Applicability of one-stage partial nitritation and anammox in MBBR for anaerobically pre-treated municipal wastewater

Comammox Nitrospira cooperate with anammox bacteria in a partial nitritation-anammox membrane bioreactor treating low-strength ammonium wastewater at high loadings

Research has revealed that comammox Nitrospira and anammox bacteria engage in dynamic interactions in partial nitritation-anammox reactors, where they compete for ammonium and nitrite or comammox Nitrospria supply nitrite to anammox bacteria. However, two gaps in the literature are present: the know-how to manipulate the interactions to foster a stable and symbiotic relationship and the assessment of how effective this partnership is for treating low-strength ammonium wastewater at high hydraulic loads. In this study, we employed a membrane bioreactor designed to treat synthetic ammonium wastewater at a concentration of 60 mg N/L, reaching a peak loading of 0.36 g N/L/day by gradually reducing the hydraulic retention time to 4 hr. Throughout the experiment, the reactor achieved an approximately 80 % nitrogen removal rate through strategically adjusting intermittent aeration at every stage. Notably, the genera Ca. Kuenena, Nitrosomonas, and Nitrospira collectively constituted approximately 40 % of the microbial community. Under superior intermittent aeration conditions, the expression of comammox amoA was consistently higher than that of Nitrospira nxrB and AOB amoA in the biofilm, despite the higher abundance of Nitrosomonas than comammox Nitrospira, implying that the biofilm environment is favorable for fostering cooperation between comammox and anammox bacteria. We then assessed the in situ activity of comammox Nitrospira in the reactor by selectively suppressing Nitrosomonas using 1-octyne, thereby confirming that comammox Nitrospira played the primary role in facilitating the nitritation (33.1 % of input ammonium) rather than complete nitrification (7.3 % of input ammonium). Kinetic analysis revealed a specific ammonia-oxidizing rate 5.3 times higher than the nitrite-oxidizing rate in the genus Nitrospira, underscoring their critical role in supplying nitrite. These findings provide novel insights into the cooperative interplay between comammox Nitrospira and anammox bacteria, potentially reshaping the management of nitrogen cycling in engineered environments, and aiding the development of microbial ecology-driven wastewater treatment technologies.

Genome-centered metagenomics illuminates adaptations of core members to a partial Nitritation-Anammox bioreactor under periodic microaeration

The partial nitritation-anaerobic ammonium oxidation (anammox; PN-A) process has been considered a sustainable method for wastewater ammonium removal, with recent attempts to treat low-strength wastewater. However, how microbes adapt to the alternate microaerobic-anoxic operation of the process when treating low ammonium concentrations remains poorly understood. In this study, we applied a metagenomic approach to determine the genomic contents of core members in a PN-A reactor treating inorganic ammonium wastewater at loading as low as 0.0192 kg-N/m³/day. The metabolic traits of metagenome-assembled genomes from 18 core species were analyzed. Taxonomically diverse ammonia oxidizers, including two Nitrosomonas species, a comammox Nitrospira species, a novel Chloroflexota-related species, and two anammox bacteria, Ca. Brocadia and Ca. Jettenia, accounted for the PN-A reactions. The characteristics of a series of genes encoding class II ribonucleotide reductase, high-affinity bd-type terminal oxidase, and diverse antioxidant enzymes revealed that comammox Nitrospira has a superior adaptation ability over the competitors, which may confer the privileged partnership with anammox bacteria in the PN-A reactor. This finding is supported by the long-term monitoring experiment, showing the predominance of the comammox Nitrospira in the ammonia-oxidizing community. Metagenomic analysis of seven heterotrophs suggested that nitrate reduction is a common capability in potentially using endogenous carbohydrates and peptides to enhance nitrogen removals. The prevalence of class II ribonucleotide reductase and antioxidant enzymes genes may grant the adaptation to cyclically microaerobic/anoxic environments. The predominant heterotroph is affiliated with Chloroflexota; its genome encodes complete pathways for synthesizing vitamin B6 and methionine. By contrast, other than the two growth factors, Nitrospira and anammox bacteria are complementary to produce various vitamins and amino acids. Besides, the novel Chloroflexota-related ammonia oxidizer lacks corresponding genes for detoxifying the reactive oxygen species and thus requires the aid of co-existing members to alleviate oxidative stress. The analysis results forecast the exchanges of substrates and nutrients as well as the collective alleviation of oxidative stress among the core populations. The new findings of the genomic features and predicted microbial interplay shed light on microbial adaptation to intermittent microaeration specific to the PN-A reactor, which may aid in improving its application to low-strength ammonium wastewater.

