Search Results (192)

Wastewater nitrogen pollution is a serious environmental problem, and traditional treatment techniques are frequently constrained by their high energy requirements and operational complexity. The anaerobic ammonium oxidation (anammox) process combined with membrane bioreactor (MBR) technology (anammox-MBR) offers a practical and energy-efficient solution for the sustainable removal of nitrogen, further enhanced by its potential to minimize emissions of nitrous oxide (N₂O), a potent greenhouse gas with a global warming potential nearly 300 times that of carbon dioxide. This review outlines the most recent advancements in anammox-MBR systems, highlighting their ability to achieve nitrogen removal efficiencies of more than 70–90% and, in integrated systems with reverse osmosis, to recover up to 75% of the inflow as high-quality reusable water. Significant advancements such as high-rate activated sludge coupling, reverse osmosis integration, microaeration methods, and membrane surface modifications have decreased membrane fouling, accelerated startup times, and enhanced system stability. Despite these achievements, there are still issues that hinder widespread use, such as membrane fouling exacerbated by hydrophobic anammox metabolites, sensitivity to low temperatures (≤10 °C), and the persistent challenge of suppressing nitrite-oxidizing bacteria (NOB), which compete for the essential nitrite substrate. To enable cost-effective, energy-efficient, and environmentally sustainable large-scale applications, future research directions will focus on creating cold-tolerant anammox strains, advanced anti-fouling membranes, and AI-driven process optimization. Full article

Nitrous oxide (N₂O), a potent greenhouse gas, is an important environmental concern associated with biological nitrogen removal in wastewater treatment plants. Anaerobic ammonium oxidation (anammox), recognized as an advanced carbon-neutral nitrogen removal technology, requires a continuous supply of nitrite, which also serves as a key precursor for N₂O generation. However, the regulation of the carbon-to-nitrogen (C/N) ratio to minimize N₂O emission in mainstream anammox systems remains insufficiently understood. In this study, we evaluated the long-term nitrogen removal performance and N₂O emission potential of an oxygen-limited anammox biofilm reactor treating synthetic municipal wastewater with a typical C/N range of 4.0–6.0. Experimental results demonstrated that the highest nitrogen removal efficiency (95.3%), achieved through coupled anammox and denitrification, and the lowest N₂O emission factor (0.73%) occurred at a C/N ratio of 5.0. As the C/N ratio increased from 4.0 to 5.0, N₂O emissions decreased progressively, but rose slightly when the ratio was further increased to 6.0. High-throughput sequencing revealed that microbial community composition and the abundance of key functional taxa were significantly influenced by the C/N ratio. At a C/N ratio of 5.0, proliferation of anammox bacteria and the disappearance of Acinetobacter populations appeared to contribute to the significant reduction in N₂O emission. Furthermore, gene annotation analysis indicated higher abundances of anammox-associated genes (hzs, hdh) and N₂O reductase gene (nosZ) at this ratio compared with others. Overall, this study identifies a C/N-dependent strategy for mitigating N₂O emissions in mainstream anammox systems and provides new insights into advancing carbon-neutral wastewater treatment. Full article

The anaerobic ammonium oxidation (anammox) process offers potential for saline wastewater treatment but is hindered by salt inhibition. This study investigates the salt tolerance mechanisms of granular (R1), biofilm-carrier (R2), and floccular (R3) sludge in up-flow anaerobic sludge blanket (UASB) reactors under 0–20 g/L NaCl. Granular sludge outperformed other biomass types, maintaining >90% ammonia nitrogen (${\mathrm{NH}}_4^{+}$-N) removal at 20 g/L NaCl due to structural stability and extracellular polymeric substances (EPS) adaptation (shift from hydrophobic proteins to polysaccharides). Microbial analysis revealed a transition from Planctomycetes/Proteobacteria to salt-tolerant Pseudomonadota, with Candidatus_Kuenenia replacing Candidatus_Brocadia as the dominant anaerobic ammonium oxidation bacteria (AnAOB) (reaching 14.5% abundance in R1). Genetic profiling demonstrated coordinated nitrogen metabolism: Hzs/Hdh inhibition (>85%) and NirBD/NrfAH activation (0.23%) elevated ${\mathrm{NH}}_4^{+}$-N, while NarGIV/NapA decline (1.10%→0.58%) increased nitrate nitrogen (${\mathrm{NO}}_3^{-}$-N). NxrB/NirSK maintained low nitrite nitrogen (${\mathrm{NO}}_2^{-}$-N), and GltBD upregulation (0.43%) enhanced osmoregulation. These findings underscore the superior resilience of granular sludge under high salinity, linked to microbial community shifts and metabolic adaptations. This study provides critical insights for optimizing anammox processes in saline environments, emphasizing the importance of biomass morphology and microbial ecology in mitigating salt inhibition. Full article

