Ion Chromatography and 16S rRNA Profiling Reveal Temperature-Driven Nutrient Removal Dynamics in A2O Wastewater Treatment

Studying how bacterial communities in wastewater change over time and location helps us understand how they remove waste, phosphorus, and nitrogen, and how wastewater treatment affects nearby rivers and ecosystems. A joint study conducted by researchers at Tokyo University of Agriculture and the Institute of Science Tokyo (both in Japan) investigated the bacterial dynamics within an anaerobic-anoxic-oxic (A2O) wastewater treatment plant (WWTP), comprising anaerobic, anoxic, and aerobic tanks, in Tokyo and its impact on the receiving Tama River. 16S rRNA gene analysis and ion chromatography (IC) were used to monitor bacterial composition and nutrient concentrations, respectively, to assess the effectiveness of nutrient removal across seasonal temperature variations, and the influence of treated wastewater on riverine bacterial communities. A paper based on this research was published in PLOS One.¹

How Do Wastewater Treatment Plants Effect the Environment?

WWTPs use bacteria to remove nutrients from wastewater and help protect rivers and oceans where the treated water is released. While phosphorus and nitrogen are important for life, releasing too much of them without treatment can harm the environment.^2-5Water quality often gets worse where treated wastewater is released. The water can become warmer, have more nutrients, and contain less oxygen. Studies show these changes can harm small aquatic organisms and fish.^6-10

The researchers involved in this study hypothesized that seasonal temperature variations act as a deterministic factor reducing the abundance of key nitrifiers, such as the bacteria Nitrospira, within the A₂O process. This would then alter the bacterial composition discharged into the environment. They further hypothesized that, while treated wastewater discharge introduces distinct bacterial taxa into the receiving river, their persistence would be spatially limited due to physical dispersion and environmental removal processes. To test their hypotheses, the researchers conducted this analysis.¹

^“Understanding wastewater treatment processes using bacteria and their impact on riverine ecosystems,” wrote the authors of the paper,¹ “is crucial for environmental conservation and preservation of water quality.”

What Did the Analysis Reveal?
The research team discovered that the A2O treatment process removed nutrients well, but colder temperatures made it less effective at certain steps, as key bacteria became less common. The plant’s bacteria stayed mostly stable overall. After treated water entered the river, its impact faded downstream as introduced bacteria gradually decreased.¹

“This study,” wrote the authors of the paper,¹ “demonstrated the temperature sensitivity of WWTP processes, and the transient impact of treated wastewater discharge on river bacterial communities, thereby emphasizing the importance of understanding these dynamics for effective environmental conservation.”

The researchers pointed out that they observed a decrease in microbial DNA in the treated water as it flowed downstream. Previous studies, however, have reported that the impact of treated water persists more in river sediments than in river water. The research team, therefore, believes that it is crucial to investigate the influence on river sediment in future studies.¹

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References

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2. Seitzinger, S.; Harrison, J. A.; Böhlke, J. K. et al. Denitrification Across Landscapes and Waterscapes: A Synthesis. Ecol Appl. 2006,16 (6), 2064–2090. DOI: DOI: 10.1289/ehp.122-A304
3. Manuel, J. Nutrient Pollution: A Persistent Threat to Waterways. Environ Health Perspect. 2014, 122 (11), A304-309. DOI: 10.1289/ehp.122-A304
4. Maavara, T.; Parsons, C. T.; Ridenour, C. et al. Global Phosphorus Retention by River Damming. Proc Natl Acad Sci U S A 2015, 112 (51), 15603–15608. DOI: 10.1073/pnas.1511797112
5. Mallin, M. A.; Cahoon, L. B. The Hidden Impacts of Phosphorus Pollution to Streams and Rivers. BioScience 2020, 70 (4), 315–329. DOI: 10.1093/biosci/biaa001
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7. Enns, D.; Cunze, S.; Baker, N. J. et al. Flushing Away the Future: The Effects of Wastewater Treatment Plants on Aquatic Invertebrates. Water Res. 2023, 243, 120388. DOI: 10.1016/j.watres.2023.120388
8. Albini, D.; Lester, L.; Sanders, P. et al. The Combined Effects of Treated Sewage Discharge and Land Use on Rivers. Glob Chang Biol. 2023, 29 (22), 6415–6422. DOI: 10.1111/gcb.16934
9. Albini, D.; Lester, L.; Sanders, P. et al. Early Detection and Environmental Drivers of Sewage Fungus Outbreaks in Rivers. Ecol Sol and Evidence 2023, 4 (3). DOI: 10.1002/2688-8319.12277
10. González, J. M.; de Guzmán, I.; Elosegi, A. et al. Tertiary Wastewater Treatment Combined with High Dilution Rates Fails to Eliminate Impacts on Receiving Stream Invertebrate Assemblages. Sci Total Environ. 2023, 859 (Pt 2),160425. DOI: 10.1016/j.scitotenv.2022.160425