Search Results (220)

Feeds rich in protein are the dominant nitrogen input in intensive aquaculture, yet only part of dietary nitrogen is retained as animal biomass; the remainder enters water and sediment through uneaten feed, feces, dissolved wastes, mucus, sloughed tissue, and branchial ammonia excretion. This review aims to integrate nutritional, physiological, microbial, and disease-related evidence into an evidence-graded framework that positions ammonia nitrogen as a reactive node linking feed, host, water, sediment, and pathogen risk. To assemble this evidence, we conducted a structured narrative search of Web of Science and PubMed for records in English or Chinese published from 2006 to July 2026, with no restriction on publication type, and classified evidence as direct, indirect, or conceptual. The strongest evidence shows that dietary protein supply, amino acid balance, digestibility, and feeding regime regulate nitrogen retention and ammonia output, while microbial ammonification, nitrification, denitrification, dissimilatory nitrate reduction to ammonium, anammox, and assimilation determine whether reactive nitrogen is regenerated, retained, or removed. Experimental studies further show that ammonia impairs oxidative balance, mucosal barriers, immunity, and disease resistance. In contrast, evidence that pathogen infection quantitatively alters nitrogen retention, ammonia excretion, organic nitrogen release, and sedimentary ammonium regeneration remains limited and largely indirect. Accordingly, ammonia nitrogen is framed as a measurable reactive node rather than a unique source or a universally validated causal loop. Practical management should combine precision nutrition with water, biofloc, sediment, and disease surveillance, while future factorial studies and isotope tracer studies should quantify the complete nitrogen budget under pathogen challenge. Full article

Constructed wetlands (CWs) are widely used for wastewater treatment but can also serve as significant sources of nitrous oxide (N₂O), a potent greenhouse gas. Balancing efficient nitrogen removal with N₂O mitigation remains a critical challenge for sustainable wastewater management. This review systematically elucidates the key microbial mechanisms underlying N₂O emissions in CWs and summarizes corresponding mitigation strategies. Mechanistically, N₂O production is primarily driven by hydroxylamine oxidation and nitrifier denitrification mediated by ammonia-oxidizing microorganisms, as well as incomplete heterotrophic denitrification resulting from electron-donor limitation. These pathways are tightly regulated by spatiotemporal redox gradients, carbon-to-nitrogen ratios, and influent strength conditions. To address these emissions, this review synthesizes mitigation strategies from an engineering perspective. Optimization of operational parameters, such as intermittent aeration and water-level regulation, together with the application of novel functional substrates, such as biochar and iron-carbon micro-electrolysis, can effectively facilitate electron transfer and improve micro-redox conditions. Furthermore, optimized plant species selection and community design, along with emerging low-carbon biological nitrogen removal processes, such as autotrophic denitrification and partial denitrification coupled with anammox, offer promising approaches for substantial emission reduction. Overall, this review provides practical guidance for designing efficient, low-carbon CWs toward carbon neutrality. Full article

In recent years, the simultaneous partial nitrification, anammox, and denitrification (SNAD) process has attracted considerable attention due to its advantages such as low energy consumption and low sludge production. This study investigated the long-term performance and microbial mechanisms of a single-stage moving bed biofilm reactor (MBBR) employing the SNAD process for treating real domestic sewage at room temperature. A pre-carbon adsorption unit (reactor A) reduced the influent C/N ratio from 5.68:1 to 3.13:1, enabling efficient nitrogen removal in reactor B. Results demonstrated that dissolved oxygen (DO) and C/N ratio critically influenced system performance. At DO ~0.3 mg/L, stable SNAD operation achieved 65% total nitrogen (TN) removal, with synergistic contributions from partial nitrification, anammox, and heterotrophic denitrification. Elevated C/N ratios (4.71:1) reduced TN removal by ~30%, linked to decreased abundances of anammox bacteria. Microbial analysis revealed Candidatus Brocadia as key anammox bacteria, Nitrospirae as dominant ammonia-oxidizing bacteria and Denitratisoma as main denitrifying bacteria to drive nitrogen conversion. This study confirms the feasibility of SNAD-MBBR for real domestic sewage under ambient conditions, highlighting optimal DO and C/N control for microbial synergy and process stability. Full article

