Improving performance and efficiency of partial anammox by coupling partial nitrification and partial denitrification (PN/A-PD/A) to treat municipal sewage in a step-feed reactor

Leveraging primary effluent- and glycerol-driven partial denitrification-anammox within a pilot-scale tertiary step-feed moving bed biofilm reactor treating high-rate activated sludge systems effluent

This study investigated the possibility of utilizing primary effluent (PE) carbon as an internal carbon source to drive tertiary partial denitrification-anammox (PdNA) for treating high-rate activated sludge (HRAS) system effluent, so as to offset the consumption of external carbon such as glycerol. This pilot study was conducted in a tertiary step-feed moving bed biofilm reactor (MBBR) over 478 days, using full-scale HRAS secondary effluent as the influent. Unlike most PdNA applications that rely on the expensive supplemental carbon like methanol or glycerol, this study is the first to demonstrate that PE carbon can be utilized as a naturally available carbon source within wastewater to drive PdNA. By taking advantage of this free internal carbon source to driven PdNA, 63% to 74% savings in PE carbon consumption and ∼36% offset in glycerol consumption were achieved. Additionally, glycerol-driven PdNA further reduced both supplemental carbon and aeration energy demands by 70% and 18%. Mechanistic insights from in-situ and ex-situ batch tests revealed that the PE-driven PdNA was facilitated by an anammox-driven nitrite sink, a novel observation that allowed stable PdNA performance without nitrite accumulation. Furthermore, batch tests indicated that endogenous respiration could support PdNA. These findings highlight the potential of applying PE-driven PdNA in full-scale facilities, ushering in a new era of mainstream anammox applications in wastewater treatment, as PdNA is no longer reliant on costly external carbon addition.

Advanced nitrogen removal from extremely low carbon/nitrogen ratio municipal wastewater by optimizing multiple pathways based on step-feed and intermittent aeration

The advantages of step-feed and intermittent aeration have been well-documented, however, combining them to enhance nitrogen removal in anaerobic/oxic/anoxic systems has been rarely explored. This study established the non-single-form anoxic stages by step-feed and intermittent aeration and finally enhanced the nitrogen removal of real municipal wastewater with step-feed anaerobic/oxic/anoxic/oxic/anoxic operation mode. Results revealed that Candidatus_Brocadia increased from 0.00 % to 0.21 % in the suspended sludge system, contributing 54.7 % of the nitrogen removal. Partial nitrification (PN) and endogenous partial denitrification (EPD) supplied nitrite for Anammox. A comprehensive multi-pathway nitrogen removal system, encompassing PN, nitrification, partial denitrification, Anammox, EPD/Anammox, and denitrification was constructed. The system effectively reduced total inorganic nitrogen concentration to 3.6 ± 1.2 mg/L at a carbon/nitrogen ratio of 3.0 ± 0.3, achieving a nitrogen removal efficiency of 95.3 ± 1.5 %. This study provides a novel approach for the advanced treatment of municipal wastewater and enrichment of anaerobic ammonia-oxidizing bacteria.

The interactive application and impacts of iron/nitrogen biogeochemical cycling in distributed ponds for non-point source pollution control in a watershed

The linkages of distributed ponds are utilized in conjunction with one another to remediate non-point source (NPS) pollution in a water-scarce basin. This study provides an overview of a state-of-the-art thorough evaluation of ponds, which offers insight into the majority of topics covered by the ongoing scientific studies, including their various functions and factors affecting their functioning on the hydrological, physicochemical, and biological processes, such as environmental climate factors and basin-specific landscape configuration parameters, as well as process parameters for design, operation and management aspects. The linkages of ponds provide a variety of sustainable services (6R functions), such as resources, restoration, reduction, reuse, recycling, and recovery. The significance of regional environmental geochemical substrates in the ponds, such as red soil, as a hotspot for microbial reaction is emphasized to demonstrate the significant contribution of the migration and transformation of Fe/N cycles to the pollution removal process. In this review, 178 original research publications were thoroughly analyzed to improve our knowledge of the iron-nitrogen cycle in wetlands. From a molecular biology standpoint, the identification of functional microbe species and genes linked to microbially driven iron-nitrogen cycle activities is delved. Reliable data and homogeneous datasets from 42 studies were collected. The correlation analysis results demonstrated Feammox rates contributed to the N loss amount (r = 0.871; p < 0.01), and they had a positive correlation with Fe(III) concentration (r = 0.965; p < 0.01). The proposal for the treatment of NPS pollution by large-scale linkages of ponds in a basin involves optimizing Fe/N microbial processes to promote iron crystallization and efficient circulation of Fe(II) and Fe(III). The co-benefits of geochemistry, biotechnology, and environmental science should be considered when managing contamination in engineering applications. The linkages framework for integrated ponds, which incorporates macro (watershed management) and micro (biogeochemical cycle mechanism) investigations, provides a systematic approach to the application of integrated ponds and sustainable water management for NPS pollution control.

