Water filtration is an important step in drinking water infrastructure and wastewater treatment. But filters don't last forever — bacteria can attach to filtration membranes (structures that separate contaminants from water) and form biofilms in a process called biofouling. Biofouling reduces membrane lifetime and water quality. 

Water filtration membranes often have a mesh, called a spacer, that separates different layers of the membrane from each other. Bacteria can attach to this spacer. One way to reduce bacterial adhesion to the spacer is by making it water repellent, or superhydrophobic. In a study published in ACS Applied Bio Materials, scientists used candle soot to create superhydrophobic membrane spacers and keep biofouling cells away. 

Researchers from the Zuckerberg Institute for Water Research in Israel coated the filtration spacer with a chemical called polydimethylsiloxane. They then held the spacer over a candle flame until it was covered with particles of soot. To test the effectiveness of the spacer, the researchers treated them with two species of bacteria and one species of diatom. 

The common bacterium Pseudomonas aeruginosa, and the salt water species Cobetia marina and Navicula perminuta could not form biofilms on the soot covered spacers, unlike on uncoated spacers. These results demonstrate a simple way of creating biofouling-resistant membrane spacers cheaply using household candles. If this technique can translate to the water purification industry, superhydrophobic soot membranes could ead to less waste and lower filtration costs.