Nitrification process in integrated fixed-film activated sludge (IFFAS) system

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Liu, Yupeng
IFFAS , Wastewater , Anammox , Nitrification
The ammonia released from wastewater is a key factor in detrimental environment concerns such as eutrophication. Nitrogenous waste is most commonly removed from wastewater through biological means, typically involving the use of ammonia oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB), and denitrifying bacteria (DEN). This study looked at alternative nitrification processes, including anaerobic ammonia oxidiation (anammox) reactions that may be innately present in an integrated fixed-film activated sludge (IFFAS). Due to the unique characteristics of IFFAS configuration, the biofilm component allowed for anoxic zones, as well as higher biomass retention, both factors favouring the growth of anammox bacteria. One of the main goals of this thesis project was to look for the presence of anammox bacteria, which could be a group of microorganism that is involved in removal of ammonia and nitrite, in addition to the conventional nitrifiers found in the IFFAS system. Through the use of batch experiments, the different forms of nitrogen in the microbial nitrogen cycle (ammonia, nitrite, and nitrate) were measured over the course of the IFFAS reaction period, under aerated and non-aerated conditions. Subsequently, fluorescence in-situ hybridization (FISH) techniques were utilized to confirm anammox presence. Although, initial data from the batch experiment was strongly suggestive of anaerobic ammonia oxidation in the IFFAS system, the FISH experiments did not detect anammox bacteria. Incorporating data from a parallel experiment, it was possible that a different group of bacteria, known as Rhodanobacter, may be responsible for the AOB to NOB imbalance rather than anammox bacteria. Certain species of Rhodanobacter are able to utilize nitrite and nitrate as oxidizers in the denitrification process under anoxic conditions, which may be present in the biofilms of the IFFAS system. Therefore, it is possible that Rhodanobacter is involved in the removal of any excess nitrite produced by the higher levels of AOB in the IFFAS reactors.
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