Increasing the discharge of saline wastewater from an industrial field poses a challenge for applicable Anammox-based technologies. This study established the integrated partial sulfur-driven denitrification and Anammox (SPDA) system to explore the effects of different salinity levels on nitrogen conversion features. The results of batch tests suggested that sulfur-driven denitrification exhibited progressive suppression of nitrate reduction (97.7% → 12.3% efficiency at 0% → 4% salinity) and significant nitrite accumulation (56.4% accumulation rate at 2% salinity). Anammox showed higher salinity tolerance but still experienced drastic TN removal decline (97.6% → 17.3% at 0% → 4% salinity). Long-term operation demonstrated that the SPDA process could be rapidly established at 0% salinity and stabilize with TN removal efficiencies of 98.1% (1% salinity), 72.8% (2% salinity), and 70.2% (4% salinity). The robustness of the system was attributed to the appropriate strategy of gradual salinity elevation, the promoted secretion of protein-dominated EPS, the salinity-responsive enrichment of Sulfurimonas (replacing Thiobacillus and Ferritrophicum) as sulfur-oxidizing bacteria (SOB), and the sustained retention and activity of Brocadia as AnAOB. The findings in this study deepen the understanding of the inhibitory effects of salinity on the SPDA system, providing a feasible solution for saline wastewater treatment with low cost and high efficiency. Full article

Nanotechnology plays an increasingly important role in the economy and human life, which means that more and more amounts of nanosubstances, including nanoparticles of metal oxides, together with wastewater, end up in the environment. This study aimed to study the impact of iron(III) oxide nanoparticles (n-Fe₂O₃), which have magnetic properties, on the efficiency of the Anammox wastewater treatment process. The results indicate that n-Fe₂O₃ in the range of low concentrations may have a positive effect on nitrogen metabolism, increasing the efficiency of NH₄-N removal to 98% in 120 min and at 30 °C. During the first 30 min of the process, when almost anaerobic conditions arose, nanoparticles of Fe₂O₃, stabilized the system by producing ROS. However, a constant control of TOC and pH is necessary because of the constant increase in the amount of organic compounds and H⁺ ions during the reaction. However, a longer contact of n-Fe₂O₃ with biomass causes the efficiency to decrease, and, as a result, the efficiency is lower compared to the system containing only Anammox. Full article

This study combines machine vision technology and deep learning models to rapidly assess the activity of anaerobic ammonium oxidation (Anammox) granular sludge. As a highly efficient nitrogen removal technology for wastewater treatment, the Anammox process has been widely applied globally due to its energy-saving and environmentally friendly features. However, existing sludge activity monitoring methods are inefficient, costly, and difficult to implement in real-time. In this study, we collected and enhanced 1000 images of Anammox granular sludge, extracted color features, and used machine learning and deep learning training methods such as XGBoost and the ResNet50d neural network to construct multiple models of sludge image color and sludge denitrification efficiency. The experimental results show that the ResNet50d-based neural network model performed the best, with a coefficient of determination (R²) of 0.984 and a mean squared error (MSE) of 523.38, significantly better than traditional machine learning models (with R² up to 0.952). Additionally, the experiment demonstrated that under a nitrogen load of 2.22 kg-N/(m³·d), the specific activity of Anammox granular sludge reached its highest value of 470.1 mg-N/(g-VSS·d), with further increases in nitrogen load inhibiting sludge activity. This research provides an efficient and cost-effective solution for online monitoring of the Anammox process and has the potential to drive the digital transformation of the wastewater treatment industry. Full article

