Search Results (60)

Agricultural ammonium pollution from farmland drainage and low-value crop straw utilization are two critical rural environmental problems that cannot be solved by single remediation approaches. Herein, a novel composite was prepared by immobilizing effective microorganisms (EM) on corn straw biochar to construct a synergistic adsorption–biodegradation system, and its nitrogen removal mechanism was systematically investigated at structural and molecular levels. Metagenomic analysis detected a complete set of heterotrophic nitrification–aerobic denitrification (HN-AD) functional genes (amoA, hao, napA, nirK, norB, nosZ) in the isolated strain Bacillus thuringiensis A1, revealing the genetic potential of this strain for ammonium biodegradation. EM modification optimized biochar pore structure and increased the equilibrium adsorption capacity to 1.215 mg/g, which was 66.4% higher than that of pristine biochar (0.73 mg/g). Sterilization control tests indicated that physicochemical adsorption occupied the dominant position in ammonium removal, while microbial biodegradation acted as an auxiliary removal pathway. Importantly, the synergistic relationship between the two pathways should be interpreted cautiously, since autoclaving may subtly alter biochar physicochemical properties, and direct paired characterization of viable composites before and after sterilization is technically unavailable. Kinetic and thermodynamic results further validated the improved adsorption performance after modification. Overall, EM immobilization promoted ammonium adsorption via pore optimization, while pore-confined microbes achieved sustainable HN-AD biotransformation, jointly realizing synergistic nitrogen removal. This study provides a mechanistic reference for the optimized design and application of biochar–microbe composites in agricultural nitrogen pollution control. Full article

Biochar has attracted increasing attention for aquatic pollution control, particularly due to its capacity to accelerate the rate-limiting steps of denitrification in wastewater treatment. While early research primarily focused on the adsorption capacity of biochar, recent studies have increasingly investigated its role as a redox-active mediator that facilitates electron transfer. This review critically synthesizes the multifaceted mechanisms of biochar-enhanced denitrification, establishing a link between synthesis parameters (feedstock, pyrolysis kinetics) and physicochemical functionalities (pore architecture, redox-active functional groups). Specifically, we elucidate how precise regulation of pyrolysis temperature dictates the dominant electron transfer pathway: low-temperature biochar (<500 °C) facilitates electron shuttling via oxygen-containing functional groups (e.g., quinone moieties), whereas high-temperature biochar (>700 °C) promotes direct interspecies electron transfer (DIET) through graphitic conduction. We systematically decouple biochar-mediated electron transfer into three pathways: functional group-driven shuttling, solid-state conductive matrix transfer via conjugated π-electrons, and material-assisted DIET. Crucially, we emphasize that validating true DIET requires direct biological evidence of electroactive machinery. Furthermore, the review details how biochar modulates the biological microenvironment, upregulating key denitrification genes (narG, nirS/K, nosZ) and enriching functional microbial consortia. By integrating advances in surface modification—such as heteroatom doping and metal loading—we propose strategies to engineer biochar for optimized nitrate-to-nitrogen conversion. Future perspectives underscore the need for balancing electron-donating capacity with structural stability, developing low-energy functionalization techniques, and conducting life-cycle assessments to facilitate the scale-up of sustainable, high-efficiency nitrogen removal systems. Full article

In this study, a mathematical model based on nonlinear differential equations was developed to describe nitrate (NO₃⁻) removal in a woodchip denitrification bioreactor treating tile drainage water. The model captures temperature-dependent denitrification kinetics and transport processes under variable operating conditions. The model was validated using pilot-scale experimental data collected at different inflow water temperatures. The results indicated a strong temperature dependence of nitrate removal efficiency, with higher performance at elevated temperatures due to increased microbial activity and reaction rates. After validation, numerical simulations using a finite difference scheme were performed to evaluate bioreactor performance under varying hydraulic and geometric conditions. The analysis focused on the effect of bioreactor length, assuming constant width and depth (1.0 m each). Results showed that increasing reactor length enhances NO₃⁻ removal by extending hydraulic retention time, although the effect becomes nonlinear due to substrate limitation along the flow path. Simulations further demonstrated that a target NO₃⁻ removal efficiency of approximately 40% can be achieved through different combinations of temperature, bioreactor length, and hydraulic loading, indicating a compensatory relationship between kinetic and design parameters. Overall, this study provides a predictive framework for optimizing bioreactor design and operation, offering practical guidance for improving nitrate removal in agricultural drainage systems. Full article

