Engineers at University of Cincinnati in Ohio developed a nanoscale filter powered by sunlight that can clean biochemical compounds, such as antibiotics, from lakes and rivers. Environmental engineering professor David Wendell and Ph.D. candidate Vikram Kapoor published their findings online last week in the journal Nano Letters (paid subscription required).
The presence of antibiotics from residential, industrial, and agricultural wastes poses risks to water sources by breeding bacteria resistant to antibiotics as well as killing helpful microorganisms in the food chain. Antibiotics in surface waters can also degrade the endocrine systems of fish, birds, and other wildlife.
Current water filters use activated carbon that requires external energy sources for operation, as well as high temperatures to burn off the antibiotics. Activated carbon also grabs all contaminants in the water, which leads to frequent clogging of the filters.
Wendell and Kapoor created a nanoscale filter — 1 nanometer equals 1 billionth of a meter — made of two bacterial proteins that perform the filtering and power functions. The filtering work is done by the gene acriflavine resistance B (AcrB) that protects bacteria by pumping out harmful substances. “These pumps are an amazing product of evolution” says Wendell. “They are essentially selective garbage disposals for the bacteria.” In these filters, the AcrB proteins pump the antibiotics out of the water for collection.
In addition to filtering antibiotics from water the technology makes it possible to extract the filters and recycle the collected antibiotics. A second protein, delta-rhodopsin — a light-enabled protein that responds to sunlight in a process similar to photosynthesis — provides the filter’s energy source.
The Nano Letters paper reports on lab tests of the technology against activated carbon, where the nanoscale protein filters absorbed 64 percent of antibiotics in surface waters, compared to 40 percent absorbed by the activated carbon filters. Wendell and Kapoor also tested the technology on water from the Little Miami River. In these tests, the researchers were able to extract the human and veterinary antibiotics ampicillin and vancomycin, as well as the compound ethidium bromide used to stain nucleic acids for detection, but requires careful handling and disposal.
“So far, our innovation promises to be an environmentally friendly means for extracting antibiotics from the surface waters that we all rely on,” says Wendell. “Next, we want to test our system for selectively filtering out hormones and heavy metals from surface waters.”
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