Simultaneous Nitrogen Removal Research Articles

Synchronous and efficient removal of carbon, nitrogen, and phosphorus from actual rural sewage by composite wetlands enhanced with functional fillers

A composite wetland (CECW) was constructed by introducing P-adsorption filler (EPAF) and activated sludge into traditional wetlands for treating actual sewage. The results showed that EPAF improved P removal through physico-chemical adsorption, and it could be stably regenerated after adsorption saturation without potential risks. Meanwhile, zeolite promoted NH4+-N reduction in sewage by cation exchange. In addition, simultaneous biological removal of carbon, nitrogen, and phosphorus was achieved through nitrification, denitrification, anammox, and aerobic P-accumulation processes induced by Nitrobacter, Proteus Hauser, Candidatus Paracaedibacter, and Brevundimonas. Under the coupling of filler interception/adsorption, microbial assimilation/transformation, flocculation, and plant uptake, CECW obtained the removal rates of 93.22 %, 85.75 %, 91.80 %, 95.38 %, 97.07 %, and 78.05 % for turbidity, TN, NH4+-N, TP, PO43−-P, and TCOD, which met the Class 1A standard (GB18918-2002). Therefore, the experiment systematically investigated the effects and mechanism of CECW in treating actual sewage, which could provide reference for rural sewage treatment and sludge utilization.

Start-up phase performance evaluation of a pilot-scale sequential anaerobic-aerobic hybrid algal-bacterial suspended growth reactor for the domestic wastewater treatment

This study evaluated the start-up phase performance of an 80-cubic-meter pilot-scale anaerobic-aerobic hybrid algal-bacterial reactor treating real domestic wastewater operated at 24 h hydraulic retention time. The aerobic chambers of the reactor were inoculated with heterotrophic bacterial biomass and mixed microalgal culture. Blue light-emitting-diode (LED) lights were provided in the aerobic chambers to facilitate algal photosynthesis. The influent chemical oxygen demand (COD), total nitrogen (TN), and phosphorus (P) values were 241 ± 45 mg/L, 26.8 ± 4.2 mg/L, and 6.7 ± 0.9 mg/L, respectively. After thirty days of operation, the effluent COD, TN, and P values were observed to be 26.7 ± 6.5 mg/L, 15.6 ± 0.73 mg/L, and 4.45 ± 0.16 mg/L, respectively. The sludge volume index of the mixed liquor was 43 mL/g, indicating high settleability. During the operation, an increase in the chlorophyll to biomass ratio was observed, which implies that the algal-bacterial symbiosis might have played a role in simultaneous carbon and nitrogen removal from the domestic wastewater.

Simultaneous removal of groundwater manganese and ammonia nitrogen based on high-flux gravity driven ceramic membrane (HF-GDCM) coupled with aerated fluidized birnessite

High concentrations of manganese ion (Mn2+) and ammonia nitrogen (NH3-N) in groundwater are indicative of a critical environmental issue that necessitates immediate attention. The gravity-driven ceramic membrane (GDCM) technology has shown great potential for groundwater treatment in rural communities, owing to its low energy demand and user-friendly operation. Active manganese oxide (MnOx) is extensively used for the concurrent removal of Mn2+ and NH3-N, leveraging its large specific surface area and abundant adsorption sites. Our research group has developed a GDCM-MnOx coupled system to address this challenge. However, membrane fouling, manifested as a reduction in flux or an increase in transmembrane pressure, has been a significant barrier to its widespread adoption. To address this challenge, we have implemented a continuous aeration system in conjunction with GDCM to fluidize birnessite to achieve the higher membrane flux, which has also proven effective in mitigating fouling while maintaining high water purification performance. Over a period of 100 days or more, the high membrane flux in the high-flux GDCM system (HF-GDCM) enhanced with aerated fluidized birnessite has been consistently maintained at approximately 34 L/(m2·h) at a water head of 1 m. Moreover, the HF-GDCM system efficiently removed manganese and NH3-N from groundwater under a hydraulic retention time (HRT) of less than 2.5 h, while also improving membrane permeability. The involvement of manganese oxidizing bacteria (MnOB) and ammonium-oxidizing bacteria (AOB) of Hypomicrobium and Nocardioides in the removal processes within the HF-GDCM system was confirmed. Additionally, XPS analysis confirmed the predominant oxidation state of MnOx to be Mn(III). The MnOx, deposited on powdered activated carbon (PAC) particles in a flower-like configuration, progressively formed a birnessite-like functional layer as the manganese ion content increased over time. Consequently, the HF-GDCM coupled with aerated fluidized birnessite is deemed suitable for water purification in small-scale rural or reservoir settings.