Neonicotinoid pesticides are persistent in aquatic environments, posing ecological risks. To address the limited removal efficiency of conventional soil infiltration systems, this study developed an electrochemically enhanced modular ecological infiltration system (MEIS) integrating iron–carbon micro-electrolysis to synergistically remove conventional pollutants (COD, NH₃-N, TN, TP) and two typical neonicotinoids (NNs): imidacloprid (IMI) and imidaclothiz (IMIZ). Under optimized hydraulic loading (1.2 m³/(m²·d)), C/N ratio (3:1), and current density (0.016 mA/cm²), the system achieved high removal efficiencies for conventional pollutants (COD > 99%, NH₃ N 99.8%, TN 81.7%, TP 85.4%). Notably, electrochemical enhancement significantly improved the removal of IMI and IMIZ to 78.1% and 69.1%, respectively, outperforming the non-electrified control. Adsorption kinetics indicated that the filler designed for autotrophic denitrification exhibited the highest adsorption capacity for both pesticides, with a chemisorption-dominated mechanism. Electrochemical enhancement likely enhanced the performance of MEIS by facilitating the release of anodic Fe²⁺ and the generation of reactive species, thereby achieving higher removal efficiencies for conventional pollutants and pesticides. This study presents an efficient and promising ecological technology for the treatment of pesticide-contaminated water, demonstrating strong initial performance and offering substantial potential for further optimization in terms of long-term stability. Full article

Water scarcity continues to challenge arid regions such as Egypt, where growing population demands, climate change impacts, and increasing agricultural pressures intensify the need for sustainable water management. Treated wastewater has emerged as a viable alternative resource, provided that the effluent meets stringent quality standards for safe reuse. The purpose of this study was to develop a comprehensive model of the Khorshed Wastewater Treatment Plant (KWWTP) to depict the processes used for biological nutrient removal. Operational data was gathered and examined over a period of 18 months to describe the quality of wastewater discharged by the Advanced Sequencing Batch Reactor (ASBR) of the plant, using specific physicochemical parameters like TSS, COD, BOD₅, and N-NO₃⁻. A process flow diagram integrating the Activated Sludge Model No. 1 (ASM1) for biological nutrient removal was created using the GPS-X. The study determined the parameters influencing the nutrient removal efficiency by analyzing the responsiveness of kinetic and stoichiometric parameters. Variables related to denitrification, autotrophic growth, and yield for heterotrophic biomass were the main focus of the calibration modifications. The results showed that the Root Mean Square Error (RMSE) for the dynamic-state was COD (0.02), BOD₅ (0.07), N-NO₃⁻ (0.75), and TSS (0.82), and for the steady state was COD (0.04), BOD₅ (0.11), N-NO₃⁻ (0.67), and TSS (0.10). Since the model’s accuracy was deemed acceptable, it provides a validated foundation for future scenario analysis and operational decision support that produces a trustworthy model for predicting effluent data for the concentrations of TSS, COD, BOD₅, and N-NO₃⁻ in steady state conditions. Dynamic validation further confirmed model reliability, despite modest discrepancies in TSS and nitrate predictions; addressing this issue necessitates further research. Full article

