Denitrification System Research Articles

Activated carbon and anthraquinone-2,6-disulfonate as electron shuttles for enhancing carbon and nitrogen removal from simultaneous methanogenesis, Feammox and denitrification system.

Anthraquinone-2,6-disulfonate (AQDS) and activated carbon (AC) were employed as exogenous electron shuttles (ESs) for enhancing the performance of an integrated simultaneous methanogenesis, Feammox, and denitrification (SMFD) system treating fish sludge. The addition of AQDS and AC led to an increased total nitrogen removal efficiency by 30.2% and 66.5%, an increased total chemical oxygen demand removal efficiency by 9.5% and 24.5%, and an improved methane yield by 5.2% and 12.6%, respectively. Regarding nitrogen removal, AQDS mainly facilitated NH4+-N oxidation into NO3--N via Feammox, while AC facilitated both Feammox and denitrification. Regarding carbon removal, both ESs promoted the hydrolysis-acidification process via stimulating dissimilatory iron reduction and established direct interspecies electron transfer (DIET) between methanogens and syntrophic bacteria. Microbial analysis confirmed the enrichment of iron-reducing bacteria, denitrifiers, DIET-related methanogens and syntrophic partners in the presence of ESs. The study provides an ESs-assisted strategy for enhancing simultaneous nitrogen and carbon removal from high-strength wastewater.

Novel mixotrophic denitrification biofilter for efficient nitrate removal using dual electron donors of polycaprolactone and thiosulfate.

A novel mixotrophic denitrification biofilter for nitrate removal using polycaprolactone and thiosulfate (MD-PT) as electron donors was investigated. MD-PT achieved high nitrate removal efficiency of approximately 99.8%. The nitrate removal rates of MD-PT reached 1820 gN/m3/d, which was 304 gN/m3/d higher than that of autotrophic denitrification biofilter using thiosulfate (AD-T). Autotrophic and heterotrophic denitrification pathways in MD-PT were responsible for 67.6-94.5% and 4.7-32.4% of the nitrate removal, respectively. The production of SO42- in MD-PT was lower than that in AD-T, and the effluent pH was maintained at approximately 7.3 without acid-base neutralization. The abundance of key genes involved in carbon, nitrogen, and sulfur transformation was enhanced, which improved the nitrate removal of MD-PT. Alicycliphilus and Simplicispira related to organic compounds degradation were enriched after the addition of polycaprolactone. This research provided new insights into mixotrophic denitrification systems.

Metagenomic insights into nitrite accumulation in sulfur-based denitrification systems utilizing different electron donors: functional microbial communities and metabolic mechanisms

Sulfur-based autotrophic denitrification (SADN) offers new pathway for nitrite supply. However, sequential transformation of nitrogen and sulfur forms, and the functional microorganisms driving nitrite accumulation in SADN with different reduced inorganic sulfur compounds (RISCs), remain unclear. Desirable nitrite accumulation was achieved using elemental sulfur (S0-group), sulfide (S2--group) and thiosulfate (S2O32--group) as electron donors. Under equivalent electron supply conditions, S2O32--group exhibited a superior nitrate conversion rate (NCR) of 0.285 kg N/(m³·d) compared to S2--group (0.103 kg N/(m³·d)). Lower NCR in S2--group was attributed to sulfide strongly inhibiting energy metabolism process of TCA cycle, resulting in reduced reaction rates. Moreover, the NCR of S0-group (0.035 kg N/(m³·d)) was poor due to the chemical inertness of S0. Specific microbial communities were selectively enriched in phylum level, with Proteobacteria increasing to an astonished 96.27-98.49%. Comprehensive analyses of functional genus, genes, and metabolic pathways revealed significant variability in the active functional genus, with even the same genus showed significant metabolic differences in response to different RISCs. In S0-group, Thiomonas (10.0%) and Acidithiobacillus (5.1%) were the primary contributor to nitrite accumulation. Thiobacillus was the most abundant sulfur-oxidizing bacteria in S2--group (43.84%) and S2O32--group (18.92%). In S2--group, it contributed to nitrite accumulation, while in S2O32--group, it acted as a complete denitrifier (NO3--N→N2). Notably, heterotrophic denitrifying bacteria, Comamonas (12.52%), were crucial for nitrite accumulation in S2O32--group, predominating NarG while lacking NirK/S. Overall, this work advances our understanding of SADN systems with different RISCs, offering insights for optimizing nitrogen and sulfur removal.

