How are water treatment technologies used in developing countries and which are the most effective? An implication to improve global health

Background

Water contamination has been a serious public health concern all over the world even in developed countries. According to the World Health Organization (WHO), improvements in drinking water, sanitation, hygiene, and water resource management may reduce the global disease burden by 10% (1). One of the Millennium Developed Goals is to decentralize drinking water (2), making it available globally, therefore reducing the risk of health complications and morbidity all across the globe. In developing countries, the most common form of contamination comes from water that has been stored in poor conditions (3), urging the need for better water treatment technologies. It is imperative to treat water for bacteria and other chemical/microbial components that may compromise public health safety. Advanced and affordable water treatment technologies are continue to be developed to provide assistance to those who cannot afford clean water. Prevention strategies such as treating water, educating guidelines for the safe storage of drinking water, and practicing improved sanitation techniques, can significantly reduce the risk of deadly waterborne diseases.

One common prevention strategy for treating water is chlorination. Chlorination method requires people to add one full bottle cap of sodium hypochlorite solution to clear water, or two bottle caps for turbid water, in a standard sized container, mixed thoroughly by agitating, and waiting approximately 30 minutes before consumption (4). This method effectively inactivates most bacteria and viruses that cause diarrheal disease however it is not as effective at removing protozoa, such as Cryptosporidium (4). Chlorination is inexpensive, generally easy to use and maintain, however there is a lower disinfection effectiveness in turbid waters, and it has potential for long-term health effects, such as some types of cancers such as Colorectal (4,5). This water treatment method has also been distributed free of charge in a number of disaster areas including Indonesia, India and Myanmar.

One of the widely used prevention strategies to treat water, Solar Water Disinfection (SODIS), is a safe and simple way to kill pathogens in water, making it safe to drink (6). Results have shown that exposing a filled water bottle to the sun for at least 6 hours reduces the number of pathogens in the water, and thus greatly reduces health complications (e.g., diarrhea) (7). SODIS uses the sun’s ultraviolet radiation to improve the quality of the water. It is an inexpensive and easy method to improve the quality of drinking water in a household. Studies also investigated low-cost SODIS-based point-of-use (POU) household devices in Pakistan (7). The study concluded that SODIS were successful in treating contaminated water and can be used for people living in large cities facing shortage of potable water (7).

Another well-known prevention strategies are ceramic and biosand water filters (BSF). Biosand filtration is a slow-sand filter adapted for use in the home. The most widely used version of the BSF is a concrete container approximately 0.9 meters tall and 0.3 meters square filled with sand. The water level is maintained at 5–6 centimeters above sand layer to grow on top of sand which in turn helps reduce disease-causing organisms. A plate with holes is placed on top of the sand to prevent disruption of the bioactive layer when water is added to the system. The filters can be effective POUs due to their versatility and ability to be used easily in homes. These technologies thus make it easier for people to keep sanitary water in their own home (8). Studies also showed that the ceramic filters are 3–6 times more cost-effective than the centralized water system in place for reduction of waterborne diseases (e.g., diarrheal illness) among children under five (9). The filters are known to be environmentally friendly in terms of low energy use, water use, and particulate matter emissions (9,10).

Slow sand filtration (SSF) is another simple method that can remove pathogens and particles in drinking water (11). When sand surface area increases, it leads to an increase in possible adsorption spaces on sand and biofilm attached to the sand grains. It was reported that an increase of 0.25 to 0.63 mm in d 10 of filter sand ended up decreasing the total coliform bacteria removal from 98.6% to 96%, which shows the high efficiency (11).

Membrane filters are typically manufactured as flat sheet stock or as hollow fibers then formed into membrane modules. Modules typically involve potting or sealing the membrane material into an assembly which are designed for long-term use. Some examples of modules used include, hollow-fiber modules and spiral-wound modules.

In this study, we will investigate the strengths and weaknesses of various water treatment technologies. Our study will be based on published pee-reviewed journal articles as well as our observations of drinking water industry trends. It is noted that our study is specifically designed for applications in developing countries. We will also provide recommendations to promote drinking water treatment technology guidelines and suggestions, so that many people in developing countries can access safe drinking water. We do believe that this work will be beneficial to local communities in developing countries, Engineers without Borders (EWB), and other stakeholders who need substantial understanding of available water treatment technologies for well-informed decision-making.