With the acceleration of industrialization, the demand for NO_x abatement is becoming increasingly urgent. Finding safer and more stable reducing agent replacements and efficient catalysts is crucial for selective catalytic reduction (SCR) industrial NO_x abatement. Low-temperature hydrocarbon-assisted NO_x reduction (HC-SCR) remains attractive for industrial abatement. A series of industrial-grade TiO₂ support catalysts modified with a bimetallic MnCe active component, represented as TiO₂-ig, was prepared by the impregnation method to test the NO conversion performance under a 200–400 °C window with C₃H₆ as a reducing agent, and the physical properties were characterized using the BET and XRF methods. Under the feed of 150 ppm NO, 150 ppm C₃H₆, and 3%O₂—the optimal composition—Mn₁₅Ce₁₀/TiO₂-ig catalyst exhibited the highest NO_x conversion of 77.3% among industrial-grade TiO₂ support catalysts, with the corresponding temperature reduced to 275 °C. Furthermore, a slight improvement in catalytic activity was observed upon changing the TiO₂ support type. The industrial-grade and nano-sized TiO₂ supports predominantly exhibited mesoporous structures, while the anatase TiO₂ support contained a greater proportion of macropores. A steady-state kinetic model constructed for Mn₁₅Ce₁₀/TiO₂-ig catalyst indicates that the NO reaction rate is independent of C₃H₆ and O₂ concentrations at 200 and 250 °C. At 300 °C, C₃H₆ inhibits the reaction, while both O₂ and NO promote it. Changes in activation energy and the pre-exponential factor suggest a mechanistic shift from adsorption-limited at lower temperatures to reaction-limited at higher temperatures. Overall, using industrial-grade TiO₂ with MnCe promoters delivers meaningful NO_x reduction in a low-temperature regime and provides kinetic insights relevant to process design for industrial C₃H₆-SCR. Full article

The primary objective of the present study is to evaluate the effect of conglomerate microorganisms on nitrification in activated sludge. The present study compares this process with activated-sludge technology to explore the variables that influence the complex biochemical processes taking place in bioreactors. The research under consideration involves monitoring the effectiveness of optimizing the wastewater treatment process using kinetic modeling for the nitrification and denitrification processes. The system is designed to simulate various operating scenarios and adjust process parameters in real time. The nitrification rate demonstrates a 99.03% performance, while the denitrification rate ranges from 19.08% to 91.01%. A substantial correlation has been demonstrated between this variable and the temperature of the treated wastewater. This provides the possibility of accurately assessing the ammonium oxidation potential. Furthermore, kinetic equations facilitate the estimation of parameters that are not typically measured, yet are essential for optimizing operational parameters (e.g., dissolved oxygen levels in the aeration tank, sludge dosage, and influent flow rate). This estimation is crucial for enhancing the effectiveness of the process and attaining the desired or anticipated outcomes. This validation underscores the efficacy of the technology, thereby establishing a foundational framework for subsequent research endeavors. These research efforts are directed towards providing decision-makers and stakeholders with actionable insights. The validation underscores the significance of optimized practices in the context of water resource protection. Moreover, it signifies a substantial advancement in the instrumentation of wastewater treatment plants. Full article

While temperature, pH, DO, and ammonia nitrogen concentration are known to affect nitrous oxide (N₂O) emissions from ammonia-oxidizing bacteria (AOB), the specific responses of individual AOB species to these environmental variables have yet to be fully elucidated. The present study reports the isolation and pure culture of a new AOB strain, designated as N.eA1, from a stable CANON bioreactor. The strain’s denitrification and N₂O emission were systematically evaluated through a comprehensive analysis of growth kinetics, morphological characteristics, genetic composition, and nitrogen transformation under various environmental processes. Our results indicated that N.eA1 shares 95.33% sequence homology with Nitrosomonas europaea H1 AOB3, and exhibited higher nitrite (NO₂⁻-N) conversion efficiency. Morphological examination revealed white, semi-transparent spherical colonies. The bacterial growth kinetics included adaptation phase (0–12 h), exponential growth phase (12–36 h), stationary phase (36–72 h) and decline phase (after 72 h). Under optimal cultivation conditions (30 °C, DO concentration of 7.3 mg∙L⁻¹, pH 8.0, and NH₄⁺-N concentration of 260 mg∙L⁻¹), the culture achieved a maximum growth rate of 0.0723 h⁻¹, a maximum ammonia oxidation rate (AOR) of 10.74 mg∙(MLVSS∙h)⁻¹, and a minimum doubling time of 9.59 h. The peak time of nitrogen conversion was earlier than that of N₂O emission, with a maximum N₂O-N conversion from NH₄⁺-N of 1.039%. Full article

