High Concentration Of Ammonia Nitrogen Research Articles

Evaluation of the aerobic process performance for treating tannery effluent in the fungicide presence and ammoniacal nitrogen high concentration

Leather processing is characterized by the generation of effluents with a high concentration of ammonia nitrogen (N-NH4+) and the presence of fungicides. This study evaluated the interference of these two constituents on the removal of chemical oxygen demand (COD) and N-NH4+. To this end, an aerated reactor operating in a batch system was used. The effects of cycle time, fungicide volume, and initial N-NH4+ concentration on COD and N-NH4+ removal was evaluated using a Centralized Rotational Composite Design. The highest COD removal (45.45%) occurred under the conditions of 72 h, 0.55 mL of fungicide, and 62.5 mg L-1 of N-NH4+, and the lowest removal (8.24%) occurred under the conditions of 24 h, 0.28 mL of fungicide and 84.8 mg L-1 of N-NH4+. The highest removal of N-NH4+ (38.49%) occurred under the conditions of 42 h, 0.55 mL of fungicide, and 62.5 mg L-1 of N-NH4+, and the lowest removal (4.26%) occurred under the conditions of 24.1 h, 0.82 mL of fungicide and 84.8 mg L-1 of N-NH4+. Through statistical analysis, it was possible to obtain mathematical models for the two response variables, which satisfactorily described the removal efficiency of COD and N-NH4+, and through the desirability analysis, it was possible to optimize the treatment process operation with a cycle time of 58.15h, with the addition of 0.62 mL of fungicide and 57.91 mg L-1 of ammoniacal nitrogen. Although the removal of N-NH4+ via nitrification is an efficient technique in industrial effluent treatment, the results obtained in this work indicate that the removal of N-NH4+ was significantly affected by the presence of the fungicide. Keywords: biological treatment, chemical oxygen demand, DCCR, TCMTB.

Improved Anaerobic Digestion of Food Waste under Ammonia stress by Side-Stream Hydrogen Domestication

High ammonia concentration inhibits archaea's activity, causing the accumulation of H2 and acetate, which suppresses methane production in anaerobic digestion (AD). The study aimed to enhance microbial hydrogen metabolism through a side-stream hydrogen domestication (SHD) strategy, which involves applying hydrogen stimulation to a portion of the sludge separately. SHD maintained a stable methane yield of 407.5 mL/g VS at a high total ammonia nitrogen (TAN) concentration of 3.1 g/L. In contrast, the control group gradually decreased and stopped methane production at a TAN concentration of 2.3 g/L. Further analysis using enzyme activity assays, flow cytometry, and metagenomics explored the mechanisms underlying ammonia tolerance of SHD-treated group. SHD reshaped the microbial community, enriching homoacetogens and Methanosaeta-dominated methanogenic archaea. Key metabolic pathways including homoacetogenesis, butyrate degradation, propionate degradation, and methane production were enhanced. The activity of related enzymes also increased. Gene abundance in energy-generating pathways, such as glycolysis, was enhanced, ensuring adequate ATP production. Additionally, the high gene abundance of ion transport systems contributed to regulating proton imbalance and supplementing intracellular K+. This study provides important insights and practical guidance for developing novel techniques in the field of anaerobic digestion.

Recovery effects of the long-term cryopreserved Anammox sludge by adjusting the sludge amount

ABSTRACT Anammox process was one of the most promising nitrogen removal technologies. This study investigated the recovery performance of Anammox sludge after 83 days of cryopreservation in two reactors (R1 and R2). Reactor R1 utilized Anammox sludge pretreated with low-substrate simulated wastewater prior to long-term cryopreservation, and successful recovery was achieved by discharging sludge under ammonia nitrogen concentrations of 100 mg/L. The total nitrogen removal efficiency (TNRE) reached 70.0% on day 48. Reactor R2 used Anammox sludge pretreated with high-substrate simulated wastewater before cryopreservation. At an ammonia nitrogen concentration of 100 mg/L, the TNRE reached 87.0% on day 18. After increasing the ammonia nitrogen concentration to 300 mg/L and discharging sludge, the TNRE reached 84.6% on day 38. When the ammonia nitrogen concentration was elevated to 500 mg/L, system performance deteriorated. Recovery was unsatisfactory when the ammonia nitrogen concentration was reduced back to 300 mg/L. Finally, adding Anammox sludge restored the TNRE to 85.6% after 35 days of operation. The results suggest that adding Anammox sludge is essential for nitrogen removal recovery in reactors under high ammonia nitrogen concentration inhibition, while sludge discharge is crucial when free ammonia (FA) is present. This study provides a simple and effective strategy for recovering the activity of Anammox sludge after long-term cryopreservation.

