Initial Nitrate Concentration Research Articles

The denitrification ability and nitrogen metabolism pathway of aerobic denitrifier Marinobacter alkaliphilus SBY-1 under low C/N ratios

Mariculture tail water is characterized as the low C/N ratios and thus blocks the conventional heterotrophic denitrification process due to insufficient carbon source. Therefore, oligotrophic marine bacteria with heterotrophic nitrification and aerobic denitrification (HN-AD) are urgently required to bioaugment aerobic biological filter. In this study, Marinobacter alkaliphilus SBY-1 was isolated and confirmed optimal nitrate removal capacity at a rate of 716 mg/L·d without ammonia production or nitrite accumulation under initial nitrate concentration of 800 mg/L, pH 7, salinity 20 ‰, sodium acetate as the carbon source, and low C/N ratios of 3.6. SBY-1 also demonstrated heterotrophic nitrification capability with a maximum ammonia removal rate reaching 69.21 % when ammonia was used as the nitrogen source. The enzymes involved in the HN-AD process including ammonia monooxygenase (AMO), nitrate reductase (NR), and nitrite reductase (NIR) were all detected in SBY-1 with superior activity observed for NR and NIR. Additionally, analysis of EPS and auto-aggregation revealed that SBY-1 exhibited excellent auto-aggregation ability under high influent nitrogen concentration conditions, making it more suitable for biofilm formation and further application in biofilm-based denitrification process. Genome analysis identified genes associated with Nar, Nap, Nas, Nir, Nif, Nrt, Nrf, Nor, Nos which confirmed that SBY-1 possessed a complete HN-AD pathway for nitrogen metabolism. The predicted nitrogen metabolism pathway of SBY-1 was NO3−-N → NO2−-N → NO→N2O → N2. These findings provide new insights into the efficient removal of nitrate by SBY-1 under lower C/N conditions.

Synthesis of gamma aluminum oxide nano-powder for adsorptive removal of nitrate from aqueous solutions

Nitrate pollution of surface and groundwater could be a worldwide issue resulting in the threat to the environment and public health. The removal of nitrate from water was carried out using gamma aluminum oxide (γ-Al2O3) nano powder. The nano powder was synthesized from aluminum oxide powder using the aqueous-based reflux method and applied for nitrate removal. The surface properties of the activated γ-Al2O3 were characterized using FTIR, XRD, and BET surface area analysis. Analysis of variance (ANOVA) was used to analyze nitrate removal to determine the appropriate regression model, which was found to be the quadratic model with a coefficient of determination (R2 = 0.99). The adsorption process was observed to be dependent on initial nitrate concentration, adsorbent dose, and time. The optimized nitrate removal efficiencies were 97.01% using a dose of 2.26 gL−1, an initial nitrate concentration of 10 mgL−1, and a contact time of 45 min. Additionally, the kinetics of nitrate ion adsorption was discussed based on pseudo-first order and pseudo-second order kinetic models. The experimental data fitted well with the pseudo-second order kinetic model, indicating that the adsorption mechanism is chemisorption. The equilibrium adsorption of nitrate experimental data followed the both Freundlich and Langmuir isotherm (R2 = 0.95), implying a homogeneous nature of the γ-Al2O3 surface sites. These results suggest further consideration of the practical application of γ-Al2O3 for nitrate treatment for domestic purposes.

Enhanced electrochemical nitrate removal from groundwater by simply calcined Ti nanopores with modified surface characters

