Microbial community structure and stability during optimization of a full-scale biological nutrient removal process
As regulatory limits on nutrient discharge from wastewater treatment facilities (WWTF) become more stringent, optimizing the secondary treatment process, rather than building new infrastructure, has been gaining popularity. Biological nutrient removal (BNR) is commonly the focus of such optimizations, where typically a reactor is modified to create a dissolved oxygen gradient enabling simultaneous nitrification and denitrification (SND), and enhanced biological phosphorus removal (EBPR). This study aims to elucidate how functionally relevant microbial communities adapt to such optimizations, and whether the community and the process stabilize over time. The WWTF of Cookeville, Tennessee began optimizing its secondary treatment process in 2015 to accommodate SND. By altering the brush aeration patterns of the oxidation ditches, a dissolved oxygen gradient was generated both laterally and vertically, resulting in anaerobic, anoxic, and oxic environments within a single ditch. For three years, we investigated the stability of this process optimization, by monitoring the microbial community and wastewater characteristics. The denitrifiers showed a significant increase in diversity over time, suggesting optimization resulted in a more resilient denitrifying community. Apart from SND, Cookeville also observed some EBPR. Interestingly, polyphosphate accumulating organisms were ranked among the top ten genera of the activated sludge community. The microbial community composition between sampling events was distinct. However, shifts in composition showed trends that may indicate stabilization of community structure, supporting optimization to possibly be a reliable practice. Two other WWTFs in TN that did not undergo optimization were also investigated for comparison. Results comparing all three WWTFs will be presented.