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• TNRE increased to 87.89 ± 1.82 % after dosing low concentration exogenous glycine. • Candidatus Brocadia and Candidatus Kuenenia emerged as primary enriched genus. • Glycine modulated nitrogen metabolism by altering the content of Hzs & NirS genes. • High dose of exogenous gly in cross-feeding broke the equilibrium of anammox system. • Gly cleavage system could be the initiating point for the cross-feeding imbalance. Strategies to break the cross-feeding equilibrium by dosing essential metabolites and thus enriching and isolating anammox bacteria (AnAOB) have been proposed, but amino acids have not been investigated as important cross-feeding pathways in anammox consortia. In this study, long-term experiments were designed to verify the effect of exgenous glycine on anammox consortia and changes in the bacterial community and metabolic activity after the addition of glycine in a highly active anammox system were investigated. The results showed that the impact of glycine on the activity of anammox highly depended on glycine concentrations, which was manifested as a promotive effect at low concentrations (0–150 mg/L) and an inhibitory effect at high concentrations (300–600 mg/L). The addition of low concentrations of glycine not only enhanced the diversity and richness of bacterial communities but also promoted the enrichment of Candidatus Kuenenia. The qPCR results showed that the content of functional genes Hzs, NirS and anammox 16S rRNA increased while the expression of amoA and NrfA genes was suppressed when glycine acted positively on AnAOB; Hzs and amoA were suppressed when glycine acted negatively on AnAOB, while the expression of NirS and NrfA genes increased dramatically. Specific anammox activity (SAA) experimental results show that 50–150 mg/L glycine was the optimal amount for promoting the activity of AnAOB. Analysis of community metabolic functions indicated that the addition of exogenous glycine resulted in a imbalance of glycine cross-feeding and promoted AnAOB enrichment mainly by affecting pathways such as other glycan degradation and Lysosome. Overall, this study provided new insights into understanding the glycine cross-feeding, which is essential for improving anammox-based technologies. [ABSTRACT FROM AUTHOR]

[Display omitted] • Multiple mediators function as electron shuttles to promote anammox process; • The EET capability of anammox bacteria can be facilitated by external mediators; • The concurrent presence of mediators triggered the activation of essential enzymes; • The application perspective should focus on the EET-enhanced anammox optimization. The anaerobic ammonium oxidation (anammox) process, transforming ammonia into nitrogen gas in oxygen-free environments using nitrite as an electron acceptor, is increasingly recognized for its potential in treating ammonium-rich wastewater. A major challenge for widespread application of this technology is the limited presence of nitrite in most wastewaters. The intrinsic electroactivity of anammox bacteria implies that the introduction of exogenous additives through the extracellular electron transfer (EET) process could effectively stimulate ammonia oxidation even in the absence of nitrite. This comprehensive review consolidates various approaches to enhance EET-dependent anammox, including the utilization of carbonaceous materials, metal ions, and humic substances. Molecular mechanisms involved in enhancing nitrogen removal performance based on extracellular electron transfer capacity are expounded. The co-occurrence of electron acceptors and exogenous electron shuttles is proposed to increase the activity of c-type cytochromes (c -Cyts) and N-acyl-homoserine lactones (AHLs) in extracellular polymeric substances (EPS), as well as enzymes such as hydrazine synthase (HZS) and hydrazine dehydrogenase (HDH), leading to stable a nitrogen removal performance. This review presents novel insights into the engineering of the EET-enhanced anammox process, providing a theoretical framework for its advancement and optimization. [ABSTRACT FROM AUTHOR]

The mainstream anaerobic ammonium oxidation (anammox) has attracted extensive attention recently, particularly due to its potential of transforming current wastewater treatment plants from energy consuming to energy neutral or positive. However, the presence of biodegradable chemical oxygen demanding (COD, 20–80 mg COD L −1 ) in the mainstream anammox reactor stimulates the growth of heterotrophic bacteria, which would compete for oxygen with ammonia-oxidizing bacteria (AOB) and for nitrite with anammox bacteria, thus interfering with the autotrophic nitrogen removal process. In the present work, with consideration of granule size distribution, a one-dimensional model describing the mainstream simultaneous partial nitrification, anammox and denitrification (SNAD) in a granule-based reactor was established, calibrated and validated, based on the long-term experimental results. Through applying the verified model, simulation studies were conducted and the results showed that the effluent total nitrogen concentration of <5 mg N L −1 could be achieved at C/N ratio of 0.2–0.6, DO concentration of 0.2–0.4 mg L −1 and granule radius of 300–600 μm. The combined effects indicated that the SNAD process with TN removal efficiency >90% was obtained at C/N ratio and DO concentration of 0.2–1.0 and 0.2–0.4 mg O 2 L −1 respectively. Finally, the various granule size distribution patterns were simulated, which confirmed that the size distribution needed to be incorporated in the model to accurately describe the granular anammox system, considering a model based on a uniform granule size does not reflect the real situations. These results provide guides to optimize the operation of mainstream granular autotrophic nitrogen removal process. [ABSTRACT FROM AUTHOR]