Simple and convenient preparation method with high catalytic reduction activity is crucial for the remediation of nitrate contamination. In this study, the innovation for fabricating a nanoelectrode was developed by calcinating the anodized plate to alter the surface crystalline phase of the material. The prepared calcined Ti nano-pores (TNPs) electrode could effectively remove up to 95.1% nitrate from simulated groundwater at 30 mA·cm–2 electrolysis for 90 min, while under the same conditions, the removal efficiency of nano electrode prepared by conventional methods was merely 52.5%. SEM images indicated that the calcined-TNPs nanoelectrode was porous with different pore sizes. The higher nitrate removal efficiency of TNPs-500 (95.1%) than TNPs-400 (77.5%) and TNPs-550 (93.4%) may resulted from the positive nonlinear response of the larger ECSA, the improved electron transfer and suitable surface structure, and not the “anatase-to-rutile” of surface TiO2 nanotubes. After 90 min of electrolysis, by using RuO2 as an anode and adding 0.3 g·L–1 NaCl solution, 87.5% nitrate was removed, and the by-products (ammonia and nitrite) were negligible. Increased temperature and alkaline conditions can enhance the nitrate removal, while higher initial nitrate concentration only improved the nitrate removal slightly. Moreover, The TNPs-500 electrode also exhibited excellent nitrate removal performance in real groundwater with the efficiency at 82.9% and 92.1% after 90 and 120 min, which were 0.87 (removal efficiency=95.1%), 0.92 (removal efficiency=100%) of the efficiency for simulated groundwater, indicating the widely applicable conditions of the TNPs-500 electrode. This approach of surface bonded elements and structure modification through calcination significantly improves catalytic activity, and will guide the simple designing of functional nanostructured electrodes with wide application conditions.

Concurrent elimination of arsenic and nitrate from aqueous environments through a novel nanocomposite: Fe3O4-ZIF8@eggshell membrane matrix

The high concentration of nitrate and arsenic as potentially toxic elements (PTEs) with carcinogenic properties in many groundwater sources worldwide is a concern for health and the environment. This work checked the capacity of a novel nanocomposite, Fe3O4-ZIF8@eggshell membrane matrix (F-ZIF8@EMM) for concurrently eliminating arsenic and nitrate, two of the most encountered hazardous pollutants in drinking water. Contact time (30–120 min), pH (3–10), initial arsenic concentration (25–100 μg/L), initial nitrate concentration (60–120 mg/L) and adsorbent dose (0.25–5 mg/L) as various operating influences were investigated on the co-adsorption of arsenic and nitrate from water by a new nanocomposite thru diverse experimental tests. Characteristics of F-ZIF8@EMM were determined through X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR) and Brunauer–Emmett–Teller (BET) analyses. Taguchi model was used to determine the optimal co-adsorption conditions. The results revealed that the optimal conditions for the simultaneous adsorption of 94.32 % of these two elements were at pH = 7, adsorbent dose 1 mg/L, primary nitrate concentration 120 mg/L, initial arsenic concentration 100 μg/L, and contact time 90 min. Correspondingly, the simultaneous adsorption of arsenic and nitrate best fit the Langmuir isotherm, and the pseudo-second-order (PSO) model was the best model that fitted with experimental kinetic data (R2 = 1). The maximum experimental adsorption capacity of F-ZIF8@EMM was 128.5 mg/g. This study indicated that the efficiency of nanocomposite F-ZIF8@EMM in the co-adsorption of arsenic and nitrate was promising.

Enhancing sand liquefaction resistance through microbial-induced partial saturation: An experimental study

The liquefaction potential of saturated sand can be significantly reduced by inducing partial saturation in the soil. Conventional soil liquefaction mitigation methods, namely soil densification, drainage, cementing, and groundwater lowering, pose environmental concerns and are challenging to apply to pre-existing structures. However, the microbially induced partial saturation (MIPS) method is emerging as a novel and eco-friendly approach to mitigate liquefaction. The MIPS method involves microbial denitrification, which produces nitrogen gas and results in a desaturating effect in the saturated soil. The current study conducted a series of stress-controlled undrained cyclic triaxial tests on saturated sandy soil and microbially-desaturated sandy soil under different relative densities and loading conditions. In addition, the study systematically analyzed the effects of temperature and pH on bacterial activity and the denitrification process. Batch experiments were conducted to establish a relationship between the initial nitrate concentration in the bacterial media and the resulting desaturation.Comprehensive analyses of cyclic resistance curves were performed to gain a thorough understanding. Additionally, the study conducts detailed analyses of the accumulation of excess pore pressure and the resulting axial strains and deformation patterns in both treated and untreated sand. This study demonstrates that the MIPS treatment considerably enhances the liquefaction resistance of treated sand.

