
Treating wastewater for safe reuse could provide an invaluable freshwater resource. Credit: © 2023 KAUST; Heno Hwang.
Key points:
- During wastewater treatment, bacteria encounter a combination of chemical and physical stressors that affect the transfer of genes between them.
- Researchers found that certain stressor combinations produce a synergistic increase in the gene-transfer rate, while others reduce it.
- The study’s findings can inform best practice design and management of wastewater treatment.
During wastewater treatment, bacteria face a combination of chemical and physical stressors that affects the transfer of genes between them. In fact, a new study published in Nature Water, shows that certain combinations of stressors increase the gene-transfer rate, while others reduce it.
Treated wastewater contains bacteria and extracellular DNA (eDNA) in high concentrations. Bacteria take up eDNA and integrate any of its functional genes into their genome. Stressors including UV light, disinfection chemical byproducts, and pharmaceuticals enhance bacteria’s ability to uptake and integrate eDNA. Meanwhile, elements like solar irradiation damage DNA.
“When a stressor that can increase bacterial cell wall permeability, such as the pharmaceutical carbamazepine, was combined sequentially with a stressor that causes DNA damage, like solar irradiation, the stressors had a synergistic effect,” said study lead Bothayna Al-Gashari of King Abdullah University of Science and Technology (KAUST). “We also established that if one stressor interacts detrimentally and directly with the eDNA, it can impede integration of DNA into the bacterial genome.”
This complexity makes the combinatorial effect of multiple stressors difficult to predict, complicating the ability to assess whether unintentional consequences can arise in the downstream reuse environment. However, the findings show clear conclusions on wastewater treatment, according to the research team.
The findings can inform best practice design and management of wastewater treatment as many regions are now looking to treated wastewater as an invaluable freshwater source. The key is to keep bacteria and eDNA at low concentrations that minimize gene transfer and avoid the complexity and unpredictability of stressor combination effects.
The researchers also outline important steps wastewater treatment facilities should take in order to ensure safe reuse.
“Rather than sand filtration, wastewater treatment facilities should retrofit microfiltration membranes because they can remove both bacteria and extracellular DNA to levels that would not facilitate natural transformation,” said Peiying Hong, professor at KAUST.