Transformation fate of bisphenol A in aerobic denitrifying cultures and its coercive mechanism on the nitrogen transformation pathway.

Bisphenol A (BPA) is a commonly used endocrine-disrupting chemical found in high levels in wastewater worldwide. Aerobic denitrification is a promising alternative to conventional nitrogen removal processes. However, the effects of BPA on this novel nitrogen removal process have rarely been reported. Herein, we investigated the removal and interaction effects of BPA (0, 0.1, 1, and 10 mg/L) in aerobic denitrifying cultures. Our experimental results demonstrated that the aerobic denitrification system could remove 66%-86% of BPA from wastewater. Fourier transform infrared spectroscopy revealed that polysaccharides and amides were the primary sites for adsorption. An increase in the type and number of intermolecular hydrogen bonds might enhance the ability of aerobic denitrifying cultures to adsorb BPA. Adsorption kinetics analysis demonstrated that inhomogeneous multilayer adsorption was the leading cause of BPA removal. Adsorbed BPA decreased the sedimentation, flocculation, and hydrophobicity of aerobic denitrifying cultures, triggering changes in the levels of proteins and polysaccharides in extracellular polymeric substances. As the influent BPA increased from 0 to 10 mg/L, the nitrate-nitrogen and total organic carbon in the reactor effluent increased from 0.4 ± 0.2 and 26 ± 7.9 mg/L to 18.8 ± 9.3 and 116.2 ± 55.6 mg/L, respectively. BPA (initial concentration range: 1-10 mg/L) significantly influenced the abundance of genes involved in the nitrogen transformation pathway, contributing to the increase in the abundance of gaseous NOx-transformed genes and altering the relative abundance of denitrifying bacteria, particularly Thauera. Correlation analyses revealed that Pseudomonas, Thauera, and AKYH767 are important for maintaining systemic nitrogen transformations and BPA adsorption.

Evaluation of nitrous oxide reduction in solid carbon source-driven counter-diffusional biofilm denitrification system

Evaluation of nitrous oxide reduction in solid carbon source-driven counter-diffusional biofilm denitrification system

A mixotrophic denitrification composite for treatment of nitrate-contaminated water: Performance, microbial community and functional genes

A mixotrophic denitrification composite was prepared with sulfur, pyrite, sawdust and calcium carbonate (SPSC) for the treatment of nitrate-contaminated wastewater. As a homogeneous integrated composite, fast mass transfer, convenient operation and transportation and easy attachment for microorganisms were obtained in the SPSC-based denitrification system. The long-term operation result showed that SPSC bioreactor exhibited strong resistance to the fluctuations of influent nitrate load, and 98.3% of the nitrate in the influent was reduced even under low hydraulic retention time (HRT). The SPSC system achieved an average nitrate removal rate of 4.59 mg-N/L/h, which was nearly triple the rate of sulfur autotrophic denitrification (SAD) system that utilized sulfur as its sole electron donor. The sulfate yield of the SPSC system (4.52mg SO42-/ mg NO3--N) was significantly lower than those of the SAD system (9.36mg SO42-/ mg NO3--N). Heterotrophic and autotrophic denitrifiers coexisted in the SPSC system, which was beneficial for the denitrification process. Metagenomic analysis indicated that the SPSC composite enriched the functional genes, which encoding key enzymes (nitrate reduction, sulfur oxidation and energy generation) involved in nitrogen, sulfur and carbon metabolism. Collectively, the SPSC composite synthesized in this study has provided a high efficiency, low-cost and promising technology for the treatment of nitrate-contaminated water.