Increasing biomass concentration facilitates simultaneous nitrogen removal and sludge reduction under low C/N conditions

To overcome the issues of limited carbon source and high sludge production in partial denitrification/anammox (PD/A) process, the effects of mixed liquor suspended solids (MLSS) and carbon/nitrogen ratio (C/N) on PD/A were investigated through parallel experiments. Nitrogen removal efficiencies decreased significantly when C/N was reduced (1.5 → 0.75). When MLSS was doubled, the nitrogen removal efficiencies in the two parallel reactors increased from 75.3 %, 72.9 % to 86.9 %, 89.7 %, respectively, and sludge yields decreased obviously. Combining with in-situ test, it was speculated when MLSS increased, fermentation was enhanced, providing substrate for partial denitrification. Thauera, involved in partial denitrification, decreased obviously with reduced C/N, but increased from 9.93 % to 38.16 % when MLSS doubled, which could promote the PD/A process. Terrimonas and Ignavibacterium (fermentative bacteria) increased from 1.26 %, 5.22 % to 6.62 %, 6.30 %, respectively. These results proved that increasing MLSS under low C/N ratios promoted fermentation in PD/A system, facilitating efficient nitrogen removal and sludge reduction.

Insight into simultaneous urea hydrolysis and total nitrogen removal in textile printing wastewater: Focus on the impact of sodium sulfate salinity

The textile printing industry discharges large volumes of effluent containing high concentrations of urea and nitrogenous compounds. Anoxic-oxic (AO) treatment is a promising method for treating printing wastewater. However, the effect of sodium sulfate (Na2SO4) salinity on the urea hydrolysis and nitrogen removal simultaneously in the AO process has received little attention. In this study, five batch reactors were used to treat synthetic printing wastewater with high urea and nitrogen concentrations. A strategy was applied to increase the Na2SO4 concentration from 0 to 19 g/L in the anoxic stage of each reactor. The effect of Na2SO4 on urea hydrolysis, total nitrogen removal and COD removal, sludge characteristics, and bacterial community structure were investigated. The findings showed that urea hydrolysis increased with increasing Na2SO4 concentration. The main mechanism of urea removal was intracellular hydrolysis, with a urea removal efficiency (URE%) of approximately 98% in all batch reactors. In addition, under the stress of Na2SO4, the total nitrogen and COD removal performances were partially inhibited. The most significant removal performances after AO treatment were observed at 0 g/L Na2SO4, with nitrogen and COD removal efficiencies of 88% and 95%, respectively. When Na2SO4 concentration reached 19 g/L, the sludge settling performance and compactness were enhanced. The extracellular polymeric substance (EPS) components in the sludge were dependent on their ability of removing organics. Bacterial community diversity analysis revealed that the enrichment of the Proteobacteria, Firmicutes, and Gemmatimonadota phyla in the anoxic stages of batch reactors was related to intracellular urea hydrolysis. Bacteriodota and Chloroflexi were responsible for total nitrogen removal in all anoxic and oxic stages. This research will develop the understanding of Na2SO4 salinity impact on simultaneous urea hydrolysis and nitrogen removal during AO treatment process.