Bacterial biofilm and extracellular polymeric substances in the moving bed biofilm reactor for wastewater treatment: A review

Among the several biofilm-based bioreactors, moving bed biofilm reactors (MBBR) have been extensively used for wastewater treatment due to low operational costs, technical feasibility, and stability. Biofilm forming strains, e.g., Stenotrophomonas maltophila DQ01, achieved 94.21% simultaneous nitrification and denitrification (SND) and 94.43% removal of total nitrogen (TN) at a cycle time of 7 h, and a biofilm consortium consisting of Chryseobacteriumsp. andRhodobactersp. achieved 86.8% removal of total organic carbon (TOC) at hydraulic retention time (HRT) of 24 h using lab-scale MBBR. Modifications in the surface properties of the biocarrier materials achieved 99.5 ± 1.1% chemical oxygen demand (COD) and 93.6 ± 2.3% NH₄⁺-N removal, significantly higher than the conventional commercial carrier. This review article summarizes the application of MBBR technology for wastewater treatment. The importance of bacterial biofilm and extracellular polymeric substances (EPS), anammox-n-DAMO coupled processes, and carrier surface modifications in MBBR technology have also been discussed.

Achieving stable mainstream nitrogen and phosphorus removal assisted by hydroxylamine addition in a continuous partial nitritation/anammox process from real sewage

Hydroxylamine (NH₂OH) as the putative intermediate for anammox ensures the robustness of partial nitritation/anammox (PN/A) process; however, the feasible for NH₂OH addition to improve the stability of PN/A process under low-strength ammonia (NH₄⁺-N) condition need to be further investigated. In this study, the restoration and steady operation of mainstream PN/A process were investigated to treat real sewage with in situ NH₂OH added in a continuous alternating anoxic/aerobic with integrated fixed-film activated sludge (A³-IFAS) reactor. Results showed that the deteriorated PN/A process caused by nitrate (NO₃^--N) built-up was rapidly restored with a distinct decrease of the NO₃^--N_produced/NH₄⁺-N_consumed ratio from 28.7% to <10.0% within 20 days, after 5 mg N/L of NH₂OH was added daily into the aerobic zone of A³-IFAS reactor. After 230 days of operation, the average total nitrogen (TN) and phosphate (PO₄^3--P) removal efficiencies of 80.8% and 91.5%, respectively were stably achieved, with average effluent sCOD, NH₄⁺-N, TN and PO₄^3--P concentrations reaching 23.1, 2.3, 7.7 and 0.4 mg/L, respectively. Microbial community characterization revealed Candidatus Brocadia (3.60% and 2.92%) and Ignavibacteriae (1.56% and 2.66%) as the dominant anammox bacteria and denitrifying bacteria, respectively, jointly attached in the biofilm_1 and biofilm_2, while Candidatus Microthrix (5.17%) dominant in floc sludge was main responsible for phosphorus removal. This study confirmed that NH₂OH addition is an effective strategy for nitrite-oxidizing bacteria suppression, contributing to the in situ restoration of PN/A process and high stable mainstream nitrogen and phosphorus removal in a continuous PN/A process from real sewage.