Thermodynamic characteristics of nitrifiers reveal the potential NOB inhibition strategies at low temperatures

Nitrification is a highly temperature-sensitive biological process, yet relatively little research has explored thermodynamic characteristics of enzyme-catalyzed nitrification processes in wastewater treatment systems. In this study, a variety of thermodynamic models were employed to evaluate thermodynamic characteristics of four activated sludge samples cultivated under various temperatures (10, 15, and 20 °C) and ammonia nitrogen concentration (40 mg/L and 300 mg/L). Results revealed a higher maximum temperature (Tmax) for ammonia oxidizing bacteria (AOB) compared to nitrite oxidizing bacteria (NOB), suggesting the robust resistance to high temperatures of AOB. Conversely, the lower minimum temperature (Tmin) of NOB indicated its stronger tolerance to low temperatures. Notably, both low temperatures and high-ammonia nitrogen concentrations are conducive to the competition of Nitrotoga over Nitrospira, resulting in Nitrotoga emerging as the dominant NOB within 10∼15 °C. Moreover, heat capacity (ΔCpǂ) of enzymes exhibited a similar trend across all samples, i.e. HAO > AMO > NOR, indicating that HAO exhibited the strongest thermodynamic stability, followed by AMO, and NOR has the worst thermodynamic stability. Additionally, the difference in optimal temperature (Topt) between dominant AOB-Nitrosomonas and dominant NOB-Nitrotoga cultivated at high nitrogen concentration and low temperature could reach up to +8.13 °C, enabling selective inactivation of NOR through thermal treatment at Topt,AOB ∼ Topt,NOB. However, despite insignificant differences in Topt,AOB and Topt,NOB under low-temperature and low-ammonia nitrogen concentration, the smaller the difference between Tmax and Top (Tmax-Topt) of NOB and smaller D-value of NOR made NOB more susceptible to inhibition than AOB. However, the presence of low-abundance Nitrospira renders thermal treatment alone inadequate for complete NOB inhibition, combing it with other strategies is necessary for effective inhibition. Therefore, the fundamental differences in thermodynamic characteristics of AOB and NOB determine the potential of NOB inhibition strategies at low temperatures.

Lipase pretreatment enhances biochar‐assisted anaerobic digestion of food waste

AbstractAnaerobic digestion is a promising technology for the treatment of food waste (FW) but it requires optimization to improve its performance. This study investigated whether combining the addition of biochar with lipase pretreatment could improve the anaerobic digestion of FW. The results showed that biochar stimulated the release of soluble substances, resulting in an increase in the methane yield of groups with added biochar by 16.24% to 19.36% in comparison with the group without biochar. Lipase pretreatment substantially shortened the fermentation time required to complete the anaerobic digestion, from 15 to 9 days. Lipase pretreatment further improved microbial abundance and promoted the enrichment of functional microbes in the anaerobic digestion of FW mediated by biochar. It also changed the methane production pathway from acetotrophic to hydrogenotrophic, thereby ensuring the stability of the anaerobic digestion system in the presence of a high ammonia nitrogen concentration.