Municipal wastewater treatment plants (WWTPs) are essential for protecting public health, however, their contribution to greenhouse gas (GHG) emissions has often been overlooked. Achieving carbon-neutral operation requires more than incremental improvements in energy efficiency; it calls for a rethinking of process design, energy flows, and resource recovery strategies. This review examines recent developments across several key pathways, including carbon capture through A-B configurations, energy recovery via anaerobic digestion, and low-carbon nitrogen removal based on autotrophic processes such as partial nitritation–anammox. Emerging technologies, such as microalgal and bioelectrochemical systems, are also reviewed, although their large-scale applicability remains uncertain. Particular attention is given to the trade-offs introduced by advanced treatment for micropollutant removal, which can significantly increase energy demand if not carefully integrated. Beyond individual technologies, the paper highlights the importance of system-level optimization, life-cycle assessment, and data-driven control strategies. A staged roadmap is proposed to distinguish near-term improvements from longer-term transitions. Rather than presenting a single solution, the review emphasizes that feasible pathways depend strongly on local conditions, including influent characteristics, climate, and energy mix. Full article

Spent mushroom substrate (SMS) return is a vital strategy for agricultural waste recycling and soil fertility improvement, yet its ecological impacts of duration remain poorly understood. This study employed metagenomic sequencing to explore soil fertility, microbial dynamics, and nitrogen cycling across different SMS return durations (0, 1, and 3 years) within rice–mushroom crop rotation systems. Soil nutrients (organic matter, total nitrogen, total phosphorus) initially decreased and then increased throughout the rice growth cycle. The one-year return (y1) induced early nutrient depletion, whereas the three-year return (y3) significantly enhanced late-stage nutrient accumulation. With increasing duration, bacterial and archaeal assembly shifted from stochastic toward deterministic processes, while fungal diversity and stochasticity decreased continuously. Co-occurrence network analysis demonstrated that SMS return increased network complexity and intercommunity competition. This transition was accompanied by a functional shift in keystone taxa from those responsive to exogenous organic matter in y1 to those mediating nitrogen fixation, anammox, and sulfur metabolism in y3. Nitrogen cycling in y1 increased potential N₂O emission risks through nirS upregulation and nosZ downregulation, whereas y3 mitigated inorganic nitrogen loss by upregulating gene abundances of ammonia assimilation, nitrification, and DNRA genes. Notably, the structure of nitrogen-cycling genes fluctuated in y1 but was resilient to y0 levels in y3. These findings demonstrated that while initial SMS return triggered ecological fluctuations and environmental risks, continuous return (y3) achieved functional stability by reshaping microbial niches. This study highlights the importance of SMS return duration in balancing soil fertility enhancement with environmental risk mitigation in sustainable paddy ecosystems. Full article

