Abstract
Nitrification is an essential microbial process in the global nitrogen cycle. The first step of nitrification is ammonia oxidation which is achieved by bacteria and archaea and is crucial in decreasing ammonia concentrations that are persistently high in wastewater. This study examined the composition, abundance and identity of the microbial community in activated sludge with a focus on characterizing ammonia oxidizing bacteria and archaea in a full-scale municipal wastewater treatment plant (MWTP). Specifically, two pharmaceutical compounds Tetracycline and Ibuprofen, and their effects on the community composition of bacteria and protozoa in activated sludge was investigated using PCR coupled with denaturing gradient gel electrophoresis (DGGE). In addition, the composition, abundance and activity of the ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA) were analyzed from aerobic activated sludge, recycled sludge and anaerobic digesters of the Humber MWTP using molecular techniques such as PCR, Quantitative PCR, Reverse Transcription-PCR and DGGE. The findings demonstrated that Tetracycline did not appear to alter community composition of bacteria in the activated sludge, rather, the operational parameters of the sequencing batch reactors such as feeding rates and SRT have shown to alter the richness of bacterial communities. However, Ibuprofen affected some members in the protozoan community in activated sludge. In the full-scale Humber MWTP using the conventional activated sludge system, the aeration tanks contained 1.8 × 105 copies of the AOB amoA gene per 100 ng of DNA. In contrast, the anaerobic digester tanks contained 7.3 × 102 copies of the AOA amoA gene per 100ng of DNA. This study also found that AOB were dominant in activated sludge samples, regardless of the operational parameters. The quantification of cDNA transcripts of the amoA gene also indicated that AOB may be more active than AOA in the activated sludge system. Overall, it appears that AOA are very niche specific and thrive in very low oxygenated environments, while AOB proliferate and play a major role in aerobic ammonia oxidation occurring in MWTPs.
Highlights
Nitrogen (N) availability in the environment can often be looked at as a doubleedged sword
Recommendations the presence of ammonia oxidizing archaea in municipal wastewater treatment has been previously observed in activated sludge samples (Park et al, 2006; Zhang et al, 2009), the abundance of ammonia oxidizing bacteria (AOB) and AOA populations and their relative contribution to the ammonia oxidation process under various operational parameters of the activated sludge system was not elucidated
The results from this study clearly show that AOB are dominant in both relative and absolute abundance in all activated sludge samples from a full-scale municipal wastewater treatment plant, especially in the aerated bioreactors where the dissolved oxygen concentration is >2 mg/ L and contained high ammonia concentrations
Summary
Nitrogen (N) availability in the environment can often be looked at as a doubleedged sword. Ammonia oxidizing bacteria have garnered considerable attention because they were thought to be the only group capable of performing the first and the rate limiting step of nitrification (Francis et al, 2005) This all changed when the first ammonia oxidizing archaea (AOA) strain Nitrosopumilis maritimus was isolated using inoculum from the rocky substratum of a tropical marine aquarium tank (Könneke et al, 2005). The primary focus of this report is to detect and quantify the presence of ammonia oxidizing archaea and bacteria from various stages of a full-scale municipal wastewater activated sludge treatment system using both the 16S rRNA and functional gene amoA as indicators. This research will examine the nature of functional redundancy between AOA and AOB and how this relationship can impact the ammonia oxidation process under various conditions in activated sludge systems
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