A synthetic bacterial community engineered from Miscanthus floridulus roots enhances ammonia nitrogen removal in ionic rare earth mine tailings

Ammonium sulfate, as the primary leaching agent, has caused significant nitrogen pollution in rare earth elements (REEs) mining areas. Phytoremediation is a promising remediation method, relying on the synergistic relationships between plants and their root-associated microbiome. Nevertheless, harnessing the microbiome to accelerate nitrogen transformation and absorption by plants is challenging. Here, we investigated the composition, activities and culturable fraction of the root bacterial microbiome of the pioneer plant Miscanthus floridulus grown in a REEs tailing soil containing a high ammonia nitrogen (AN) concentration at 344.35 mg kg−1. Based on this, we constructed a simplified synthetic microbial community (SynCom) derived from the roots of M. floridulus, possessing nitrification and denitrification capabilities, to help REEs mine plants efficiently convert pollutant AN into nutrients, thereby enhancing plant growth and AN removal. This SynCom, consisting of 10 bacterial strains, included species of the genera Burkholderia (5) Paraburkholderia (1), Curtobacterium (1), Leifsonia (1) and Sinomonas (2). As a result, this SynCom alone achieved a significant reduction of 24.8% in AN content in tailing soil. When the SynCom inoculated with plants, the reduction in AN was even more significant (32.6%), surpassing the reduction achieved solely by plants (25.5%). Moreover, live SynCom inoculation significantly increased shoot and root biomass by 39.8% and 49.7%, respectively, compared to dead SynCom inoculation. These results indicate that the reduction in AN can be attributed to the SynCom's nitrification and denitrification capabilities, as well as its ability to enhance plant nitrogen absorption by stimulating their growth. Notably, seven nitrifying and denitrifying strains of the SynCom are particularly enriched, suggesting that plant roots selectively recruit nitrogen cycle-related bacteria to accelerate nitrogen transformation and absorption. These results provide a practical solution for harnessing the synergistic relationships between plants and their root microbiome in environmental remediation efforts.

Bifunctional system constructed by NiCu-F/DSA electrode self-coupling for efficient removal of ammonia nitrogen from landfill leachate

ABSTRACT Landfill leachates containing high concentrations of ammonia nitrogen, due to its strong toxicity, large discharge and great environmental hazard, is in urgent need of efficient cleaning treatment. In this work, Ni1Cu0.25-F/DSA catalytic electrode was prepared via electrodeposition by means of fluorination-induced surface reconstruction. The surface of electrode was determined to be a porous sponge-like structure by physical characterizations. The electrode exhibited a superior ammonia oxidation reaction (AOR) activity and stability by a series of electrochemical tests. On this basis, a Ni1Cu0.25-F/DSA || Ni1Cu0.25-F/DSA bifunctional system was developed for efficient removal of ammonia nitrogen in landfill leachate. The results of denitrification experiment indicated that the removal efficiency of NH4 +-N and TN were 99.89% and 68.9%, respectively, when the electrolytic cell potential was 1.7 V, pH was 13 and the initial ammonia concentration was 600 mg L−1. The NH4 +-N removal efficiency remained above 95% after the cyclic denitrification experiment lasting for 6 days, which validates the robust stability of the electrode.

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.

The native fish diversity with environmental influencing factors in the Daqing River basin, China

IntroductionInvestigating and assessing native fish diversity and conducting regional assessments of threats are vital for the conservation of aquatic biodiversity. For this specific study, the Daqing River basin in China was chosen as the research area. Field surveys were carried out between 2018 and 2019, supplemented by a review of pertinent literature and other records.MethodsTo evaluate fish diversity, the following parameters are selected for analysis: Relative abundance (Pi), Frequency of occurrence (Fi), Margalef richness index (D) , Shannon Wiener diversity index (H′) , and Pielou evenness index (J′).Relative abundance levels are categorized as follows: dominant species make up more than 10%, common species account for 1%–10%, and occasional species constitute less than 1%. Canoco 5.0 software was utilized to conduct Redundancy Analysis (RDA) on the fish species composition and environmental factors at 34 sampling sites.ResultsThe findings revealed that 85 fish species have been recorded in the basin, consisting of 78 freshwater species categorized into 8 orders, 17 families, and 59 genera, among which Cypriniformes comprised 64% of the total catch. The low proportion of threatened and endemic species was an important feature of the fish diversity of the Daqing River. Despite the theoretical presence of 85 species, field surveys managed to collect only 42 species, of which 33 were confirmed as naturally occurring within the basin. The average values of Margalef richness index, 22 Shannon Wiener diversity index and Pielou evenness index were 1.72, 2.04 and 0.80 respectively, signifying a low fish diversity with relatively uniform distribution across the sampled regions.DiscussionThis study found that the community structure and diversity of fish were closely related to environmental factors, particularly water quality. Among these factors, ammonia nitrogen emerged as a significant determinant of fish diversity. High concentrations of ammonia nitrogen inhibit fish growth, endanger health, and can even lead to death. Additionally, dams and other water infrastructure also impact fish community structure and diversity. This baseline study can provide a basis for the protection and ecological restoration of fish resources in the Daqing River.