A novel phosphorus removal process in the sulfide-based autotrophic denitrification system

A novel phosphorus removal process in the sulfide-based autotrophic denitrification system

Application of an Improved State Feedback Control in the Selective Catalytic Reduction Denitrification Systems of Coal Power Units Under Variable Load Conditions

Selective catalytic reduction (SCR) flue gas denitrification systems are inherently complex, typically embodying characteristics of non-linearity, significant time delays, and susceptibility to multiple disturbances. In the context of coal power units engaging in deep load cycling and rapid frequency adjustment, conventional proportional-integral-derivative (PID) control struggles to meet the demands of effective control. This study introduces a control strategy that incorporates a “state observer + Linear Quadratic Regulator (LQR) state feedback + Improved Quantum Genetic Algorithm (IQGA) optimized PID”. Initially, local linear mathematical models of an SCR denitrification system at 340 MW, 450 MW, and 540 MW loads were used to design state observer and LQR state feedback control parameters for each operational condition. At a single load point, the IQGA was employed to optimize the outer loop PID parameters, followed by simulation experiments of load increases and decreases between 340 MW and 540 MW. The results demonstrated that, compared to two other strategies, the proposed approach reduced the overshoot by a minimum of 1.5% and shortened the adjustment time by 31.7% under conditions of step disturbances and internal perturbations. Throughout variable operational conditions, the strategy consistently exhibited minimal output fluctuations, rapid adjustment capabilities, strong disturbance rejection, and robust stability. This algorithm proves to be an effective method for controlling NOx concentrations, offering insights for precise ammonia injection control in future applications.

Amorphous Cu/Fe nanoparticles with tandem intracellular and extracellular electron capacity for enhancing denitrification performance and recovery of co-contaminant suppressed denitrification

In this study, a functionally stable insoluble Cu/Fe nanoparticles (Cu/Fe NPs) were synthesized and applied denitrification with different contaminants. The results showed that 50 mg/L Cu/Fe NPs increased NO3–-N reduction rate up to 14.3 mg/(L·h) about 3 folds compared with the control system (4.7 mg/(L·h)), and Cu/Fe NPs exhibited excellent restorative effects on NO3–-N reduction under the stress of Cd2+, Nitrovin and Methyl Orange. Meanwhile, electrochemical analyses, enzyme activities, and related genes abundance together showed that pilus, cytochrome c and flavin mononucleotide were electron carriers to tandem extracellular and intracellular, increasing electron flux acting on NO3–-N in the respiratory chain. Metagenomic sequencing showed that microbial metabolic activity, electroactive bacteria (EAB) abundance with bi-directional electron transfer and Cu/Fe-compatible bacterial abundance were increased. Furthermore, denitrification performance was maintained by establishing C-EAB-Cu/Fe NPs cycling network. This study provided insights and applications for expanding the use of insoluble mediators in denitrification systems.

Impact of tetracycline on mixotrophic denitrification process under different sulfur to nitrogen ratios

The sulfur-based autotrophic-heterotrophic denitrification, i.e., mixotrophic denitrification, is suitable for the nitrate and antibiotics removal in aquaculture tailwater at a low COD to nitrogen (C/N) ratio. This study focused on the effect of tetracycline (TC) on mixotrophic denitrification under different S/N ratios. Two bioreactors were simultaneously operated with or without dosing tetracycline under different sulfur to nitrogen (S/N) ratios of 3.94, 4.64 and 5.94. The results showed that the removal rate of total inorganic nitrogen (TIN) increased from 0.25 to 0.69 mg N L−1 min−1 with the rise of S/N ratio, while TC dosage significantly declined the removal efficiency of TIN. Dissimilatory nitrogen reduction to ammonia (DNRA) bacteria was detected when exposing to TC, indicating that DNRA presented more resistance to TC. The removal efficiency of TC in the denitrification system reached the maximum of 22.87 % at S/N of 4.64. Meanwhile the genus Marinicella was detected at this phase, which was conducive to the degradation of organic pollutants. This study found that TC promoted the accumulation of ammonia nitrogen, and had a great effect on sulfur autotrophic bacteria at S/N of 5.94. The removal of TC mainly depended on microbial co-metabolism, and there was a significant correlation between the reduction of TC concentration and the decrease of sulfur compounds (p < 0.05). 4.64 is the best S/N ratio for the mixotrophic denitrification process, which revealed maximum nitrate and TC removal rates.