A 56-day trial was conducted to assess the effects of rice straw (RS) and bamboo flour (BF) on growth performance, water quality, gill histology, and the bacterial community of water and the intestine of mandarin fish (Siniperca chuatsi) in biofloc technology systems. The results showed that mandarin fish in the RS and BF groups had comparable survival rates of 100.00 ± 0.00 and 93.33 ± 3.85%; feed conversion ratios of 1.13 ± 0.02 and 1.40 ± 0.15; and weight gain rates of 112.21 ± 1.56 and 100.92 ± 6.45%, respectively. From days 11 to 56 of the farming period, the BF group was more effective than the RS group in removing total ammonia nitrogen (TAN) and NO₂⁻-N, maintaining TAN levels below 0.24 ± 0.05 mg/L. During the early stage of the experiment, the TAN level in the RS group was higher; however, with the supplementation of a carbon source, it gradually decreased and eventually stabilized at 0.13 ± 0.03 mg/L later in the farming period. The secondary gill lamella in the RS group was curved and showed hyperplasia, and the basal gill lamellae showed an increase in the volume of interlamellar cell mass in the BF group. Genes related to denitrification (narG, napA, nirS, nirK, and nosZ) and anammox showed higher expression levels in the BF group than in the RS group, although the differences were not statistically significant (p > 0.05). The results of 16S rRNA sequencing research showed that both treatment groups’ intestinal and water bacterial communities had comparable levels of richness and diversity. Pseudomonas mosselii was the dominant bacterial species in the water. In the BF group, the dominant intestinal species were Bacillus halodurans and Caldalkalibacillus thermarum, while in the RS group, the dominant species was Plesiomonas shigelloides. In conclusion, rice straw and bamboo flour are applicable in BFT systems for mandarin fish culture, with good growth performance and water quality. The BF group showed higher nitrogen removal efficiency and denitrification gene expression than the RS group. Full article

Spartina alterniflora invasion has posed severe ecological threats to coastal wetlands. Deep tillage is considered an effective physical method for ecological restoration in such wetlands; however, its effects on sediment nitrogen transformation processes remain unclear. In this study, we investigated the impacts of deep tillage on soil physicochemical properties and key nitrogen transformation pathways, including nitrification, denitrification, anammox, and DNRA, across different soil depths (0–10, 10–20, 20–30, 30–50, and 50–100 cm) in Spartina alterniflora-invaded coastal wetlands. Deep tillage significantly restructured the distribution of soil moisture (p < 0.05), pH (p > 0.05), electrical conductivity (p < 0.05), and nutrients, promoting NO₃⁻-N accumulation in deeper layers while reducing NH₄⁺-N concentrations in surface soils (p < 0.05). It markedly enhanced denitrification and DNRA rates (p < 0.05), suppressed surface nitrification (p < 0.05), and altered the vertical distribution of anammox activity. Correlation analysis revealed that NH₄⁺-N and NO₃⁻-N concentrations were the primary drivers of nitrogen transformation, with pH and electrical conductivity playing secondary roles. Overall, deep tillage stimulated nitrogen removal processes and affected net ammonium changes. These findings reveal that deep tillage can stimulate nitrogen removal processes by alleviating soil compaction and altering nitrogen transformation pathways, thus supporting biogeochemical recovery mechanisms after deep tillage. These insights provide scientific guidance for the ecological restoration of Spartina alterniflora-invaded coastal wetlands. Full article

The structure of microbial communities in sponge-sand filters, used for the treatment of real domestic sewage with elevated ammonium nitrogen concentrations (approximately 155 mg·dm⁻³), was characterized using 16S rRNA gene sequencing. Analyses using the Illumina technique allowed us to perform a comparison of filters by layer (two or three layers) and type of fill (waste PUR foams with 95% open porosity, sand). Proteobacteria, actinobacteria, and firmicutes were shown to be the most abundant phyla. The number and type of fill layers had a significant impact on the diversity of nitrifying bacteria. The presence of Nitrosomonas and Nitrospira was observed in every sponge fill sample, but the abundance of autotrophic nitrifiers was negligible in the two-layer filter. The conditions there proved more favorable for the growth of aerobic heterotrophic bacteria. Also in the Schmutzdecke layer, a dominance of heterotrophic nitrifiers was found. The abundance of bacteria with nitrifying activity (AOB, comammox, HNAD) in the biomass of spongy fill placed in casings was 1.7 times lower than in foams without casings. In addition, anammox bacteria (unidentified Planctomycetes), found mainly in the sponge fill and Schmutzdecke of the three-layer filters, may have been responsible for NH4⁺-N removal exceeding 70%. In the case of the two-layer filter, the removal of this pollutant reached 92%. Burkholderia and Sphingopyxis were identified as the predominant denitrifying bacteria. The foam-filled filter in the casings showed an increase in o_Caldilineaceae, involved in nitrate removal as non-denitrifiers. Actinomycetes Pseudonocardia and Amycolatopsis, as well as Proteobacteria Devosia, Acinetobacter, and Bdellovibrio, were found to be involved in phosphorus removal in the waste PUR foams. Full article