Synergistic treatment of digested wastewater with high ammonia nitrogen concentration using straw and microalgae

Microalgae as a promising approach for wastewater treatment, has challenges in directly treating digested piggery wastewater (DPW) with high ammonia nitrogen (NH4+-N) concentration. To improve the performance of microalgae in DPW treatment, straw was employed as a substrate to form a straw-microalgae biofilm. The results demonstrated that the straw-microalgae biofilm achieved the highest NH4+-N removal rate of 193.2 mg L−1 d−1, which was 28.8 % higher than that of culture system without straw. The final NH4+-N concentration in the effluent met the discharge standard of 5 mg L−1. Furthermore, the total organic carbon (TOC) released from straw facilitated bacterial proliferation and the secretion of extracellular polymeric substances (EPS). The EPS and TOC increased the suspension viscosity and surface tension, thereby enhancing the residence time of CO2 in the liquid phase and promoting CO2 fixation. This study presented a novel method for the biological treatment of high-ammonia–nitrogen DPW.

Nitrogen recovery from biogas slurry with high ammonia nitrogen concentration through struvite precipitation utilizing acid leaching solution of collophanite tailings

ABSTRACT The high concentration of ammonia nitrogen (NH4+) and chemical oxygen demand (COD) in biogas slurry pose great challenges to the efficiency of traditional wastewater treatment systems. Collophanite tailings are solid waste, characterized by significant concentrations of phosphorus (PO43-) and magnesium (Mg2+), represent a potential resource for the reduction and recovery of NH4+ in biogas slurry via struvite precipitation. This study systematically explored the optimal leaching parameters employing sulfuric acid for the extraction of PO43− and Mg2+ from collophanite tailings. The effect of [PO43-]:[NH4+] molar ratio and pH on the recovery of NH4+ in biogas slurry was investigated. The physicochemical properties of the precipitates were confirmed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and chemical analysis. Results suggested that the highest removal efficiency of NH4+ (88.5%) was achieved when employing a [PO43-]:[NH4+] molar ratio of 1.0 at pH 9.5. Evaluation of effluent quality demonstrates a significant enhancement in the biodegradability of the treated biogas slurry, evidenced by an increase in the COD/TN ratio increased from 2.1 to 10.4. Economic analysis shows that the net income would be approximately 21.33 USD/m3 for proposed produces. These findings underscore the potential of utilizing collophanite tailings for NH4+ recovery from biogas slurry.

Treatment of landfill leachate in the MBR and catalytic ozonation coupled system based on Mn[sbnd]Ni catalyst: Efficiency and bio/chemical mechanism

Complex organic matters and high concentrations of ammonia nitrogen in landfill leachate required deep treatment before discharge. In this study, a catalytic ozonation-membrane bioreactor (MBR) process equipped with MnNi composite loaded carbon felt catalysts (Mn-Ni@CF) was proposed for landfill leachate treatment. The mechanism of catalytic ozonation was analyzed in focus. The abundant valence of manganese and nickel loaded on Mn-Ni@CF could promote the electron transfer and form the Mn4+ - O2 - Ni2+ redox couples. The redox reactions occurred in bimetallic enhanced transformation of active sites and generation of OH and O2−. It was found that the removal of humic acid substances by Mn-Ni@CF catalysts achieved 85.5 % after 2 h of catalytic ozonation reaction. Coupling with MBR, the removal efficiencies of chemical oxygen demand (COD) and NH4+-N for 25 L of landfill leachate were 99.8 % and 91.4 % after 13 days of operation, respectively. Proteobacteria and Actinobacteriota were effective to promote the nitrification-denitrification reaction. Thauera and Truepera could degrade organic matter. This study provided a new strategy for the efficient treatment of landfill leachate.