Simultaneous nitrogen and phosphorus removal by immobilized bacterial particles of denitrifying phosphorus accumulating microorganisms and its application

Enterobacter cloacae G, a novel denitrifying phosphorus-accumulating bacterial strain, was isolated from anaerobic sludge tank of a wastewater treatment plant used for pig farms. It was discovered that a pH of 7, a temperature of 30°C, an initial phosphorus concentration of 8 mg/L, and a C/N ratio of 10 were the strain's ideal growth conditions. To ensure the stability of strain G in wastewater treatment, strain G was immobilized by 5 % polyvinyl alcohol, 2 % sodium alginate, and 0.6 g of biochar and crosslinked for 9 h in 4 % calcium chloride saturated boric acid solution via an orthogonal test. After the immobilized microspheres were introduced into the sequencing batch reactor (SBR), the nitrate and phosphate removal rates achieved were 89.36 % and 65.53 %, respectively, with a hydraulic retention time (HRT) of 8 hours, a pH of 7.5, and a C/N ratio of 4.5. The immobilized microspheres containing strain G demonstrated potential for the treatment of nitrogen-rich and phosphorus-rich wastewater.

Influence of carbon to phosphorus ratio on the performance of single-stage aerobic simultaneous nitrogen and phosphorus removal by bioflocs

Effluents from intensive aquaculture typically contain high nitrate and phosphate concentrations. Biofloc technology has demonstrated the potential for simultaneous removal of nitrate and phosphate without ammonium nitrogen, and further optimization is needed to enhance the nitrogen and phosphorus removal efficiency. In this study, we investigated the efficiency of bioflocs in treating highly concentrated aquacultural wastewater at different carbon to phosphorus (C/P) ratios of 20 (G20), 30 (G30), and 40 (G40). The results showed that the nitrate removal rate in group G40 (1.25±0.07 mgN/gTSS/h) was significantly higher than in groups G20 and G30 (p < 0.05). However, there was no significant difference between the phosphate removal rates of groups G40 and G30, while both exhibited superior G20. The relative abundance of Thauera in G40 was significantly higher (p < 0.05), accounting for 8.74% of the microbial community. Additionally, the copy counts of denitrification-related genes (napA, nirS, nirK, nosZ) and inorganic phosphate transport genes (pqqC) were significantly higher in G40, correlating positively with an increased C/P ratio. Thees results suggest that the excessive carbon source in G40 enhanced denitrification and reduced biofloc assimilation, thus failing to significantly enhance the phosphate removal rate. This study demonstrates that adjusting the C/P ratio alone can improve the efficiency of nitrogen and phosphorus removal by bioflocs, and that a C/P ratio of 30 may be the most appropriate for enhancing the rate of nutrient removal while minimizing the use of carbon source.

Activation of iron oxides through organic matter-induced dissolved oxygen penetration depth dynamics enhances iron-cycling driven ammonium oxidation in microaerobic granular sludge

The iron redox cycle can enhance anammox in treating low-strength ammonia wastewater. However, maintaining an effective iron redox cycle and suppressing nitrite-oxidizing bacteria in a one-stage partial nitritation and anammox (PN/A) process poses challenges during long-term aeration. We proposed a novel and simple strategy to achieve an efficient iron redox cycle in an iron-mediated anoxic-microaerobic (A/O) process by controlling organic matter (OM) at medium-strength levels (30–110 mg COD/L) in microaerobic granular sludge (MGS)-dominated reactor. The developed A/O process consistently achieved >90 % OM removal and >75 % nitrogen removal. Medium-strength OM varied the penetration depths of dissolved oxygen (DO) in MGS, regulating redox conditions and promoting redox reactions across MGS layers, thus activating accumulated inert iron oxides. Ammonia-oxidizing bacteria (Nitrosomonas), iron-reducing bacteria (e.g., Ignavibacterium, Geobacter), and anammox bacteria (Ca. Kuenenia) coexisted harmoniously in MGS. This coexistence ensured high anammox and Feammox rates along with a robust iron redox cycle, thereby mitigating the adverse impacts of fluctuating DO and OM on one-stage PN/A process stability. The identification of iron reduction-associated genes within Ca. Kuenenia, Ignavibacterium, and Geobacter suggests their potential roles in supporting Feammox coupled in one-stage PN/A process. This study introduces an iron-cycle-driven A/O process as an energy-efficient alternative for simultaneous carbon and nitrogen removal from low-strength wastewater.