Hybrid manufacturing process for the synthesis of doped TiO2 nanoparticles and optimization to determine an efficient photocatalyst

The hybrid sol-gel method was used to synthesize the transition metals (Cu and Ag) doped TiO2 nanoparticles for achieving enhanced visible light response photocatalysts. Different characterization techniques such as UV–Visible, FESEM, EDS, and TEM were carried out to characterize prepared nanocomposites. The synthesized Cu/TiO2 and Ag/TiO2 photocatalysts exhibit redshifts with improved light absorption capacity compared with pure TiO2. Scanning electron microscopic images show almost spherical morphology with relatively uniform sizes. Photocatalytic degradation of Methylene Blue (MB) and hydrogen production were carried out to estimate the photocatalytic efficiency of synthesized photocatalysts. As a result of increased charge separation efficiency and higher visible light absorption for photoexcitation, the photocatalytic response of the modified photocatalyst was elevated. In this study, the significant factors like initial pH, nitrate concentration, and dopant were identified. These factors were investigated in terms of hydrogen generation as a response to the successful optimization for the determination of the most efficient photocatalyst. In addition, in this work, density functional theory was used to simulate metals (Cu/Ag) doped TiO2 to learn more about the impact of doping on the structural, electrical, and photocatalytic properties of TiO2. Ag/TiO2 nanocomposite prepared via nitrate precursor concentration of 0.9 M and operated at an initial pH value of 4 exhibits maximum hydrogen generation capacity.

Synthesis and characterization of a designed poly(ionic liquid‐modified graphene oxide) nanocomposite: Evaluation of nitrate removal from water and antimicrobial properties

AbstractAddressing the global challenge of water contamination, this study introduces a novel nanocomposite adsorbent—poly(ionic liquid‐modified graphene oxide) (PIL‐MGO)—designed to remove nitrates efficiently from water and combat microbial threats. Leveraging modified graphene oxide and vinyl imidazolium‐based ionic liquid, this research synthesizes an adsorbent via a facile and cost‐effective approach. The performance of PIL‐MGO was rigorously analyzed through a series of characterizations, including Frontier transform infrared spectroscopy, field emitting scanning electron microscopy, energy dispersive X‐ray spectroscopy, and thermogravimetric analysis, revealing its robust structural composition and thermal stability. In our experimental exploration, the adsorbent showcased a remarkable nitrate removal efficiency of up to 97.53%, under optimal conditions of an initial pH of 5, room temperature, initial nitrate concentration of 30 mg/L, a contact time of 30 min, and an adsorbent dosage of 40 mg, with a significant selectivity for nitrate ions over competing anions. Moreover, regeneration of the adsorbent up to 7 cycles indicated only a marginal decline in adsorption efficiency. Furthermore, PIL‐MGO demonstrated considerable antimicrobial properties against bacteria and fungi, indicating its dual utility in water purification and microbial inhibition. These findings suggest that the synthesized nanocomposite holds great promise for addressing environmental and health‐related challenges posed by water pollutants. This study not only underscores the capabilities of PIL‐MGO but also paves the way for further advancements in adsorbent technologies.Highlights A novel nanocomposite was synthesized based on vinyl imidazolium ionic liquid and modified graphene oxide. This newly developed nanocomposite was evaluated as an adsorbent for the removal of nitrate ions from water, demonstrating high removal efficiency. The adsorbent exhibited notable selectivity for nitrate ions, effectively distinguishing them from competing anions such as chloride, bicarbonate, sulfate, and phosphate. The adsorption kinetics of the nanocomposite were best described by the pseudo‐second‐order kinetic model, and the adsorption isotherm aligned well with the Langmuir model. Investigation of the nanocomposite antimicrobial activity displayed considerable inhibitory effects against both bacteria and fungi.

