What is the incidence of super-resistant bacteria in wastewater treatment plants?

An international team of researchers from the Chinese Academy of Sciences and CREAF has suggested measures for reducing the risk of antimicrobial-resistant pathogens and bacteria spreading via wastewater.

There are many kinds of pathogens on Earth, including viruses, bacteria, fungi and protozoans, which infect humans, animals and/or plants. Over the last few decades, scientists have warned that certain pathogens are becoming super pathogens or superbugs, whose ability to resist antimicrobials and cause deadly infections makes them a real, emerging threat to global health.

Where can super pathogens be found and by what means do they spread? According to researchers from the Chinese Academy of Sciences and CREAF, writing in the article 'Super pathogens from environmental biotechnologies threaten global health', published very recently in the renowned journal National Science Review, wastewater treatment plants in which environmental biotechnologies are used (i.e. the vast majority of them) should be paid special attention among the various potential sources of super pathogens.

The COVID-19 pandemic has shown how viruses spread and can be detected in wastewater treatment systems, but little has been done to eliminate the health threat super pathogens pose. To achieve that, we need to understand that there is only one health — human, animal and ecosystem health are one and the same — and that the environment, animals and people are all part of a microbial cycle.

JOSEP PEÑUELAS, CREAF-based CSIC researcher.

Superbug incubators

Wastewater treatment plants that operate with environmental biotechnologies (EBTs) use microbes to degrade pollutants in a cost-effective manner. The article states that EBTs are valuable for purifying wastewater but entail risks as they are incubators for pathogens and antimicrobial resistance genes, making them superbug hotspots.

In the long-term operation of such treatment plants, pathogens multiply, transfer genes to one another, and evolve to withstand and survive the different pollutants in wastewater. Unfortunately, that also enhances their resistance to antimicrobials.

“Microbes use very similar strategies to survive exposure to pollutants and to resist antimicrobials,” explains CREAF-based CSIS researcher Josep Peñuelas. “So, in the long-term operation of such treatment plants, pathogens multiply, transfer genes to one another, and evolve to withstand and survive the different pollutants in wastewater. Unfortunately, that also enhances their resistance to antimicrobials.”

Transmission to humans

Super pathogens from wastewater treatment plants are mainly transferred to humans through accidental contact with reclaimed water (treated water discharged from a plant) or with bioaerosols (water microparticles that become airborne via bubbles or due to the movement of water), as well as through foods contaminated as a consequence of crops being irrigated with treatment plant effluents. The article’s authors have called for the research community, industry and governments to cooperate closely to minimize the likelihood of such contact and reduce the global health threat it entails. “Know yourself and know your enemy and you will never be defeated, as our Chinese colleagues say,” remarks Peñuelas.

Scientific recommendations

The article discusses different ways of reducing the risks involved. One approach consists of learning more about the evolution of super pathogens in EBT treatment plants worldwide, investigating and monitoring the emission of super pathogens from such plants, and tracking them to see where they end up in different environments. In short, research is necessary to inform the public about contaminated products and environments to avoid and, even more importantly, to help governments supervise the EBT industry appropriately.

The authors appeal to governments to recognize the public health threat super pathogens from wastewater treatment plants pose.

In that regard, the authors appeal to governments to recognize the public health threat super pathogens from wastewater treatment plants pose. Such recognition is a vital first step towards providing guidance for the public, supervising the industry (establishing stricter standards to limit the microbial pathogens plants may emit) and supporting research.

Another approach involves replacing or complementing the technologies currently used to disinfect wastewater with others that not only remove traditional carbohydrates and nutrients but also eliminate super pathogens. Macrophyte-assisted vermifiltration, for instance, is an efficient means of treating wastewater, and the earthworms used can consume and kill pathogens. A further possibility is the implementation of sustainable disinfection processes, such as eBeam technology (which uses electron beams for disinfection and pollutant degradation) or nanobubble technology (which uses tiny, chemical-free bubbles to degrade pollutants and inactivate pathogens).

Global cooperation

Humans are connecting the whole of the planet and our activities can cause mass movements of microbes worldwide, so defeating super pathogens will require joint action from every country. According to the article’s authors, cost-effective EBTs, such as vermifiltration, could be used in low-income countries that cannot afford to construct wastewater treatment plants equipped with expensive new technologies. In high-income countries with complete wastewater treatment systems, current EBTs could be better complemented by sustainable means of disinfection, such as the eBeam and nanobubble technologies. Intergovernmental cooperation, an example of which would be high-income countries providing their low-income counterparts with financial and technological aid, is crucial to the prevention of global pandemics. Furthermore, high-income countries should improve training for scientists and engineers from low-income countries to protect the environment.

Reference article:

Xiao, Y., Zhao, F., Peñuelas, J., Huang, Q., & Zhu, Y. G. (2021). Super pathogens from environmental biotechnologies threaten global health. National Science Review.