Simultaneous removal of ammonia nitrogen, sulfamethoxazole, and antibiotic resistance genes in self-corrosion microelectrolysis-enhanced counter-diffusion biofilm system

A self-corrosion microelectrolysis (SME)-enhanced membrane-aerated biofilm reactor (eMABR) was developed for the removal of pollutants and reduction of antibiotic resistance genes (ARGs). Fe2+ and Fe3+ formed iron oxides on the biofilm, which enhanced the adsorption and redox process. SME can induce microorganisms to secrete more extracellular proteins and up-regulate the expression of ammonia monooxygenase (AMO) (0.92 log2). AMO exposed extra binding sites (ASP-69) for antibiotics, weakening the competition between NH4+-N and sulfamethoxazole (SMX). The NH4+-N removal efficiency in the S-eMABR (adding SMX and IC) increased by 44.87 % compared to the S-MABR (adding SMX). SME increased the removal performance of SMX by approximately 1.45 times, down-regulated the expressions of sul1 (−1.69 log2) and sul2 (−1.30 log2) genes, and controlled their transfer within the genus. This study provides a novel strategy for synergistic reduction of antibiotics and ARGs, and elucidates the corresponding mechanism based on metatranscriptomic and molecular docking analyses.

Fe3+ augmentation enhancing the nitrogen and phosphorus control in denitrification biofilter based on water supply sludge: Performance and microbial characteristics

The intricate mechanisms of iron (Fe) enhancing the simultaneous nitrogen (N) and phosphorus (P) removal in the denitrification biofilter (DNBF) remain enigmatic and warrant further investigation. Fe2+ and Fe3+ were added to compare the enhancing performances and the dosage concentration was optimized in this study, and the effects of Fe3+ on microbial characteristics were elucidated furtherly. Results demonstrated that the N removal performance with Fe3+ enhancing was better than Fe2+, and the optimal FeCl3 concentration was 0.56 mg/L. The effluent concentrations of total phosphorus (TP), total nitrogen (TN), and chemical oxygen demand (COD) lowed to 0.27, 4.2, and 13.4 mg/L, respectively. Fe3+ promoted microbial richness and diversity, with Proteobacteria, Bacteroidetes and Firmicutes emerging as the advantageous phyla for N and P removal in the DNBF. Microorganisms facilitated Fe3+ reduction to enhance denitrification process, and P was predominantly removed through the precipitation formed by the interaction of Fe and P. Furthermore, Fe3+ was noted to promote functional metabolism, thereby aiding in N removal. This study can reveal the effect of Fe3+ on N removal in the DNBF, and provide a theoretical foundation for advanced N and P removal.

Simultaneous nitrogen and phosphorus removal from polluted water using a novel bacterial consortium (BACON-38): Promising application for wastewater remediation

A novel mixed bacterial consortium, BACON-38, was developed with efficient heterotrophic nitrification, aerobic denitrification, and phosphorus accumulation abilities. The BACON-38 exhibited efficient NH4+-N, NO3−-N, PO43−-P, and COD removal from real wastewater with removal efficiencies of 93.4 ± 1 %, 90 ± 0.75 %, 87.8 ± 0.25 % and 92 ± 1.5 %, respectively, under aerobic condition. Further, efficient removal of these pollutants from synthetic wastewater was also achieved by employing this consortium. Optimal conditions for maximum N and P removal efficiency were identified through response surface methodology (dissolved oxygen: 3.75 ± 0.5 mg L−1, pH: 7.5 ± 0.55, C/N ratio: 8.96 ± 0.75, temperature: 23.5 ± 1.25 °C). Amplification of key genes (amoA, hao, napA, narG, nirK, nirS, ppk) and enzyme expression confirmed simultaneous nitrification, denitrification, and phosphorus removal by BACON-38. The proposed nitrogen and phosphorus removal pathway aligned with the N and P balance, showing their assimilation into intracellular components. These results indicate that BACON-38 has significant potential for effectively removing nitrogen and phosphorus, making it a promising and sustainable solution for wastewater remediation.

