Search Results (87)

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

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 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

The partial nitrification–anammox process offers a cost-effective, energy-efficient, and environmentally sustainable approach for nitrogen removal in wastewater treatment. However, its application under low ammonia nitrogen conditions faces operational challenges including prolonged start-up periods and excessive nitrite oxidation. This study employed a strategy combining polyurethane surface positive charge enhancement and zeolite loading to develop a carrier capable of microbial enrichment and inhibition of nitrate generation, aiming to initiate the partial nitrification-anammox process in a sequencing batch reactor. Operational results demonstrate that the modified carrier enabled the reactor to achieve a total nitrogen removal efficiency of 78%, with the effluent nitrate nitrogen reduced to 6.03 mg-N/L, successfully initiating the partial nitrification-anammox process. The modified carrier also exhibited accelerated biofilm proliferation (both suspended and attached biomass increased). Additionally, 16S rRNA revealed a higher relative abundance of typical anammox bacteria Candidatus Brocadia in the biofilm of the modified carrier compared to the original carrier, alongside a decline in nitrifying genera, such as Nitrolancea. These microbial shifts effectively suppressed excessive nitrite oxidation, limited nitrate accumulation, and sustained efficient nitrogen removal throughout the reactor’s operation. Full article

The leachate from ion-adsorbed rare earth tailings poses challenges to the application of the anaerobic ammonium oxidation (anammox) process in this field due to its large fluctuations in ammonia nitrogen concentration (50–300 mg/L) and high flow rate (4000–10,000 m³/d). This study investigated the effects of nitrogen-loading rate (NLR) regulation on denitrification performance through reactor operation and elucidated the mechanisms of NLR impacts on anammox processes via microbial community analysis and metabolic profiling. The results revealed a nonlinear relationship between nitrogen loading and system performance. As NLR increased, both denitrification efficiency and anammox bacterial abundance (rising from 5.85% in phase P1 to 11.43% in P3) showed synchronous enhancement. However, excessive nitrogen loading (>3.68 kg/m³·d) or nitrogen starvation led to performance deterioration and reduced anammox bacterial abundance. Microbial communities adopted modular collaboration to counteract loading stress, with modularity indices of 0.563 and 0.545 observed in the inhibition phase (P2) and starvation phase (P4), respectively. Zi-Pi plot analysis demonstrated a significant increase in inter-module connectivity, indicating reinforced interspecies interactions among microorganisms to resist nitrogen-loading fluctuations. Full article

Anaerobic ammonium oxidation (anammox) technologies have attracted substantial interest due to their advantages over traditional biological nitrogen removal processes, including high efficiency and low energy demand. Currently, multiple side-stream applications of the anammox coupling process have been developed, including one-stage, two-stage, and three-stage systems such as completely autotrophic nitrogen removal over nitrite, denitrifying ammonium oxidation, simultaneous nitrogen and phosphorus removal, partial denitrification-anammox, and partial nitrification and integrated fermentation denitritation. The one-stage system includes completely autotrophic nitrogen removal over nitrite, oxygen-limited autotrophic nitrification/denitrification, aerobic de-ammonification, single-stage nitrogen removal using anammox, and partial nitritation. Two-stage systems, such as the single reactor system for high-activity ammonium removal over nitrite, integrated fixed-film activated sludge, and simultaneous nitrogen and phosphorus removal, have also been developed. Three-stage systems comprise partial nitrification anammox, partial denitrification anammox, simultaneous ammonium oxidation denitrification, and partial nitrification and integrated fermentation denitritation. The performance of these systems is highly dependent on interactions between functional microbial communities, physiochemical parameters, and environmental factors. Mainstream applications are not well developed and require further research and development. Mainstream applications demand a high carbon/nitrogen ratio to maintain levels of nitrite-oxidizing bacteria, high concentrations of ammonium and nitrite in wastewater, and retention of anammox bacteria biomass. To summarize various aspects of the anammox processes, this review provides information regarding the microbial diversity of different genera of anammox bacteria and the engineering aspects of various side streams and mainstream anammox processes for wastewater treatment. Additionally, this review offers detailed insights into the challenges related to anammox technology and delivers solutions for future sustainable research. Full article

