Search Results (46)

Low reactivation efficiency of idle anaerobic ammonia oxidation (anammox) sludge hinders its reapplication. To address this issue, rape straw biochar (RSB) was added in the reactivation process of idle anammox sludge, and its effects on the nitrogen transformation and sludge characteristics were investigated, and the mechanism of RSB to enhance the reactivation performance was explored. Results indicated that adding 5 g/L RSB for 35 days successfully reactivated anammox sludge that had been idle for 270 days. The reactivation time was reduced by 34% compared to the control without RSB. During the stable operation period, the average TN removal efficiency reached 90.6%, and the sludge exhibited higher activity. After completion of reactivation, the specific surface area, total pore volume, and average pore diameter of RSB decreased by 59.4%, 66.9%, and 55.2%, respectively, compared with that before reactivation, and the carbon–oxygen functional groups also changed. RSB not only provided a habitat for the enriched growth of nitrogen transforming functional flora but also possessed the potential to supply sufficient electron donors and acceptors for the nitrogen transforming process, which promoted the synergistic removal of nitrate by denitrification, resulting in an effective enhancement of reactivation efficiency and nitrogen removal performance. The addition of RSB provides a novel strategy to enhance the reactivation efficiency of idle anammox sludge, which is of positive significance in promoting its efficient reuse and stable operation. Full article

In sulfate-rich environments, the mechanisms of ammonia nitrogen removal and the role of potential electron acceptors remain unclear. To investigate this, an upflow spiral bed reactor (USBR) operated for 173 days using batch experiments and microbial analysis. The reactor maintained stable ammonia removal, while sulfate levels stayed nearly unchanged, indicating sulfate was not the primary electron acceptor. Batch results showed that trace dissolved oxygen (0.1~0.2 mg/L) and reactive oxygen species (ROS) caused partial nitrification. The resulting nitrite interacted with anaerobic ammonium oxidation (Anammox) to remove nitrogen. Bicarbonate (HCO₃⁻) served only as an inorganic carbon source; when its concentration exceeded 1000 mg/L, it inhibited ammonia removal and was consumed internally, confirming it was not an electron acceptor. Microbial analysis revealed Proteobacteria and Chloroflexi supported short-range nitrification, while Planctomycetota (Candidatus Brocadia) facilitated Anammox. Sulfate-reducing bacteria decreased significantly, consistent with the absence of sulfate reduction. Functional prediction indicated enrichment of nitrogen metabolism genes but limited sulfur metabolism. This study uncovers a new pathway for ammonia nitrogen removal in sulfate-rich environments. Unlike traditional sulfate-dependent ammonium oxidation (SRAO), the process observed occurred without sulfate reduction and was instead driven by a micro-oxygen/ROS-induced ammonia oxidation–Anammox coupling mechanism. These results broaden the current understanding of nitrogen transformation in sulfate-rich wastewater systems. 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

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 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 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

Nutrient removal in conventional wastewater treatment systems is expensive due to the high aeration costs. An alternative method for effective and sustainable nitrogen removal in wastewater treatment is anaerobic ammonium oxidation (Anammox) implemented with other innovative technologies, such as membrane-aerated biofilm reactors (MABRs). A major challenge associated with the Anammox process is effective control of nitrite-oxidizing bacteria (NOB). High temperature operation in wastewater treatment systems can promote Anammox bacterial growth and inhibit NOB activity. This research aims to investigate the feasibility of integrating Anammox processes with a lab-scale MABR and to examine the effects of high temperature aeration supplied to MABR systems on Anammox bacterial growth and NOB suppression. Experimental results indicate that the membrane’s air permeability was a critical parameter for the successful operation of Anammox-integrated MABR systems due to its influence on the system’s dissolved oxygen concentration (0.41 ± 0.39 mg O₂/L). The ammonia removal by AOB and Anammox bacteria was determined to be 7.53 mg N/L·d (76.5%) and 2.12 mg N/L·d (23.5%), respectively. High temperature aeration in MABRs with the Anammox process shows a promising potential for improving energy consumption and sustainable nitrogen removal in wastewater treatment systems. Full article

Anammox, a reaction in which microorganisms oxidize ammonia under anaerobic conditions, is used in the industry to remove ammonium from wastewater in an environmentally friendly manner. This process does not produce intermediate products such as nitrite or nitrate, which can act as secondary pollutants in soil and water environments. For industrial applications, anammox bacteria should be obtained from the environment and cultivated. Anammox bacteria generally exhibit a slow growth rate and may not produce a large number of cells due to their anaerobic metabolism. Additionally, their habitats appear to be limited to specific environments, such as oxidation-reduction transition zones. Consequently, most of the anammox bacteria that are used or studied originate from marine environments. In this study, anammox bacterial evidence was found in rice paddy soil and cultured under various conditions of aerobic, microaerobic, and anaerobic batch incubations to determine whether enrichment was possible. The anammox-specific gene (hzsA) and microbial community analyses were performed on the incubated soils. Although it was not easy to enrich anammox bacteria due to co-occurrence of denitrification and nitrification based on the chemistry data, potential existence of anammox bacteria was assumed in the terrestrial paddy soil environment. For potential industrial uses, anammox bacteria could be searched for in rice paddy soils by applying optimal enrichment conditions. Full article