A sustainable, zero-waste approach for production of biohydrogen from chicken manure slurry by hybrid recycling of digestate

This study provides a sustainable approach to produce biohydrogen through the long-term hydrogenic fermentation of chicken manure (CM) in a semi-continuous stirred tank reactor (CSTR) under different organic loading rates (OLRs). To ensure the zero-waste route and sustainability, the total digestate was mechanically separated into liquid and solid fractions. The solid digestate fraction was thermally treated to produce biochar, while the liquid digestate fraction was biologically treated through bioaugmentation with a novel heterotrophic nitrification-aerobic denitrification (HD-AN (bacterial strain (Alcaligenes sp. ME-1). The results showed that the high concentration of free ammonia nitrogen (FAN) contents of CM could inhibit methanogenesis and induce hydrogen production. The ORLs of 2.5, 3.5, 4.5, and 5.5 gVS/L.d imposed to the CSTR resulted in volumetric hydrogen production (VHP) of 643.3 ± 37, 908.8 ± 64.5, 1077.8 ± 95.17, and 1383.3 ± 156.8 mL/L.d, respectively. The microbial community structures indicated the long-term adaptation of hydrogen-producing bacteria and methanogenesis inhibition. The bioaugmentation process removed 83.3 % of total ammonia and 66.2 % of the chemical oxygen demand (COD) from the liquid digestate fraction. The characteristics of the biochar derived solid digestate is suitable for land applications as fertilizer. The hybrid approach combining biohydrogenation, pyrolysis, and bioaugmentation, maximizes the utilization of chicken manure slurry while conforming to the sustainable development goals.

Unveiling the synergy of volatile fatty acids and ammonia nitrogen in optimizing methane production during dry anaerobic digestion of pig manure and corn straw

Dry anaerobic digestion (AD) is vulnerable to volatile fatty acids (VFA) and ammonia nitrogen. Understanding their synergy is crucial for optimizing strategies. In this study, the digestive performance, microbial dynamics, metabolic pathways, and synergistic relationships were investigated in the dry AD process by adding different concentrations of acetic acid (2, 5, and 8 mg/g) and urea (1, 5 mg/g N). Results showed that acid inhibition was caused by excessive pH reduction due to VFA accumulation. Propionic acid was the primary form of VFA accumulation. The inhibition of VFA accumulation could be alleviated using a low concentration of ammonia nitrogen (1 mg/g N urea) or be strengthened using a high concentration of ammonia nitrogen (5 mg/g N urea). Compared with the control group (82.2 mL/g VS), VFA and 1 mg/g N urea had a synergistic facilitation effect on the methane production (increasing by 1.7 %-18.1 %). This synergistic effect shortened the lag phases, enhanced the activity of Caldicoprobacter and Methanosarcina, increased the expression of genes encoding functional enzymes involved in the acetoclastic-methanogenic pathway. By contrast, VFA and 5 mg/g N urea had a synergistic inhibition effect on methane production (decreasing by 65.7 %–69.8 %). This synergistic effect prolonged lag phases, increased the relative abundance of ammonia-tolerant and acid-tolerant microbial (such as Methanoculleus) and reduced the expression of genes encoding functional enzymes involved in the hydrogenotrophic-methanogenic pathway. These results improve the understanding of methane regulation during dry AD.