The challenge of attaining energy–efficient nitrogen removal at low carbon–to–nitrogen (C/N) ratios is a fundamental issue in the sustainable management of municipal wastewater treatment plants (WWTPs). This study investigates a pilot–scale Anaerobic–Swing–Anoxic–Oxic (ASAO) system coupled with an AvN (Ammonia versus NOx⁻–N)–based aeration control strategy. A systematic evaluation of the system’s performance, nitrogen removal mechanisms, and microbial communities under a 350–day long–term pilot–scale operation using real municipal sewage is presented. The results reveal that the AvN control strategy can optimize aeration intensity and enhance nitrogen removal efficiency. Even under low influent C/N conditions, the ASAO system maintained stable operation with low dissolved oxygen levels (0.5–1.5 mg L⁻¹), and the AvN control strategy effectively optimized aeration intensity and stabilized nitrogen conversion, achieving a total nitrogen (TN) removal rate of 83% and an average effluent TN concentration of 4.9 ± 2.6 mg L⁻¹. Mechanistic analysis indicated that AvN regulation could alleviate over–nitrification and enhance intracellular carbon storage, thereby creating conditions that support the coordinated operation of multiple nitrogen removal routes, such as simultaneous nitrification–denitrification (SND), endogenous denitrification (EnD), and potentially anaerobic ammonium oxidation (anammox). These findings suggest that the AvN–controlled ASAO process offers a robust and scalable strategy for achieving high–efficiency nitrogen removal with reduced aeration demand, providing a promising technological pathway toward energy–neutral and sustainable municipal wastewater treatment. Full article

This study designed an integration of anaerobic digestion, partial nitrification/Anammox (PN/A), and Fenton process to efficiently treat high-concentration organic liquor wastewater (HCLW). Results indicated that when the diluted ten-fold mixture of boiler bottom water and cellar bottom water with the ratio of 5:1 was used as influent, the average concentrations of COD, TN, NH₄⁺-N, NO₂⁻-N, and NO₃⁻-N in effluent of biological treatment for this process were 180.00, 12.64, 1.74, 0.13, and 2.45 mg/L, respectively. To meet the requirement for direct discharge of HCLW, Fenton oxidation with 600 mg H₂O₂/L and 300 mg Fe²⁺/L was used to further reduce the COD concentration. Three-dimensional fluorescence spectra analysis revealed that the process effectively altered the organic molecular structure and degraded some large molecular proteins. Microbial community analysis showed that Methanobacterium (20.98% → 31.52%) and Methanosaeta (9.70% → 19.34%) in AD, Azoarcus (no detected → 10.49%) and Nitrosomonas (1.68% → 6.16%) in PN, and Candidatus_Brocadia (18.80% → 20.31%) and Ignavibacterium (no detected → 5.11%) in Anammox were dominant in this system. This study provided a pioneering industrial solution for the efficient and stable treatment of HCLW. Full article

Achieving stable partial nitritation (PN) in mainstream municipal wastewater treatment is critical for energy-efficient anammox-based nitrogen removal. However, selectively suppressing nitrite-oxidizing bacteria (NOB) while retaining ammonia-oxidizing bacteria (AOB) remains challenging. This study investigated the performance and microbial mechanisms of PN in a membrane-aerated biofilm reactor (MABR) under zero-pressure aeration. The results showed that zero-pressure aeration achieved a nitrite accumulation ratio (NAR) of 82.14%, significantly higher than that under constant aeration (13.2%) and intermittent aeration (53.5%). Zero-pressure aeration led to a significant increase in the fluorescence intensities of tyrosine/tryptophan protein in extracellular polymeric substances. 16S rRNA sequencing revealed that zero-pressure aeration achieved a modest reduction in the relative abundance of NOB Nitrospira from 3.39% to 2.74% while increasing the relative abundance of AOB Nitrosomonas from 0.04% to 1.09%. Enzyme activity assays further showed that zero-pressure aeration significantly decreased nitrite oxidoreductase (NXR) activity while maintaining ammonia monooxygenase (AMO) and hydroxylamine oxidoreductase (HAO) activities, providing direct functional evidence for NOB suppression. Zero-pressure operation required no external air supply, representing a passive aeration strategy for PN. These results suggest that zero-pressure aeration may reshape the competition between AOB and NOB by enriching AOB and suppressing NOB, providing a new energy-efficient pathway for mainstream nitrogen removal. Full article

