Off-the-Grid Water Purifier Inspired by Pufferfish

Innovation: Academia

Princeton University

2021

Image: Vlad Tchompalov / Unsplash / CC BY SA - Creative Commons Attribution + ShareAlike

Capture, Absorb, or Filter Organisms

Many living systems must secure organisms for food. But just as one living system must capture its prey to survive, its prey must escape to survive. This results in capture and avoidance strategies that include trickery, speed, poisons, constructed traps, and more. For example, a carnivorous plant called the pitcher plant has leaves formed into a tube that collect water. Long, slippery hairs within the tube face downward. When insects enter the tube seeking nectar, they lose their footing and slide inside, unable to climb out and escape being eaten and digested by the plant.

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Capture, Absorb, or Filter Chemical Entities

Living systems often require chemical elements and chemical compounds, including complex sugars, proteins, and odor-making compounds, to perform critical activities. These compounds exist in various states–solid, liquid, and gas–and are ubiquitous in soil, water, and air. This requires that living systems not only have ways to capture, absorb, or filter them, but also ways to differentiate among them, selecting those that are valuable or harmful. For example, mangrove trees live with their roots in salty water and sediments. Various mangrove species have different strategies for removing salt from the water they take in so that their tissues can use the fresh water.

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Capture, Absorb, or Filter Solids

Some living systems must secure solid particles such as sediment, usually to keep the particles from hindering their health or activity. The most common way in which they do this is through filtering. To be effective, a filtering system must be appropriate to the sizes of solid particles to be captured and must capture only what is needed. It must also be effective in the appropriate media–air, water, or sometimes solids like soil. An example is mangroves, which are trees that grow along ocean coasts. Their root system slows down and settles sediment out of the water, building up soil to support the mangrove ecosystem.

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Water purifier from Princeton University is made of a hydrogel that expands and contracts to extract contaminants from water.

Benefits

Reduced costs
Non-toxic
Efficient

Applications

Water filtration
Water treatment

UN Sustainable Development Goals Addressed

Goal 3: Good Health & Wellbeing
Goal 9: Industry Innovation & Infrastructure

The Challenge

Water is essential for human survival, and access to clean drinking water is critical for good health. Contaminated drinking water can cause numerous health concerns, namely exposure to bacteria and viruses. However, wastewater treatment systems can be expensive to build and require specialized materials, making them inaccessible in many places. Moreover, the impacts of climate change will soon make it harder than ever to acquire clean water in vulnerable locations, endangering human health and straining vital energy resources. Therefore, any technologies that extract potable water from tainted sources must be environmentally friendly.

Innovation Details

The solar absorber gel (SAG) consists of three layers, resembling a large sponge that soaks up water while removing pollutants like pathogens, lead, and oil. The innermost layer is composed of a sponge-like elastic gel, called a hydrogel. The hydrogel holds water between its long entangled polymers, and when heated, the structure contracts, squeezing out excess water. Surrounding this hydrogel is a layer of melanin-based molecules that absorb sunlight to provide energy to the purifier. This layer is also capable of removing heavy metals and organic dyes through chemical bonding, doing so as excess water is squeezed out of the inner hydrogel. Lastly, the outer layer is a filter layer that blocks impurities and pathogens. Altogether, the purifier exhibits efficient production of high-quality water in remote locations.

Biomimicry Story

The team was inspired to create this condition-based water-holding gel by the condition-based water retention of pufferfish. When in danger, pufferfish take in water to enlarge their bodies and raise their spines, making them appear larger and more threatening to predators. Once the threat is gone, the fish release the water and return to a smaller form. Similarly, the solar absorber gel takes in water when relatively cool, and then releases it when slightly warmed by the sun.

See Related Strategy

Biological Strategy

Inflating for Protection

Porcupine fish

The skin of a porcupine fish protects from predators via embedded spines that erect when the fish inflates using sips of water.

References

Journal article

A Bioinspired Elastic Hydrogel for Solar‐Driven Water Purification

Advanced Materials

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