Rapid start-up and metabolic evolution of partial denitrification/anammox process by hydroxylamine stimulation: Nitrogen removal performance, biofilm characteristics and microbial community

Enhanced nitrogen removal by hydroxylamine (NH2OH) on anammox-related process recently received attention. This study investigated the impact of NH2OH on the partial-denitrification/anammox (PDA) biosystem. Results show that NH2OH (≤10 mg N/L) immediately induced nitrite accumulation and provided sufficient NO2- to anammox, achieving a 18.1 ± 4.3 % increase of nitrogen removal efficiency compared to the absence of NH2OH. Long-term exposure to NH2OH accelerated the functional microbial community transformation to PDA. Thauera was highly enriched (6.1 % → 26.9 %) along with Candidatus Brocadia increased in the biofilms, which mainly favor the coupling process of nitrate reduction and anammox. Although the migration mechanism of anammox and denitrifier revealed by CLSM-FISH alleviates the adverse effects of NH2OH, the anammox was inhibited when NH2OH exceeding 15 mg N/L through destroying the inner reduction of NO2-. These results suggested appropriate NH2OH addition favors the synergy between denitrifying and anammox bacteria, providing a promising option for wastewater treatment.

Feasibility of double nitrite supply through partial nitrification and partial denitrification driven by sludge fermentation

Challenges in obtaining stable nitrite have impeded the use of anammox in municipal wastewater treatment. This study explored the feasibility of using sludge fermentation products as carbon source and selective nitrification inhibitor to supply nitrite via partial nitrification (PN) and partial denitrification (PD). PD was initiated within 15 days, achieving nitrite transformation rate of over 90 % with a carbon/nitrogen ratio of 3 and a reaction time of 0.75 h. The dominant genus, Romboutsia, increased in relative abundance from 4.1 to 35 %. Organic acids in sludge fermentation products, like acetate (200 mg/L) and propionate (400 mg/L), selectively suppressed nitrite-oxidizing bacteria (NOB) more than ammonia-oxidizing bacteria (AOB), leading to PN. Combining anaerobic exposure with sludge fermentation products addition achieved PN with over 80.0 % nitrite accumulation. AOB increased tenfold in the long term, significantly outpacing NOB growth. This strategy simplifies difficulty of anammox application and shows broad application potential in municipal wastewater treatment.

Metabolic evolution and bottleneck insights into simultaneous autotroph-heterotroph anammox system for real municipal wastewater nitrogen removal

When biological nitrogen removal (BNR) systems shifted from treating simulated wastewater to real wastewater, a microbial succession occurred, often resulting in a decline in efficacy. Notably, despite their high nitrogen removal efficiency for real wastewater, anammox coupled systems operating without or with minimal carbon sources also exhibited a certain degree of performance reduction. The underlying reasons and metabolic shifts within these systems remained elusive. In this study, the simultaneous autotrophic/heterotrophic anammox system demonstrated remarkable metabolic resilience upon exposure to real municipal wastewater, achieving a nitrogen removal efficiency (NRE) of 82.83 ± 2.29 %. This resilience was attributed to the successful microbial succession and the complementary metabolic functions of heterotrophic microorganisms, which fostered a resilient microbial community. The system's ability to harness multiple electron sources, including NADH oxidation, the TCA cycle, and organics metabolism, allowed it to establish a stable and efficient electron transfer chain, ensuring effective nitrogen removal. Despite the denitrification channel's nitrite supply capability, the analysis of the interspecies correlation network revealed that the synergistic metabolism between AOB and AnAOB was not fully restored, resulting in selective functional bacterial and genetic interactions and the system's PN/A performance declined. Additionally, the enhanced electron affinity of PD increased interconversion of NO3--N and NO2--N, limiting the efficient utilization of electrons and thereby constraining nitrogen removal performance. This study elucidated the metabolic mechanism of nitrogen removal limitations in anammox-based systems treating real municipal wastewater, enhancing our understanding of the metabolic functions and electron transfer within the symbiotic bacterial community.