Nitrate removal from aqueous solution using fuller’s earth and modified fuller’s earth

ABSTRACT Water, a vital resource for ecosystems and human populations, is facing increasing nitrate contamination due to agricultural runoff, industrial discharge and improper waste disposal. The present study focuses on the efficacy of nitrate removal through adsorption using fuller’s earth (FE) and modified fuller’s earth (acid-treated) (MFE) as adsorbents. The impact of initial pH (2.0–7.0), contact time (5–240 min), adsorbent dosage (1–30 g/L), initial nitrate concentration (50–250 mg/L) and temperature (30–50°C) on nitrate removal using fuller’s earth were studied. The maximum nitrate removal was observed at pH 2.0, and equilibrium was reached in 120 min at 30℃. The Freundlich isotherm best fit the equilibrium data. The maximum nitrate uptake of fuller’s earth and modified fuller’s earth were 84.75 mg/g and 85.47 mg/g, respectively. Nitrate removal by FE and MFE followed a second-order kinetic equation. Thermodynamic studies showed spontaneity and the exothermic nature of the nitrate adsorption process. ∆H° values were −44.96 and −42.63 kJmol−1 for FE and MFE and ΔS° was −85.11 and −74.52 Jk−1mol−1 for FE and MFE, respectively. FE, known for its exceptional adsorption capacity owing to its porous structure and high ion-exchange capacity, has demonstrated a remarkable affinity for nitrate ions in batch studies.

Nitrate recovery from groundwater and simultaneous upcycling into single-cell protein using a novel hybrid biological-inorganic system

Nitrate pollution in groundwater is a serious problem worldwide, as its concentration in many areas exceeds the WHO-defined drinking water standard (50 mg/L). Hydrogen-oxidizing bacteria (HOB) are a group of microorganisms capable of producing single-cell protein (SCP) using hydrogen and oxygen. Furthermore, HOB can utilize various nitrogen sources, including nitrate. This study developed a novel hybrid biological-inorganic (HBI) system that coupled a new submersible water electrolysis system driven by renewable electricity with HOB fermentation for in-situ nitrate recovery from polluted groundwater and simultaneously upcycling it together with CO2 into single-cell protein. The performance of the novel HBI system was first evaluated in terms of bacterial growth and nitrate removal efficiency. With 5 V voltage applied and the initial nitrate concentration of 100 mg/L, the nitrate removal efficiency of 85.52 % and raw of 47.71 % (with a broad amino acid spectrum) were obtained. Besides, the HBI system was affected by the applied voltages and initial nitrogen concentrations. The water electrolysis with 3 and 4 V cannot provide sufficient H2 for HOB and the removal of nitrate was 57.12 % and 59.22 % at 180 h, while it reached 65.14 % and 65.42 % at 5 and 6 V, respectively. The nitrate removal efficiency reached 58.40 % and 50.72 % within 180 h with 200 and 300 mg/L initial nitrate concentrations, respectively. Moreover, a larger anion exchange membrane area promoted nitrate removal. The monitored of the determination of different forms of nitrogen indicated that around 60 % of the recovered nitrate was assimilated into cells, and 40 % was bio-converted to N2. The results demonstrate a potentially sustainable method for remediating nitrate contaminant in groundwater, upcycling waste nitrogen, CO2 sequestration and valorization of renewable electricity into food or feed.

From waste to value: Electrocatalytic reduction of nitrate into ammonia at mono and bimetallic-CNT modified electrodes

The electrochemical transformation of nitrate ions into ammonia (NH3), which ranks among the most widely employed chemicals globally, using mono (Pd, Pt) and bimetallic catalysts (Pd-Cu, Pt-Cu, Ru-Cu) supported on carbon nanotubes (CNT) was studied in acidic medium. The higher conversion and best selectivity towards NH3 corresponding, respectively, to 88 and 80 % were found for Pt_CNT modified electrode, with an initial nitrate concentration of 12.9 mM. The addition of copper as a second metal provides lower percentage of ammonia in comparison with the monometallic Pt_CNT and Pd_CNT electrocatalysts. The prepared electrocatalysts show good mechanical and chemical stability, under the experimental conditions. Principal Component Analysis (PCA) was carried out in order to highlight the effect of experimental parameters on selectivity.

Effect of plasma-activated water on planktonic and biofilm cells of Vibrio parahaemolyticus strains isolated from cutting board surfaces in retail seafood markets.