The bacterial strains JAM1T and GP59 of the species Methylophaga nitratireducenticrescens differ in their expression profiles of denitrification genes in oxic and anoxic cultures.

Strain JAM1T and strain GP59 of the methylotrophic, bacterial species Methylophaga nitratireducenticrescens were isolated from a microbial community of the biofilm that developed in a fluidized-bed, methanol-fed, marine denitrification system. Despite of their common origin, both strains showed distinct physiological characters towards the dynamics of nitrate ( ) reduction. Strain JAM1T can reduce to nitrite ( ) but not to nitric oxide (NO) as it lacks a NO-forming reductase. Strain GP59 on the other hand can carry the complete reduction of to N2. Strain GP59 cultured under anoxic conditions shows a 24-48h lag phase before reduction occurs. In strain JAM1T cultures, reduction begins immediately with accumulation of . Furthermore, is reduced under oxic conditions in strain JAM1T cultures, which does not appear in strain GP59 cultures. These distinct characters suggest differences in the regulation pathways impacting the expression of denitrification genes, and ultimately growth. Both strains were cultured under oxic conditions either with or without , or under anoxic conditions with . Transcript levels of selected denitrification genes (nar1 and nar2 encoding reductases, nirK encoding reductase, narK12f encoding / transporter) and regulatory genes (narXL and fnr) were determined by quantitative reverse transcription polymerase chain reaction. We also derived the transcriptomes of these cultures and determined their relative gene expression profiles. The transcript levels of nar1 were very low in strain GP59 cultured under oxic conditions without . These levels were 37 times higher in strain JAM1T cultured under the same conditions, suggesting that Nar1 was expressed at sufficient levels in strain JAM1T before the inoculation of the oxic and anoxic cultures to carry reduction with no lag phase. Transcriptomic analysis revealed that each strain had distinct relative gene expression profiles, and oxygen had high impact on these profiles. Among denitrification genes and regulatory genes, the nnrS3 gene encoding factor involved in NO-response function had its relative gene transcript levels 5 to 10 times higher in strain GP59 cultured under oxic conditions with than those in both strains cultured under oxic conditions without . Since NnrS senses NO, these results suggest that strain GP59 reduced to NO under oxic conditions, but because of the oxic environment, NO is oxidized back to by flavohemoproteins (NO dioxygenase; Hmp), explaining why reduction is not observed in strain GP59 cultured under oxic conditions. Understanding how these two strains manage the regulation of the denitrification pathway provided some clues on how they response to environmental changes in the original biofilm community, and, by extension, how this community adapts in providing efficient denitrifying activities.

Intra/extracellular electron transfer and metagenomic analysis elucidated the roles of magnetic iron powder (Fe3O4) on mixotrophic denitrification system

Elemental iron provides a viable strategy to improve the denitrification efficiency by expediting electron transport. However, the roles of magnetic iron powder (Fe3O4) on mixotrophic denitrification remains unknown. In this study, the intra/extracellular electron transfer (IET/EET) and microbial metabolism mechanisms were explored in a Fe3O4-mediated sulfide-autotrophic and heterotrophic denitrification system. The results showed that Fe3O4 promoted the formation of dense clump structure with filamentous cross-linking in activated sludge. Fe3O4 could increase the coenzyme Q activity in IET and the content of free riboflavin and cytochrome c in EET. Metagenomic analysis indicated that denitrification, sulfide oxidation and sulfate reduction were the main pathways of nitrogen and sulfur metabolism, and the enriched denitrifying bacteria (Halomonas and Hypobacterium) and sulfur-oxidizing bacteria (Marinicella) could stably support nitrate removal. This study expands our understanding of the IET/EET during Fe3O4-mediated mixotrophic denitrification process, providing a novel insight for nitrogen removal from marine recirculating aquaculture wastewater.

