In a groundbreaking study published in The Science of the Total Environment on January 16, 2024, researchers Hong Jin-Kyung, Lee Tae Kwon, Kim Ilho, and Park Saerom have uncovered critical factors influencing the microbial colonization of microplastics in wastewater treatment plants. This study, titled “Determinants of microbial colonization on microplastics through wastewater treatment processes: The role of polymer type and sequential treatment,” assesses how various types of polymer microplastics interact with complex microbial communities across different stages of wastewater treatment (DOI: 10.1016/j.scitotenv.2024.170072).

With plastic pollution being a major global concern, particularly in aquatic environments, the interaction between microplastics (MPs) and bacterial communities is drawing increasing scrutiny as we attempt to understand and mitigate the environmental impact of MPs. The study conducted by a team of environmental scientists at Yonsei University and Korea Institute of Civil Engineering and Building Technology sheds light on this critical area.

The researchers focused on two common types of MPs—High-Density Polyethylene (HDPE) and Polyethylene Terephthalate (PET)—which are frequently found in wastewater systems, originating from a plethora of consumer products. Their research aimed to identify whether these MPs serve as breeding grounds for bacterial colonies and how the wastewater treatment stages affect MP colonization.

Key Findings and Methodology

The team implemented individual and sequential deployment approaches within a wastewater treatment plant, examining how bacterial colonization on MPs differed when introduced at each treatment stage individually or when allowed to pass through the entire process from primary to tertiary stages.

They discovered that the type of polymer had a significant influence on the types of bacteria that would colonize the surface. HDPE MPs were found to be highly sensitive to the composition of wastewater, leading to the formation of selective biofilms, which are communities of bacteria that attach to surfaces. For instance, during primary treatment, Firmicutes—a group of bacteria—were prevalent on HDPE, accounting for 25.1% of the bacterial population.

However, as the HDPE passed through to the tertiary treatment stage, there was a marked increase in Alphaproteobacteria, with these bacteria representing 19.8% of the population. This highlights a clear niche-dependent colonization pattern, demonstrating how specific environmental conditions within each treatment stage favor different bacterial groups.

Conversely, PET displayed a more random, or stochastic, pattern of bacterial colonization. Researchers speculate this may be attributed to PET’s varying surface hydrophilicity, which influences how water interacts with the surface and consequently affects bacterial attachment.

Another key finding concerned sequential deployments: it was noted that moving from primary through tertiary treatment stages induced a shift towards a more stochastic bacterial attachment, particularly on HDPE. Shannon diversity values—used to measure the diversity of the bacterial communities on MP biofilms—were consistently higher for MPs than for the wastewater itself at all treatment stages. Notably, for PET in sequential deployments, the Shannon diversity index saw a significant increase during tertiary stage treatments, reaching 5.01.

Implications for Wastewater Treatment and Environmental Health

This research has vital implications for the treatment of wastewater and for the preservation of our water systems. The findings suggest that MPs act as carriers of diverse bacteria through WWTPs. Considering that different bacteria could have varying impacts on the environment—ranging from benign to pathogenic—the study underscores the need for effective strategies to address MPs in wastewater treatment processes.

Moreover, the research calls for heightened awareness of the role that different polymer types play in microbial colonization, with MPs potentially aiding the spread of harmful bacteria if not properly managed. Wastewater treatment plants may need to adopt new techniques tailored to the different behaviors of MPs observed in the study.

Conclusion and Recommendations

The authors, who declare no competing financial interests or personal relationships potentially influencing their work, have delivered a pioneering contribution to the field of environmental science.

This study not only advances our understanding of the relationship between microplastics and bacteria but also highlights the urgent need for enhanced wastewater treatment protocols that specifically target MPs and their bacterial passengers.

References

1. Jin-Kyung, H., Tae Kwon, L., Ilho, K., & Saerom, P. (2024). Determinants of microbial colonization on microplastics through wastewater treatment processes: The role of polymer type and sequential treatment. Science of the Total Environment, 170072. https://doi.org/10.1016/j.scitotenv.2024.170072

2. McCormick, A., Hoellein, T. J., Mason, S. A., Schluep, J., & Kelly, J. J. (2014). Microplastic is an abundant and distinct microbial habitat in an urban river. Environmental Science & Technology, 48(20), 11863-11871.

3. Zettler, E. R., Mincer, T. J., & Amaral-Zettler, L. A. (2013). Life in the “Plastisphere”: Microbial communities on plastic marine debris. Environmental Science & Technology, 47(13), 7137-7146.

4. Bryant, J. A., Clemente, T. M., Viviani, D. A., Fong, A. A., Thomas, K. A., Kemp, P., … & DeLong, E. F. (2016). Diversity and activity of communities inhabiting plastic debris in the North Pacific Gyre. mSystems, 1(3), e00024-16.

5. Hoellein, T., Rojas, M., Pink, A., Gasior, J., & Kelly, J. (2014). Anthropogenic litter in urban freshwater ecosystems: distribution and microbial interactions. PloS one, 9(6), e98485.

Keywords

1. Microplastic colonization WWTP
2. Bacterial biofilm on microplastics
3. Wastewater treatment microplastic impact
4. Microbial attached to plastic pollution
5. High-Density Polyethylene in wastewater