Methods

We searched literature through PubMed, Google Scholars, and Medline (EBSCO) using the key words “water treatment technology”, “world”, “disease”,” drinking water”, “public health and drinking water”, “public health drinking water and disease”. Initially we retrieved 56 papers however, after reviewing them, only 38 were considered for this study (Box 1).

These articles were selected based off of multiple factors including a discussion regarding various water treatment methods, their impacts on global health, strengths and weaknesses of specific water treatment technologies and the level of filtration or treatment capacities. We chose to analyze papers that discussed if the specific treatment effectively inactivated pathogens and removed chemicals such as arsenic, or if they only filtered pathogens. Each paper was analyzed according to cost, consistency/reliability of filtration capacities/efficiency, accessibility to filtration, cultural integration of filtration technique, ease of use, feasibility of instruction regarding operation and management, and overall effectiveness of the filtration.

We collected information regarding each water treatment method and combined this information in a matrix. Information collected included, cost, maintenance, installation, materials, operation, the efficiency of the system killing microbes or filtering out substances such as chemicals, necessary training required, strengths and weaknesses, requirements to operate (such as environmental requirements), filtration method use in developing countries and Risks, Attitudes, Norms, Abilities, and Self-regulation (RANAS) comments regarding the filtration method. Literature search keywords included, “household water treatment” OR “developing countries” OR “RANAS” during the period 2000–2018.

Results

Study characteristics

Table 1 shows the characteristics of the articles utilized in review (n=24), which were conducted over a vast region including China, Bangladesh, Cameroon, and several other countries (12-16). The total sample size from all the studies cannot be addressed since multiple studies only focused on the effectiveness in the removal of contaminants, while others focused on usage by those in developing countries. All of the studies focused on the removal of a particular contaminant presented the specific implementations.

Quality of reporting

Only 11 of the 24 studies gave a sample size. The 13 that did not provide the sample size focused on the effectiveness of removing a specific contaminant. The studies that included a sample size often focused on how the water treatment was integrated into a community. Sources of bias as well as how methodological efforts reduce the bias, were rarely discussed.

Results of literature searches regarding water treatment methods such as chlorination and SODIS, varied and each method had benefits and drawbacks. According to information collected, SODIS proves to be the most efficient method for treating water due to its low cost, ease of use, ability to kill most viruses and bacteria, and the absence of installation/maintenance. Other treatment methods such as chlorination, are also effective and may be preferred over SODIS due to the immediate access to clean water. Membrane filtration, such as reverse osmosis, is not used often in developing countries due to their complexity, however membrane filtration may be used more often in the future due to the efficiency of the particular filtration system. In the following, the core reviews for each treatment technologies are presented (Tables 2-5).

SODIS (solar disinfection)

As mentioned earlier, SODIS is a simple and inexpensive method that has been proven to be effective in removing pathogens and bacteria in contaminated water. A study in Cameroon presented two-cross sectional surveys and intervention regarding SODIS (23). Prior to the intervention, diarrhea was found amongst 34.3% of children. After the intervention, the risk of diarrhea was reduced by 42.5% (23). Another study in Pakistan consisted of 24 experiments that used 1.5-liter Polyethylene terephthalate (PET) bottles filled with water from water sources in Karachi, Pakistan (23). In these experiments, it was shown that SODIS reduced 100% of pathogens when used correctly. In order to optimize performance, specific types of backings on bottles must be used to further positive performances. Backings that were absorptive and reflective were able to show the bacteria growing back after a week of keeping the bottles at room temperature (7,23). Another study in Indonesia introduced an episode of training 144 villages, 70 elementary schools, and a total of 130,000 people within 14 months on how to use SODIS. By integrating hygiene education and SODIS into the community, bacteria contamination of household drinking water was reduced by 97% (23). However, one drawback to SODIS, is limited capability of filtering out only pathogens, not chemical components.

Membrane filtration

A major advantage of membrane filtration is that it is versatile. This water treatment can be produced and adapted to filter out almost any substance ranging from pathogens, bacteria, arsenic, and other harmful chemical pollutants (27,33). It also requires no chemicals, little maintenance, and has a long lifespan (33). However, this is not always suitable for use in developing countries due to costs. Most of the available membranes in markets are relatively expensive in comparison with other treatment options such as solar disinfection. However, many researchers/scientists are working on creating the membranes for a cheaper price (34). The other disadvantage of the membrane filtration systems is that they can waste a lot of the water as brine which can be difficult to get rid of (33).

