A Rice University study of “superbugs” found at two wastewater treatment plants in northern China should alert operators at U.S. wastewater facilities how dangerous bacteria can enter the treatment system. The study’s author urges improved safety measures when it comes to antibiotic-resistant bacteria.
Joint research by scientists from Rice, Nankai and Tianjin Universities discovered superbugs at two Chinese wastewater plants carrying New Delhi Metallo-beta-lactamase (NDM-1), a multidrug-resistant gene first identified in India in 2010. Tests revealed significant levels of NDM-1 in the effluent released to the environment and even higher levels in dewatered biosolids applied to soils. The findings reaffirmed researchers’ beliefs that these bacteria were not only escaping purification but also breeding and spreading their dangerous cargo, which poses significant health risks.
“The most important thing we can do is recognize that sewage treatment plants can serve as a point source and breeding ground for the discharge of superbugs,” says Dr. Pedro Alvarez, Rice University professor and chair of civil and environmental engineering. Alvarez led the study, which was published in the December issue of the American Chemical Society’s journal, Environmental Science and Technology Letters.
“What’s new about our study is that it shows that not just any kind of antibiotic-resistant bacteria is present in wastewater treatment plants but that some of them are superbugs,” he says. “For every one that comes in, four or five come out, leading to infections that cannot be treated.”
The implications for operators are clear: Follow commonsense housekeeping rules and avoid direct contact with disease-causing agents. This includes washing hands, wearing gloves and goggles and other precautions.
Alvarez pointed to two things plants can do to avoid the propagation of antibiotic-resistant bacteria. First, is to improve disinfection. In China, where effluent is chlorinated this means increasing the dose or lengthening contact times. In the United States, will use more ultraviolet technology and they’ll adopt advances in disinfection using nanotechnology in combination with UV, which are extremely effective and easy to implement by minor retrofitting.
For example, if a plant already has a UV disinfection unit with a contact time of 30 seconds or a minute, it’s easy to retrofit it and introduce a nano photo-catalyst such as titanium dioxide. Water is converted into hydroxyl-radicals and turns the disinfection reactor into an advanced oxidation reactor, which kills bacteria and viruses that would otherwise propagate.
“If a facility has a disinfection unit that relies on UV, it’s simple to add some floating beads that are coated with nano photo-catalysts,” Alvarez says. “By doing so, you turn the unit into a fluidized bed reactor that both disinfects and serves as a oxidation treatment process that destroys the endocrine disruptors, pharmaceuticals and other recalcitrant compounds that are breaking through. Such a polishing unit wouldn’t cost that much.”
Superbugs are as great a problem in the United States as is in China or India, according to Alvarez. That’s because the unrestricted use of antibiotics is more widespread in Asia than in the United States, where it’s very difficult to get antibiotics without a doctor’s prescription. Bacteria develop antibiotic resistance when antibiotics enter wastewater treatment plants. Another factor is medical tourism, where people who travel to another country for cheaper medical procedures. They’re typically given antibiotics, which often end up in water supplies. Many of those who have gotten superbug infections have been tourists.
Alvarez cited previous studies that show regular antibiotic-resistant bacteria can be discharged from wastewater treatment plants. These include a study done by Professor Tim LaPara in Minnesota showing that their wastewater treatment plants were discharging antibiotic-resistant bacteria into the Duluth River. Also, Amy Pruden, a professor at Virginia Tech’s Department of Civil and Environmental Engineering, has conducted studies that have identified antibiotic-resistant bacteria not only in wastewater treatment plants but also in drinking water treatment plants.
“While I don’t think superbugs are that much of a problem in the United States, we have to recognize that instances of antibiotic-resistant bacteria are on the rise,” Alvarez says. “We need to understand where the reservoirs of antibiotic-resistant bacteria are hiding when they’re not harming us and where they propagate. This study underscores the importance to control them in wastewater treatment plants.”