High-ammonia-nitrogen organic wastewater poses significant challenges to traditional nitrogen removal processes due to their high energy consumption and carbon dependency, conflicting with global sustainability goals. Anammox presents a sustainable alternative with lower energy demands, yet its application is constrained by organic matter inhibition. This study aimed to optimize nitrogen and organic matter removal in Anammox systems by comparing two strategies: effluent recirculation and micro-aeration. Anammox reactors were operated under three conditions: (1) no recirculation (control group), (2) 100–300% effluent recirculation, (3) micro-aeration at 50–150 mL/min. The effects on total nitrogen (TN) and chemical oxygen demand (COD) removal were evaluated, alongside microbial community analysis via high-throughput sequencing. The results show that micro-aeration at 100 mL/min achieved 78.9% COD and 88.3% TN removal by creating micro-anaerobic conditions for metabolic synergy. Excessive aeration (150 mL/min) inhibited Anammox, dropping TN removal to 49.7%. Recirculation enriched Planctomycetota, while micro-aeration slightly increased Planctomycetota abundance at 45 cm and enhanced Proteobacteria and Chloroflexi for denitrification. Optimal conditions—200% recirculation and 100 mL/min aeration—improve efficiency via dilution and synergistic metabolism, providing a novel comparative framework for treating high-ammonia-nitrogen organic wastewater and filling a research gap in the parallel evaluation of Anammox enhancement strategies. Full article

The sustainable restoration of river and lake ecosystems requires advanced wastewater treatment technologies to control nitrogen pollution, a key driver of aquatic degradation. This study explores the physiological responses of anammox granular sludge (AnGS) to varying nitrogen loading rates (NLRs), offering insights into microbial stability under environmental stress. AnGS samples with different particle sizes (<1.0 mm, 1–2 mm, >2 mm) were subjected to NLRs ranging from 0.9 to 3.6 gN/L/d. As the NLR increased, the NO₂⁻-N/NH₄⁺-N consumption ratio rose from 1.0 to 1.2, and the most active particle size shifted to 1–2 mm. Hydroxyapatite (HAP) crystals formed at higher NLRs, enhancing the settling and activity of 1–2 mm AnGS but inhibiting larger granules (>2 mm). Microbial analysis revealed that Candidatus Brocadia dominated at high NLRs (10.5%), outperforming Candidatus Kuenenia (2.47%). The enrichment of these key genera across granules indicates adaptive microbial migration under loading stress. These findings provide critical operational strategies for sustaining AnGS performance through particle size regulation, contributing to nitrogen control solutions vital for river and lake restoration efforts. Full article

The majority of extant studies concentrate on the reactivation of dormant Anammox biomass or the recovery of activity under specific storage conditions. Research on rehabilitation strategies for anaerobic ammonium oxidation (Anammox) systems is limited, with the exception of research on inhibitory factors. The recovery characteristics of biofilm systems after collapse induced by varying degrees of ammonia-nitrogen and small-molecular organic compound composite shocks have not been thoroughly elucidated. This study addresses the collapse of Anammox biofilm systems caused by sodium acetate inhibition through multi-phase rehabilitation strategies, stoichiometric analysis, and microbial community succession dynamics. Two regression algorithms—Support Vector Regression (SVR) and eXtreme Gradient Boosting (XGBoost)—were employed to construct predictive models for Total Nitrogen Removal Efficiency (TNRE) and Total Nitrogen Removal Rate (TNRR) in the CANON system, with model performance evaluated via coefficient of determination (R²) and root mean square error (RMSE). Results demonstrated that after terminating moderate-to-high sodium acetate dosing (300 mg/L and 500 mg/L), reactors R300 and R500 achieved TNRE recovery to 57.98% and 58.86%, respectively, and TNRR of 0.281 and 0.275 kgN/m³·d within 60–100 days, indicating the reversibility of high-concentration sodium acetate inhibition but a positive correlation between recovery duration and inhibition intensity. Microbial community analysis revealed that Planctomycetota (including Candidatus_Kuenenia) rebounded to 46–49% relative abundance in R100, synchronized with TNRE improvement. In contrast, R300 and R500 exhibited ecological niche replacement of denitrifiers (Denitratisoma) and partial TNRE restoration despite enhanced performance. Model comparisons showed SVR outperformed XGBoost in TNRE prediction, whereas XGBoost demonstrated superior TNRR prediction accuracy with R² approaching 1 and RMSE nearing 0, significantly surpassing SVR. This work provides critical insights into recovery mechanisms under organic inhibition stress and establishes a robust predictive framework for optimizing nitrogen removal performance in CANON systems. Full article