Red mud has been demonstrated to improve the methane production performance of anaerobic digestion (AD). However, the influence of red mud on ammonia nitrogen inhibition during AD through the mediating role of bacteria–phages interactions in this process remains poorly understood. Thus, this study investigated the impact of red mud on nitrogen metabolism in AD and characterized the phage and prokaryotic communities through a metagenomic analysis. The results showed that red mud significantly increased methane production by 23.1% and promoted the conversion of ammonia nitrogen into organic nitrogen, resulting in a 4.8% increase in total nitrogen. Simultaneously, it enriched the key microbial genera Methanothrix, Proteinophilum, and Petrimonas by 0.5%, 0.8%, and 2.7%, respectively, suggesting an enhancement in syntrophic acetate oxidation with greater ammonia tolerance. A viral metagenomic analysis identified seven nitrogen-metabolism-related auxiliary metabolic genes (AMGs), with glnA (encoding glutamine synthetase) being the most abundant. Compared to the control treatments, the red mud treatments led to a higher abundance of temperate phages and an increased number of AMGs. Furthermore, two new hosts carrying glnA (Mycolicibacteria smegmatis and Kitasatopola aureofaciens) were predicted, indicating that red mud expanded the host range of phages and promoted the spread of AMGs. Overall, our findings highlight the importance of phages in alleviating ammonia nitrogen inhibition and provide a novel understanding of the role of red mud in the AD of swine manure. Full article

Oxidation ditch and Anaerobic–Anoxic–Oxic (A²/O) processes have been applied in urban wastewater treatment plants for decades, but the differences between two processes in engineering applications are less studied. Based on the continuous monitoring of Ningyang’s sewage treatment plant (Shandong, China) for one year, this study systematically analyzed the removal efficiencies of nutrients in the oxidation ditch and the modified high-efficiency multi-cycle A²/O processes. The results showed that chemical oxygen demand (COD) and total phosphorus (TP) removal in the modified high-efficiency multi-cycle A²/O process of the Phase II project was better than that in the oxidation ditch process of the Phase I project, and the average concentration of COD and TP in the effluent was 49.9% and 51.7% lower than that in the oxidation ditch process, respectively. The removal rate of ammonia nitrogen (NH₄⁺-N) by the two processes was basically the same, while the total nitrogen (TN) effluent concentration of the oxidation ditch process was 31.4% lower than that in the high-efficiency multi-cycle A²/O process. In summary, the high-efficiency multi-cycle A²/O process had a better treatment performance regarding nutrient removal than the oxidation ditch process under the same conditions. Furthermore, the engineering and operational costs of the high-efficiency multi-cycle A²/O process were lower. Full article

Nitrogen removal in the sewage treatment process is a significant challenge. The increase in nitrogen content in sewage leads to the eutrophication of water bodies and the deterioration of water quality in polluted environments. Therefore, converting nitrogen into non-polluting gases is a crucial and essential part of the sewage treatment process. Compared to physical, chemical, and physicochemical methods, biological denitrification is not only simple to operate and economically effective but also has less secondary pollution and saves energy. This paper summarizes the latest research progress on mainstream biological denitrification technology in WWTPS (wastewater treatment plants) and discusses its research background, methodology, and challenges. It is noted that the traditional biological nitrogen removal method is stable and widely used, but it has drawbacks such as high costs and long reaction times, especially in high-nitrogen-load wastewater treatment where its effectiveness is limited. The short-cut nitrification–denitrification process suits high-nitrogen-loading and a low C/N ratio wastewater as it reduces carbon source consumption. However, the problems of water quality fluctuation and unstable dissolved oxygen still need to be solved. The anaerobic ammonia oxidation process efficiently converts ammonia and nitrite to nitrogen using anaerobic ammonia-oxidizing bacteria, consuming less energy but facing limitations due to slow bacterial growth rates and stringent environmental conditions. The heterotrophic nitrification–aerobic denitrification process merges the traits of heterotrophic nitrifying bacteria and aerobic denitrifying bacteria, effectively reducing the ecological footprint and enhancing treatment efficiency. This approach is a pivotal focus for future research endeavors. Full article