This research aimed to analyze cutting board surfaces in seafood markets to find Vibrio parahaemolyticus, assess the isolates' ability to form biofilms, generate and evaluate characteristics of plasma-activated water (PAW), and compare the effect of PAW on planktonic and biofilm cells of the isolated V. parahaemolyticus strains. A total of 11V. parahaemolyticus strains were isolated from 8.87% of the examined cutting boards. Biofilm-forming ability was evaluated for these isolates at temperatures of 10°C, 20°C, and 30°C using crystal violet staining. Four strains with the highest biofilm potential were selected for further analysis. The pH of the PAW used in the study was 3.41±0.04, and the initial concentrations of hydrogen peroxide, nitrate, and nitrite were 108±9.6, 742±61, and 36.3±2.9µM, respectively. However, these concentrations decreased significantly within 3-4 days during storage at room temperature. PAW exhibited significant antimicrobial effects on V. parahaemolyticus planktonic cells, reducing viable bacteria up to 4.54 log CFU/ml within 20 min. PAW also reduced the number of biofilm cells on stainless steel (up to 3.55 log CFU/cm2) and high-density polyethylene (up to 3.06 log CFU/cm2) surfaces, although to a lesser extent than planktonic cells. PAW exhibited significant antibacterial activity against V. parahaemolyticus cells, although its antibacterial properties diminished over time. Furthermore, the antibacterial activity of PAW against biofilm cells of V. parahaemolyticus was less pronounced compared to the planktonic cells. Therefore, the actual effectiveness of PAW in seafood processing environments can be affected by biofilms that may form on various surfaces such as cutting boards if they are not cleaned properly.

Application of artificial intelligence in modeling of nitrate removal process using zero-valent iron nanoparticles-loaded carboxymethyl cellulose.

This study explores nitrate reduction in aqueous solutions using carboxymethyl cellulose loaded with zero-valent iron nanoparticles (Fe0-CMC). The structures of this nano-composite were characterized using various techniques. Based on the characterization results, the specific surface area of Fe0-CMC measured by the Brunauer-Emmett-Teller analysis were 39.6m2/g. In addition, Scanning Electron Microscopy images displayed that spherical nano zero-valent iron particles (nZVI) with an average particle diameter of 80nm are surrounded by carboxymethyl cellulose and no noticeable aggregates were detected. Batch experiments assessed Fe0-CMC's effectiveness in nitrate removal under diverse conditions including different adsorbent dosages (Cs, 2-10mg/L), contact time (t, 10-1440min), initial pH (pHi, 2-10), temperature (T, 10-55°C), and initial concentration of nitrate (C0, 10-500mg/L). Results indicated decreased removal with higher initial pHi and C0, while increased Cs and T enhanced removal. The study of nitrate removal mechanism by Fe0-CMC revealed that the redox reaction between immobilized nZVI on the CMC surface and nitrate ions was responsible for nitrate removal, and the main product of this reaction was ammonium, which was subsequently completely removed by the synthesized nanocomposite. In addition, a stable deviation quantum particle swarm optimization algorithm (SD-QPSO) and a least square error method were employed to train the ANFIS parameters. To demonstrate model performance, a quadratic polynomial function was proposed to display the performance of the SD-QPSO algorithm in which the constant parameters were optimized through the SD-QPSO algorithm. Sensitivity analysis was conducted on the proposed quadratic polynomial function by adding a constant deviation and removing each input using two different strategies. According to the sensitivity analysis, the predicted removal efficiency was most sensitive to changes in pHi, followed by Cs, T, C0, and t. The obtained results underscore the potential of the ANFIS model (R2 = 0.99803, RMSE = 0.9888), and polynomial function (R2 = 0.998256, RMSE = 1.7532) as accurate and efficient alternatives to time-consuming laboratory measurements for assessing nitrate removal efficiency. These models can offer rapid insights and predictions regarding the impact of various factors on the process, saving both time and resources.