Hangzhou Bay has long experienced excessive nitrogen loading coupled with limited hydrodynamic exchange, leading to some of the highest nitrogen concentrations in China’s coastal waters. As critical land-sea ecotones, intertidal wetlands play a crucial role in mitigating nitrogen pollution across the bay. However, rapid urbanization and extensive reclamation since 1990 have led to a loss of over 50% of the intertidal wetlands in southern Hangzhou Bay. In this study we measured sediment denitrification and anammox potentials across key habitats: salt marshes (vegetated by Spartina alterniflora, Phragmites australis, and Scirpus mariqueter), bare mudflats, and shellfish aquaculture zones. We used ¹⁵N isotope tracing techniques coupled with slurry incubation experiments. Analysis of sediment physicochemical properties was conducted to elucidate the driving mechanisms of nitrogen removal. By integrating wetland landscape evolution with regional nitrogen budgets, we evaluated the nitrogen sink function of these intertidal wetlands. Our results revealed a distinct spatial hierarchy in denitrification potential, decreasing in the order: S. alterniflora (13.02 ± 3.54 μmol·N·kg⁻¹·h⁻¹) > shellfish aquaculture zones (12.86 ± 7.50 μmol·N·kg⁻¹·h⁻¹) > P. australis (11.54 ± 1.80 μmol·N·kg⁻¹·h⁻¹) > S. mariqueter (7.33 ± 2.08 μmol·N·kg⁻¹·h⁻¹) > bare mudflats (5.99 ± 1.62 μmol·N·kg⁻¹·h⁻¹). S. alterniflora has higher primary productivity, biomass accumulation, and a more robust root system structure. It regulates the content and availability of sediment organic carbon, the supply of nitrate nitrogen, pH, and water content. These regulations subsequently enhance denitrification. In contrast, shellfish aquaculture zones enhance denitrification potential primarily through bioturbation, which increases water content and lowers pH conditions. An integrated assessment of denitrification potential and landscape patterns revealed that, despite ongoing habitat loss, the remaining intertidal wetlands in southern Hangzhou Bay still remove about 30.65% of exogenous inorganic nitrogen. This finding underscores their critical role as effective pollution buffers under high nitrogen loading. Full article

Low-temperature stress severely restricts the engineering application of anaerobic ammonia oxidation (anammox) technology in municipal mainstream wastewater treatment, leading to its slower large-scale implementation relative to industrial wastewater and reject water treatments. The inhibitory effects of low temperatures on the anammox process cannot be merely ascribed to conventional microbial metabolic responses. Elucidating the specific mechanisms underlying low-temperature impacts on anammox bacteria is therefore critical for formulating targeted mitigation strategies. In this study, a meta-analysis was performed to compare the response patterns of specific anammox activity (SAA) and nitrogen removal rate (NRR) to temperature variations. SAA declines gradually with decreasing temperature, while NRR displays a more dramatic and stepwise reduction. The T₅₀ values (temperature corresponding to 50% of the performance at 30 °C) for these two parameters are 20 °C and 15 °C, respectively. Low-temperature inhibition of anammox is a multifaceted process, encompassing direct physiological disturbances to individual anammox cells and impaired nitrite bioavailability within the microbial community. To address these temperature-related bottlenecks, a conceptual hybrid nitrogen removal system was rationally optimized by integrating conventional strategies with an innovative split-flow influent regulation strategy. This hybrid system is anticipated to enhance the stability and treatment efficiency of anammox under low-temperature conditions, thus facilitating its broader engineering application in cold climate regions. Full article