An effective strategy for in situ start-up of mainstream anammox process treating domestic sewage

The feasibility of in situ start-up of mainstream anammox process was investigated in three parallel sequencing batch biofilm reactors (SBBRs) inoculated with nitrification sludge, partial nitrification sludge, and denitrifying phosphorus removal sludge, respectively. The SBBRs were operated under alternate anaerobic/aerobic/anoxic pattern at ambient temperature (16.5-26.8 °C). The influent organic and nitrogen loading rates were increased stepwise. Anammox bacteria grew exponentially with relative abundance and overall bacterial activity increasing from 0 to 0.004% to 0.29-0.40% and 'not detected' to 6-7 mg N/L/h, respectively. Desirable nitrogen removal efficiency of about 86% was obtained in 3-4 months for the influent nitrogen of 40.5-73.6 mg N/L. Anammox was the primary nitrogen transformation pathway. For the anammox bacterial enrichment, biofilm, alternate anaerobic/aerobic/anoxic pattern, and limited aeration played important roles. Seed sludge with high ammonium oxidizing bacterial activity further promoted the start-up of anammox process. The in situ start-up strategy could promote the full-scale application of mainstream anammox.

Key factors governing the performance and microbial community of one-stage partial nitritation and anammox system with bio-carriers and airlift circulation

A one-stage airlift internal circulation biofilm reactor was continuously operated for 668 days to treat 50 mg/L of ammonia wastewater to pursue the long-term stability of partial nitritation and anammox (PNA) process. The operational performance and microbial community structure of the biofilm and the flocs were investigated. A nitrogen removal efficiency (NRE) of 70% was obtained successfully at a dissolved oxygen (DO) of 0.05-0.15 mg/L by regulating aeration rate. The microbial analysis indicated Candidatus Brocadia (29.5%) and Nitrosomonas (6.8%) were dominant in both biofilms and flocs. It was found that DO control and aeration rate were the key factors in performance stability, and a stable performance could be recovered and maintained under oxygen-limiting conditions. Further, the achievement of activated ammonia oxidation bacteria (AOB), dominated anammox bacteria (AMX), suppressed NOB, and controlled heterotrophic bacteria (HB) in the biofilms played a major role in the long-term stable operation.

Comammox Nitrospira Species Dominate in an Efficient Partial Nitrification-Anammox Bioreactor for Treating Ammonium at Low Loadings

Bacteria capable of complete ammonia oxidation (comammox) are widespread and contribute to nitrification in wastewater treatment facilities. However, their roles in partial nitrification-anaerobic ammonium oxidation (anammox) systems remain unclear. In this study, a bench-scale bioreactor with continuous stirring was operated for more than 1000 days with limited oxygen supply to achieve efficient nitrogen removal (70.1 ± 2.7%) at a low ammonium loading of 35.2 mg-N/L/day. High-throughput amplicon sequencing analysis of the comammox ammonia monooxygenase subunit A (amoA) gene revealed seven sequence types from two clusters in clade A of comammox Nitrospira. Quantitative polymerase chain reaction analyses suggested that the comammox species dominated the ammonia-oxidizing community, with an abundance as high as 89.2 ± 7.9% in total prokaryotic amoA copies. Multiple linear regression further revealed the substantial contribution of the comammox Nitrospira to ammonia oxidation in the bioreactor. The investigation with bioreactor and batch experiments consistently showed that activities of comammox Nitrospira were inhibited by free ammonia far more severely than other ammonia-oxidizing microbes. Overall, this study provided new insight into the ecology of comammox Nitrospira under hypoxic conditions and suggested comammox-associated partial nitrification-anammox as a potential method for treating low-strength ammonium-containing wastewater.

A Highly Packed Biofilm Reactor with Cycle Cleaning for the Efficient Treatment of Rural Wastewater

Biological treatment processes perform satisfactory in wastewater treatment, but the relatively high cost and complicated maintenance limit its application in rural areas. In this study, a highly packed biofilm reactor (HPBR), with a 90% packing ratio of carriers in the bioreactor, was designed for rural wastewater treatment. The results showed that the removal rates for chemical oxygen demand (COD) and ammonia were 3.04 ± 1.81 kg/m3/d and 0.49 ± 0.18 kg/m3/d, respectively. Besides, the removal efficiency of total inorganic nitrogen (TIN) was 35.4% by the HPBR. The removal capacity of the HPBR is higher than other reported systems with fewer operational costs and maintenance. High-throughput sequencing was applied to further investigate the kinetics and principals. Microorganisms capable of simultaneous nitrification-denitrification were found to be dominant species in the HPBR system, which indicated that the nitrogen removal in HPBR is governed by simultaneous nitrification-denitrification. These findings suggest that HPBR can be used as an efficient reactor for rural wastewater treatment, demonstrating its feasibility in real applications.