Ultrasound-induced structural changes in partial nitrification sludge: Unravelling the mechanism for improved nitrogen removal

Low-intensity ultrasound, as a form of biological enhancement technology, holds significant importance in the field of biological nitrogen removal. This study utilized low-intensity ultrasound (200 W, 6 min) to enhance partial nitrification and investigated its impact on sludge structure, as well as the internal relationship between structure and properties. The results demonstrated that ultrasound induced a higher concentration of nitrite in the effluent (40.16 > 24.48 mg/L), accompanied by a 67.76% increase in the activity of ammonia monooxygenase (AMO) and a 41.12% increase in the activity of hydroxylamine oxidoreductase (HAO), benefiting the partial nitrification. Based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theoretical analysis, ultrasonic treatment enhanced the electrostatic interaction energy (WR) between sludge flocs, raising the total interaction energy from 46.26 kT to 185.54 kT, thereby causing sludge dispersion. This structural alteration was primarily attributed to the fact that the tightly bonded extracellular polymer (TB-EPS) after ultrasound was found to increase hydrophilicity and negative charge, weakening the adsorption between sludge cells. In summary, this study elucidated that the change in sludge structure caused by ultrasonic treatment has the potential to enhance the nitrogen removal performance by partial nitrification.

Insights into the carbon and nitrogen metabolism pathways in mixed-autotrophy/heterotrophy anammox consortia in response to temperature reduction

While the multi-coupled anammox system boasts a substantial research foundation, the specific characteristics of its synergistic metabolic response to decreased temperatures, particularly within the range of 13-15 °C, remained elusive. In this study, we delve into the intricate carbon and nitrogen metabolism pathways of mixed-autotrophy/heterotrophy anammox consortia under conditions of temperature reduction. Our macrogenomic analyses reveal a compelling phenomenon: the stimulation of functional genes responsible for complete denitrification, suggesting an enhancement of this process during temperature reduction. This adaptation likely contributes to maintaining system performance amidst environmental challenges. Further metabolic functional recombination analyses highlight a dramatic shift in microbial community composition, with denitrifying MAGs (metagenome-assembled genomes) experiencing a substantial increase in abundance (up to 200 times) compared to autotrophic MAGs. This proliferation underscores the strong stimulatory effect of temperature reduction on denitrifying species. Notably, autotrophic MAGs play a pivotal role in supporting the glycolytic processes of denitrifying MAGs, underscoring the intricate interdependencies within the consortia. Moreover, metabolic variations in amino acid composition among core MAGs emerge as a crucial adaptation mechanism. These differences facilitate the preservation of enzyme activity and enhance the consortia's resilience to low temperatures. Together, these findings offer a comprehensive understanding of the microbial synergistic metabolism within mixed-autotrophy/heterotrophy anammox consortia under temperature reduction, shedding light on their metabolic flexibility and resilience in dynamic environments.

Insight into the microbial community of denitrification process using different solid carbon sources: Not only bacteria

There is a lack of understanding about the bacterial, fungal and archaeal communities' composition of solid-phase denitrification (SPD) systems. We investigated four SPD systems with different carbon sources by analyzing microbial gene sequences based on operational taxonomic unit (OTU) and amplicon sequence variant (ASV). The results showed that the corncob-polyvinyl alcohol sodium alginate-polycaprolactone (CPSP, 0.86±0.04 mg NO3--N/(g·day)) and corncob (0.85±0.06 mg NO3--N/(g·day)) had better denitrification efficiency than polycaprolactone (PCL, 0.29±0.11 mg NO3--N/(g·day)) and polyvinyl alcohol-sodium alginate (PVA-SA, 0.24±0.07 mg NO3--N/(g·day)). The bacterial, fungal and archaeal microbial composition was significantly different among carbon source types such as Proteobacteria in PCL (OTU: 83.72%, ASV: 82.49%) and Rozellomycota in PVA-SA (OTU: 71.99%, ASV: 81.30%). ASV methods can read more microbial units than that of OTU and exhibit higher alpha diversity and classify some species that had not been identified by OTU such as Nanoarchaeota phylum, unclassified_ f_ Xanthobacteraceae genus, etc., indicating ASV may be more conducive to understand SPD microbial communities. The co-occurring network showed some correlation between the bacteria fungi and archaea species, indicating different species may collaborate in SPD systems. Similar KEGG function prediction results were obtained in two bioinformatic methods generally and some fungi and archaea functions should not be ignored in SPD systems. These results may be beneficial for understanding microbial communities in SPD systems.

Treatment of low-C/N nitrate wastewater using a partial denitrification-anammox granule system: Granule reconstruction, stability, and microbial structure analyses

Industrial wastewater discharged into sewer systems is often characterized by high nitrate contents and low C/N ratios, resulting in high treatment costs when using conventional activated sludge methods. This study introduces a partial denitrification-anammox (PD/A) granular process to address this challenge. The PD/A granular process achieved an effluent TN level of 3.7 mg/L at a low C/N ratio of 2.3. Analysis of a typical cycle showed that the partial denitrification peaked within 15 min and achieved a nitrate-to-nitrite transformation ratio of 86.9%. Anammox, which was activated from 15 to 120 min, contributed 86.2% of the TN removal. The system exhibited rapid recovery from post-organic shock, which was attributed to significant increases in protein content within TB-EPS. Microbial dispersion and reassembly were observed after coexistence of the granules, with Thauera (39.12%) and Candidatus Brocadia (1.25%) identified as key functional microorganisms. This study underscores the efficacy of PD/A granular sludge technology for treating low-C/N nitrate wastewater.

