Just like humans, wastewater treatment plants can get sick through viral attacks. Research from Chalmers University of Technology, Sweden, reveals the implications for the local environment if a plant gets ‘sick’.
In the sewage industry, the ‘work’ of wastewater plants is often executed by microscopic bacteria. Biological processes carried out by these bacteria turn the wastewater into cleaned water that is safe to discharge into the environment. Essentially the bacteria break down the pollutants and purify the water, keeping the plant running efficiently.
“A large treatment plant has billions of bacteria that work in a treatment process called ‘activated sludge’,” says Oskar Modin, Professor at the Department of Architecture and Civil Engineering at Chalmers.
“The bacterial communities are constantly exposed to viruses that infect them, so the question we asked ourselves was whether the process can periodically be more exposed and what happens then.”
Researchers measured the concentration of virus particles released from four different wastewater treatment plants in Sweden and compared this with how much organic carbon was released at the same time. This relationship between virus and effluent quality is a first step in understanding the impact of a viral infection on a treatment plant.
‘Sick’ wastewater plants might affect aquatic ecosystems
The study showed a clear relationship between virus concentration and the amount of dissolved organic carbon present in the effluent water. This is because viruses could affect the concentration in two ways, firstly because they themselves contain carbon and secondly because they rupture host bacteria cells, causing carbon to be released.
“When we measured virus particles in the water, we found a connection between viruses and organic carbon – when there was more of one there was also more of the other,” says Oskar Modin.
More dissolved organic carbon in the effluent water means that more oxygen is consumed by microorganisms in the surrounding bodies of water where the effluent is discharged.
This could have potential negative impacts on nearby aquatic ecosystems. Therefore, tough regulations are in place for wastewater treatment plants to reach low concentrations of biodegradable organic carbon in their effluent. A small increase of organic carbon in the plant can also lead to increased resource consumption, including money, energy and materials in processes for disinfection and pharmaceuticals removal, which are implemented at wastewater treatment plants in some parts of the world. Organic carbon in the water affects the efficiency of these processes.
No infection risk for humans
Viruses are dependent on a host to replicate. Since biological wastewater treatment processes have a high concentration of active bacteria that can serve as hosts, there will be a lot of viruses capable of infecting those bacteria. This leads to a net increase in virus particles as the wastewater moves through a plant.
Oskar adds, “Viruses are often specialised in a certain species, which means that humans and bacteria cannot be infected by the same virus. So, the viruses ‘generated’ in a wastewater treatment plant do not infect humans, but only affect microbial communities. One possible way to influence the number of viruses in treatment plants could be to adjust the way the treatment plant is operated. We saw differences between the treatment plants in the study, which we believe may be related to the design or control of the biological treatment processes.”
References
The scientific article “A relationship between phages and organic carbon in wastewater treatment plant effluents” published in Water Research X was written by Oskar Modin, Nafis Fuad, Marie Abadikhah, David l’Ons, Elin Ossiansson, David J. I. Gustavsson, Ellen Edefell, Carolina Suarez, Frank Persson, Britt-Marie Wilén
The researchers are active at Chalmers University of Technology, University of Connecticut, Gryaab AB, VA SYD, and Lund University
The study behind the paper was financed by Svenskt Vatten through VA Teknik Södra, and involved wastewater treatment plants in the Swedish municipalities of Lund, Malmö, Kalmar and Gothenburg. Funding was also provided by the Swedish Research Council for Sustainable Development (FORMAS).