Biosand filtration

Biosand is one of the simplest filtration systems to use since it requires little knowledge to prepare/install/use. The only requirements are to change the top layer of sand periodically and know how to pour the water over the sand. The products needed for biosand filtration can be made locally, at a low cost and they have a long life span (11). The biosand filtration filters out not only pathogens such as bacteria and protozoa, but can also filter out inorganic materials that can make water turbid (35). About 81–100% of bacteria and protozoa are filtered out on average (23). The major drawback to biosand filtration, is that it requires constant maintenance since the sand must be replaced often. If the sand on the top of the filter is not replaced, not only will the filtration be ineffective, the water that is being filtered can become even more contaminated (23,25,26).

Ceramic filters

Ceramic water filters (CWF) have been proven to be one of the most effective and sustainable methods for improving household water quality in reducing waterborne diseases and related death. These filters are widely used in developing countries where water quality is poor. It can remove turbidity, organic matter, and microbes (14). Other advantages include simple cleaning, improved environmental performance in terms of energy use, potential to impact global warming, turbidity, and particulate matter emissions. Ceramic filters are 3–6 times more cost effective than a centralized water system (9). Filter units can last for long periods but will need a supply of replacement parts due to breakage. The major weakness to ceramic filters are the ineffectiveness in removing viruses since viruses are smaller than the porous sizes of CWFs and therefore, are not effectively removed from water (14). The use of chitosan coagulation as a pretreatment for ceramic filtration has been shown to increase virus and bacteria reductions (14).

Chlorination

Chlorination is presently a commonly used, effective method for removing bacteria and viruses from drinking water. Numerous studies have shown the complete removal of bacteria in drinking water. In seven randomized, controlled trials, chlorination has resulted in reductions of diarrheal disease incidence among users ranging from 22–84% (4). These studies were conducted in urban and rural regions and have included a wide range of users, both adults and children, living in poor regions, and users drinking highly turbid, contaminated water (4). A bottle of hypochlorite solution that treats 1,000 liters of water typically costs approximately 10 cents when using refillable bottles and 11–50 cents for disposable bottles (4). Water bottles can increase this price therefore refillable bottles are recommended. A major drawback to this method is the risk of potential long-term health issues, such as colorectal cancers (5), as well as the lower disinfection effectiveness in turbid waters and the lower protection against protozoa.

Arsenic treatment

In many part of the developing countries, arsenic contamination is becoming a serious and emerging critical concern. To address that, we analyzed various techniques regarding arsenic removal technologies (36). One of the technologies that is designed to remove arsenic from drinking water, oxidation filtration, removes arsenic from iron and manganese containing groundwater (16). This process requires less investment and has a low operating cost which is why this technology is widely accepted by developing countries (16). However, other technique such as precipitation/co-precipitation, which are used to treat both drinking water and wastewater, has a higher cost but is very effective at treating arsenic and other pollutants (16). There are other low cost technologies such as ion exchange, filtration, and adsorption, as well as bioremediation which require training and education for proper maintenance and operations (16).

Discussion

SODIS can be used in any developing countries or areas as long as there is a regular access to sunlight. Since this method can only treat waterborne pathogens, areas that have high chemical contaminations would not be able to use SODIS. Based on authors’ experiences, some of the prime areas that can adopt SODIS include, but not limited to, Chad, Kenya, Bangladesh, Botswana, and Pakistan. This method can be used almost anywhere ranging from rural villages to urban centers. This can also be used during floods and droughts to store and purify water. Overall, SODIS is an inexpensive and effective method that is constantly available for developing countries. There is still a need to pretreat water that appears turbid. In addition, there is a lower user acceptability of this method due to the limited amount of water that can be treated at a time, especially when the climate conditions are not suitable for the method to work. SODIS also requires a large supply of intact, clean, and properly sized plastic water bottles. It is clear that SODIS can be used in Asian and African countries, where there is enough sunlight and where water scarcity is an issue (16).

Biosand can work on turbid water however, it is more expensive than SODIS and requires that someone be present nearby to regularly change the top layer of sand. It improves the microbiological quality of drinking water. In laboratory testing, this method consistently reduces bacteria by about 81–100 percent and protozoa by 99.98–100 percent. It removes less than 90 percent of indicator viruses (23). Biosand may pose a threat for further contamination if the sand is not changed regularly. This may not be an ideal method for treating water since water can become more contaminated resulting in an increase in health complications and deaths.

