title: Biotransformation of Trace Organic Compounds via Microbial Ammonia Oxidation in Biofiltration Systems for Water Reuse
Creators: name: Babcock, Nicholas
Publisher: name: University of Nevada, Las Vegas
Year: 2021

description: The use of ozone-biofiltration (BAF) for water reuse has recently been viewed as an attractive option due its low cost and ability to achieve high quality effluent. However, one challenge that is particularly problematic for ozone-biofiltration is the occurrence of trace organic compounds (TOrCs), such as pharmaceuticals and personal care products, in domestic wastewater, primarily due to their uncertain public health impacts. These TOrCs might be degraded by three ammonia oxidizing microorganisms (AOMs), including ammonia oxidizing bacteria (AOBs), ammonia oxidizing archaea (AOAs), and Comammox that have been found in biofiltration systems. Cometabolism, the fortuitous biodegradation of compounds by enzymes used for primary metabolism, allow AOMs to biodegrade some TOrCs, but the extent of degradation is dependent on chemical structure and composition of the microbial community.

The goal of this thesis research was to determine the role of AOMs in degrading TOrCs in wastewater reuse biofilters, primarily focusing on acetaminophen, caffeine, ibuprofen, and naproxen. The research focused on investigating TOrC biodegradation by evaluating three pilot biofiltration columns: 1) a control column, fed only secondary effluent, 2) a column fed secondary effluent with 2 mg N/L additional ammonia, and 3) a column fed secondary effluent with 0.3 mg/L of monochloramine. Each column contained 10-year old biological activated carbon media and was operated with a 10 min empty bed contact time. The control BAF served as a baseline and displayed extremely limited nitrification and no denitrification. The ammonia dosed BAF exhibited nitrification and very limited denitrification. The chloramine dosed BAF exhibited extremely limited nitrification and denitrification. The chloramine dosed column iv outperformed the control in the reduction of ibuprofen and naproxen. Additionally, the chloramine dosed column outperformed the ammonia column in degradation of nearly all TOrCs. The addition of ammonia was surprisingly significantly worse in TOrC reduction than the control for all TOrCs that were analyzed. For biological analysis, it was assumed that the biomass was consistent across all three columns given that the effluent adenosine triphosphate levels were consistent throughout the study. Therefore, the AOM community assay results were normalized by the 16S rRNA gene assay results to provide relative abundances that are suitable for comparison. The AOM community in the ammonia dosed BAF was dominated by AOBs, unlike those in the control and chloramine dosed BAFs, which were dominated by Comammox. Interestingly, the chloramine dosed BAF displayed the highest overall relative abundance of AOMs in the top and bottom depths. The results of this study suggest that it is not AOB, but Comammox that may be responsible for effective TOrC reduction and the presence of excess ammonia into a BAF system is not beneficial for TOrC attenuation. However, the addition of a low dose of monochloramine in BAF systems can be beneficial for AOM development and the removal of certain TOrCs.