Pilot-scale experimental measurements and simulations were utilised to evaluate the nutrient removal efficiency of three submerged membrane bioreactor designs. This study compared setups with post- and pre-denitrification processes. A 625 L pilot plant for treating primary effluent provided the operational data necessary for calibrating the activated sludge model, specifically for chemical oxygen demand and nitrogen removal under steady-state flow. Identical influent conditions were maintained for all configurations while varying the sludge retention times (from 5 to 100 d), hydraulic retention times (ranging from 4 to 15 h), return activated sludge flow rates (between 0.1 and 3.0), and aerobic volume fractions (from 0.3 to 1.0). The pilot plant tests showed high COD and ammonia removal (above 90%) but moderate total nitrogen removal (above 70%). The simulation results successfully forecasted the effluent concentrations of COD and nitrogen for each configuration. There were noticeable variations in the kinetic parameters, such as mass transfer coefficients and biomass decay rates, related to the activated sludge model. However, increasing the sludge retention time beyond 20 d, hydraulic retention time beyond 8 h, return activated sludge rates above 2.0, or aerobic volume fractions beyond 0.4 did not significantly enhance nutrient removal. The post-denitrification setup showed a clear benefit in nitrogen removal but required a greater oxygen supply. Full article

Sludge alkaline fermentation liquid (AFL) is a potential carbon source for biological denitrification. However, its effectiveness is limited due to the presence of nutrients and heavy metals. In this study, acid-modified sepiolite (MSEP) was used to extract short-chain fatty acids (SCFAs) from AFL under optimized conditions and then with the prepared MSEP-AFL as a carbon source for denitrification. The optimal condition with an MSEP dosage of 1.96 g/L and pH 7.93 at 30 °C was obtained based on single-factor experiments and response surface methodology (RSM). Carbon balance revealed that 96.2% of the SCFAs, including 43.7% acetate and 23.5% propionic acid, was retained in the MSEP, demonstrating its high selectivity. The adsorption process followed the pseudo-second-order kinetic and Langmuir isothermal model, indicating dominant physical adsorption on the surface or in the fiber pores. This was further supported by the changes in the morphological features and surface properties of the MSEP. In the batch nitrate utilization experiments, the prepared MSEP-AFL was proven to be efficient as a carbon source, with a nitrate removal efficiency of 88.7% and a specific denitrification rate of 8.2 mg NOx-N/g VSS·h, which was 22% higher than that of the AFL. This was due to the establishment of a delicate “release–utilization” balance. These findings contribute to our understanding of the use of AFL for denitrification. Full article

Water warming and nutrient pulses following extreme rainfall events, both consequences of climate change, may have a profound impact on the biogeochemical dynamics of large temperate rivers, such as the Po River (Northern Italy), affecting denitrification capacity and the delivery of N loads to terminal water bodies. Manipulative experiments on denitrification kinetics were carried out using dark laboratory incubations of intact sediment cores collected from the lower Po River. Denitrification was measured along temperature and NO₃⁻ concentration gradients using ¹⁵N additions, in summer and autumn, the two seasons when climate change-induced warming has been shown to be higher. The combination of increased temperatures and pulsed NO₃⁻-enhanced denitrification, suggesting that electron acceptor availability limits the process. The direct link between climate change-induced effects and the positive response of denitrification may have implications for the improvement of water quality in the coastal zone, as it may help to partially buffer N export, especially in summer, when the risk of eutrophication is higher. Further research is needed to investigate the quality and quantity of sediment organic matter as important drivers regulating river denitrification. Full article

High concentrations of activated sludge are an excellent biological treatment; in particular, simultaneous nitrification and denitrification play a huge role in nitrogen removal. However, the influencing factors of SND have not been fully elucidated. The effects of sludge concentration and dissolved oxygen (DO) concentration on the performance of SND in a high-concentration activated sludge reactor assisted by chemical agents were investigated, and the SND reaction effect was de-termined by analyzing the along-stream changes of elemental nitrogen in the reactor. The results showed that the SND phenomenon in the reactor was most obvious when the system activated sludge concentration (MLSS) was maintained at 7–9 g/L and DO concentration at 1–2 mg/L. When MLSS decreases within the range of 5–9 g/L, the nitrification reaction improves, but the SND phe-nomenon decreases or even disappears; the SND phenomenon diminishes with increasing DO con-centration. Thus, high sludge concentrations and low dissolved oxygen concentrations are im-portant influences associated with SND and promote unconventional nitrogen removal pathways. In addition, the average value of MLVSS/MLSS for the high-concentration activated sludge process was 0.586, which indicates that the system has a higher activated sludge volume and better sludge activity, which is very effective in enhancing SND. In addition, this study also further investigated the influencing factors of SND in the high-concentration method by exploring the kinetic modeling of the SND reaction in the high-concentration method. Full article

