of population and limited financial resources often leads to the lack of proper maintenance and operation of the system. It can be therefore concluded that although centralized water supply systems could work in developing countries, the issues associated with their implementation and maintenance pose an impediment to them and make them unlikely feasible candidates for rural communities. As a result,

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decentralized solutions need to be examined. Point-of-use water supply systems seem to be the most feasible solution where governments and are unable or unwilling to improve the water supply service.

4.0 Limited Water Quantity Decentralized Solutions

Decentralized water purification systems in Developing countries are fed by two main water quantity solutions. In regions where water is scarce or its quantity is limited, the two main sources for water are groundwater wells and rainwater harvesting. If a centralized supply of water is not available or there are no rivers close by, wells are usually the next option for water supply. That is, of course, if there is a potential for their implementation in the area of interest. Some of the problems with wells are that they are usually in close proximity with pollution sources and a lack of proper shielding or lack of education leads to their unintended pollution. Rainwater harvesting, on the other hand, is usually employed in semi-arid areas. This is usually done by each household and provides the source right at the point where point-of-use water purification systems can employ it. Common problems with it are the variability in the supply, due to meteorological and seasonal conditions, and the potential for contamination during storage. Also, while there are other sources of water, since these are the most common, they are the only ones discussed in this paper. Some of the different low-cost water purification systems will now be examined.

5.0 Low Cost Decentralized Water Purification Systems

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Boling One of the most common water purification systems is the boiling or heating of water. This is a very effective way of destroying a majority of water-borne pathogens and is an effective way even in waters with high turbidity. Even though boiling is more effective, just raising the water temperature to about 60 degrees Celcius (pasteurization temperatures) for about ten minutes will destroy the majority of pathogens. One of the disadvantages of boiling is that it requires energy and depends on a fuel source. In addition, it does address the issue of water turbidity and chemical contaminants. However, it is a very effective way of microbial removal and it is one of the most currently used ways to purify water in developing countries.

Thermal Treatement with Solar Radiation Water can obtain pasteurization temperatures of around 60 degrees Celsius in transparent bottles that are exposed to sunlight if the bottle lies against a dark surface what will collect and radiate heat or has one side painted black. If this is carried out for a few hours then the water could obtain the benefits of pasteurization mentioned earlier. The Ultraviolet radiation of the sun in conjunction with the thermal effects of sunlight works to destroy the majority of water-borne pathogens. This can be an extremely low cost alternative for water purification, but it is highly dependent on the amount of sunlight present in the region of interest. Seasonal and geographic locations can limit this method’s application and effectiveness. Another limitation is the satisfactory determination of the water temperature in the water, since this method only works if temperatures around 60 deg Celsius are obtained. In addition, water should not have high turbidity or this method would not be as effective. It must be stressed, however, that this is likely one of the lowest cost methods.

UV Disinfection using Lamps Lamps have been used for disinfecting water since the early 1900s, however it received a renewed interest recently since it is effective against two protozoans that are resistant to chlorine, Cryprospodidum parvum oocysts and Giardia lamblia cysts. It, however, runs into a similar limitation as the system mentioned before. The ability of the lamps to radiate UV light is 7

hindered by the presence of solid matter so the water turbidity has a great result on the effectiveness of this method. Some of the disadvantages of this method are its relatively high cost, requirement of regular maintenance, and need of electricity and a piped water supply.

Fiber, Fabric, and Membrane Filters The majority of paper and fabric filters do not have pores sizes small enough to contain virus and bacteria as their diameters are significantly smaller. However, there are certain membrane and fiber filters that can have small enough pore sizes, about one micrometer, to remove parasites. Even when these are not available, paper or even cloth filters can be effective at removing certain elements harboring parasites, such as zooplankton and phytoplankton that contains Vibrio cholera. Some of the disadvantages of these methods are the cost, the requirement by some to be cleaned regularly, and the various efficacy depending on the pore sizes. The most promising of this technology are the ceramic membrane filters, which have been shown to be very effective at removing microorganisms.

Porous Ceramic Filters The usual setup for porous ceramic filters involved a vessel shaped in the form of a hollow cylinder and water either flow from the outside in or vice versa. The size of the pores can be controlled and has been manufactured to micron or submicron pore sizes. On some of the more technologically advanced one, the use of a small silver layer has been employed in order to prevent the formation of a biofilm at the interface. Due to their small pore size, they can be very effective at removing microorganisms but one of their main issues is the requirement to regularly clean them in order to maintain an adequate flow rate and efficacy. In addition, they can be one of the more costly methods described here.

