- The new wood membrane can remove water contaminants using far less energy than commercially available membrane.
- Its thermal efficiency, water flux, sustainability, and scalability make it a perfect material for membrane distillation applications.
According to the United Nations’ report, about 3.6 billion people (half of the world population) are currently living in potential water-scarce areas. This figure is expected to increase to 5 billion by 2050. Climate change and rapid urbanization will make the situation even worse.
We currently use the desalination process to reduce water stress. This includes extracting drinkable water from various contaminated sources, such as wastewater, brackish groundwater, and seawater. Recent advances in nanotechnology and advanced manufacturing have boosted the development of desalination.
However, current water desalination processes are still not efficient. They consume a lot of energy and require specialized engineering. One of the emerging thermally driven separation process named Membrane Distillation holds great potential for high-salinity water desalination using renewable source of energies.
The membranes available in the market are made of synthetic polymers that provide thermal efficiency of up to 60%. But since these polymers are derived from petroleum products, they are quite expensive and raise several environmental concerns.
To tackle this problem, researchers at Princeton University have come up with a new membrane directly fabricated from natural wood material instead of plastic. This wood can be formed into thermally insulating bulk material with low thermal conductivity, superior mechanical strength, and extremely high porosity. These properties make it an ideal material for membrane.
The Wood Membrane
The conventional water filtration systems require high-pressure pumping to squeeze the water through a thin polymer film, which has tiny pores that filter out water contaminants. Usually, these systems consume a significant amount of energy to generate high pressures.
Reference: ScienceAdvances | DOI:10.1126/sciadv.aaw3203
The new membrane, one the other hand, is made of a thin piece of American basswood. It is chemically treated to strip away undesired fibers within the wood and to make the surface slippery for water.
The membrane is heated from one side so that water gets vaporized when it flows over that side. The vapors than gradually travel through the membrane’s pores toward its colder side, leaving the salt behind. Eventually, the other side (the colder one) gives fresh, cool water.
The hydrophobic nanowood membrane | Courtesy of researchers
Since you don’t have to boil all of the saltwater (only a thin layer of water needs to be heated at a time), the process takes less energy. And unlike other commercial membranes, it does not use fossil fuel-based materials.
The new system is capable of filtering out 20 liters of water per square meter of membrane every hour. It is not as fast as other polymer membranes, but the process can be sped up in the near future.
Researchers didn’t have the tools to make their membranes as thin as required: it is only 500 micrometers thick, whereas other polymer membranes are usually 130 micrometers thick. The functional layer of the wood membrane is only one micrometer thick, while the rest is to make the structure hard enough so that it doesn’t break easily.