Vast swarms of miniature robots are coming -- and they might be the answer to scrubbing our waters clean of lead.
"Microbots" smaller than the width of a human hair could be highly effective and cost-efficient tools for removing lead and other contaminants from industrial wastewater, according to a new study published in the journal Nano Letters last month.
In the space of a single hour, the study showed, self-propelled microbots could remove up to 95 percent of lead from water.
Lead is commonly found in wastewater from mines or factories that make batteries and electronic devices, and can pose a serious risk to public health, as the water crisis in Flint, Michigan demonstrates. Industrial activities can also contaminate water with arsenic, mercury and other metals.
Heavy metal pollution can cost big cities billions of dollars a year, said Samuel Sánchez, co-author of the study and ICREA professor at the Institute for Bioengineering of Catalonia in Spain. He added that current methods to remediate the pollution are either expensive or produce secondary waste.
Sánchez said his team envisions using the microbots "for the pre-treatment of industrial wastewater before dumping into a river." At the moment, the bots aren't ready for open water, so they would swim in "a controlled environment, such as small reservoirs, pipes, containers."
The microbots are composed of three layers. The outer layer is made of graphene oxide to absorb heavy metals, while a middle layer made of nickel makes the microbots ferromagnetic so they can be steered by external magnets. A platinum inner layer reacts when hydrogen peroxide is added to the wastewater, producing a stream of oxygen micro-bubbles that the microbots eject to propel themselves in the water.
Once the bots finish their clean-up work, external magnets collect them for reuse. The heavy metal contaminants can also be recycled, making the process even more efficient.
"This technique is scalable, so we envision that small companies could use microbots to decontaminate their water in case they cannot afford bringing their waste water to decontamination plants," Sánchez said. "In my opinion, we should see first commercial use of self-propelled microbots in the next couple of years."