Engineering Water Filtration Devices

Students apply their knowledge of groundwater and aquifer contamination to design a water filtration device that mitigates negative impacts on the environment by cleaning polluted water.

• According to some estimates, more than 1 billion people are affected by polluted water.
• Filtration is the process of separating solid matter from a fluid by having the fluid pass through the pores of another substance, called a filter.
• Engineers can use what they know about Earth’s water, aquifers, and pollution to design solutions that solve the problem of polluted water.

• How can an aquifer become polluted?
• Why is polluted groundwater a problem for people?
• How can engineers address the growing problem of water pollution?
• Why might engineers who are trying to solve the problem of polluted water research the properties of an aquifer?
• How can engineers apply what they know about aquifers to help them design a solution to water pollution?
• What kinds of materials scientists could use to help them mimic an aquifer?
• Why does the speed that water can move through certain materials need to be considered when designing a water filtration device?

Misconception: There is the same amount of groundwater everywhere on Earth.

Fact: Groundwater is distributed unevenly around the planet. Its presence depends on many factors, including the amount of precipitation that falls and the properties of the rock that make up a region—specifically whether the rocks are porous and permeable.

Ecosystem service : the positive benefits that an ecosystem provides to people

Filtration : the process of separating solid matter from a fluid by having the fluid pass through the pores of another substance, called a filter

Permeability : the ease with which substances such as water move through a material

Porosity : the amount of space between particles in a substance

Water pollution : the contamination of natural water bodies by substances that harm organisms and the environment

The Problem of Water Pollution

In 2011, a team of students and engineers traveled to a small town in Bolivia in South America. Remember that engineers are different from scientists. Scientists gain knowledge from experimentation. Engineers apply that knowledge to create new technologies that solve problems.

The Problem of Polluted Water

The team of students and engineers had a problem: how to provide clean drinking water for two small villages in Bolivia.

Similar problems face engineers around the world as the human population continues to grow. According to some estimates, more than 1 billion people around the planet are affected by polluted water.

Engineering a Solution to Water Pollution

Once the team of students and engineers in Bolivia identified their problem, they did background research. They learned that groundwater is some of the cleanest water on Earth. This is because the particles of rock that make up aquifers act as a natural filter. As water moves from Earth’s surface underground, the water is filtered. Filtration is the process of separating solid matter from a fluid by having the fluid pass through the pores of another substance, called a filter.

Because they act as filters, aquifers provide an ecosystem service. Ecosystem services are the positive benefits that an ecosystem provides to people. By the time water has moved through the aquifer, many pollutants have been removed.

Coffee Pots and Aquifers

Picture a coffee pot. When you pour hot water into the pot, it mixes with coffee grounds. A coffee filter traps the coffee grounds but allows liquid coffee to flow through. Coffee filters are semi-permeable. They have pores that are large enough for water to travel through, but small enough that coffee grounds cannot move through them. The coffee grounds get trapped in the filter.

Aquifers work in the same way. Some aquifers have cleaner water than other aquifers because they are better able to filter out contaminants as water moves through them. Scientists have to look at an aquifer’s properties, and the porosity and permeability of the rock, to figure out how well it can filter water.

Design Possibilities

After they researched their problem, the team in Bolivia surveyed the materials available for this problem. They had to analyze the pore size of any material used to filter out pollutants. The smaller the pore size is, the purer the water will be. This is because everything that cannot fit through the pores will be filtered out. However, water flows more quickly through larger pore sizes. Any filtration technology would need to balance the need to filter out pollutants with the need for the water to move through it.

The team next brainstormed possible solutions that could solve the problem. After weighing the pros and cons of various ideas, they decided on a solution. Their solution used sand and gravel to filter the water. They drew a hand-sized scientific diagram of the prototype. They used their diagram to build a prototype.

Once they had their prototype, they were able to test it. The goal of testing is to find out how well the prototype solves the problem. The team wanted to know how well their mixture of sand and gravel filtered out pollutants. They tested the water purity after it filtered through the prototype.

They then analyzed their data to see how well their prototype filtered water. They used this analysis to determine whether the technology should be refined or replicated. After several tries, they designed a technology that effectively filtered out the majority of water pollutants, leaving behind water that was safe to drink.

This kind of engineering solution is common in communities around the United States. Many communities have designed filtration basins that use sand, gravel, soil, or other porous material to filter the water. Sand is the most common filter material, although some filters have used wood chips and even leaf mold to purify water.

In this lesson, students engineer prototypes to solve the problem of aquifer contamination by engineering a water filtration device to treat samples of simulated polluted stormwater runoff. First, students come up with possible solutions to the problem, and then build a prototype of the solution they believe would have the greatest likelihood of success. Then, they use the data from their prototypes to analyze how well their prototypes solved the problem, and to revise their design to improve the cost and/or purity of the filtered water.