Due to involved cost, membrane technology can be difficult to integrate culturally into a community in developing countries even though their proven effectiveness in treatment. Ceramic Filtration, however, has an advantage over SODIS and membrane technology in the fact that it can be integrated with the cultural aspects of numerous countries. Laboratory testing has shown bacteria is mostly filtered through the filter’s small pores however colloidal silver is necessary to inactivate 100 percent of the bacteria (28). However, it is unknown if the filter inactivates viruses or removes them. For instance, ceramic pots are already used in Chad, where the ceramic filters fit well with the culture. Ceramic filters cost more on average than SODIS, but this cost could potentially decrease over time. These ceramic filters may also have the potential to be produced locally, which may provide and stimulate the local community to decrease the cost.

Slow sand filters may not completely remove (can remove 99% of bacteria) all of the infection-causing bacteria in contaminated water, but they will often remove enough pathogens to a level that is safe enough to drink and will be tolerated (28).

Although chlorination is typically used to filter drinking water, it can have potential long-term effects on health due to the chlorination by-products (e.g., trihalomethane). Some drawbacks of this method include lower protection against protozoa, lower disinfection effectiveness in turbid waters, potential taste and odor objections, and ensure the quality control of the hypochlorite solution (37). Some benefits include, proven reduction of most bacteria and viruses in water, residual protection against recontamination, general ease-of-use and acceptability, proven reduction of diarrheal incidence, and it is a cost-effective method. Even though chlorination is usually the most widely accepted method for treating drinking water, it may not the most ideal method since there are other complications, such as the cost of disposable water bottles, the risk of over chlorinated water, and the risk of potential long-term health effects.

Arsenic contamination is a well-known problem in many developing countries. Not all of these countries have centralized water to treat the arsenic therefore other measures, such as ion exchange and adsorption, need to be educated at the local-levels. These countries can use mainstream and social media to train their citizens. This also may not be the ideal method for treating water due to the amount of training needed and specific guidelines that need to be followed in order to ensure proper usage.

In developing countries, budget is certainly a limiting factor for adopting specific water treatment methods. For instance, membrane filtration can be the universal filter, but membrane filtration can be quite expensive. A way to make the membrane filtration more cost-effective, is to create a membrane using locally available resources in the area (38). This can significantly reduce the cost of membranes because they would not have to be made/imported from another country. Presently, SODIS appears to be the most practical method of treating water however, membrane filtration is becoming a more practical method than SODIS. As time progresses, membrane filtration will likely become the most effective means of water filtration. Membranes can be designed to filter not only waterborne pathogens but also arsenic, fluoride, and other chemicals as well. The knowledge required to create membranes cheaply is the major obstacle holding back membrane filtration from becoming more widespread. Membrane filtration will likely become more prevalent in third world countries if membranes will be created at a lower cost and knowledge is spread regarding the impact it will have on improving health.

Conclusions

Waterborne diseases are one of the top public health/safety concerns, urging a necessity for advanced/affordable water treatment technologies in developing countries. There are several water treatment technologies such as biosand filtration, membrane filtration, chlorination, SODIS, and ceramic filtration. Each of these, as well as many other methods, have had a positive impact on treating water and decreasing health complications however, they also have drawbacks. Based on our review, the most versatile and cost-effective method for treating water at this time is SODIS. It requires little technical knowledge to operate and can be utilized easily. It is also very cost-effective because the only resources required are plastic bottles. SODIS also has a long lifespan due to the nature of the plastic bottles. Currently, SODIS, as well as chlorination, is widespread, therefore continued use prevents having to redistribute a new type of filtration. However, as time progresses, membrane filtration will likely become the most effective means of water filtration. Membranes can be designed to filter not only waterborne pathogens but arsenic, fluoride, and other chemicals as well, which is an attribute that SODIS may achieve as it only filters pathogens and not chemicals. All of the water treatment technologies discussed have an impact on improving global public health. We must continue improving these water treatment technologies to ensure that everyone has access to clean water. This will have a major impact on reducing the number of people worldwide who are affected with water-borne illness and morbidity.

Acknowledgments

Funding: None.

Footnote

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at http://dx.doi.org/10.21037/jphe.2018.06.02). UH serves as an unpaid editorial board member of Journal of Public Health and Emergency from Jan 2017 to Dec 2019. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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