The construction of double short-cut sulfur autotrophic denitrification and PN/Anammox partition and its effect on the coupling performance of nitrogen and sulfur removal

How to reduce NO3−-N from partial nitrification/Anammox (PN/Anammox) for low carbon emissions, thus achieve deep nitrogen removal, is a significant issue when applying PN/Anammox to treatment inorganic high-ammonia wastewater. This study designed a prepositioned double short-cut sulfur autotrophic denitrification (DSSADN) system integrated with PN/Anammox, achieving simultaneous sulfur recovery and complete autotrophic denitrification. It also examined the impact of reflux changes on the nitrogen and sulfur transformation characteristics in the coupled system when treating ammonia and sulfur-containing wastewater. Results indicate that the coupling of DSSADN zone (zone C1) enhanced TN removal by PN/Anammox, with the TN removal rate (TNRRT), TN removal efficiency (TNRET), and S2− removal rate reaching 0.54 kg/(m³·d), 95.1%, and 100%, respectively. The NO2−-N accumulation efficiency (NiAEC1) of DSSADN reached 87.1%, with ΔSO42--S consistently less than 11.8 mg/L, and the S0 accumulation efficiency (S0AEC1) reaching 82.4%. A small amount of O2 carried in the reflux can effectively reduce residual S2− in zone C1, preventing its entry into the PN/Anammox zone (zone C2) and mitigating its toxic effects on Anammox. However, O2 also increases the expression of soxB in zone C1, causing more S2− to be oxidized to SO42−, and reducing S0AEC1. When DOC1 was between 0.05 mg/L and 0.34 mg/L, nirK expression was significantly increased, and the abundance of related functional microorganisms changed, led to more NO3−-N being reduced to N2. When DOC1 exceeds 0.34 mg/L, it inhibits the denitrification process, leading to elevated NiAE. Therefore, when regulating reflux in DSSADN + PN/Anammox partitioned integrated coupling system, attention should be given to changes in DOC1, controlling it within 0.05 mg/L.

Applications and analyses of ammonia slip control based on precise ammonia injection technologies guided by big data

Abstract After the implementation of ultra-low emission policies, the pollutant emissions from the coal-fired power generation systems in China have been further reduced, which creates more critical requirements for the control accuracies of denitrification systems using selective catalytic reduction technology and controls of ammonia slip. This article presents big data-based technologies for controlling ammonia slip, through precise ammonia injections, which were applied and demonstrated for a flue gas denitrification system of a Chinese coal-fired power plant. Through examinations and analyses of the basic operating conditions of the unit and parameters, such as NOx emission control efficiency, ammonia injection amount of the denitrification system, and non-uniformity of NOx concentrations in the denitrification zone were compared before and after the implementation of these technologies, the outcome proves that this artificial intelligence algorithm based on big data can effectively solve the automatic control problem of denitrification system under complex working conditions such as varied unit loads, day and night operation changed coal source. In addition to the effective controls of the ammonia slip of the system, the controls of NOx emission of the system become more stabilized, creating a successful example for wider applications of these precise ammonia injection control technologies in the future. Analyses show that NOx non-uniformities can be reduced by more than 50% under both stable and variable load conditions. NOx fluctuations at the unit outlet are tightly controlled within ±10 mg/Nm3 under variable load conditions and within ±5 mg/Nm3 under stable conditions. The average ammonia injection amounts under various load conditions have decreased by 15.7%.