Novel and innovative approaches to partial denitrification coupled with anammox: A critical review

The partial denitrification (PD) coupled with anaerobic ammonium oxidation (Anammox) (PD/A) process is a unique biological denitrification method for sewage that concurrently removes nitrate (NO3--N) and ammonium (NH4+-N) in sewage. Comparing PD/A to conventional nitrification and denitrification technologies, noticeable improvements are shown in energy consumption, carbon source demand, sludge generation and emissions of greenhouse gasses. The PD is vital to obtaining nitrites (NO2--N) in the Anammox process. This paper provided valuable insight by introduced the basic principles and characteristics of the process and then summarized the strengthening strategies. The functional microorganisms and microbial competition have been discussed in details, the S-dependent denitrification-anammox has been analyzed in this review paper. Important factors affecting the PD/A process were examined from different aspects, and finally, the paper pointed out the shortcomings of the coupling process in experimental research and engineering applications. Thus, this research provided insightful information for the PD/A process's optimization technique in later treating many types of real and nitrate-based wastewater. The review paper also provided the prospective economic and environmental position for the actual design implementation of the PD/A process in the years to come.

Comammox and unknown ammonia oxidizers contribute to nitrite accumulation in an integrated A-B stage process that incorporates side-stream EBPR (S2EBPR)

A novel integrated pilot-scale A-stage high rate activated sludge, B-stage short-cut biological nitrogen removal and side-stream enhanced biological phosphorus removal (A/B-shortcut N-S2EBPR) process for treating municipal wastewater was demonstrated with the aim to achieve simultaneous and carbon- and energy-efficient N and P removal. In this studied period, an average of 7.62 ± 2.17 mg-N/L nitrite accumulation was achieved through atypical partial nitrification without canonical known NOB out-selection. Network analysis confirms the central hub of microbial community as Nitrospira, which was one to two orders of magnitude higher than canonical aerobic oxidizing bacteria (AOB) in a B-stage nitrification tank. The contribution of comammox Nitrospira as AOB was evidenced by the increased amoB/nxr ratio and higher ammonia oxidation activity. Furthermore, oligotyping analysis of Nitrospira revealed two dominant sub-clusters (microdiveristy) within the Nitrospira. The relative abundance of oligotype II, which is phylogenetically close to Nitrospira_midas_s_31566, exhibited a positive correlation with nitrite accumulation in the same operational period, suggesting its role as comammox Nitrospira. Additionally, the phylogenetic investigation suggested that heterotrophic organisms from the family Comamonadacea and the order Rhodocyclaceae embedding ammonia monooxygenase and hydroxylamine oxidase may function as heterotrophic nitrifiers. This is the first study that elucidated the impact of integrating the S2EBPR on nitrifying populations with implications on short-cut N removal. The unique conditions in the side-stream reactor, such as low ORP, favorable VFA concentrations and composition, seemed to exert different selective forces on nitrifying populations from those in conventional biological nutrient removal processes. The results provide new insights for integrating EBPR with short-cut N removal process for mainstream wastewater treatment.

Advanced nitrogen removal from municipal wastewater through partial nitrification-denitrification coupled with anammox in step-feed continuous system

Combined partial nitrification-denitrification/anammox (PN-PD/A) processes have attracted great attention from researchers in recent years to achieve high nitrogen removal from low carbon /nitrogen (C/N) municipal wastewater. In this context, a step-feed anoxic/oxic (A/O) process was conducted in this study through the combination of the partial nitrification-anammox (PN/A) and partial denitrification-anammox (PD/A) to remove N from municipal wastewater with low C/N. The enhancement of the PN-PD/A process resulted in N removal efficiency of 85.6% at C/N of 2.8. The contributions of the anammox reached 36.4 and 8.8% in the anoxic and oxic chambers, respectively. The biocarriers added to the anoxic and oxic chambers increased the relative abundance of the anammox bacteria in biofilms from 0.61% to 1.51% and 1.02%, respectively. This study demonstrated that employing the step-feed A/O process can create optimal conditions for the anammox bacteria growth, thereby ensuring advanced N removal from low C/N municipal wastewater.

