Environmental, Health and Safety

Treating Water Using Nails? Now That’s a Sharp Idea!

12 January 2016

Filling a glass of clean water from your kitchen sink is easy and something that many people take for granted. However, the people living in the community La Salitrera, a small agricultural community in the state of Guanajuato, Mexico, did not have such a luxury.

A glass of water may look clear and clean, but contaminants invisible to the human eye may lurk. Such was the case for the residents of La Salitrera. The community of approximately 100 people draws its drinking water from a groundwater well. Water is pumped from the well into two storage tanks and then distributed to the households of La Salitrera and those of six other communities that share the water system. Water quality testing revealed that the water supply contained arsenic at a concentration twice the World Health Organization recommended limit of 10 micrograms per liter. The water also contained bacterial pathogens that can cause diarrheal diseases.

The arsenic in La Salitrera’s water is naturally occurring and dissolves into the groundwater over time. Arsenic is toxic to humans, and chronic consumption can lead to skin lesions, respiratory problems, cardiovascular disease and cancers of the skin, bladder and lung. Children are especially susceptible to the effects of arsenic exposure.

Community Driven Partnerships

In 2010, the Utah State University (USU) Chapter of Engineers Without Borders (EWB) USA stepped in to help solve the water quality problem in a way that was both functional and practical. EWB-USA partners with communities to help meet basic human needs in some of the toughest areas of the world. With 300 student and professional chapters across the United States, EWB-USA’s community-driven projects span 45 countries on five continents. Project teams focus on sustainable, long-term solutions that are based on relationships built with communities. Teams commit to a five-year partnership with a community to help ensure that the community is properly trained on how to maintain their project.

(Click to enlarge.) Typical construction of a concrete biosand filter using sand and gravel as filter media. Image source: Center for Affordable Water and Sanitation Technology (Click to enlarge.) Typical construction of a concrete biosand filter using sand and gravel as filter media. Image source: Center for Affordable Water and Sanitation Technology Rather than just build a drinking water system, EWB-USA volunteers commit to teaching communities how to build and maintain these systems themselves. EWB-USA has a staff of project engineers who oversee quality control for each volunteer-led project team. These engineers guide each project through a technical approval process. Indeed, the USU Chapter project with La Salitrera went through this technical approval process and the team began work in 2010 to improve drinking water quality for the community.

Local Problem, Local Solution

Treating drinking water at the source and then distributing it to households is a typical treatment solution in the United States. But this type of project isn’t so easy for a small rural community without adequate materials or resources to maintain it. Instead, the La Salitrera community and the USU team came up with a novel, localized solution to treat the drinking water.

The USU volunteers traveled to the community several times to establish a relationship with residents, assess the problem and work with leaders to determine the best water treatment option. Together the volunteers and the community decided on biosand filters. Similar filters are installed in many communities to help remove bacterial contaminants via the use of layers of sand and gravel. A biological layer of microorganisms (also called a biofilm) develops at the sand surface, which contributes to water treatment.

Because typical biosand filters do not remove arsenic from water, the design for the Mexico project was modified. It used local materials such as concrete, washed sand, PVC pipes and rusty nails, a somewhat surprising addition. The nails removed arsenic from the water by forming a precipitate in which the arsenic sits on the surface of the iron, thus remaining in place and rather than moving through the filter. Inside the filter, the nails are placed on top of a diffuser plate which itself sits on top of the sand and gravel. Water passes over the nails, through the diffuser plate, and then through the sand and gravel filter. Both arsenic and bacterial pathogens are removed as a result.

Community members helped to build the system, and ultimately will be responsible for their maintenance and operation. Image source: USUCommunity members helped to build the system, and ultimately will be responsible for their maintenance and operation. Image source: USUIn the summer of 2014, USU students and mentors traveled to La Salitrera with the goal of constructing three filters in 10 days. With the community’s help, they built twice as many filters as planned, says team lead Anellise Reynolds. Community members stopped their normal daily work duties to help build the filters alongside the volunteers. It was back-breaking work as large amounts of sand and gravel were gathered from a nearby river and hauled to the community.

“It was exhausting but totally worth it,” says Reynolds. The La Salitrera community now has the resources and materials to construct filters for the remaining households in the community.

Not Without Challenges

Designing a water treatment system may seem like a routine task for engineers. But in a rural community like La Salitrera, things aren’t always cut and dry. Nathan Stacey, a mechanical engineering student at USU and project volunteer, says that unexpected challenges may arise.

“We had to work with the community and explain that drinking water contaminated with arsenic has long-term health effects,” he says. In particular, because they have been drinking the well water for several years and haven’t seen any health effects so far, it was hard for some to understand why water treatment was necessary.

Project success also depended on good communication and education on how to properly use and maintain the filters. For example, water must be cycled through the filters every day to maintain the biofilm layer on the sand. Training on this aspect was particularly important.

“No matter how good our ideas were, they had to be communicated to the community members for them to be effective,” says Nathan. The USU volunteers held community meetings to train residents on how to use and maintain the filters. The volunteers also performed home visits to work one-on-one with families. People were more comfortable asking questions about the filters during the home visits, Nathan says. “The community members need to feel comfortable maintaining and building the filters themselves for the project to be successful,” he says.

Another challenge was the difference in materials available to construct the filters in Mexico versus the United States. The sand and gravel in Mexico were of different sizes, the cement wasn’t necessarily the same quality and the iron filings used in the laboratory for arsenic removal weren’t easily available on site. Because of these factors, the filters didn’t perform the same as those built in the lab and adjustments had to be made.

For one thing, rusty nails were used in place of iron filings. The same arsenic binding reaction occurs on rusty nails, but it became apparent that a greater mass of nails was required because the nails have a lower surface-area-to-mass ratio than iron fillings. The volunteers made adjustments using the materials available and built filters that performed at the desired level.

Looking Toward the Future

Now that the filters have been constructed, the La Salitrera water filtration project is in the monitoring phase. The USU Chapter returned in 2015 to assess the state of the project and to determine whether more training was necessary. The Chapter also hopes to start another project in the village or with another community nearby.

La Salitrera is typical of many communities around the world that are challenged with meeting basic needs. These types of projects require many different skills to be successful. It is important to keep an open mind and realize that the local community needs to fully understand the issues they are facing. Ultimately, community members must be involved in choosing the type of solution that will work best for them.

Powered by CR4, the Engineering Community

Discussion – 0 comments

By posting a comment you confirm that you have read and accept our Posting Rules and Terms of Use.
Engineering Newsletter Signup
Get the Engineering360
Stay up to date on:
Our flagship newsletter covers all the technologies engineers need for new product development across disciplines and industries.

Upcoming Events