How Bacteria Build Up in a Wastewater Cleaning System

Jenn Hoskins
13th March, 2024

How Bacteria Build Up in a Wastewater Cleaning System

Image Source: Natural Science News, 2024

Key Findings

  • At Lund University, researchers found that specific bacteria initially dominate wastewater biofilms
  • As conditions change, like increased nitrogen, different bacteria take over, affecting treatment efficiency
  • These insights can help optimize wastewater treatment by managing biofilm development
Understanding the intricate processes involved in wastewater treatment is crucial for maintaining environmental health. One such process is partial nitritation-anammox (PNA), a biological method used to remove nitrogen from wastewater. Researchers at Lund University have made significant strides in understanding how biofilms—communities of microorganisms that adhere to surfaces—develop in PNA systems[1]. This is vital because the way these biofilms form can affect the efficiency of nitrogen removal. Biofilms in PNA systems are essential since they retain the necessary bacteria to convert ammonium, a nitrogen-rich waste product, into nitrogen gas which is harmless to the environment. However, the development of these biofilms has been somewhat of a mystery. The study from Lund University sheds light on this by tracking the formation of a biofilm over 175 days in a full-scale PNA reactor using a technique called shotgun metagenomics, which sequences DNA from environmental samples to identify the microorganisms present. Initially, the biofilm's diversity was low, dominated by a group of bacteria called Proteobacteria. This suggests that environmental filtering—a process where only certain organisms can establish in a particular environment due to specific conditions—played a significant role at this stage. As the biofilm matured, a phenomenon known as facilitative priority effects came into play. This refers to the idea that the successful establishment of certain microorganisms can pave the way for others to follow, a concept previously reviewed in microbial communities[2]. Among the early settlers were 'oligotrophic' ammonia oxidizers, which thrive in environments with low nutrient levels. These included comammox Nitrospira and Nitrosomonas cluster 6a, both types of aerobic ammonia-oxidizing bacteria (AOB) that begin the nitrogen conversion process. The presence of these bacteria is crucial as they start the nitrogen removal by first converting ammonia to nitrite. As the nitrogen load in the reactor increased, more nutrient-loving 'copiotrophic' bacteria like Nitrosomonas cluster 7 AOB began to colonize the biofilm. Interestingly, this shift led to the exclusion of the initial ammonia- and nitrite-oxidizing bacteria. This exclusion is a direct demonstration of how changes in environmental conditions can influence the microbial composition of biofilms, which is essential for the optimization of PNA systems. The findings from this study are significant in several ways. They show that the assembly of biofilms in PNA systems is a dynamic process influenced by both the environment and the microbes that arrive first. This knowledge can be used to improve the start-up and stability of PNA bioreactors, which is essential for efficient wastewater treatment. Understanding the roles of different bacteria in this process is also critical. For example, the study highlights the importance of nitrite-oxidizing bacteria like Cand. Nitrotoga, which were previously found to be crucial for maintaining nitrite oxidation, especially under cold conditions in wastewater treatment plants[3]. The current study adds to this by showing how different conditions, such as nutrient levels, can influence the presence and activity of various AOB in biofilms. Furthermore, the ability of certain bacteria to cope with oxygen exposure, such as Clostridia, which have been shown to redirect their metabolism and induce specific genes in response to oxygen stress[4], may also be relevant in understanding how aerobic and anaerobic bacteria coexist and function in the biofilms of PNA systems. In conclusion, the research from Lund University provides valuable insights into the development and management of biofilms in wastewater treatment. The study demonstrates that the initial community structure and environmental conditions play a significant role in shaping the biofilm's microbial composition. This, in turn, affects the efficiency of the PNA process. By understanding these complex dynamics, we can better control and optimize the biological processes that are essential for the sustainability of our water resources.



Main Study

1) Biofilm colonization and succession in a full-scale partial nitritation-anammox moving bed biofilm reactor.

Published 12th March, 2024

Related Studies

2) Priority effects in microbiome assembly.

3) Relevance of Candidatus Nitrotoga for nitrite oxidation in technical nitrogen removal systems.

4) Responses of Clostridia to oxygen: from detoxification to adaptive strategies.

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