Unraveling the mechanism of assimilatory nitrate reduction and methane oxidation by Methylobacter sp. YHQ through dual N-O isotope analysis and kinetic modeling

Assimilatory nitrate reduction and methane (CH4) oxidation by bacteria play important roles in carbon (C) and nitrogen (N) biogeochemical cycles. Here, an investigation of enzymatic assimilatory nitrate reduction and CH4 oxidation by Methylobacter sp. YHQ from the wetlands is presented, specifically concentrating on N and oxygen (O) isotope fractionation with various initial nitrate and oxygen concentrations. The N enrichment factors (15εassimilation) increased from 4.2 ± 0.7‰ to 6.9 ±1.3‰ and the O isotope enrichment factors (18εassimilation) increased from 2.7 ± 0.9‰ to 4.7 ± 0.8‰ during nitrate assimilation when initial nitrate concentrations increased from 0.9 mM to 2 mM. Similar 18ε and 15ε values were observed at different oxygen concentrations. The values of 18ε and 15ε provided vital parameters for the assessment of assimilatory nitrate reduction via the Rayleigh equation approach. The ratios of O and N isotope enrichment factors (18ε:15ε)assimilation ranged from 0.64 ± 0.15 to 0.74 ± 0.18 during nitrate assimilation by Methylobacter sp. YHQ with Nas, which were different from (18ε:15ε)assimilation for assimilatory eukaryotic nitrate reductase (eukNR) from literature data. Thus, N and O isotope fractionation could be useful tools to distinguish eukNR from Nas during nitrate assimilation. Additionally, the rates of CH4 oxidation and nitrate reduction were evaluated with a reaction-based kinetic model, and it quantitatively described the enzymatic reactions of nitrate assimilation. Combining dual N-O isotope analysis with kinetic modeling provides new insights into the microbially driven C-N interactions.Graphical

Inhibition of zinc ions in sulfur-driven autotrophic denitrification process: What is the behavior of extracellular polymeric substances?

Sulfur-driven autotrophic denitrification (SAD) process is a cost-effective and sustainable method for nitrogen removal from wastewater. However, a higher concentration of zinc ions (Zn(II)) flowing into wastewater treatment plants poses a potential threat to the SAD process. This study examined that a half maximal inhibitory concentration (IC50) of Zn(II) was 7 mg·L−1 in the SAD process. Additionally, the addition of 20 mg·L−1 Zn(II) resulted in a severe accumulation of nitrite to 150.20 ± 6.00 mg·L−1 when the initial concentration of nitrate was 500 mg·L−1. Moreover, the activities of nitrate reductase, nitrite reductase, dehydrogenase and electron transport system were significantly inhibited under Zn(II) stress. The addition of Zn(II) inhibited EPS secretion and worsened electrochemical properties. The result was attributed to the spontaneous binding between EPS and Zn(II), with a ΔG of −17.50 KJ·mol−1 and a binding constant of 1.77 × 104 M−1, respectively. Meanwhile, the protein, fulvic acid, and humic-like substances occurred static quenching after Zn(II) addition, with -OH and -C=O groups providing binding sites. The binding sequence was fulvic acid→protein→humic acid and -OH → -C=O. Zn(II) also reduced the content of α-helix, which was unfavorable for electron transfer. Additionally, the Zn(II) loosened protein structure, resulting in a 50 % decrease in α-helix/(β-sheet+random coil). This study reveals the effect of Zn(II) on the SAD process and enhances our understanding of EPS behavior under metal ions stress.

Sulfur autotrophic electrodialysis ion exchange membrane bioreactor (SEDIMB) for nitrate removal in water: Synergism and adaptability of electrodialysis and sulfur autotrophy

In this study, the novel sulfur autotrophic electrodialysis ion-exchange membrane bioreactor (SEDIMB) with high denitrification performance was developed without the addition of carbon source. Sulfur autotrophic denitrification occurs at the same time of nitrate enrichment by electric field to achieve harmless nitrate transformation in water. The final nitrate concentration in water chamber was 2.16 mg-N/L (removal efficiency of 94.49 %) at an initial nitrate concentration of 40 mg-N/L, with the maximum nitrate concentration in biological chamber of 4.09 mg-N/L. Nitrate removal in water chamber of the SEDIMB conformed to the first-order kinetic model (R2 = 0.98) and reaction rate constant K1 = 0.0030 (1/min). The effect of environmental variables (i.e., voltage, initial nitrate concentration and water body) on the SEDIMB denitrification performance was investigated. Increasing voltage could promote nitrate migration in water chamber, and when the voltage was 7 V, initial nitrate concentrations of 20 ∼ 60 mg-N/L was effectively removed (all > 93.54 %). Moreover, the change of water body (i.e., tap water, lake water and deionized water) did not affect denitrification performance of SEDIMB. Microbial community structure analysis indicated that Betaproteobacteria were dominant in the SEDIMB. Membrane characterizations (ATR-IR, SEM and CLSM) confirmed that the bacteria in biological chamber tended to accumulate and grow on one side of the anion exchange membrane (AEM), while could not affect the selective permeability of AEM.

