Bottoms up: Engineers Without Borders provides clean water to La Salitrera
Jamie Vawdrey, an environmental engineering senior, is used to solving complicated problems in her textbooks.
But from May 9 to 18, Vawdrey’s education went beyond algorithms.
The Utah State University chapter of Engineers Without Borders spent part of their summer vacation in La Salitrera, Mexico building water filters for the community.
“It makes me a lot more interested in studying,” Vawdrey said. “Up until this point, it has been looking at equations, or we just see these things in our textbooks and there’s really no way to apply it. On this trip, we designed the filters using what we learned in school, and then we were actually able to apply it.”
And applying what they learned included building water filters in La Salitrera, because clean water there doesn’t come from a tap.
If community members want water they have two options: river water — which is only available four months of the year — or well water that’s distributed two to three times a week.
Dr. Ryan Dupont, head of the Division of Environmental Engineering at USU and mentor of the Mexico team, said that the river water lacks harmful chemicals, but contains harmful bacteria, and the well water contains arsenic, a potentially deadly metalloid.
“The long-term exposure problems (to arsenic) are linked to things like bladder cancer and liver cancer,” he said. “At the exposure level that exists in that water, there are no toxic effects, but there are long-term effects.”
Consumed for about seven years by locals, the long-term effects of the arsenic-laced well water won’t affect the adults in the community nearly as much as it will the 25 to 30 children, he said.
To prevent these long-term effects from manifesting in the children of La Salitrera, the team built water filters using three layers: sand, fine gravel and coarse gravel all encased in concrete cylinders.sand, fine gravel and coarse gravel all encased in concrete cylinders.
The contaminated water passes through the sand, then the fine and coarse gravel. Iron shavings at the bottom also help to bind left over arsenic and the clean water is pushed through a tube.
The sand is sifted and the gravel is washed by the team and community members, but part of the reason the team uses this water filter model is the low cost of materials
“All of the material, all the gravel and all the sand that we use, it all comes from the local river bed,” Dupont said. “So the only thing they really have to pay for is the concrete.”
But the key to the filter’s success is a thin layer of biological material that collects on the top of the sand, he said.
“It’s called a schmutzdecke,” he said. “It’s sort of like what happens on the bottom of a river when you get a sand layer at the bottom of a river. You get a biological mat that grows on the top of the sand that does a variety of different things. It helps remove the biological contamination of the water.”
Without the film of biological matter, which can only form if two to three gallons of water is poured three to five times a day to keep the sand saturated, the filter is not nearly as effective, he said.
But pouring gallons of water on filters several times a day is not how some members of the La Salitrera community want to do with their water that only comes a few times a week, as mechanical engineering senior Nathan Stacey learned.
“I learned that ideas don’t matter unless you communicate them to others,” Stacey said. “In Mexico, we had to communicate with people why they needed these filters. We had to communicate how to correctly put water into the filters everyday, because they would just store what water they got in cisterns instead. This made it so the filters wouldn’t work like they should, so we had to show them why it was important to pour water in the filters instead.”
Next year, the team will return to La Salitrera to analyze the results from this year’s water filters.
“I think the most worthwhile thing was getting to know the people we were helping,” Vawdrey said. “It was really cool to see that it’s not just going to some people that we don’t know. That we’re not just sending it somewhere foreign without getting to know them.”
—katherine.l.larsen@gmail.com