Aluminum and Iron Coagulation and Sedimentation The use of aluminum and iron derived salts to coagulate certain pollutants in contaminated water has been shown to be effective with regard to the reduction of fecal coliform contamination. However this process solely deals with the removal of solid matter suspended in 8

the water, and is not as effective with the removal of microorganisms. In addition, it can be time consuming, as the process requires coagulation, flocculation, and sedimentation and could be costly in terms of infrastructure. It can also give a metallic taste to the water that could deter certain communities from using it.

Charcoal and Activated Carbon Adsorption The primary use of charcoal and activated carbon is for the diminution of organic compounds that are toxic. In addition, taste and odor in water are commonly treated with this method. Charcoal and activated carbon that has not been used is effective at removing microorganism and pathogens but organic matter usually takes up sites for adsorption and carbon also develops a biofilm. When impregnated with silver, this is reduced and the microorganisms can be controlled in a more effective manner. Some of the problems with this method are the requirement to clean the medium regularly and the replacement of the media and regular intervals.

Ion Exchange Disinfection Ion exchange disinfection is usually performed through the use of tri-iodide or pentaiodide exchange resins. This method is one of the more developed ones, and it can either be employed though pour cups, columns containing the iodine on the resin, or tablets that are placed into the water. The inactivation of water-borne pathogens has been shown to be very effective with this system. Although this is a very simple method, the cost associated with it is usually high and it requires regular maintenance or cleaning in the methods that don’t involve tablets.

Chlorine Treatement Chlorine treatment is next to boiling, one of the staple treatment methods due to its moderate cost but high microbial removal efficacy. It is very effective against nearly all the water-borne pathogens with only very few exceptions. In addition, it provides a residual effect and is very widely known and used. However, one of the major limitations is that is not as effective in water with high turbidity. 9

Comparison of Methods The table shown below summarizes the various household technologies for water purification based on their availability and practicality, cost, microbial removal efficacy, and limitations. It can be seen that no one method seems to be perfect in all categories, although there are certain that excel at particular ones. It is therefore a very logical consideration to establish some of these systems in series, in order to maximize the effectiveness of some while trying to keep the overall costs low. The use of two or more systems in series for improved treatment and the creation of multiple barriers is something developing countries could greatly benefit from. Examples of this could be to combine treatments that provide no residual disinfectant or reduction of water turbidity, like boiling or UV lamp or solar radiation, with membranes filters. In addition, the use of a process that removes turbidity, like membrane filters could be combined with chlorination to provide a multiple barrier approach.

Table 1: Comparison of Household Purification Interventions (Agrawal & Bhalwar, 2009).

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7.0 Conclusions

As discussed earlier, the importance of potable water to developing countries is paramount not only because it is a basic necessity for a healthy life but also to help battle social and economic problems. This is more pronounced in rural areas of developing countries since urban areas usually favor the implementation of a centralized potable water solution, with governments being more prone to achieve a successful solution. Although there are several technologies that allow the purification of water for both microorganism and solid matter, some of them are costly and require electricity, something that rural areas of many developing countries don’t have as accessible as urban ones. It is therefore required to look at decentralized water supply solutions, or the use of point-of-use purification systems. Further research is required in the field of decentralized water purification systems for developing countries. Future developments in the comparison of the current technologies and in the proposal of implementation plans need to be carried out. In addition, an increased education in the benefits of the different types of systems needs to be pursued if these countries are to implement them. As proposed in this paper, a combination of several low cost systems could prove to be the most effective solution, combined with a relatively low cost.

7.0 References

Agrawal, C. V., & Bhalwar, B. (2009). Household Water Purification: Low Cost Intervention. MJAFI , 260-263. Arnal, J., Fernandez, M., Verdu, G., & Garcia, J. (2001). Design of a Membrane Facility for Water Potabilization and its application to Third World countries. . Desalination , 63-69. Brown, K. (2002). Water Scarcity: Forecasting - The Future wth Spotty Data. Science , 297. Thomas, D., & Ford, R. (2005). Crisis in Innovation in Water and Wastewater. Edward Elgar, Cheltenham , 1-19. WHO. (1992). Our Planet, Out Health: Report of the WHO Commission on Health and Environment. Geneva, pp. 79-83. 11