The Anaerobic–Swing Aerobic–Anoxic–Oxic (ASAO) process was developed to tackle problems such as temperature sensitivity during the Anaerobic–Oxic–Anoxic (AOA) process. By introducing a swing zone (S zone) with adjustable dissolved oxygen (DO), during the 112-day experimentation period, the ASAO system achieved removal rates of 88.18% for total inorganic nitrogen (TIN), 78.23% for total phosphorus (TP), and 99.78% for ammonia nitrogen. Intermittent aeration effectively suppressed nitrite-oxidizing bacteria (NOB), and the chemical oxygen demand (COD) removal rate exceeded 90%, with 60% being transformed into internal carbon sources like polyhydroxyalkanoates (PHAs) and glycogen (Gly). The key functional microorganisms encompassed Dechloromonas (denitrifying phosphorus-accumulating bacteria), Candidatus Competibacter, and Thauera, which facilitated simultaneous nitrification–denitrification (SND) and anaerobic ammonium oxidation (ANAMMOX). The enrichment of Candidatus Brocadia further enhanced the ANAMMOX activity. The flexibility of DO control in the swing zone optimized microbial activity and mitigated temperature dependence, thereby verifying the efficacy of the ASAO process in enhancing the removal rates of nutrients and COD in low-C/N wastewater. The intermittent aeration strategy and the continuous low-dissolved-oxygen (DO) operating conditions inhibited the activity of nitrite-oxidizing bacteria (NOB) and accomplished the elimination of NOB. Full article

Anammox is a novel and energy-efficient biological nitrogen removal technology. Enhancing its performance in treating low-strength nitrogen wastewater is essential for expanding its practical applications. In response to challenges such as low nitrogen removal efficiency (NRE), poor operational stability, limited environmental resistance, and the interference of organic compounds commonly found in real wastewater, this study developed a two-stage upflow anammox biofilm reactor system (R1 and R2) enhanced by an Fe²⁺-coupled organic substrate strategy for deep nitrogen removal under low-nitrogen conditions. Results showed that sodium acetate at a chemical oxygen demand (COD) concentration of 40 mg/L provided the greatest enhancement to anammox activity, achieving an average total nitrogen removal efficiency (NRE) of 90.02%. However, the reactor performance was significantly inhibited under higher COD conditions (e.g., COD = 60 mg/L). Under an influent Fe²⁺ concentration of 10 mg/L, the reactors’ NRE increased and then decreased as the COD concentration rose from 0 to 100 mg/L, resulting in the highest efficiency being achieved at an average NRE of 94.11%, observed under 10 mg/L Fe²⁺ coupled with 60 mg/L of COD in the two-stage anammox system. Scanning electron microscopy revealed that the co-addition of Fe²⁺ and organic substrates led to the formation of granular protrusions and pores on the sludge surface, which favored the structural stability of the biomass. At a COD level of 40 mg/L, the contents of extracellular polymeric substances and heme c in anammox biofilm were significantly higher compared to the addition of 10 mg/L Fe²⁺ alone, whereas excessive COD inhibited both indicators. These findings suggest that moderate levels of Fe²⁺ coupled with organic matter can promote anammox activity for deep nitrogen removal, while excessive organics have inhibitory effects. This study provides theoretical support for enhancing nitrogen removal from low-strength wastewater using Fe²⁺ and organic-substrate-assisted anammox processes. Full article

The construction of an anaerobic digester coupled with post-digestion low-level aeration for agricultural wastewater treatment is described. The digester employs underwater speakers to accelerate the anaerobic digestion process while retaining solids to reduce the strength of the effluent. The effluent is sent to a holding tank and fed at a low flow rate to an aeration tank to effect partial nitrification of the wastewater. The outlet of this tank is sent to a settling tank to retain biomass that developed in the aeration tank, and the effluent is sent to a small constructed wetland to further reduce wastewater nitrogen and phosphorus. The wetland was planted with the broadleaf cattail, Typha latifolia, and hence led to the formation of a retention basin. The system has reduced energy consumption due to the use of underwater sonic treatment and low-level aeration that is not designed to achieve full nitrification/denitrification but rather to achieve a mixture of ammonium, nitrite, and nitrate that might foster the development of a consortium of organisms (i.e., nitrifiers and Anammox bacteria) that can remediate wastewater ammonium at low cost. The system is meant to serve as a complex where various technologies and practices can be evaluated to improve the treatment of agricultural wastewater. Preliminary data from the system are presented. Full article