A novel aerobic denitrifying bacterium Bacillus cereus J1 was isolated from a sewage treatment plant. Its characteristics under two distinct nitrogen sources were systematically investigated. According to the results of whole-genome sequencing, we inferred that strain J1 removes nitrogen through processes such as aerobic denitrification, dissimilatory nitrate reduction to ammonium, and ammonium assimilation. The degradation process of COD and total inorganic nitrogen (TIN) correlated to the zero-order degradation kinetics equation, and the maximum removal rate of NO₃⁻−N reached 3.17 mg/L/h and that of NH₄⁺−N was 3.79 mg/L/h. Utilizing single-factor experiments and response surface methodology, the optimal conditions for nitrate removal were determined as a shaking speed of 115 rpm, COD/nitrogen mass (C/N ratio) of 12.25, and salinity of 3.44 g/L, with the C/N ratio exerting the most significant influence. Similarly, for the maximum ammonium removal, the ideal conditions involved a shaking speed of 133 rpm, C/N ratio of 29, and salinity of 13.30 g/L, with the shaking speed exerting the most significant influence. These findings demonstrate that large amounts of ammonium and nitrate can be quickly removed with the help of Bacillus cereus J1, indicating that strain J1 may be applied to alleviate nitrogen pollution in aquatic environments. Full article

In this study, the heterotrophic nitrification–aerobic denitrification strain JQ1004 was investigated in terms of its nitrogen removal mechanism and kinetic properties, laying the foundation for its application in the field of wastewater treatment. Nitrogen balance analysis revealed that the final metabolic product was N₂, and approximately 54.61% of N was converted into cellular structure through assimilation. According to the fitting of the Compertz model, the maximum degradation rates of ammonia and nitrate were 7.93 mg/(L·h) and 4.08 mg/(L·h), respectively. A weakly alkaline environment was conducive to N removal, and the sensitivity of functional genes to acidic environments was amoA > nirS > narG. An appropriate increase in dissolved oxygen significantly enhanced heterotrophic nitrification activity, and notably, the denitrification-related functional gene narG exhibited greater tolerance to dissolved oxygen compared to nirS. The transcription level of amoA was significantly higher than that of narG or nirS, confirming that there might have been direct ammonia oxidation metabolic pathways (NH₄⁺→NH₂OH→N₂) besides the complete nitrification and denitrification pathway. The annotation of nitrogen assimilation-related functional genes (including gltB, gltD, glnA, nasA, nirB, narK, nrtP, cynT, and gdhA genes) in the whole-genome sequencing analysis further confirmed the high assimilation nitrogen activity of the HN-AD strain. Full article

Hormesis in soil enzymes is well-established, yet the underlying mechanism remains elusive. In this novel study, we investigated the effects of low-dose Cd exposure (0, 0.03, 0.3, 3, and 30 mg·kg⁻¹) in farmland soil within a typical constructed wetland environment. We assessed the activities of four soil enzymes (urease (URE), denitrification enzyme (DEA), dehydrogenase (DHA), and alkaline phosphatase (ALP)) at varying exposure durations (0 h, 24 h, and 48 h), evaluating hormetic characteristics across these time intervals. Additionally, we determined kinetic parameters, specifically the Michaelis constant (K_m) and maximum reaction velocity (V_max), for these enzymes while examining potential alterations in microbial community structure. Our findings revealed hormesis in all four soil enzymes at 24 h of exposure, with varying stimulus width and maximum hormesis rates. Interestingly, heavy metals did not significantly influence the diversity of soil microbial communities, but they did inhibit the ability of soil microbial communities to secrete extracellular enzymes. This resulted in a reduction in the soil enzyme pool and a consequential shift in overall soil enzyme activities. The conclusion of this study is that low-dose Cd primarily reduced extracellular enzyme secretion by soil microorganisms, leading to a reduction in the size of the soil enzyme pool and thereby inducing hormesis in soil enzyme activities. Full article