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

Unlocking the potential of sidestream EBPR: exploring the coexistence of PAO, GAO and DGAO for effective phosphorus and nitrogen removal

Wastewater treatment facilities use enhanced biological phosphorus removal (EBPR) to meet discharge quality limits. However, the EBPR process can experience upsets due to a lack of influent carbon or inadequate anaerobic zones. By using a sidestream EBPR (S2EBPR) process, carbon can be generated internally through fermentation processes and a higher anaerobic mass fraction can be attained in smaller volumes. This study investigates nutrient removal and microbial community trends in a full-scale S2EBPR demonstration at the Calumet Water Reclamation Plant. The study aims to improve a process model of the system by better representing the activity of glycogen-accumulating organisms (GAO) and potential competitors of phosphorus-accumulating organisms (PAO), which were found in high abundance in this study. Modifying anaerobic hydrolysis, GAO glycogen storage and ORP activity parameters resulted in model prediction improvements of approximately 5% for nitrate and nitrite and 10-60% for phosphorus. The study also uses shotgun metagenomic sequencing to profile denitrification pathways of PAO and GAO. It shows that denitrifying GAO may contribute to nitric oxide reduction to a greater degree than denitrifying PAO. This study improves process modeling predictions for S2EBPR and highlights the potential role of denitrifying PAO and GAO in combined phosphorus and nitrogen removal in S2EBPR.

Acidobacteria as the dominant microorganism on the nitrogen-removal wastewater treatment with a low chemical oxygen demand/ammonium nitrogen ratio in biological contact oxidation reactor

Nitrogen-removal promotion is a significant problem when biological nitrogen removal is used to treat ammonium nitrogen (NH4+-N) wastewater with a low chemical oxygen demand (COD)/NH4+-N (C/N) ratio. In this work, the biological nitrogen removal capacity of the biological contact oxidation reactor (BCOR) system was enhanced through the enrichment of Acidobacteria. The system was successfully started from Day 1 to Day 50 and stably operated through temperature, pH, and dissolved oxygen (DO) regulation from Day 51 to Day 254. The average ammonium nitrogen-removal efficiency over the performance period was 96.2%, whereas the average total nitrogen-removal efficiency was 86.9%, according to the data. In the meantime, the predominant microbes in the BCOR system were initially found to belong to the phylum Acidobacteria (relative abundance of 48.39%). Additionally, it was found for the first time in this system that three different genera of unnamed microorganisms (two of which belonged to the phylum Acidobacteria and one to the phylum Chlorobi), the relative abundances of which were 30.46%, 11.45% and 16.00%, respectively. Candidatus Xiphinematobacter (belonging to the phylum Verrucomicrobia, relative abundances of 8.81%), and Pseudomonas (belonging to the phylum Proteobacteria, relative abundances of 5.59%). This new finding will be very beneficial for future research into the microbiological mechanisms and technological engineering applications of the BCOR system for treating ammonium nitrogen wastewater with a low C/N ratio.

Synergistic Integration of Anammox and Endogenous Denitrification Processes for the Simultaneous Carbon, Nitrogen, and Phosphorus Removal

The feasibility of a synergistic endogenous partial denitrification-phosphorus removal coupled anammox (SEPD-PR/A) system was investigated in a modified anaerobic baffled reactor (mABR) for synchronous carbon, nitrogen, and phosphorus removal. The mABR comprising four identical compartments (i.e., C1-C4) was inoculated with precultured denitrifying glycogen-accumulating organisms (DGAOs), denitrifying polyphosphate-accumulating organisms, and anammox bacteria. After 136 days of operation, the chemical oxygen demand (COD), total nitrogen, and phosphorus removal efficiencies reached 88.6 ± 1.0, 97.2 ± 1.5, and 89.1 ± 4.2%, respectively. Network-based analysis revealed that the biofilmed community demonstrated stable nutrient removal performance under oligotrophic conditions in C4. The metagenome-assembled genomes (MAGs) such as MAG106, MAG127, MAG52, and MAG37 annotated as denitrifying phosphorus-accumulating organisms (DPAOs) and MAG146 as a DGAO were dominated in C1 and C2 and contributed to 89.2% of COD consumption. MAG54 and MAG16 annotated as Candidatus_Brocadia (total relative abundance of 16.5% in C3 and 4.3% in C4) were responsible for 74.4% of the total nitrogen removal through the anammox-mediated pathway. Functional gene analysis based on metagenomic sequencing confirmed that different compartments of the mABR were capable of performing distinct functions with specific advantageous microbial groups, facilitating targeted nutrient removal. Additionally, under oligotrophic conditions, the activity of the anammox bacteria-related genes of hzs was higher compared to that of hdh. Thus, an innovative method for the treatment of low-strength municipal and nitrate-containing wastewaters without aeration was presented, mediated by an anammox process with less land area and excellent quality effluent.