Optimizing carbon sources on performance for enhanced efficacy in single-stage aerobic simultaneous nitrogen and phosphorus removal via biofloc technology

Bioflocs can efficiently achieve simultaneous nitrate and phosphate removal through a single-stage aerobic process, provided they are continuously supplemented with an organic carbon source. This study investigated the effects of different carbon sources on this process. Results revealed that phosphate removal rate in the glucose group was 0.61 ± 0.02 mg/L/h, significantly higher than those in the acetate (0.28 ± 0.01 mg/L/h) and propionate (0.29 ± 0.03 mg/L/h) groups (p < 0.05). However, the three groups observed no significant differences in nitrate removal rates (p > 0.05). The superior performance of the glucose group in simultaneous nitrogen and phosphorus removal is likely due to the higher biomass synthesis. In contrast, nitrate removal in the acetate and propionate groups was primarily driven by denitrification, resulting in lower sludge production and reduced phosphate uptake. For practical application of bioflocs in simultaneous nitrogen and phosphorus removal, glucose is recommended as the optimal carbon source.

Synergy between Nitrogen Removal and Fermentation Bacteria Ensured Efficient Nitrogen Removal of a Mainstream Anammox System at Low Temperatures.

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.

Simultaneous hydroxyapatite-based phosphorus recovery and partial denitrification-anammox-based nitrogen removal during sludge leachate treatment

Anammox has been widely applied for treating high ammonia‑nitrogen leachate, but challenges remain due to the phosphorus in the wastewater and by-products nitrate (NO3−). Therefore, we combined partial denitrification-anammox and hydroxyapatite crystallization within a single UASB reactor. This method achieved an effluent with a 4.27 ± 0.45 mg TN/L and a maximum PO43− removal efficiency of 68.31 ± 5.42 %. The addition of excess calcium led to an increase in phenylalanine-like substances, the humification index (HIX) of extracellular polymeric substances (EPS), and the MLVSS/MLSS ratio. These changes indicated that hydroxyapatite coated the initial granular sludge, causing it to crack and re-granulate, but the MLVSS didn't decrease significantly. Therefore, calcium addition didn't significantly impact the function of biomass. Metagenomic analysis revealed that by-products NO3− was removed through partial denitrification using in-situ refractory dissolved organic matters in SL. The formation of hydroxyapatite crystals is the main pathway for PO43− removal, and biological process also contributed to some PO43− removal. Overall, our study provided a viable solution for the simultaneous removal of nitrogen and recovery of phosphorus from high ammonia‑nitrogen wastewater.

One-stage anammox and thiocyanate-driven autotrophic denitrification for simultaneous removal of thiocyanate and nitrogen: Pathway and mechanism

The coupled process of anammox and reduced-sulfur driven autotrophic denitrification can simultaneously remove nitrogen and sulfur from wastewater, while minimizing energy consumption and sludge production. However, the research on the coupled process for removing naturally toxic thiocyanate (SCN-) is limited. This work successfully established and operated a one-stage coupled system by co-cultivating mature anammox and SCN--driven autotrophic denitrification sludge in a single reactor. In this one-stage coupled system, the average total nitrogen removal efficiency was 89.68±3.33 %, surpassing that of solo anammox (81.80±2.10 %) and SCN--driven autotrophic denitrification (85.20±1.54 %). Moreover, the average removal efficiency of SCN- reached 99.50±3.64 %, exceeding that of solo SCN--driven autotrophic denitrification (98.80±0.65 %). The results of the 15N stable isotope tracer labeling experiment revealed the respective reaction rates of anammox and denitrification as 106.38±10.37 μmol/L/h and 69.07±8.07 μmol/L/h. By analyzing metagenomic sequencing data, Thiobacillus_denitrificans was identified as the primary contributor to SCN- degradation in this coupled system. Furthermore, based on the comprehensive analysis of nitrogen and sulfur metabolic pathways, as well as the genes associated with SCN- degradation, it can be inferred that the cyanate (CNO) pathway was responsible for SCN- degradation. This work provided a deeper insight into coupling anammox with SCN--driven autotrophic denitrification in a one-stage coupled system, thereby contributing to the development of an effective approach for wastewater treatment involving both SCN- and nitrogen.