Deammonification process in municipal wastewater treatment: Challenges and perspectives

The deammonification process has been proved to be an efficient nitrogen removal process in treating high NH₄⁺-N concentration wastewater (sidestream deammonification). It is very hopeful to bring WWTP close to energy autarky. However, the feasibility of applying mainstream deammonification to sewage treatment need to be further explored. Therefore, this review attempts to give an overview of challenges in applying mainstream deammonification and to discuss the impacts of unfavorable conditions on main functional species. In addition, some novel control strategies to maintain the dominant position of desired species were summarized. Efficient solution to the conflict between AnAOB (Anaerobic ammonium-oxidizing bacteria) biomass retention and NOB (Nitrite oxidizing bacteria) wash out was also reviewed. Ultimately, we suggested further studies including effective improved process that achieve combination of autotrophy and organotrophy species based on the metabolic diversity of AnAOB.

Performance and microbial community analysis of two sludge type reactors in achieving mainstream deammonification with hydrazine addition

The deammonification process is a promising and energy efficient nitrogen removal technology. Since deammonification process has succeeded in high-strength ammonia nitrogen wastewater treatment (sidestream deammonification) but its application in treating low-strength ammonium nitrogen wastewater (mainstream deammonification) remains a great challenge. In this study, mainstream deammonification process in two reactors maintained stability with hydrazine (N₂H₄) addition. The two reactors consisted of a deammonification granular reactor and a mixed ammonia oxidizing bacteria (AOB) flocculent with anaerobic ammonia oxidizing bacteria (AnAOB) granular reactor. Deammonification granular reactor had a more efficient total nitrogen removal efficiency (TNRE, 80.5 ± 5.8%) and nitrogen removal rate (NRR, 0.33 ± 0.04 g/(L·day)). The advantage of retain biomass in granular sludge reactor lead to a more balanced ex-situ activity between AOB (0.37 mg N/(g VSS·h)) and AnAOB (0.43 mg N/(g VSS·h)). Candidatus Brocadia and Nitraspira were detected the dominant genus responsible for the observed AnAOB and nitrite oxidizing bacteria (NOB), respectively. The more obvious effect of N₂H₄ on enhancing AnAOB and suppressing NOB both in ex-situ activity and genus abundances in mixed sludge reactor were also founded may due to loose spatial distribution among species.

A review on mainstream deammonification of municipal wastewater: Novel dual step process

The conventional biological nitrogen removal process is receiving increasing pressure partially due to its energy-negative operation. To address this challenge, various mainstream deammonification processes have been explored for energy-neutral municipal wastewater treatment, whereas these processes appear challenging to be sustainably and stably achieved in conventional process configurations. Therefore, this review aimed to provide a comprehensive analysis of the state-of-the-art of mainstream deammonification, while highlighting the major technical challenges. It appeared that recently developed novel dual step process, i.e. A-B processes, could provide a feasible engineering option for mainstream deammonification, where A-stage is designed for COD capture with the aim to enhance energy recovery, and B-stage is tailored for nutrient removal/recovery. This indeed may lead to a promising integrated mainstream deammonification process towards energy-efficient and environmentally sustainable nitrogen removal. Meanwhile, this review also offered an opinion on future municipal wastewater treatment, aiming for concurrent water reclamation and energy recovery.

