Comparing methanol and glycerol as carbon sources for mainstream partial denitrification/anammox in an IFAS process.

This study explored the implementation of mainstream partial denitrification with anammox (PdNA) in the second anoxic zone of a wastewater treatment process in an integrated fixed film activated sludge (IFAS) configuration. A pilot study was conducted to compare the use of methanol and glycerol as external carbon sources for an IFAS PdNA startup, with a goal to optimize nitrogen removal while minimizing carbon usage. The study also investigated the establishment of anammox bacteria on virgin carriers in IFAS reactors without the use of seeding, and it is the first IFAS PdNA startup to use methanol as an external carbon source. The establishment of anammox bacteria was confirmed in both reactors 102 days after startup. Although the glycerol-fed reactor achieved a higher steady-state maximum ammonia removal rate because of anammox bacteria (1.6 ± 0.3 g/m2/day) in comparison with the methanol-fed reactor (1.2 ± 0.2 g/m2/day), both the glycerol- and methanol-fed reactors achieved similar average in situ ammonia removal rates of 0.39 ± 0.2 g/m2/day and 0.40 ± 0.2 g/m2/day, respectively. Additionally, when the upstream ammonia versus NOx (AvN) control system maintained an ideal ratio of 0.40-0.50 g/g, the methanol-fed reactor attained a lower average effluent TIN concentration (3.50 ± 1.2 mg/L) than the glycerol-fed reactor (4.43 ± 1.6 mg/L), which was prone to elevated nitrite concentrations in the effluent. Overall, this research highlights the potential for PdNA in IFAS configurations as an efficient and cost-saving method for wastewater treatment, with methanol as a viable carbon source for the establishment of anammox bacteria. PRACTITIONER POINTS: Methanol is an effective external carbon source for an anammox startup that avoids the need for costly alternative carbon sources. The methanol-fed reactor demonstrated higher TIN removal compared with the glycerol-fed reactor because of less overproduction of nitrite. Anammox bacteria was established in an IFAS reactor without seeding and used internally stored carbon to reduce external carbon addition. Controlling the influent ammonia versus NOx (AvN) ratio between 0.40 and 0.50 g/g allowed for low and stable TIN effluent conditions.

Co-Occurrence and Cooperation between Comammox and Anammox Bacteria in a Full-Scale Attached Growth Municipal Wastewater Treatment Process.

Cooperation between comammox and anammox bacteria for nitrogen removal has been recently reported in laboratory-scale systems, including synthetic community constructs; however, there are no reports of full-scale municipal wastewater treatment systems with such cooperation. Here, we report intrinsic and extant kinetics as well as genome-resolved community characterization of a full-scale integrated fixed film activated sludge (IFAS) system where comammox and anammox bacteria co-occur and appear to drive nitrogen loss. Intrinsic batch kinetic assays indicated that majority of the aerobic ammonia oxidation was driven by comammox bacteria (1.75 ± 0.08 mg-N/g TS-h) in the attached growth phase, with minimal contribution by ammonia-oxidizing bacteria. Interestingly, a portion of total inorganic nitrogen (∼8%) was consistently lost during these aerobic assays. Aerobic nitrite oxidation assays eliminated the possibility of denitrification as a cause of nitrogen loss, while anaerobic ammonia oxidation assays resulted in rates consistent with anammox stoichiometry. Full-scale experiments at different dissolved oxygen (DO = 2 - 6 mg/L) setpoints indicated persistent nitrogen loss that was partly sensitive to DO concentrations. Genome-resolved metagenomics confirmed the high abundance (relative abundance 6.53 ± 0.34%) of two Brocadia-like anammox populations, while comammox bacteria within the Ca. Nitrospira nitrosa cluster were lower in abundance (0.37 ± 0.03%) and Nitrosomonas-like ammonia oxidizers were even lower (0.12 ± 0.02%). Collectively, our study reports for the first time the co-occurrence and cooperation of comammox and anammox bacteria in a full-scale municipal wastewater treatment system.