Crucial role of extracellular polymeric substances from anammox sludge in wastewater phosphorus recovery via magnesium phosphate crystallization

The magnesium phosphate (Mg-P) crystallization based on anaerobic ammonia oxidation is of interest for simultaneous nitrogen and phosphorus removal in wastewater treatment due to cost-effectiveness. Understanding the role of extracellular polymeric substances (EPS) in crystal growth is pivotal for bio-induced Mg-P crystallization. In this work, the effects of EPS in Mg-P crystallization were thoroughly investigated. Results indicated that EPS decreased the initial crystallization rate but slightly improved the final crystallization yield. The maximum removal efficiencies of Mg and P ions increased by 2.8 % and 3.1 %, respectively, when EPS concentration was 80 mg/L. Additionally, the presence of EPS enhanced Mg3(PO4)2·10 H2O production and facilitated the formation of larger rhombic plate-like structures crystals (maximum particle size increased by 215 %). Analysis of EPS composition changes during the crystallization process and characterization of the final crystals suggested that tryptophan-like proteins preferentially involved in the Mg-P crystallization process, while β-sheet proteins potentially influencing crystal morphology. Furthermore, the formation of phosphate ester groups, hydrogen bonding, and COOH-Mg2+ complexes were considered triggering factors for the interaction between EPS and Mg-P crystals. This study elucidated the underlying mechanism of EPS on Mg-P crystallization, further enhancing the understanding of the interaction between inorganic mineralization processes and microorganisms.

Exploring the promoting behavior of weak electric mediation on indole and pyridine biodegradation under anaerobic condition

Indole and pyridine, which are highly produced refractory compounds in the industrial wastewater, exhibit poor degradation capabilities in natural environments. In this study, we developed an anaerobic digestion system coupled with weak electric mediation (ED), and investigated the promoting effect of weak electricity on indole and pyridine biodegradation. The degradation characteristics were systematically explored, and the results showed that the degradation rate and mineralization of indole and pyridine were significantly enhanced, the production of CH4 was increased 1.4-fold, and the optimal voltages were 1.0 V and 0.8 V in the ED, respectively. Moreover, simultaneous removal of carbon and nitrogen was achieved. Gas chromatography–mass spectrometry analysis verified the transformation products, and possible pathways were proposed. Several byproducts of indole and pyridine were identified, with oxindole and glutaric dialdehyde being the main metabolites, respectively. Additionally, density functional theory (DFT) analysis was performed to investigated the radical indices and stabilities of the molecules to further confirm the degradation pathway. Microbial structure analysis demonstrated that the electrically mediated enhanced metabolism and activity of functional microbes, led to the promotion of indole and pyridine mineralization. Moreover, such species as degrading bacteria (Alicycliphilus, Shinella) and electroactive bacteria (Achromobacter), anaerobic ammonia-oxidizing bacteria (SM1A02), and denitrifying bacteria (Thiobacillus) coexisted. This study demonstrates that weak electric mediation is a promising methodology for enhancing the removal of indole and pyridine from wastewater under anaerobic conditions.