A novel sulfur autotrophic denitrification in-situ coupled sequencing batch reactor system to treat low carbon to nitrogen ratio municipal wastewater: Performance, niche equilibrium and pollutant removal mechanisms

A novel integrated sulfur fixed-film activated sludge in SBR system (IS0FAS-SBR) was proposed to treat the low C/N ratio municipal wastewater. The effluent total inorganic nitrogen (TIN) and PO43--P decreased from 17 mg/L and 3.5 mg/L to 8.5 mg/L and 0.5 mg/L, and higher nitrogen removal efficiency was contributed by the autotrophic denitrification. Microbial response characteristics showed that catalase (CAT), reduced nicotinamide adenine dinucleotide (NADH) and extracellular polymeric substance (EPS) alleviated the oxidative stress of sulfur carrier to maintain cell activity, while metabolic activity analysis indicated that the electron transfer rate was enhanced to improve mixotrophic denitrification efficiency. Meanwhile, the increased key enzyme activities further facilitated nitrogen removal and sulfur oxidation process. Additionally, the microbial community, functional proteins and genes revealed a niche equilibrium of C, N, S metabolic bacteria. Sulfur autotrophic in-situ coupled SBR system enlarged a promising strategy for treatment of low C/N ratio municipal wastewater.

Response of nitrite accumulation, sludge characteristic and microbial transition to carbon source during the partial denitrification (PD) process

Partial denitrification (PD, nitrate (NO3--N) → nitrite (NO2--N)) as a novel pathway for NO2--N production has been widely concerned, but the specific conditions for highly efficient and stable nitrite maintenance are not yet fully understood. In this study, the effects of carbon sources (acetate, R1; propionate, R2; glucose, R3) on NO2--N accumulation was discussed without seeding PD sludge and the mechanism analysis related to sludge characteristic and microbial evolution were elucidated. The optimal NO2--N, nitrate-to-nitrite transformation ratio (NTR) and nitrite removal efficiency (NRE) reached up to 32.10 mg/L, 98.01 %, and 86.95 % in R1. However, due to the complex metabolic pathway of glucose, the peak time of NO2--N production delayed from 30 min to 60 min. The sludge particle size decreased from 154.2 μm (R1), 130.8 μm (R2) to 112.6 μm (R3) with the increasing extracellular polymeric substances (EPS) from 80.75-85.44 mg/gVSS, 82.68-92.75 mg/gVSS to 106.31-110.25 mg/gVSS, where the ratio of proteins/polysaccharides (PN/PS) was proved to be closely associated with NO2--N generation. For the microbial evolution, Saccharimonadales (70.42 %) dominated the glucose system, while Bacillus (7.42-21.63 %) and Terrimonas (4.24-5.71 %) were the main contributors for NO2--N accumulation in the acetate and propionate systems. The achievement of PD showed many advantages of lower carbon demand, minimal sludge production, lesser greenhouse gas emission and prominent nutrient removal, offering an economically and technically attractive alternative for NO3--N containing wastewater treatment.

Bacillus thuringiensis EM-A1: A novel bacterium for high concentration of ammonium elimination with low nitrite accumulation

The biological elimination of high concentration of ammonium from wastewater has attracted increasing attention in recent years. However, few studies on the efficient elimination of high concentration of ammonium by a single bacterium have been reported. Here, the efficient elimination of NH4+-N (>99%) and total nitrogen (TN) (>77%) were attained by Bacillus thuringiensis EM-A1 under 150 rpm at pH 7.2 with sodium succinate and a carbon/nitrogen ratio of 15 at 30 °C with an inoculum size (as measured by absorbance at 600 nm) of 0.2. Strain EM-A1 effectively eliminated 100 mg/L of inorganic nitrogen with maximal NH4+-N, NO3--N, and NO2--N elimination rates of 4.88, 2.57, and 3.06 mg/L/h, respectively. The elimination efficiencies of NH4+-N were 99.87% and 97.13% at initial concentrations of 500 and 1000 mg/L, respectively. Only 0.91 mg/L of NO2--N was accumulated with the elimination of 1000 mg/L NH4+-N. A concentration of 5 mg/L exogenous hydroxylamine was toxic and further inhibited heterotrophic nitrification and aerobic denitrification (HN-AD). The NH4+-N and NO2--N elimination capacities of strain EM-A1 were specifically inhibited by 2-Octyne (OCT) over 4 μmol/L and diethyldithiocarbamate (DDC) over 0.5 mmol/L, respectively. Above 25 mg/L procyanidin (PCY) inhibited the bioconversion of NO3--N and NO2--N. The results demonstrated that strain EM-A1 had HN-AD capacity under halophilic conditions, and has great potential for use in the treatment of nitrogen pollution wastewater; this study also provides new insights into this strain's nitrogen elimination mechanism, helping advance environmental biotechnology.