Deammonification, which is based on partial nitritation and anammox (PN/A), is a well-established sidestream treatment for nitrogen removal. However, transferring deammonification to mainstream wastewater treatment remains challenging due to low temperatures, the need to retain slow-growing anammox bacteria (AnAOB), and their competition for nitrite with nitrite-oxidizing bacteria (NOB) and heterotrophic denitrifiers. This work investigates cubic polyurethane foam carriers to promote growth and retention of AnAOB. A moving bed biofilm reactor (MBBR) and an integrated fixed-film activated sludge (IFAS) reactor were compared over a three-year experimental period at lab-scale. The feasibility of the biofilm carriers for deammonification was first evaluated under sidestream conditions, followed by a stepwise transition to mainstream operational conditions. The impact of operational parameters, including dissolved oxygen concentration, pH value, and aeration strategy, was evaluated with respect to the activity of aerobic ammonium-oxidizing bacteria (AOB), NOB, and AnAOB, as well as nitrogen removal rates. Deammonification reached nitrogen removal rates of 0.04–0.12 kg N m⁻³ d⁻¹ (IFAS reactor) and 0.02–0.28 kg N m⁻³ d⁻¹ (MBBR) at subphases with reactor bulk concentrations above 60 mg NH₄-N L⁻¹. Highest nitrogen removal degrees of 77 ± 6% (IFAS) and 76 ± 5% (MBBR) were achieved at reactor bulk concentrations of 96 mg NH₄ L⁻¹ and 97 mg NH₄ L⁻¹, respectively. Lower concentrations triggered NOB activity in both reactors, leading to an increase in nitrate concentration up to 22 mg NO₃-N L⁻¹. AOB and AnAOB activities were on average 6-fold higher on the carriers compared to suspended biomass throughout all experimental phases, demonstrating the feasibility of using cubic polyurethane foam carriers for deammonification. This was also confirmed by fluorescence in-situ hybridization (FISH) measurements. Median nitrogen removal rates over all experimental phases of 0.07 kg N m⁻³ d⁻¹ for the IFAS reactor and 0.05 kg N m⁻³ d⁻¹ for the MBBR were achieved, which are comparable to conventional activated sludge systems performing nitrogen removal via nitrification–denitrification. While at lower nitrogen concentrations, the IFAS reactor yielded superior nitrogen removal rates, peak nitrogen removal rates of 0.28 kg N m⁻³ d⁻¹ were measured in the MBBR configuration. However, controlling NOB activity at lower temperatures and concentrations remains a challenge in MBBR and IFAS configurations. In our study, in the IFAS reactor NOB activities were visible on fewer days than in MBBR. At mainstream-like conditions, higher nitrogen removal rates of IFAS (0.09–0.12 kg N m⁻³ d⁻¹) were achieved compared to the MBBR (0.06–0.09 kg N m⁻³ d⁻¹). This demonstrates the advantage of the IFAS reactor in treating mainstream wastewater via deammonification. As an autotrophic nitrogen removal process, the implementation of deammonification in the mainstream of municipal wastewater treatment plants enables enhanced recovery of biogas from sewage organic matter. The latter would otherwise be consumed during the conventional nitrification-denitrification pathway. Consequently, the overall energy balance for wastewater treatment can be improved, contributing to a more environmentally sustainable process. Full article

Sulfate-reducing ammonium oxidation (SRAO) is an emerging anaerobic autotrophic nitrogen removal process that combines ammonium oxidation with sulfate reduction. However, it faces some challenges, such as the slow growth of autotrophic microorganisms, weak synergistic interaction between different microorganisms, and poor substrate transfer capability. Herein, graphene oxide (GO) was added to a lab-scale bioreactor to promote SRAO reaction, and its effect on nitrogen removal was systematically investigated. The results demonstrated that GO served not only microbial carriers but also electron shuttles, which were conducive to microbial spatial distribution and better electron transfer, improving the sulfur cycle-driven multi-pathway nitrogen removal performance. The addition of 50 mg/L GO not only enhanced the SRAO activity and increased the ammonium removal efficiency by 24.7%, but also reduced the effluent nitrite concentration and promoted nitrogen production. After reaction, the main functional groups on the surface of GO had been changed, and the composite aggregates of microorganisms were formed. Mass balance analysis revealed that SRAO was the dominant pathway, while Anammox and sulfur-autotrophic denitrification (SADN) played complementary roles. Moreover, after adding GO, the relative abundances of Desulfosarcinaceae and Bacillus, which were functional microorganisms in the SRAO reaction, were increased by 35.7% and 58.5%, respectively. This study will provide an in-depth understanding of the mechanisms for nitrogen removal in the SRAO bioreactor. Full article