The threshold of influent ammonium concentration for nitrate over-accumulation in a one-stage deammonification system with granular sludge without aeration

Low-strength ammonium is still a challenge for the mainstream deammonification because of nitrate over-accumulation. In this study, the threshold of influent ammonium concentration of one-stage deammonification system with granular sludge was investigated, by stepwise decreasing influent ammonium from high concentrations (280mg/L to 140mg/L) to the low concentration (70mg/L) in 108d at 32°C without aeration. Results showed that, under 70mg/L NH₄⁺-N, ΔNO₃^--N/ΔNH₄⁺-N ratio increased to 0.2, deviated from the theoretical value of 0.11, with ammonium and TN removal efficiencies of 91% and 71%, respectively. However, under both high ammonium concentrations (280mg/L and 140mg/L), nitrate production stabilized at only 13%. Chloroflexi, Planctomycetes and Proteobacteria contributed >70% of the communities under all three ammonium concentrations. As influent ammonium decreasing, the relative abundances of bacteria for anammox, aerobic oxidizing and denitrifying decreased, while NOB (nitrite oxidizing bacteria) abundance increased greatly. So 70mg/L was the threshold of influent ammonium concentration for stable deammonification without organic influent. It was the decrease of functional bacteria and overgrowth of NOB that worsen the deammonification performance under low-strength ammonium.

Status, Challenges, and Perspectives of Mainstream Nitritation-Anammox for Wastewater Treatment

  The nitritation-anammox process is an efficient and cost-effective approach for biological nitrogen removal, but its application in treating mainstream wastewater remains a great challenge. Mainstream nitritation-anammox processes could create opportunities for achieving energy self-sufficient, or energy-generating water resource recovery facilities. Significant advancements have been achieved via pilot- and full-scale trials to overcome the major obstacles under mainstream conditions, such as repression of nitrite-oxidizing bacteria, limiting the overgrowth of denitrifiers, and effective selection and retention of ammonia-oxidizing bacteria and anammox bacteria. This review paper intends to provide a detailed update of research progress on mainstream nitritation-anammox processes, discuss metabolic interactions, and examine major challenges and possible solutions towards the future development.

Good servant, bad master: sulfide influence on partial nitritation of sewage

When applying partial nitritation (PN) to anaerobically pre-treated sewage, ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) will be exposed to dissolved sulfide and methane. Both sulfide and methane may inhibit nitrification. To gain knowledge necessary for sustaining PN under these conditions, we exposed an AOB enrichment and a mixed nitrifying culture to dissolved sulfide and methane. In the mixed nitrifying culture, sulfide selectively inhibited NOB activity (K_I,AOB1 = 150 mg-S L^-1, K_I,NOB = 10 mg-S L^-1) which shows that sulfide may help establish PN. The AOB enrichment showed similar K_I,AOB2 (130 mg-S L^-1), but nitritation activity lagged longer than the time necessary to remove sulfide from the liquid. This demonstrates that feeding of sulfide into established PN should be avoided. Methane inhibition of AOB enrichment was assessed in batch assays with 10 mg-CH₄ L^-1. As compared to control without methane, AOB enrichment activity was identical. Up to 51% of methane was converted to methanol, thus reducing the greenhouse gas emissions.

High-Rate Partial Nitritation of Municipal Wastewater after Psychrophilic Anaerobic Pretreatment

Partial nitritation/anammox can provide energy-efficient nitrogen removal from the main stream of municipal wastewater. The main bottleneck is the growth of nitrite oxidizing bacteria (NOB) at low temperatures (<15 °C). To produce effluent suitable for anammox, real municipal wastewater after anaerobic pretreatment was treated by enriched ammonium oxidizing bacteria (AOB) in suspended sludge SBR at 12 °C. NOB were continually washed out using aerobic duration control strategy (ADCS). Solids retention time was set to 9-16 days. Using this approach, average ammonia conversion higher than 57% at high oxidation rate of 0.4 ± 0.1 kg-N kg-VSS^-1 d^-1 was achieved for more than 100 days. Nitrite accumulation (N-NO₂^-/N-NO_X) of 92% was maintained. Thus, consistently small amounts of present NOB were efficiently suppressed. Our mathematical model explained how ADCS enhanced the inhibition of NOB growth via NH₃ and HNO₂. This approach will produce effluent suitable for anammox even under winter conditions in mild climates.