Determination of partial denitrification kinetic model parameters based on batch tests and metagenomic sequencing

In this study, a model was developed to investigate the partial denitrification(PD) process. The heterotrophic biomass (X_H) proportion in the sludge was determined to be 66.4% based on metagenomic sequencing. The kinetic parameters were first calibrated, then validated using the batch tests results. The results showed rapid decreases in the chemical oxygen demand (COD) and nitrate concentrations and gradual increases in the nitrite concentrations in the first four hours, then remained constant from 4 to 8 h. Anoxic reduction factor (η_NO3 and η_NO2) and half saturation constant (K_S1 and K_S2) were calibrated at 0.097, 0.13, 89.28 mg COD/L, and 102.29 mg COD/L, respectively. Whereas the simulation results demonstrated that the increase in carbon-to-nitrogen (C/N) ratios and the reduction in X_H contributed to the increase in the nitrite transformation rate. This model provides potential strategies for optimizing the PD/A process.

Towards advanced simultaneous nitrogen removal and phosphorus recovery from digestion effluent based on anammox-hydroxyapatite (HAP) process: Focusing on a solution perspective

In this paper, the state-of-the-art information on the anammox-HAP process is summarized. The mechanism of this process is systematically expounded, the enhancement of anammox retention by HAP precipitation and the upgrade of phosphorus recovery by anammox process are clarified. However, this process still faces several challenges, especially how to deal with the ∼ 11% nitrogen residues and to purify the recovered HAP. For the first time, an anaerobic fermentation (AF) combined with partial denitrification (PD) and anammox-HAP (AF-PD-Anammox-HAP) process is proposed to overcome the challenges. By AF of the organic impurities of the anammox-HAP granular sludge, organic acid is produced to be used as carbon source for PD to remove the nitrogen residues. Simultaneously, pH of the solution drops, which promotes the dissolution of some inorganic purities such as CaCO₃. In this way, not only the inorganic impurities are removed, but the inorganic carbon is supplied for anammox bacteria.

Performance of anammox enchanced by pulsed electric fields under added organic carbon sources using integrated network and metagenomics analyses

This paper aims to investigate the function of a pulsed electric field (PEF) in the anaerobic ammonia oxidation (anammox) process after adding certain chemical oxygen demand (COD) through integrated network and metagenomics analyses. The findings showed that the presence of COD was detrimental to anammox, but PEF could significantly reduce the adverse effect. The total nitrogen removal in the reactor for applying PEF was 16.99% higher on average than the reactor for only dosing COD. Additionally, PEF upgraded the abundance of anammox bacteria subordinate to the phylum Planctomycetes by 9.64%. The analysis of molecular ecological networks promulgated that PEF resulted in an increase in network scale and topology complexity, thereby boosting the potential collaboration of the communities. Metagenomics analyses demonstrated that PEF dramatically promoted anammox central metabolism in the presence of COD, specifically enhancing pivotal N functional genes (hzs, hdh, amo, hao, nas, nor and nos).

Resilience of anammox application from sidestream to mainstream: A combined system coupling denitrification, partial nitritation and partial denitrification with anammox

Anaerobic ammonium oxidation (anammox) is a potential process to achieve the neutralization of energy and carbon. Due to the low temperature and variation of municipal sewage, the application of mainstream anammox is hard to be implemented. For spreading mainstream anammox in practice, several key issues and bottlenecks including the start-up, stable NO₂^--N supply, maintenance and dominance of AnAOB with high activity, prevention of NO₃^--N buildup, reduction of sludge loss, adaption to the seasonal temperature and alleviation of COD impacts on AnAOB are discussed and summarized in this review in order to improve its startup, stable operation and resilience of mainstream anammox. Hence a combined biological nitrogen removal (CBNR) system based on conventional denitrification, shortcut nitrification-denitrification, Partial Nitritation and partial Denitrification combined Anammox (PANDA) process through the management of organic matter and nitrate is proposed correspondingly aiming at adaptation to the variations of seasonal temperature and pollutants in influent.

Using an innovative umbrella-shape membrane module to improve MBR for PN-ANAMMOX process

Membrane fouling has been a key factor limiting the applications of membrane bioreactor (MBR). In this study, a novel umbrella-shape membrane module was applied to construct two MBRs for two-stage partial nitrification-anaerobic ammonia oxidation (PN-ANAMMOX) process. After 55 days operation, the ANAMMOX process was started and the PN process was well controlled. Then, the ANAMMOX and PN process were successfully coupled to run the PN-ANAMMOX process. On 103 days, the best nitrogen removing effect was achieved with the maximum nitrogen loading rate (NLR) of 0.4 kg N·(m³·d)^-1 and the corresponding maximum total nitrogen removal rate (TNRR) of 75.23%. The umbrella-shape membrane module in both reactors only needed to be cleaned once during the operation for 105 days, indicating that the membrane module had better resistance to membrane fouling. The functional bacteria were cultivated in suspension state; moreover, the cell densities of ammonia oxidizing bacteria (AOB) and ANAMMOX bacteria (AnAOB) reached 58.32 × 10¹² copies/g sludge and 28.39 × 10¹² copies/g sludge. Their abundances reached 73.25% and 57.80% of the total bacteria, respectively. MBR improved by umbrella-shape membrane module could realize the rapid start-up of ANAMMOX process, effective control of PN process, and stable operation of PN-ANAMMOX process. This study provided a novel approach to control membrane fouling by optimizing the membrane module shape and widened applications of MBRs in PN-ANAMMOX process.