Optimization of ammonia nitrogen benchmarks and ecological risk assessment in monsoon freezing lakes based on species sensitivity distribution with Lake Chagan in northeastern China as an example

There is an urgent need to determine reasonable water-quality benchmarks and risk assessment results to accurately characterize the relationship between crop yield enhancement and ammonia nitrogen pollution caused by excessive nitrogen fertilizer application. Through the collection of monitoring data from 2016 to 2023 in Chagan Lake, the first development of ecological criteria for ammonia nitrogen and risk evaluation for Northeast China was carried out based on the secondary ecological risk models (the quotient value method and joint probability curve). In addition, the species sensitivity distribution (SSD) model is improved through the use of genetic algorithms to identify more suitable ammonia water-quality benchmarks for ecological risk assessment. The results showed that high ammonia nitrogen concentration in wet season is primarily influenced by agricultural irrigation and drainage activities, whereas the dry season is driven by low temperatures and the nitrogen and phosphorus concentrations. The biological benchmark of improved SSD model with a genetic algorithm has a maximum error reduction of 23.84 % compared with other distributions, which is more than twice that of the median water-quality benchmark under the traditional Class III water-quality standard and empirical formula. Risk evaluation using traditional water-quality standards leads to the overprotection of the biological environment. Evaluations using quotient value methods and joint probability curves yield consistent results. The severity of the ecological risk of ammonia nitrogen follows the order: wet season > flat season > dry season. Using a genetic algorithm to optimize SSD model can effectively reduce the uncertainty of the model, providing a more accurate and reasonable ammonia nitrogen water-quality benchmark. This study improves the evaluation of the ecological risk of ammonia nitrogen in Lake Chagan, provides ideas for reducing the uncertainty of the selection of ammonia nitrogen water-quality benchmarks, and effectively prevents the overprotection of the lake from ammonia nitrogen.

Material flow analysis of an upgraded anaerobic digestion treatment plant with separated utilization of carbon and nitrogen of food waste

Anaerobic digestion of food waste can recover carbon in the form of biogas, while the high concentration of ammonia nitrogen in the digestion effluent becomes troublesome. Therefore, some new treatment plants use three-phase centrifugation to separate homogenized food waste into nitrogen-rich fine slag for insect cultivation and carbon-rich liquid for anaerobic digestion. To analyze the effects of the carbon–nitrogen separation, an upgraded plant’s material and elementary flows were investigated. The three-phase separation process redistributed carbon and nitrogen, and the biogas slurry was the primary output. The principal endpoint for C was the crude oil, capturing 57.1 ± 13.1 % of the total input; the find slag collected 48.3 ± 6.9 % of the total N input, and the biogas slag accepted 52.9 ± 4.4 % of the P input. The carbon–nitrogen separation strategy can improve digestion efficiency and increase treatment benefits significantly, marking a promising direction for future developments in food waste utilization.

Preliminary investigation on the causes of red tides in Qinhuangdao coastal areas in 2022.

To explore the causes of red tides in Qinhuangdao coastal water, we conducted surveys on both water quality and red tides during April to September of 2022 and analyzed the relationships between main environmental factors and red tide organisms through the factor analysis and canonical correspondence analysis. The results showed that there were eight red tides along the coast of Qinhuangdao in 2022, with a cumulative blooming area of 716.1 km2. The red tides could be divided into three kinds based on the major blooming organisms and occurrence time, Noctiluca scintillans bloom, diatom-euglena (Skeletonema costatum, Eutreptiella gymnastica, Pseudo-nitzschia spp.) bloom, and dinoflagellate (Scrippsiella trochoidea and Ceratium furca) bloom. Seasonal factor played roles mainly during July to September, while inorganic nutrients including nitrogen and phosphorus influenced the blooms mainly in April and July. The canonical correspondence analysis suggested that N. scintillans preferred low temperature, and often bloomed with high concentrations of ammonium nitrogen and dissolved inorganic phosphorus. S. costatum, E. gymnastica, and Pseudo-nitzschia spp. could tolerate broad ranges of various environmental factors, but favored high temperature and nitrogen-rich seawater. C. furca and S. trochoidea had higher survival rate and competitiveness in phosphate-poor waters. Combined the results from both analyses, we concluded that the causes for the three kinds of red tide processes in Qinhuangdao coastal areas in 2022 were different. Adequate diet algae and appropriate water temperature were important factors triggering and maintaining the N. scintillans bloom. Suitable temperature, salinity and eutrophication were the main reasons for the diatom-euglena bloom. The abundant nutrients and seawater disturbance promoted the germination of S. trochoidea cysts, while phosphorus limitation caused the blooming organism switched to C. furca and maintained the bloom hereafter.