Simultaneous removal of fluoride and nitrate from an aqueous mixture and semiconductor wastewater by sodium chloride mediated electro-generated aluminas (EGAs): Conversion of recovered fluoride into fluorapatite using plasterboard waste

Electro-generated aluminas (EGAs) were synthesized using sodium chloride electrolyte of 100 mM with Al/Al and Al/Fe electrodes operated at 800 mA for 1.5 h. The synthesized mesoporous EGAs, EGA (Al) and EGA (Fe) belonging to H2 type hysteresis contain the boehmite and bayerite phases as confirmed by XRD analysis and whose proportions are estimated to be 49.6 ± 0.3% and 50.4 ± 0.3% respectively by thermo-gravimetric study. The batch adsorption studies were conducted using the binary (F−/NO3−) mixture from which the adsorption efficiency was studied as a function of time (0–60 min), pH (3–10), initial concentration of fluoride or nitrate (100, 300, 500 and 1000 mgL−1) and temperature (15 °C, 25 °C, 35 °C and 45 °C) using EGA (Al) and EGA (Fe) adsorbents. The adsorptive removal of fluoride and nitrate from real effluent samples using EGAs was significant particularly in effluents E1 and E3 with residual concentrations within the safe limit of World Health Organization (WHO). Regeneration using 100 mM NaOH was quite consistent up to five consecutive cycles and the recovered fluoride was converted into fluorapatite. Taking into account the regeneration aspect, the cost analysis showed that 1 g EGA (Al) and EGA (Fe) was 0.464 USD and 0.508 USD respectively. The endothermic nature of adsorption through chemical forces was confirmed by the compliance of pseudo – second – order (kinetic), Langmuir and DKR (isotherm) models (R2 ≈ 0.99) along with thermodynamic parameters. Characterization of EGAs using FTIR, FESEM, XRD, XPS and BET was done to understand the adsorptive behavior between EGAs and the adsorbate (F−/NO3−) ions. The exhausted EGAs after fifth cycle of regeneration was mixed with ariake clay, plasterboard waste and cement in proper proportions and, made as specimens for the construction of bank bodies.

Feasibility of in-situ sludge fermentation coupled with partial denitrification: Key roles of initial organic matters and alkaline pH

Achieving partial denitrification (PD) by using fermentation products extracted from waste activated sludge (WAS) rather than commercial organic matters is a promising approach for providing nitrite for anammox, while sludge reduction could also be realized by WAS reutilization. This study proposed an In-situ Sludge Fermentation coupled with Partial Denitrification (ISFPD) system and explored its performance under different conditions, including initial pH, nitrate concentrations, and organic matters. Results showed that nitrite production increased with the elevation of initial pH (from 6 to 9), and the highest nitrate-to-nitrite transformation ratio (NTR) reached 77% at initial pH 9. The PD rates and NTR were observed to be minimally influenced by initial nitrate concentrations. Acetate was preferred by denitrifying bacteria, while macromolecules such as proteins necessitated be hydrolyzed to be suitable for further utilization. The insights gained through this study paved the way for efficient nitrite production and sustainable WAS reutilization in harmony.