Recent discovery of ammonia-oxidizing archaea (AOA) not only substantially improved our understanding of the global nitrogen cycle, but also provided new possibilities for nitrogen removal from wastewater. In particular, compared to ammonia-oxidizing bacteria (AOB), the high ammonia oxidation under oxygen-limited conditions driven by AOA is potentially more suitable for autotrophic nitrogen removal in a single-stage membrane aerated biofilm reactor (MABR) through coupling with anaerobic ammonia oxidation (Anammox). In this work, mathematical modeling is applied to assess the system performance and associated microbial community structure of an AOA–Anammox MABR under low- (30 mg N L −1 ) and high-strength (500 mg N L −1 ) ammonium conditions, with a side-by-side comparison to an AOB–Anammox MABR system under the same conditions. Results demonstrate that both ammonium surface loading (or hydraulic retention time) and oxygen surface loading significantly affect the system performance. In contrast to AOB–Anammox system, the AOA–Anammox MABR shows higher total nitrogen (TN) removal and lower oxygen supply, with much better repression of NOB and substantially wider operating window for high-level TN removal (>80%) in terms of varied oxygen and ammonium loadings. These results provide first insights and useful information for design and operation of this novel AOA–Anammox MABR system in its potential future applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • A SPANADA process was first established in a continuous flow air-lift bioreactor. • Effluent TIN of 8.6 mg/L was achieved in low C/N real wastewater with NH 4 +-N of 100 mg/L. • Anammox was the dominant nitrogen removal pathway in SPANADA system. • Meta-omics revealed the undergoing microbial interaction for nitrogen transformation. • Nitrogen conversion flux was evaluated based on kinetic and stoichiometric parameters. This study describes the development of an air-lift internal circulation reactor that integrates partial nitrification, anammox and denitratation (SPANADA) into a single stage bioprocess for the treatment of low C/N coal gasification wastewater. During 245 days of operation, the compartmental fluidized bed reactor achieved a total inorganic nitrogen (TIN) removal efficiency of 91.4%. Reads-based metatranscriptomic analysis found the expression of the amoA and hao genes essential for nitritation and the hzsA and hdh genes essential for anammox increased dramatically as reactor performance improved and stabilized. Another notable trend was that the total expression of the napA and narG genes, essential for denitratation, was 3-fold higher than the combined reads for nirK and nirS whose products, nitrite reductases, would lower nitrite levels reducing available substrate for anammox. Analysis of metagenome-assembled genomes revealed members of Nitrosomonas and Candidatus Brocadia, were the dominant genera of ammonium-oxidizing bacteria and anammox bacteria, respectively, and accounted for 5.5% and 10.0% of the total reads in the transcriptome. For denitratation, Thiolinea , whose only relevant gene involved in N-metabolism is narG , accounted for 8.5% of the total reads in the transcriptome and, remarkably, 84.1% of narG expression. Mass balance confirmed anammox was the dominant nitrogen removal pathway, accounting for 67.0% of the TIN removed. Nitritation and denitratation accounted for 82.7% and 17.3% of the nitrite production, respectively. The analysis reported demonstrates the development of a novel and effective one-stage nitrogen removal alternative for low C/N wastewater treatment and also helps gain insight into the underlying microbial interactions. [ABSTRACT FROM AUTHOR]

• A granule model embedding metabolisms of DAMO microbes and AnAOB was proposed. • The model predictions matched experimental data from two granular sludge reactors. • The estimated parameter values indicated a stimulated growth of DAMO archaea. • The model managed to simulate the microbial abundance and stratified distribution. • Short HRT and small granule size increased DAMO archaea but reduced DAMO bacteria. The granular bioreactor, characterized by excellent settling velocity, high rate and low cost is an ideal choice for achieving coupled nitrate/nitrite dependent denitrifying anaerobic methane oxidation (n-DAMO) and anaerobic ammonium oxidation (Anammox) process. To fundamentally understand its underlining mechanisms and provide suggestions for process optimization, a granule-based model framework was developed to describe simultaneous anaerobic methane and ammonium oxidation by functional microbes. The proposed model was evaluated based on long-term experimental data from two membrane granular sludge reactors (MGSRs) with different operational conditions. The model possessed of good predictive ability to reproduce removal rates and effluent concentrations of nitrogen species. The predicted biomass abundance in two MGSRs and stratified microbial distribution along granule depth were consistent with experimental observations. The estimated parameter values, with good identifiability and reliability indicated a stimulated growth of DAMO archaea in MGSRs. Both hydraulic retention times (HRTs) and granule sizes have influences on microbial abundance in the MGSR and community distribution inside granules. Within the investigated HRTs from 1.4 h to 20 h and granule sizes from 500 μm to 2900 μm, it was revealed that a proper control of relatively short HRTs and small granule sizes resulted in an increased fraction of DAMO archaea and a reduced DAMO bacteria abundance with AnAOB less impacted, which would lower the required nitrite nitrogen to ammonium nitrogen ratio in the nitritation reactor (prior unit) and thus minimize operational cost in sidestream treatment lines. [ABSTRACT FROM AUTHOR]