Recovery of ammonia nitrogen and phosphate from livestock farm wastewater by iron-magnesium oxide coupled lignite and its potential for resource utilization.

A new adsorbent called iron-magnesium oxide coupled lignite (CIMBC) was developed to address the challenges of recovering high concentrations of ammonia nitrogen and phosphate in livestock farm wastewater and improving the inefficient use of lignite (BC) with low calorific value. CIMBC was synthesized using the modified ferromagnesium salt double-coating method. The experiments demonstrated that Fe2O3 and MgO could be effectively loaded onto the surface of BC at a Fe/Mg molar ratio of 1:2 and pyrolysis temperature of 500°C. The optimal conditions for adsorption were determined to be an N/P concentration ratio of 2:1, adsorbent dosage of 1g/L, and pH of 7. The presence of coexisting cations (Ca2+ and Mg2+) inhibited the removal of ammonia nitrogen but enhanced the removal of phosphate. Likewise, the presence of coexisting anions (CO32- and SO42-) hindered the removal of both ammonia nitrogen and phosphate. The adsorption behavior followed the pseudo-second-order model and the Langmuir model, with a maximum adsorption capacity of 95.69mg N/g for ammonia nitrogen and 101.32mg P/g for phosphate. The adsorption process was a spontaneous endothermic process controlled by multiple levels. The main mechanisms of adsorption involved electrostatic attraction, intra-particle diffusion, ion exchange, chemical precipitation, and coordination exchange. After 5 times of adsorption-desorption, the recovery rate of CIMBC is less than 50%, and the removal rate of phosphate is less than 40%. Although the RCIMBC exhibited low reusability, but also it showed potential in removing heavy metals (Pb) from wastewater and for use as a slow-release fertilizer. CIMBC is a promising new adsorbent, which can realize resource utilization of lignite with low calorific value while removing nitrogen and phosphorus.

High efficiency and stable partial nitration achieved via gel immobilization

Long-term high efficiency and stable partial nitrification (PN) performance was achieved using gel-immobilized partial nitrifying bacteria. The PN characteristics of the filler under high and low ammonia nitrogen concentrations and low temperature were comprehensively studied and the rapid reactivation was achieved after reactor breakdown or long stagnation period. The results showed that the maximum ammonia oxidation rate was 66.8 mg•(L•h)−1 and the nitrite accumulation rate was above 95 % for the filler. Efficient and stable PN performance depends on the high abundance of ammonia-oxidizing bacteria (AOB) inside the filler and dynamically microbial community. In addition, the oxygen-limited zone and competition between the microorganisms inside the filler effectively inhibited the growth of nitrite oxidizing bacteria, and the sludge outside the filler assisted in this process, which supported the dominant position of AOB in fillers. This study provides a reliable technology for the practical application of the PN nitrogen removal process.

Effects of Acute Ammonia Exposure on the Antioxidant System and Anti‐Inflammatory Factors in Opsariichthys bidens

The present experiment was performed to reveal the mechanisms of toxic effects of ammonia nitrogen on Chinese hook snout carp (Opsariichthys bidens) based on the levels of antioxidant enzyme activities and the expression of 70‐kDa heat shock protein gene (HSP70) and tumor necrosis factor‐α (TNF‐α) after 96 h of acute toxic ammonia exposure to investigate its adaptability. The result showed that activities of antioxidant enzymes and lipid peroxidation in the intestine, liver, brain, and gills showed a general trend of increasing and then decreasing when exposed to ammonia nitrogen. The intestinal tissue structure was damaged to varying degrees, the expression of the HSP70 in the brain and gills increased at 0–12 h, and the expression of the TNF‐α in brain tissues decreased at 0–12 h. The expression of TNF‐α in the liver was continuously upregulated in the late stages of stress, and it did not decrease until the stress was released. The above results indicate that high concentrations of ammonia nitrogen caused varying degrees of damage to the neurological, respiratory, and metabolic‐related organs of the O. bidens.