New method for identifying wastewater-purifying bacteria

Diet and lifestyle 12. aug 2021 3 min Professor Jeppe Lund Nielsen Written by Kristian Sjøgren

Some bacteria can remove organic micropollutants, including drug residues, from wastewater. Researchers in Denmark have developed a method for easily identifying the most suitable bacteria for performing this task.

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Bacteria have enormous potential to purify wastewater.

Some bacteria can degrade micropollutants, including drug residues that are very difficult to remove from wastewater before it is discharged into the aquatic environment.

The challenge, however, is figuring out which bacteria can most efficiently remove these micropollutants from wastewater and what conditions they need to achieve this. Researchers in Denmark have found a solution.

Instead of examining the prevalence of the environmentally harmful substances to be removed from the wastewater, the researchers analysed the development in biodegradation rates at which the substances are removed and the presence of specific bacteria and how these evolve together with the removal of specific harmful substances.

The researchers could thereby determine whether a specific composition of a microbial community is more or less efficient in reducing the harmful micropollutants in wastewater.

“This approach refines existing methods and enables us to more precisely assess more precisely how the presence of specific bacteria is associated with the biodegradation rate of micropollutants. We are thereby better able to identify which specific bacteria excel at biodegrading specific micropollutants. The method can be used to create favourable conditions for these bacteria in wastewater and thus increase the biotransformation of micropollutants,” explains Jeppe Lund Nielsen, Professor, Department of Chemistry and Bioscience, Aalborg University.

The research has been published in Chemical Engineering Journal.

Biological wastewater treatment is better than chemical or mechanical treatment

Wastewater treatment is a major societal challenge worldwide because of the risk of many harmful substances ending up in the receiving ecosystems. These include antibiotics and drug residue, which can harm both animals and plants or promote the development of antimicrobial resistance.

Drug residues can be removed from wastewater in three ways.

· Chemical treatment is the most widely used method and involves adding chemicals that degrade the micropollutants.

· Mechanical treatment using filters that separate the micropollutants from wastewater.

· Biological treatment involves getting bacteria communities able to degrade the micropollutants.

Chemical and mechanical methods to remove drug residues in wastewater treatment to remove drug residue are not a very good solution, however, because they are both cumbersome and expensive and leave behind partly degraded substances with unknown effects.

Jeppe Lund Nielsen says the best solution is therefore to combine these three methods, but biological wastewater treatment has not yet been fully mapped and still requires some development to utilise the method’s full potential.

“Bacteria and other microorganisms are very particular and individually very selective of only a few environmentally harmful micropollutants. Selecting very specific types of bacteria is therefore needed to ensure that we remove all of the harmful micropollutants from the wastewater,” says Jeppe Lund Nielsen.

Thousands of bacterial strains in wastewater

However, determining how to assemble an optimal microbial community in a wastewater treatment plant is difficult.

This involves determining which of the thousands of bacterial strains in a wastewater sample are good at degrading various types of micropollutants.

“This is the task, and once we determine which bacteria are capable of removing specific substances, we can develop the appropriate molecular biology techniques to identify whether they are present in a sample, their concentration and how we promote their growth or activity,” explains Jeppe Lund Nielsen.

Investigating the removal of 36 micropollutants from wastewater samples

Researchers previously searched for the presence of the environmentally harmful substances to determine whether the right bacteria are present in wastewater. However, in the new study, the researchers decided to investigate the bacteria themselves, and their activity.

Furthermore, the researchers specifically examined the bacteria’s capacity to remove 36 micropollutants, antibiotics and other environmentally harmful substances in the wastewater samples.

The researchers tracked the development of bacteria and environmentally harmful micropollutants in their samples for 71 days. They took samples every other day and statistically analysed the data to determine how the presence of bacteria in the ecosystem affected the micropollutant removal rates over time.

“This is the first time anyone has worked so thoroughly and analysed the biodegradation kinetics of micropollutant removal rates in wastewater samples. This enables us to determine which bacteria must be present in a sample to remove a specific micropollutant optimally,” says Jeppe Lund Nielsen.

Removing antidepressants from wastewater

Jeppe Lund Nielsen says that modern wastewater-treatment plants do not normally filter out the substances they have analysed at all and just send them directly to the receiving ecosystems.

These include micropollutants such as antidepressants and blood pressure-regulating medication.

The researchers found that the presence of specific bacteria under favourable conditions increased the biodegradation rate of these drug micropollutants up to 66 times.

“This enables us to retain these bacteria in urban wastewater systems so that they can degrade micropollutants and prevent them from reaching the environment. Our study shows that we can more precisely and sensitively discover which bacteria can remove drug micropollutants. We have refined this method so that it is now more accurate,” concludes Jeppe Lund Nielsen.

Biodegradation kinetics of organic micropollutants and microbial community dynamics in a moving bed biofilm reactor” has been published in Chemical Engineering Journal. In 2016, the Novo Nordisk Foundation awarded a grant to Jeppe Lund Nielsen for the project Novel Screening Approaches for Identification of Enzymes of Biotechnological Interests Directly in Complex Microbial Consortia.

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