Unraveling the effect mechanism of sulfamethoxazole on nitrogen biotransformation in a PHBV supported denitrifying granular sludge

Sulfamethoxazole (SMX) is prevalent as one of the most frequently detected antibiotics in rivers worldwide, and is listed as one of the priority antibiotics in China based on the persistence, bioaccumulation, toxicity and resistance. Recently, the effect of SMX on aerobic granular sludge has attracted increasing interest. However, how SMX influences the biodegradable polymer supported denitrifying granular sludge is still obscure. Herein, two groups with or without exposure to 1 mg/L SMX with initial nitrate concentrations of 15, 30, and 50 mg/L were constructed. Results showed that there was a negligible difference on nitrate removal efficiencies between two groups under stable period (all exceeded 95 %) in batch bioreactors with an HRT of 24 h, supported by an insignificance difference (p > 0.05). However, the decline in the first-order decay kinetic constants of nitrate removal rate, NAR and NIR activities verified a slight inhibition of SMX on denitrification. Meanwhile, SMX also had an impact on the chemical and microbial properties on granular sludge. SMX boosted the EPS secretion with more humic acid, a delicate rise in PN/PS ratios and a decrease in zeta potential of EPS all favored the microbes' survival under SMX stress. SMX shifted the microbial compositions, namely, the microbes directly involving in PHBV degradation (Caldimonas, denitrificans Comamonas/Diaphorobacter) were enriched instead of some denitrifying microorganism that could not directly utilize PHBV (Denitratisoma, Azospira). Additionally, even though sul1 and sul2 were enriched, which was not readily accessible to receiving waters due to a good settling properties of granular sludge. This work contributes to a deeper understanding of the impact of SMX on this system, and is of great significance for the operation of granular sludge system for nitrate removal under antibiotic's stress.

Thauera sp. for efficient nitrate removal in continuous denitrifying moving bed biofilm reactor.

Thauera is the most widely found dominant denitrifying genus in wastewater. In earlier study, MBBR augmented with a specially developed denitrifying five-membered bacterial consortium (DC5) where Thauera was found to be the most abundant and persistent genus. Therefore, to check the functional potential of Thauera in the removal of nitrate-containing wastewater in the present study Thauera sp.V14 one of the member of the consortium DC5 was used as the model organism. Thauera sp.V14 exhibited strong hydrophobicity, auto-aggregation ability, biofilm formation and denitrification ability, which indicated its robust adaptability short colonization and nitrate removal efficiency. Continuous reactor studies with Thauera sp.V14 in 10 L dMBBR showed 91% of denitrification efficiency with an initial nitrate concentration of 620 mg L-1 within 3 h of HRT. Thus, it revealed that Thauera can be employed as an effective microorganism for nitrate removal from wastewater based on its performance in the present studies.

Enhanced biosorptive incarceration of nitrate from aqueous solutions using novel green adsorbent: Performance optimization and mechanistic enlightenment

Excess nitrate contamination was lucratively addressed using the novel adsorbents prepared from waste seed pods of the Guilandina bonduc (L.) plant. Adsorbents BFP and EBFP (amino-grafted) were synthesized following a green pathway of thermo-chemical transformation. Adsorbents were successfully implemented for nitrate adhesion from natural and wastewater. The morphology of the adsorbents was studied using SEM-EDS, TGA, XRD, FTIR-ATR, and BET, including zeta potential and point of zero charges. The batch mode nitrate removal study was carried out using a colorimeter. The optimum efficiency in nitrate trapping was found to be 173.8 mg/g (EBFP) and 78.74 mg/g (BFP). The adsorption efficiency of the sorbents was further optimized using the RSM-CCD and found to be suitable. The batch sorption study was also supported by the column study with a breakthrough curve at 90% (EBFP) and 60% (BFP) for the regeneration study. The optimum value for EBFP was attained at an initial nitrate concentration of 110 mg/L, pH∼8, and a dosage of 12 g/L at room temperature within 75 minutes of contact. The Freundlich isotherm model and pseudo-second-order kinetics fit satisfactorily with the sorption trends followed by other isotherm and kinetic models. The influence of various competing ions e.g., PO43−, Cl−, HCO3−, SO42−etc., on nitrate adsorption study was investigated. The physicochemical sorption of nitrate was confirmed, and a plausible mechanism has been suggested accordingly. The field sample experiment, including the start-up opportunities with this work, has been highlighted. EBFP could be an excellent sorbent of choice at present that is ready for commercialization.