Hysteresis response of carbon release and nitrate reduction in polymer denitrification systems

Polymer denitrification has received much attention in the field of advanced wastewater treatment. It can release carbon source stably during long-term operation, which can be used as electron donor for denitrification. However, the response of the polymer denitrification system to the transient changes of nitrate is not sufficiently disclosed yet. In this study, the response of a polymer denitrification system to nitrate was comprehensively investigated through a series of experiments. Therefore, real-time response and hysteresis response phenomena were identified. The time dependence of microorganisms in the system and the recovery of the hysteresis response were elucidated. The experimental results revealed distinct response patterns before and after the hysteresis tipping point. The denitrifying microorganisms, which showed a high adaptive capacity, exhibited a real-time response over a range of low nitrate concentration variations (∼20–30 mg/L). In contrast, microbial recovery is poor over a range of high nitrate concentration variation (∼35–40 mg/L), which is referred to as a hysteresis response. Finally, the hysteresis response mechanism was revealed by monitoring the recovery of denitrification enzymes, gene and microbial communities. The results showed that transient shocks of high nitrate loads affect microbial community structure stability, denitrifying enzyme activity and gene expression. Meanwhile, the abundance of Microbacterium associated with carbon release was reduced. The combination of these factors leads to a hysteresis response in denitrification and carbon release. This work contributes to a deeper understanding of the hysteresis behavior in polymer denitrification systems, offering critical insights for optimizing system performance and improving nitrogen removal efficiency.

Effect of magnetic powder (Fe3O4) on heterotrophic-sulfur autotrophic denitrification efficiency and electron transport system activity for marine recirculating aquacultural wastewater treatment

As an efficient nitrogen removal process, heterotrophic-sulfur autotrophic denitrification (HSAD) has attracted extensive attention in wastewater treatment. However, the effects of magnetic powder (Fe3O4) on the electron transport activity in HSAD process remain unclear. Therefore, in this study, a heterotrophic-sulfur autotrophic denitrification system was established to remove nitrogen from marine recirculating aquacultural wastewater for evaluating the effects of Fe3O4. At the optimal Fe3O4 concentration of 50 mg/L, the nitrogen removal efficiency reached 100% with lower sulfate accumulation, and the start-up time was shortened. The assays of denitrifying enzymes and electron transport system activity showed that Fe3O4 improved the activities of nitrate and nitrite reductases, and increased the efficiency of electron transport. Microbial community analysis revealed that Fe3O4 enriched heterotrophic denitrifier Thauera and sulfur autotrophic denitrifier Canditatus Thiobios, and thus enhanced denitrification efficiencies. This study demonstrated that Fe3O4 is an efficient denitrification accelerator in HSAD for treating marine recirculating aquacultural wastewater.

Metagenomic analysis reveals abundance of mixotrophic, heterotrophic, and homoacetogenic bacteria in a hydrogen-based membrane biofilm reactor

Heterotrophic microorganisms are frequently observed in hydrogenotrophic denitrification systems and are presumed to contribute to their improved performance. However, their roles and metabolic pathways in the hydrogen-based membrane biofilm reactor (H2−MBfR) system remain unclear. The objective of this study was to elucidate the underlying mechanisms driving heterotrophic denitrification. For this purpose, metagenomic analysis was conducted on an H2−MBfR showing higher denitrification performance, focusing on the metabolic function of the microbial community. Functional genes related to H2 oxidation, organic carbon metabolism, and denitrification were the major targets of interest. This analysis revealed a substantial number of genes associated with the oxidation of organic carbon compounds in the biofilm, suggesting its potential for heterotrophic denitrification. Investigation of the genes of interest in metagenome-assembled genomes (MAGs) has demonstrated a predominance of mixotrophs or heterotrophs rather than obligate autotrophs. Notably, MAGs exhibiting the highest abundance of genes of interest were affiliated with Hydrogenophaga and Thauera, implying their significant role in denitrifying the H2−MBfR as mixotrophs utilizing both H2 and organic substrates. The identification of 11 MAGs, presumed to originate from homoacetogens suggested that acetate might contribute to the proliferation of heterotrophs. Based on these metagenomic findings, possible metabolic pathways were identified to explain heterotrophic denitrification within the H2−MBfR biofilms.