Elucidating the effects of nitrogen and water addition on N₂O dynamics is critical, as N₂O is a key driver of climate change (including nitrogen deposition and shifting precipitation patterns) and stratospheric ozone depletion. The temperate steppe is a notable natural source of this potent greenhouse gas. This study uses field observations and soil sampling to investigate the seasonal pattern of N₂O emissions in the temperate steppe of Inner Mongolia and the mechanism by which nitrogen and water additions, as two different types of factors, alter this seasonal pattern. It explores the regulatory roles of environmental factors, soil physicochemical properties, microbial community structure, and abundance of functional genes in influencing N₂O emissions. These results indicate that the effects of nitrogen and water addition on N₂O emission mechanisms vary throughout the growing season. Nitrogen application consistently increase N₂O emissions. In contrast, water addition suppresses N₂O emissions during the early growing season but promotes emissions during the peak and late growing seasons. In the early growing season, nitrogen addition primarily increased the dissolved organic nitrogen (DON) levels, which provided a matrix for nitrification and promoted N₂O emissions. Meanwhile, water addition increased soil moisture, enhancing the abundance of the nosZ (nitrous oxide reductase) gene while reducing nitrate nitrogen (${\mathrm{N}\mathrm{O}}_3^{-}$-N) levels, as well as AOA (ammonia-oxidizing archaea) amoA and AOB (ammonia-oxidizing bacteria) amoA gene expression, thereby lowering N₂O emissions. During the peak growing season, nitrogen’s role in adjusting pH and ammonium nitrogen (${\mathrm{N}\mathrm{H}}_4^{+}$-N), along with amplifying AOB amoA, spiked N₂O emissions. Water addition affects the balance between nitrification and denitrification by altering aerobic and anaerobic soil conditions, ultimately increasing N₂O emissions by inhibiting nosZ. As the growing season waned and precipitation decreased, temperature also became a driver of N₂O emissions. Structural equation modeling reveals that the impacts of nitrogen and water on N₂O flux variations through nitrification and denitrification are more significant during the peak growing season. This research uncovers innovative insights into how nitrogen and water additions differently impact N₂O dynamics across various stages of the growing season in the temperate steppe, providing a scientific basis for predicting and managing N₂O emissions within these ecosystems. Full article

Poyang Lake is the largest freshwater lake in China, which boasts unique hydrological conditions and rich biodiversity. In this study, metagenomics technology was used to sequence the microbial genome of soil samples S1 (sedimentary), S2 (semi-submerged), and S3 (arid) with different water content from the Poyang Lake wetland; the results indicate that the three samples have different physicochemical characteristics and their microbial community structure and functional gene distribution are also different, resulting in separate ecological functions. The abundance of typical ANME archaea Candidatus Menthanoperedens and the high abundance of mcrA in S1 mutually demonstrate prominent roles in the methane anaerobic oxidation pathway during the methane cycle. In S2, the advantageous bacterial genus Nitrospira with ammonia oxidation function is validated by a large number of nitrification functional genes (amoA, hao, nxrA), manifesting in that it plays a monumental role in nitrification in the nitrogen cycle. In S3, the dominant bacterial genus Nocardioides confirms a multitude of antibiotic resistance genes, indicating their crucial role in resistance and their emphatic research value for microbial resistance issues. The results above have preliminarily proved the role of soil microbial communities as indicators predicting wetland ecological functions, which will help to better develop plans for restoring ecological balance and addressing climate change. Full article