Aerobic and anoxic utilization of organic matter for flexible nitrite supply in nutrient conversion pathways based on anaerobic ammonium oxidation: Microbial interactive mechanism

This study investigated nutrient conversion pathways and corresponding interactive mechanisms in a mainstream partial-nitritation (PN)/anaerobic ammonium oxidation (anammox)/partial-denitrification-(PD)-enhanced biological phosphorus-removal (EBPR) (PN/A/PD-EBPR) process. A laboratory-scale sequencing batch reactor was operated for 301 days under different operational strategies. Mainstream PN/A/PD-EBPR was successfully operated with aerobic and anoxic utilization of organic matter. Aerobic utilization of organic matter was an effective strategy for conversion to denitrifying polyphosphate-accumulating organism-based phosphorus removal, referring to a biological reaction that outperformed nitrite-oxidizing bacteria. Aerobically adsorbed organic matter could be used as a carbon source for PD, which further enhanced nitrogen removal by PN/A. Ultimately, the interaction between complex nutrient conversion pathways served to achieve stable performance. High-throughput sequencing results elucidated the core microbe functioning in the mainstream PN/A/PD-EBPR process with respect to various nutrients. The outcomes of this study will be beneficial to those attempting to implement mainstream PN/A/PD-EBPR.

Side-Stream Enhanced Biological Phosphorus Removal (S2EBPR) enables effective phosphorus removal in a pilot-scale A-B stage shortcut nitrogen removal system for mainstream municipal wastewater treatment

While the adsorption/bio-oxidation (A/B) process has been widely studied for carbon capture and shortcut nitrogen (N) removal, its integration with enhanced biological phosphorus (P) removal (EBPR) has been considered challenging and thus unexplored. Here, full-scale pilot testing with an integrated system combining A-stage high-rate activated sludge with B-stage partial (de)nitrification/anammox and side-stream EBPR (HRAS-P(D)N/A-S2EBPR) was conducted treating real municipal wastewater. The results demonstrated that, despite the relatively low influent carbon load, the B-stage P(D)N-S2EBPR system could achieve effective P removal performance, with the carbon supplement and redirection of the A-stage sludge fermentate to the S2EBPR. The novel process configuration design enabled a system shift in carbon flux and distribution for efficient EBPR, and provided unique selective factors for ecological niche partitioning among different key functionally relevant microorganisms including polyphosphate accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs). The combined nitrite from B-stage to S2EBPR and aerobic-anoxic conditions in our HRAS-P(D)N/A-S2EBPR system promoted DPAOs for simultaneous internal carbon-driven denitrification via nitrite and P removal. 16S rRNA gene-based oligotyping analysis revealed high phylogenetic microdiversity within the Accumulibacter population and discovered coexistence of certain oligotypes of Accumulibacter and Competibacter correlated with efficient P removal. Single-cell Raman micro-spectroscopy-based phenotypic profiling showed high phenotypic microdiversity in the active PAO community and the involvement of unidentified PAOs and internal carbon-accumulating organisms that potentially played an important role in system performance. This is the first pilot study to demonstrate that the P(D)N-S2EBPR system could achieve shortcut N removal and influent carbon-independent EBPR simultaneously, and the results provided insights into the effects of incorporating S2EBPR into A/B process on metabolic activities, microbial ecology, and resulted system performance.