Evolution of microbial community and resistance genes in denitrification system under single and combined exposure to benzethonium chloride and methylparaben

Benzethonium chloride (BZC) and methylparaben (MeP) are commonly added into cosmetics as preservatives, which are frequently detected in wastewater treatment plants. Different response patterns of denitrification system were proposed under single and combined exposure to BZC and MeP (0, 0.5, 5 mg/L) by evaluating system performance, functional genes, extracellular polymeric substance (EPS), cytotoxicity, microbial community structure and resistance genes (RGs). The inhibition effect of BZC on denitrification system was stronger than MeP, and the co-exposure of BZC and MeP showed synergistic effect, enhancing the inhibition effect of BZC single exposure. BZC and/or MeP could promote the diffusion of RGs in sludge, including intracellular RGs (si-RGs) and extracellular RGs (se-RGs). Moreover, the single exposure of BZC and co-exposure of BZC and MeP increased the dissemination risks of RGs in water (w-RGs). IntI1 and tnpA-04, mobile genetic elements (MGEs), correlated positively with diverse RGs from different fractions. Notably, the spread of RGs through horizontal gene transfer mediated by MGEs and the flow of si-RGs into extracellular and water were observed in this study.

An active disturbance rejection stair-like generalized predictive control with time delay weakening for denitrification process in thermal power unit

The optimization control of the selective catalytic reduction (SCR) denitrification system holds significant importance in the production of the power generation industry. This paper presents an active disturbance rejection stair-like generalized predictive control with time delay weakening (WADRC-SGPC) to enhance the control performance in SCR denitrification system. Compared with classical generalized predictive control (GPC), active disturbance rejection generalized predictive control (ADRC-GPC) combines the advantages of ADRC, uses Extended State Observer (ESO) to compensate the uncertainty of the system, and regards the compensated system as a series integrator. Therefore, it has the advantages of no system identification and online calculation of Diophantine equation. In addition, a time delay weakening link is incorporated for the known part of the system model, which effectively improves the performance of the controller. The parameter selection issue of the weight function in time delay weakening is addressed using a hybrid strategy whale optimization algorithm. Finally, the superior performance of the proposed control strategy in terms of set-point tracking and disturbance rejection is verified through simulation experiments.

Nutrient removal performance and the nitrogen-sulfur conversion pathways in sulfur-iron based biofilter under acidic/alkaline conditions

The nitrate and phosphate removal in sulfur based (Vp) and sulfur-iron based autotrophic denitrification systems (Sp) with sponge iron as the iron source was investigated under different pH (6–9). In this study, Sp (>98 %) and Vp (>97 %) had higher nitrate removal efficiency at pH 7–8 and the highest phosphate removal efficiency (94.9 % ± 3.57 %) at pH 6. The flow cytometry detection revealed that the cell integrity was damaged due to the formation of iron crusts at pH 6, which resulted in irreversible inhibition in Sp. Electron transfer and nitrogen transformation showed that compared with the sustained inhibition of denitrification at pH 6, the inhibition at pH 9 occurred mainly in the initial 0–2 h due to the enhanced flow of electrons toward the formation of biological element sulfur (Sbio0). Coupled sponge iron promoted the adsorption and reduction of NO2−/N2O and reduced N2O emissions. Metatranscriptomics analysis showed that significant upregulation of key gene expression for nitrogen and sulfur metabolism in Sp, with complex regulatory mechanisms enhancing system stability and performance. Acidic conditions reduced the abundance of denitrification and sulfur oxidation functional genes. However, alkaline conditions (pH of 9) mainly caused the decreased abundance of denitrification functional genes, which was favorable for accumulation of Sbio0. This study provides a theoretical basis for the stable operation and regulation of the sulfur-iron based autotrophic denitrification process.