Partial Nitritation/Anammox and biological phosphorus removal integration in a single bioreactor under mainstream conditions.

Anammox-based nitrogen removal and enhanced biological phosphorus removal (EBPR) are increasingly applied for nutrient removal from wastewater, but are typically operated in separate reactors. Here, a novel process for integrated partial nitritation/anammox (PN/A) and EBPR in a single reactor employing integrated fixed film activated sludge was tested. The reactor was fed with mainstream municipal wastewater (5.4 ± 1.3 g COD/g N) at 20 °C for 243 days. Robust ammonium, total inorganic nitrogen, and orthophosphate removal efficiencies of 94 ± 4 %, 87 ± 7 % and 92 ± 7 % were achieved. Nitrite-oxidizing organisms suppression and ammonia-oxidizing organisms retention were achieved via solids retention time control, intermittent aeration, and suspended versus attached biomass population segregation. The contribution of anammox to nitrogen removal increased from 24 % to 74 %. In parallel, a substantial enrichment of Tetrasphaera polyphosphate accumulating organisms was observed. This work demonstrates a novel intensified bioprocess coupling PN/A and EBPR in the same reactor for efficient nutrient removal from wastewater.

Impact of operational strategies on a sidestream enhanced biological phosphorus removal (S2EBPR) reactor in a carbon limited wastewater plant.

Water resource recovery facilities are faced with stringent effluent phosphorus limits to reduce nutrient pollution. Enhanced biological phosphorus removal (EBPR) is the most common biological route to remove phosphorus; however, many facilities struggle to achieve consistent performance due to limited carbon availability in the influent wastewater. A promising process to improve carbon availability is through return activated sludge (RAS) fermentation via sidestream EBPR (S2EBPR). In this study, a full-scale S2EBPR pilot was operated with a sidestream plus carbon configuration (SSRC) at a carbon-limited facility. A model based on the pilot test was developed and calibrated in the SUMO platform and used to explore routes for improving orthophosphate (OP) effluent compliance. Modeling results showed that RAS diversion by itself was not sufficient to drive OP removal to permit limits of 1 mg L-1, therefore, other strategies were evaluated. Supplemental carbon addition of MicroC® at 1.90 L min-1 and controlling the phosphorus concentration below 3.5 mgP L-1 in the primary effluent (PE) proved to be valid supplemental strategies to achieve OP removal below 1 mg L-1 most of the time. In particular, the proposed supplemental carbon flow rate would result in an improvement of the rbCOD:P ratio from 17:1 to 26:1. The synergistic approach of RAS diversion and supplemental carbon addition increased the polyphosphate accumulating organisms (PAO) population while minimizing the supplemental carbon needed to achieve consistent phosphorus removal. Overall, this pilot and modeling study shows that joint strategies, including RAS diversion, carbon addition and PE control, can be effective to achieve optimal control of OP effluent.

Comammox Nitrospira are the dominant ammonia oxidizers in a mainstream low dissolved oxygen nitrification reactor.

Recent findings show that a subset of bacteria affiliated with Nitrospira, a genus known for its importance in nitrite oxidation for biological nutrient removal applications, are capable of complete ammonia oxidation (comammox) to nitrate. Early reports suggested that they were absent or present in low abundance in most activated sludge processes, and thus likely functionally irrelevant. Here we show the accumulation of comammox Nitrospira in a nitrifying sequencing batch reactor operated at low dissolved oxygen (DO) concentrations. Actual mainstream wastewater was used as influent after primary settling and an upstream pre-treatment process for carbon and phosphorus removal. The ammonia removal rate was stable and exceeded that of the treatment plant's parallel full-scale high DO nitrifying activated sludge reactor. 16S rRNA gene sequencing showed a steady accumulation of Nitrospira to 53% total abundance and a decline in conventional ammonia oxidizing bacteria to <1% total abundance over 400 + days of operation. After ruling out other known ammonia oxidizers, qPCR confirmed the accumulation of comammox Nitrospira beginning around day 200, to eventually comprise 94% of all detected amoA and 4% of total bacteria by day 407. Quantitative fluorescence in-situ hybridization confirmed the increasing trend and high relative abundance of Nitrospira. These results demonstrate that comammox can be metabolically relevant to nitrogen transformation in wastewater treatment, and can even dominate the ammonia oxidizing community. Our results suggest that comammox may be an important functional group in energy efficient nitrification systems designed to operate at low DO levels.