Anaerobic ammonia oxidation (anammox) is considered an efficient and low-energy biological nitrogen removal process. However, there are limited studies addressing the changes in antibiotic resistance genes (ARGs) during the startup of an anammox reactor inoculated with activated sludge. In this study, an up-flow anaerobic sludge bed (UASB) reactor was initiated with synthetic wastewater at room temperature (20–28 °C). Metagenomic sequencing was employed to analyze the shifts in the bacterial community, nitrogen removal functional genes, and ARGs in both the seeding sludge and anammox sludge. The results show that the reactor achieved anammox activity after 122 days of cultivation, with NH₄⁺-N and NO₂⁻-N removal rates reaching 99.8% and 99.6%, respectively. Compared to those in inoculated sludge, the relative abundance of the anammox bacterium Candidatus kuenenia increased from 0.01% to 50.86%, while the relative abundance of denitrifying Acidovorax bacteria decreased from 8.02% to 1.77%. Meanwhile, the relative abundance of Nitrosomonas declined from 2.91% to 1.87%. The functional genes hzs, hdh, nirK, and nirS increased in relative abundance in the anammox sludge, while the ARGs decreased in relative abundance from 294.77 RPKM to 155.62 RPKM in the sludge. These findings offer valuable insights into the initiation of the anammox process using ordinary activated sludge as an inoculum and provide a scientific basis for the mitigation of ARGs through anammox technology. Full article

Simultaneous partial nitrification, anammox, denitrification, and fermentation (SNADF) is a novel process achieving simultaneous advanced sludge reduction and nitrogen removal. The influence of low temperatures on the SNADF reactor was explored to facilitate the application of mainstream anammox. When temperature decreased from 32 to 16 °C, efficient nitrogen removal was achieved, with a nitrogen removal efficiency of 81.9–94.9%. Microbial community structure analysis indicated that the abundance of Candidatus Brocadia (dominant anaerobic ammonia oxidizing bacteria (AnAOB) in the system) increased from 0.03% to 0.18%. The abundances of Nitrospira and Nitrosomonas increased from 1.6% and 0.16% to 2.5% and 1.63%, respectively, resulting in an increase in the ammonia-oxidizing bacteria (AOB) to nitrite-oxidizing bacteria (NOB) abundance ratio from 0.1 to 0.64. This ensured sufficient nitrite for AnAOB, promoting nitrogen removal. In addition, Candidatus Competibacter, which plays a role in partial denitrification, was the dominant denitrification bacteria (DNB) and provided more nitrite for AnAOB, facilitating AnAOB enrichment. Based on the findings from microbial correlation network analysis, Nitrosomonas (AOB), Thauera, and Haliangium (DNB), and A4b and Saprospiraceae (fermentation bacteria), were center nodes in the networks and therefore essential for the stability of the SNADF system. Moreover, fermentation bacteria, DNB, and AOB had close connections in substrate cooperation and resistance to adverse environments; therefore, they also played important roles in maintaining stable nitrogen removal at low temperatures. This study provided new suggestions for mainstream anammox application. Full article

To expedite enrichment of anaerobic ammonia-oxidizing bacteria (AnAOB) as a way to reduce the start-up time, leading to a quicker transition into stable operation, the anaerobic ammonia oxidation (anammox) process was initiated by a biofilm reactor with polyurethane porous material. The enrichment of anammox bacteria was studied by progressively increasing the influent substrate concentration while simultaneously decreasing hydraulic retention time. Following a 73 d start-up and subsequent 103 d enrichment phase, the removal rates of ammonia and nitrite reached 97.87% and 99.96%, respectively, and the community was characterized by the development of brick-red anammox biofilms and granules. The predominant bacterial phyla within the reactor were Planctomycetota, Chloroflexi, and Proteobacteria, with relative abundances of 25.25%, 29.41%, and 14.3%, respectively, and the dominant genus was Candidatus brocadia, comprising 20.44% of the microbial community. These findings indicate that the polyurethane porous material biofilm reactor is conducive to the enrichment of AnAOB. After enrichment, the anaerobic microbial community exhibited significant richness and diversity, with anammox bacteria as the primary group. Full article