Inland waters are critical nodes in the global nitrogen cycle, where microbial processes govern transformations that impact water quality and ecosystem functioning. Inland waters are critical nodes in the global nitrogen cycle, where microbial processes govern transformations that impact water quality and ecosystem functioning. To systematically map the knowledge structure and to identify evolving trends in this field, a bibliometric analysis was conducted using CiteSpace on 2459 publications from the Web of Science Core Collection (1990–2024). The results reveal a significant increase in publications after 2010, peaking at 228 in 2024, with China (1541 articles) and the Chinese Academy of Sciences (776 articles) being the leading country and institution, respectively. Keyword co-occurrence and cluster analyses identify a core conceptual framework centered on microbial communities, nitrogen transformation processes (e.g., denitrification, anammox), and aquatic habitats (e.g., lakes, rivers). Based on keyword emergence and temporal trends, the analysis suggests an evolution in research focus across four dimensions: research subjects (from microbial biomass to keystone taxa), core questions (from process rates to predictive manipulation), methodological tools (from culturing to multi-omics), and mechanistic understanding (from linear pathways to complex networks). These observed patterns indicate a progressive refinement of the field. The findings provide a structured overview of the literature and may inform future research directions, but should be interpreted as bibliometric trends rather than definitive conclusions about the state of the science. Full article

The stable application of Partial Nitritation-Anammox (PN-A) in municipal wastewater treatment is primarily hindered by the ineffective suppression of Nitrite-Oxidizing Bacteria (NOB). This study systematically evaluated PN-A stability by comparing a Sequencing Batch Reactor (SBR) with two distinct Membrane Bioreactor (MBR) configurations. Results indicated that the SBR achieved superior performance through natural hydraulic selective washout, which efficiently eliminated NOB and fostered a robust AOB-AnAOB symbiotic biofilm. In contrast, MBRs were inherently susceptible to NOB proliferation due to their non-selective membrane retention. However, this study demonstrates that an intermittently aerated MBR (MBR-I) can effectively mitigate these disadvantages. By tailoring aeration control, the MBR-I successfully optimized the competitive kinetics for nitrite, suppressing NOB activity and achieving a robust total nitrogen removal rate (TNRR) of 76.38%. This work highlights that tailored aeration serves as a crucial synergistic strategy to bridge the inherent gap between membrane-based systems and conventional washout-driven reactors, providing a potential pathway for implementing PN-A within hybrid MBBR-MBR systems. Full article

This study investigated the ecological selection and enrichment of anaerobic ammonium-oxidizing bacteria (AnAOB) driven by endogenous carbon cycling in a low-oxygen SBR biofilm system without external carbon addition. The system was operated using dried biofilm inoculation, continuous low oxygen (DO < 0.1 mg/L), and complete drainage. After 117 days, AnAOB were enriched to 8.14% relative abundance and became the dominant functional group. At an influent total nitrogen (TN) of 25 mg/L, the average effluent TN and NH₄⁺-N were 6.37 and 3.75 mg/L, respectively, corresponding to a TN removal efficiency of 75% and meeting the Class A discharge standard. Metagenomic and metatranscriptomic analyses revealed that anammox was the primary nitrogen removal pathway, with nitrite supplied through partial nitrification and endogenous partial denitrification. Higher expression of nitrate reductase genes than of nitrite reductase genes favored nitrite accumulation through endogenous partial denitrification, thereby creating a self-sustaining internal cycle between nitrate reduction and anammox. Extracellular polymeric substances (EPS) served as the key internal carbon source driving this process. This ecological regulation strategy provides an energy-efficient and stable strategy for mainstream low C/N municipal wastewater treatment without external carbon addition. Full article