Simultaneous nitrogen and phosphorus removal from municipal wastewater by Fe(III)/Fe(II) cycling mediated partial-denitrification/anammox

The efficient removal of nitrogen and phosphorus remains challenging for traditional wastewater treatment. In this study, the feasibility for enhancing the partial-denitrification and anammox process by Fe (III) reduction coupled to anammox and nitrate-dependent Fe (II) oxidation was explored using municipal wastewater. The nitrogen removal efficiency increased from 75.5 % to 83.0 % by adding Fe (III). Batch tests showed that NH₄⁺-N was first oxidized to N₂ or NO₂^--N by Fe (III), then NO₃^--N was reduced to NO₂^--N and N₂ by Fe (II), and finally, NO₂^--N was utilized by anammox. Furthermore, the performance of phosphorus removal improved by Fe addition and the removal efficiency increased to 78.7 %. High-throughput sequencing showed that the Fe-reducing bacteria Pseudomonas and Thiobacillus were successfully enriched. The abundance of anammox bacterial increased from 0.03 % to 0.22 % by multiple nitrite supply pathways. Fe addition presents a promising pathway for application in the anammox process.

Enhanced nitrogen removal from municipal wastewater via a novel combined process driven by partial nitrification/anammox (PN/A) and partial denitrification/anammox (PD/A) with an ultra-low hydraulic retention time (HRT)

Anaerobic ammonia oxidation (Anammox) is a highly productive research area in municipal wastewater treatment. A novel combined process driven by partial nitrification/anammox (PN/A) and partial denitrification/anammox (PD/A) was established in this paper using a sequencing batch reactor (SBR) and two up-flow sludge beds (USBs). Municipal wastewater after carbon removal pretreatment in SBR entered PN/A-USB. PN/A process was initiated and enhanced by optimizing the intermittent aeration mode under low dissolved oxygen (DO). After enhancing and stabilizing the PD/A process, PN/A effluent entered the PD/A-USB along with raw municipal wastewater at a ratio of 4:1 and the combined system was established. Through this, this study achieved a nitrogen removal efficiency (NRE) of 84.9 % from municipal wastewater at an ultra-low total hydraulic residence time (HRT) of 3.9 h. Candidatus Brocadia (1.8 % in PN/A, 1.0 % in PD/A) was the only functional anammox bacterium in the combined process.

Insight into the microbial interactions of Anammox and heterotrophic bacteria in different granular sludge systems: effect of size distribution and available organic carbon source

Microbial interactions between Anammox and heterotrophic bacteria in different granule distributions in an Anammox system (AMX) and partial denitrification coupled with Anammox system (PDA) were analyzed in this paper. Candidatus Brocadia was the main Anammox microorganism in granules of 1.0 > d > 0.5 mm with the highest abundance of 21.5 % in AMX, significantly higher than the maximum proportion of 2.3 % in PDA sludge > 2.0 mm. However, the total nitrogen (TN) removal of 77.9 % in AMX was lower than PDA (94.0 %) because of the excessive NO3--N generated by nitrite-oxidizing bacteria (NOB). Anammox activity could be stimulated by heterotrophs via simple organic carbon, which decreased with the increasing size of sludge in AMX but increased in PDA. This highlighted that regulation of the distribution of sludge size and organic carbon source had an essential effect on efficient nitrogen removal of Anammox technology.

Recent progress in applications of Feammox technology for nitrogen removal from wastewaters: A review

Feammox process is crucial for the global nitrogen cycle and has great potentials for the treatment of low COD/NH₄⁺-N wastewaters. This work provides a systematic and comprehensive overview of the Feammox process. Specifically, underlying mechanisms and functional microbes mediating the Feammox process are summarized in detail. And key influencing factors including pH, temperature, dissolved oxygen, organic carbon, source of Fe(III) as well as various electron shuttles are discussed. Additionally, recent development trends and attempts of the Feammox technology in wastewater treatment applications are reviewed, and perspectives for future development are presented. A thorough review of the recent progress in Feammox process is expected to provide valuable information for further process optimization, which is helpful to achieve a more economical operation and better nitrogen removal performance in future field applications.