This study focused on the start-up and operating characteristics of the endogenous partial denitrification (EPD) process with different carbon sources. Two sequencing batch reactors (SBRs) with sodium acetate (SBR1^#) and glucose (SBR2^#) as carbon sources were operated under anaerobic/oxic (A/O) and anaerobic/anoxic/oxic (A/A/O) modes successively for 240 d. The results showed that COD removal efficiency reached 85% and effluent COD concentrations were below 35 mg/L in both SBRs. The difference was that faster absorption and transformation of sodium acetate was achieved compared to glucose (COD removal rate (CRR) was 7.54 > 2.22 mgCOD/(L·min) in SBR1^# compared to SBR2^#). EPD could be started up with sodium acetate and glucose as carbon sources, respectively, and desirable high nitrite accumulations were both obtained at influent NO₃⁻−N (NO₃⁻-N_inf) increased from 20 to 40 mg/L with nitrate-to-nitrite transformation ratio (NTR) and specific NO₃⁻-N deduction rate (r_Na) of 88.4~90% and 2.41~2.38 mgN/(gVSS·h), respectively. However, at NO₃⁻-N of 50~60 mg/L, both the NTR and r_Na in SBR1^# were higher compared to SBR2^# (86.5% > 83.9% and 1.58 > 1.20 mgN/(gVSS·h), respectively). Hereafter, when NO₃⁻-N was increased by 70~90 mg/L, lower NTR and r_Na were observed in SBR1^# than in SBR2^# (72% and 78%, 1.16 and 1.32 mgN/(gVSS·h), respectively). Additionally, similar internal carbon transformations were observed to drive EPD for NO₂⁻−N accumulation, especially for higher and faster carbon transformation with sodium acetate as carbon source compared to glucose. However, precise control of anoxic time as the peak point of nitrite (T_Ni,max) was still the key to achieve high NO₂⁻−N accumulation. Full article

The study of two-stage partial nitrification–anaerobic ammonium oxidation (PN/A) reactors, which are advantageous in engineering applications, still lacks research on process kinetics. Therefore, in this study, the start-up performance and process kinetics of a two-stage PN/A reactor were evaluated by controlling the reaction conditions, for which the two reactors were inoculated with sludge, incubated separately, and then operated in tandem. Increasing the ammonia load of the reactor during the 60 d stabilization period resulted in a nitrogen accumulation rate of 96.93% and a [NO₂⁻ − N]_Eff/[NH₄⁺ − N]_Eff ratio of 1.33, which is close to the theoretical value of 1.32. Successful initiation of the A reactor was achieved after 55 d of operation by inoculating with anammox-activated sludge and granular activated carbon, and the PN and A reactors then successfully operated in combination for 20 d, with an average NH₄⁺ − N efficiency of 99.04% and the NH₄⁺ − N load of the A reactor showing an “S-shaped” curve. An analysis of the microbial growth kinetic models indicated that the removal of NH₄⁺ − N could be successfully described by the logistic, modified logistic, modified Gompertz, and modified Boltzmann models. A strong association between the model and the dependent variable was observed. The process kinetic analysis showed that the removal of NH₄⁺ − N from reactor A could be simulated under steady-state conditions, using the Grau second-order model. The parameters obtained from the model analysis are expected to help predict the denitrification performance of the reactor, facilitate operational management and control, and thus provide a promising research basis for the introduction of automated control systems. Full article

The Anammox anaerobic fluidized bed microbial fuel cell (Anammox AFB-MFC) exhibits exceptional performance in both nitrogen removal and electricity generation, effectively eliminating ammonia nitrogen (NH₄⁺-N) and nitrite nitrogen (NO₂⁻-N) pollutants. This technology offers the advantages of high efficiency in nitrogen removal and low electricity consumption. By coupling an AFB with an MFC, the Anammox AFB-MFC was developed through the introduction of anaerobic ammonia-oxidizing bacteria (AnAOB) into MFC. Anammox AFB-MFC’s nitrogen removal ability was found to be superior at an influent COD concentration of 200 mg/L, as determined by a study conducted under unchanged conditions. Subsequently, an open and closed-circuit experiment was performed on the Anammox AFB-MFC system while maintaining a COD concentration of 200 mg/L in the influent. Remarkably, the reactor exhibited significantly enhanced nitrogen removal performance when electricity generation occurred. Throughout the entire experimental process, the reactor consistently maintained high nitrogen removal efficiency and electricity production performance. Under optimal experimental conditions, the reactor achieved a remarkable nitrogen removal rate of 91.8% and an impressive output voltage of 439.1 mV. Additionally, the generation of Anammox bioparticles in MFC significantly contributed to efficient pollutant removal. This study elucidates the impact of organic matter on both the nitrogen removal and electricity generation capabilities of Anammox AFB-MFC, as well as highlights the synergistic effect between MFC electricity generation and nitrogen removal in the reactor. Full article