The Role of Ammonia Oxidizing Microorganisms in Attenuating Trace Organic Compounds in Water Reuse Biofiltration Systems

Due to their uncertain public health impacts, the occurrence of persistent trace organic compounds (TOrCs) in domestic wastewater can be problematic for potable reuse systems seeking to avoid advanced treatment with reverse osmosis. By employing biofiltration, some TOrC attenuation may be achieved through cometabolic biotransformation by ammonia oxidizing microorganisms (AOMs). These include ammonia oxidizing archaea (AOA), ammonia oxidizing bacteria (AOB), and complete ammonia oxidizing (comammox) bacteria. This research aimed to investigate the role of AOMs in TOrC biotransformation by evaluating three pilot-scale biologically active filters (BAFs) fed with secondary effluent, including a control with no supplementation, one with ammonia dosed at 2 mg N per L, and one with chloramine dosed at 0.3 mg Cl2 per L. For the highly biodegradable TOrCs, the control and chloramine-dosed BAFs performed similarly and achieved average attenuation of 75 percent, whereas the ammonia-dosed BAF achieved only 55 percent. With ammonia dosing, AOB dominated the AOM community, comprising 64 percent and 44 percent of the AOMs at the top and bottom sampling depths, respectively. In contrast, the control and chloramine-dosed filters were dominated by comammox bacteria, which generally comprised greater than 80 percent of the AOM community. Our results suggest that nitrifying microorganisms may play an important role in TOrC biotransformation, but ammonia-rich environments may adversely impact important cometabolic pathways. Thus, non-nitrified systems or short-term upsets in secondary biological treatment may directly or indirectly lead to elevated concentrations of ammonia and TOrCs in biofilter effluents. On the other hand, selection of comammox bacteria in low-ammonia environments may lead to enhanced TOrC biotransformation.