Mainstream partial Anammox for improving nitrogen removal from municipal wastewater after organic recovery via magnetic separation

Total nitrogen (TN) removal from municipal wastewater after organic recovery is challenging because of the low ratio of chemical oxygen demand (COD) to TN. Anaerobic ammonium oxidation (Anammox) is promising because it has no organic requirement, but its performance in treating effluents following COD captured remains unclear. This study used mainstream partial Anammox to remove nitrogen from effluent following magnetic separation within a continuous-flow anoxic-oxic reactor. Compared with traditional nitrification and denitrification, partial Anammox increased TN removal efficiency by 15.0% and contributed 23.6% of TN removal. Quantitative polymerase chain reaction revealed that the copy number of the Anammox gene (hzsB) increased substantially, while those of the nitrite oxidation (nxrA) and denitrification (narG and nirS) genes decreased. High-throughput sequencing identified Candidatus Brocadia as the dominant genus of anaerobic ammonium-oxidizing bacteria. These findings demonstrate the effectiveness of mainstream partial Anammox for treating COD-captured effluents and its potential in municipal wastewater treatment.

Advanced nitrogen removal from real municipal wastewater by multiple coupling nitritation, denitritation and endogenous denitritation with anammox in a single suspended sludge bioreactor

Achieving advanced nitrogen removal based on anammox for treating mainstream municipal wastewater in a single suspended sludge bioreactor is a challenging research topic. In this study, multiple coupling nitritation, denitritation and endogenous denitritation with anammox (PNA-(E)PDA) was simultaneously achieved in a 10 L step-feed bioreactor, which enhanced stable nitrogen removal. After 223 days of operation, the total nitrogen concentrations of the influent and effluent were 70.7 ± 6.1 and 4.3 ± 1.8 mg/L, respectively, when treating municipal wastewater even at C/N ratio of 2.24 with only 5 h of aerobic time (DO: 0.5-0.8 mg/L). After the evolution of nitritation/anammox to PNA-(E)PDA, the contribution of anammox to nitrogen removal increased to 78.6% and the anammox activity increased from 4.3 ± 0.2 to 15.2 ± 0.7 mg NH₄⁺-N/gVSS/d. qPCR results showed that the abundance of anammox bacteria increased from 4.1 × 10⁹ to 4.5 × 10¹⁰ copies/ (g VSS). High-throughput sequencing further revealed that the relative abundance of Candidatus Brocadia, the dominant anammox genus, increased from 0.09 to 0.46%. Based on the strong competitiveness of anammox on nitrite, this novel PNA-(E)PDA process provides a potential strategy for enriching anammox bacteria in municipal wastewater treatment plants.

Effect of low salinity on nitrogen removal from municipal wastewater via a double-anammox process coupled with nitritation and denitratation: Performance and microbial structure

Saline wastewater present in municipal pipe networks poses challenges to biological nitrogen removal due to its inhibition on microorganisms. This study focuses on the effects of low salinity (0.0%, 0.4%, 0.7% and 1.0%) on a system featuring a combination of nitritation/anammox in oxic stage and denitratation/anammox in anoxic stage (double-anammox) in a step-feed SBR for municipal wastewater over a period of 130 days. The results showed that a maximum nitrogen removal efficiency of 81.2% was achieved at a salinity of 1.0% with anammox contribution of 76.5%. Analysis of anammox contribution and sludge activities discovered that low salinity promoted both nitritation and denitratation, further enhancing the coupling with anammox. Further, microbial analysis confirmed that Ca. Brocadia was enriched on biofilms from 0.21% to 0.51% and Nitrosomonas was enriched in flocs from 0.50% to 1.04%. Overall, the double-anammox process appears to be a promising method for the treatment of saline wastewater.

Mainstream double-anammox driven by nitritation and denitratation using a one-stage step-feed bioreactor with real municipal wastewater

A novel double-anammox process for advanced mainstream nitrogen removal was established using step-feed sequencing batch reactor (SBR) system with integration of suspend sludge and biofilms. Following optimization of influent distribution ratio, the effluent total inorganic nitrogen (TIN) was < 10.2 mg N/L, with influent TIN of 43.4 mg N/L, and anammox contributed 71.4% to TIN removal. Biological processes and batch tests revealed that gradient C/N reduction promoted denitratation/anammox in anoxic stage, and simultaneous nitritation and anammox were achieved in oxic stage. Specially, anammox maintained on biofilms with abundance over 10⁹ copies/ (g dry sludge). High-throughput sequencing revealed that Thauera and Nitrosomonas were enriched in flocs. Furthermore, metagenomic sequencing confirmed that Thauera owns narG and napA (NO₃^-→NO₂^-) and Nitrosomonas owns amoA (NH₄⁺→NO₂^-), support stable NO₂^- supply for double-anammox. This mainstream anammox-dominant process could potentially be used for stable nitrogen removal in municipal wastewater treatment plants.