- Research project objectives/Research hypothesis
Nitrification is an important step in the overall nitrogen cycle. Conventionally, nitrification has beenconsidered a two-step process catabolized by different groups of microorganisms. However, the complete nitrification process, i.e. complete oxidation of ammonia to nitrate (COMAMMOX), by only one microorganism belonging to Nitrospira sp. was experimentally confirmed only two years ago. This discovery adds a new dimension to the current understanding of the nitrogen cycle (especially nitrification). Moreover, it also brings opportunities to revise the approach to nitrogen management in wastewater treatment systems employing the novel nitrogen removal processes, such as deammonification or shortened nitrificationdenitrification via nitrite (so called “nitrite shunt”). Although the “comammox” Nitrospira have already been found in wastewater treatment systems (especially in biofilms), their importance for nitrogen removal has not yet been investigated yet. Therefore, the aim of the project is to identify, characterize and model the comammox process in the nitrogen cycle in different wastewater treatment systems.
- Research project methodology
In order to achieve the aim of the study, the scientific consortium has been founded, including research teams from Gdańsk University of Technology (GUT),Warsaw University of Technology (WUT), and University of Warmia and Mazury in Olsztyn (UWM). With the specific competences of the project partners a novel research approach will be applied by combining comprehensive kinetic studies in different wastewater treatment systems, advanced microbiological techniques and mathematical modeling/simulation. The planned project involve four main tasks (composed of subtasks) assigned individually to the specific partner. It is assumed that that different laboratory-scale systems (sequencing batch reactor vs. hybrid moving bed batch reactors) will be operated in parallel by the GUT research team (Task 1) and WUT research team (Task 2). Those systems will employ different biomass retention methods (suspended and attached growth, granular sludge) and different nitrogen removal processes via the nitrite pathway (nitrification vs. deammonification). However, for a reliable comparison, both systems will be fed with the same synthetic media imitating the composition of municipal wastewater and anaerobic sludge digester liquors. Furthermore, the studied systems at GUT and WUT will be operated under similar operational conditions in terms of temperature, substrate availability, dissolved oxygen concentration, and aeration strategy (continuous vs. intermittent). The performance of both systems will be compared in terms of the overall nitrogen removal efficiency, suppression or wash out of nitrite oxidizing bacteria, and composition of the microbial communities (with a special focus on “comammox” Nitrospira). With regard to the latter comparison, two advanced microbiological techniques will used, including metagenomics and metatranscriptomics (Task 3). Metagenomics will characterize the microbial communities developed in the studied reactors, whereas metatranscriptomics will analyze the functional genes activity involved in the nitrogen metabolism (amoA, nxr, hao, nirK and hzsA). Mathematical modeling and simulation will be used in order to understand relationships between the microbial groups present in the studied reactors as well as optimize the operational conditions in terms of nitrogen removal efficiencies (Task 4).
- Expected impact of the research project on the development of science
The proposed project results will help in answering the following research questions: – What is the extent of the comammox process in different wastewater treatment systems? – May comammox bacteria outcompete canonical NOB and what are the main operational factorsinfluencing the comammox survival in the studied systems (ammonia nitrogen concentration, dissolved oxygen concentration, temperature etc.)? – Is biofilm indeed a better environment for comammox growth in wastewater treatment systems? – What are the genetic and functional adaptations of comammox bacteria in wastewater treatment systems? (by applying the integrated advanced microbiological techniques). The benefits of the novel nitrogen removal processes (deammonification and “nitrite shunt”) result from suppressing nitrite oxidation which has been attributed to the growth of canonical NOB. In particular, mainstream deammonification is a promising new treatment concept that has the potential to revolutionize the way in which nitrogen removal is achieved in wastewater treatment plants. The commamox process may negatively affect those novel processes due to competition for the same substrate (ammonia). As a consequence, the comammox bacteria may significantly disturb nitrite production in partial nitrification (nitritation), which is the critical step for the successful operation of both novel processes.