Fe(II)-mediated Fe–N–P metabolism in an anammox-dominated system for enhanced nitrogen removal and Fe–P crystals (FePs) production

Low-carbon and high-efficiency processes for achieving simultaneous nitrogen removal and phosphorus recovery from wastewater are gaining increasing attention from researchers. This study investigated the performance and mechanism of a novel Fe(II)-mediated anaerobic ammonia oxidation (anammox) process characterized by stable nitrogen removal and production of high-value Fe–P crystals (FePs) as byproducts. Fe(II) promotes the synthesis of heme C and enhances the activity of nitrate reduction metabolic genes, which induce nitrate-dependent ferrous oxidation to form a complex Fe–N cycle. In addition, Fe(II) significantly enhanced the phosphorus removal efficiency up to 79.2 ± 6.9% by inducing Fe–P biomineralization. Biomolecular analysis has shown that most iron absorption and transport genes, as well as phosphate transport and regulation genes, are promoted by Fe(II). The composition and microstructure analyses of the anammox granules revealed the formation of FePs that consisted of phosphosiderite (FePO4·2H2O), ludlamite (Fe3(PO4)2·4H2O), and vivianite (Fe3(PO4)2∙8H2O). This study also provides an in-depth illustration of the structural characteristics and formation processes of anammox-FePs granules. Thus, an Fe(II)-induced Fe–N–P metabolic network in an anammox-dominated system was uncovered, offering a feasible approach for simultaneous nitrogen removal and phosphorus recovery.

Preparation of magnesium-modified steel slag and its adsorption performance for simultaneous removal of nitrogen and phosphorus from water

This study presents a novel adsorbent for the simultaneous removal of ammonia nitrogen and phosphate from wastewater, synthesized by treating steel slag with magnesium chloride to produce a low-cost and highly magnesium-modified material. The modification process has significantly increased the specific surface area and pore structure of the steel slag, thereby enhancing its adsorption capacity. The magnesium-modified steel slag demonstrated superior performance in the simultaneous removal of ammonia nitrogen and phosphate compared to single-component removal, with maximum removal rates of 88.45 % and 94.56 % for ammonia nitrogen and phosphate, respectively. SEM-EDS, XRF, and BET analysis revealed that ammonia nitrogen removal primarily occurred through ion exchange and intermolecular forces, involving substitution of metal ions and surface adsorption. On the contrary, phosphate predominantly reacted with Ca2+ ions to form hydroxyapatite (HAP) on the surface of steel slag. Furthermore, magnesium-modified steel slag provides more Mg2+ sites for NH4+ exchange and facilitates the co-precipitation of NH4+ and PO43- to form magnesium ammonium phosphate (MAP), thereby promoting collaborative removal of nitrogen and phosphorus. This environmentally beneficial approach not only offers a promising solution for efficient wastewater treatment but also contributes to the sustainable management of steel slag waste.

Simultaneous aerobic nitrogen and phosphorus removal by novel halotolerant fungus Mucor circinelloides SNDM1: Function and metabolism pathway

Fungi capable of simultaneous nitrogen and phosphorus removal from wastewater is rarely found. Here, a novel fungal strain (SNDM1) performing heterotrophic nitrification, aerobic denitrification, and phosphate removal was isolated and identified as Mucor circinelloides. The favorable nutrient removal conditions by the strain using glucose were C/N ratios of 25–30, salinities of 0 %–3 %, and pH of 7.5. Strain SNDM1 achieved ammonium, nitrite, nitrate, and phosphate removal rates of 5.23, 10.08, 4.88, and 0.97 mg/L/h. Nitrogen balance indicated that gaseous (18.60 %–24.55 %) and intracellular nitrogen (43.76 %–70.63 %) were primary fate of initial nitrogen. Enzyme activity revealed that ammonium removal occurred through heterotrophic nitrification and aerobic denitrification. Removed phosphorus was mainly transformed into cell membranes (56 %–64 %) and extracellular polymeric substances (20 %–26 %). Orthophosphate was the major intracellular phosphorus species, while polyphosphate and pyrophosphate existed extracellularly. These findings highlight the potential of this fungal strain for bioremediating polluted wastewater.