Search Results (355)

The development of an economical and efficient method for recovering phosphate (PO₄³⁻-P) and ammonium nitrogen (NH₄⁺-N) is of paramount importance for environmental remediation. The preparation of Mg/Fe-loaded biochar (Mg/Fe-BC) was achieved through chemical precipitation followed by pyrolysis in this study. Single solution adsorption studies indicated that temperature significantly affected how effectively Mg/Fe-BC could adsorb and remove NH₄⁺-N, whereas PO₄³⁻-P adsorption showed minimal temperature sensitivity. In mixed simulated solutions, In the mixed simulated solution, the maximum adsorption capacities of Mg/Fe-BC for PO₄³⁻-P and NH₄⁺-N were 145.97–153.05 mg/g and 112.63–121.51 mg/g, respectively. The optimal dosage for synergistic adsorption was determined to be 3 g/L, while pH values ranging from 3 to 9 exhibited negligible effects on the adsorption of both contaminants. The presence of Ca²⁺ and HCO₃⁻ in the solution may interfere with the simultaneous adsorption of PO₄³⁻-P and NH₄⁺-N. SEM-EDS and XPS analyses revealed that the primary adsorption mechanisms of PO₄³⁻-P and NH₄⁺-N by Mg/Fe-BC involved electrostatic attraction, ion exchange, and hydrogen bonding. In practical applications using chicken manure biogas slurry, Mg/Fe-BC demonstrated synergistic adsorption effects, achieving removal efficiencies of 86.86% for PO₄³⁻-P and 36.86% for NH₄⁺-N, thereby confirming its potential application value in wastewater treatment. Full article

Ammonia emissions in poultry houses are common and pose health concerns for animals and workers. However, effective control of these emissions with sustainable products is lacking. Therefore, we investigated if an agricultural byproduct, cottonseed hulls, could be recycled through pyrolysis and used to remove ammonia from air. In this study, the efficacy of ammonia removal was observed using cottonseed hull biomaterials pyrolyzed at seven different temperatures: 250, 300, 350, 400, 500, 600, and 700 °C. In this study, ammonia was passed through a column filled with pyrolyzed material, and ammonia in the filtered air was monitored. The results showed that materials pyrolyzed at intermediate temperatures of 350 and 400 °C were the most efficient at ammonia removal and were able to adsorb approximately 3.7 mg NH₃/g of material. Despite extensive characterization, ammonia adsorption could not be linked to intrinsic material properties. Evaluation of the materials showed that the carbon in the pyrolyzed materials would be stable over time should the spent material be used as a soil amendment. Full article

This paper presents the assessment of the possibility of ammonia adsorption on biochars from banana peels, chemically activated with potassium hydroxide (KOH) at different temperatures. The obtained materials were characterized in detail using a number of analytical techniques, including nitrogen adsorption (BET), scanning electron microscopy (SEM), elemental analysis (CHNS), thermal analysis (TG, DTG, DTA), Fourier transform infrared spectroscopy (ATR-FTIR), Raman spectroscopy, Boehm titration method and biochar surface pH. They revealed a largely developed microporous structure and a large specific surface area, ranging from 1134 to 2332 m² g⁻¹. The adsorption tests against ammonia in the gas phase showed a large adsorption capacity of the materials, up to 5.94 mmol g⁻¹ at 0 °C and 3.83 mmol g⁻¹ at 20 °C. The adsorption properties of the obtained biochars were confirmed to be significantly influenced by the surface chemistry (presence of the acidic functional groups). The research results indicate that the waste-based biomass, such as banana peels, can be an ecological and economical raw material for the production of highly effective adsorbents, useful in the removal of ammonia and other toxic gases polluting the environment. Full article

This study examined a strategy for effective reject water treatment involving hydrodynamic cavitation (HC) combined with subsequent adsorption using natural zeolites. Two experiments were conducted: The first involved the selection of optimal pre-treatment conditions of HC for biodegradability and to reduce the ammonium nitrogen and phosphate content. Three inlet pressures of 3, 5, and 7 bar and two types of cavitation inducers, i.e., multiple- and single-hole orifice plates, were evaluated. Adsorption experiments were conducted in batch mode using natural zeolite, and three doses of zeolite (50, 100, and 200 g/L) and six contact times (4–24 h) were examined. In the HC experiments, the application of 3 bar pressure, a single-hole cavitation inducer, and a cavitation time of 30 min resulted in the removal of ammonia nitrogen and phosphates amounting to 26.5 and 23%, respectively. In this case, 3.6-fold enhancement in the biodegradability index was also found. In the second experiment, the use of zeolite led to a decrease in the remaining content of both ammonia nitrogen and phosphates, improving the chemical oxygen demand-to-total nitrogen ratio. The highest removal efficacy was found for the highest zeolite dose of 200 g/L and the longest cavitation time of 24 h. Under these conditions, the ammonia nitrogen and phosphate removal rates were 70 and 94%, respectively. Full article

The development of efficient and sustainable water recycling systems is essential for long-term human missions and the establishment of space habitats on the Moon, Mars, and beyond. Humidity condensate (HC) is a low-strength wastewater that is currently recycled on the International Space Station (ISS). The main contaminants in HC are primarily low-molecular-weight organics and ammonia. This has caused operational issues due to microbial growth in the Water Process Assembly (WPA) storage tank as well as failure of downstream systems. In addition, treatment of this wastewater primarily uses adsorptive and exchange media, which must be continually resupplied and represent a significant life-cycle cost. This study demonstrates the integration of a membrane-aerated biological reactor (MABR) for pretreatment and storage of HC, followed by brackish water reverse osmosis (BWRO). Two system configurations were tested: (1) periodic MABR fluid was sent to batch RO operating at 90% water recovery with the RO concentrate sent to a separate waste tank; and (2) periodic MABR fluid was sent to batch RO operating at 90% recovery with the RO concentrate returned to the MABR (accumulating salinity in the MABR). With an external recycle tank (configuration 2), the system produced 2160 L (i.e., 1080 crew-days) of near potable water (dissolved organic carbon (DOC) < 10 mg/L, total nitrogen (TN) < 12 mg/L, total dissolved solids (TDS) < 30 mg/L) with a single membrane (weight of 260 g). When the MABR was used as the RO recycle tank (configuration 1), 1100 L of permeate could be produced on a single membrane; RO permeate quality was slightly better but generally similar to the first configuration even though no brine was wasted during the run. The results suggest that this hybrid system has the potential to significantly enhance the self-sufficiency of space habitats, supporting sustainable extraterrestrial human habitation, as well as reducing current operational problems on the ISS. These systems may also apply to extreme locations such as remote/isolated terrestrial locations, especially in arid and semi-arid regions. Full article

A sensitive method was developed for detecting diazepam residues in aquatic products using magnetic dispersive solid-phase extraction (MDSPE) coupled with ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS). Samples extracted with 1% ammonia–acetonitrile were purified using synthesized Fe₃O₄@SiO₂-PSA nanoparticles via MDSPE before UPLC-MS/MS analysis. Separation was performed on a C₁₈ column with gradient elution using 0.1% formic acid–2 mM ammonium acetate/methanol. Detection employed positive electrospray ionization (ESI⁺) in multiple reaction monitoring (MRM) mode. Characterization confirmed Fe₃O₄@SiO₂-PSA’s mesoporous structure with excellent adsorption capacity and magnetic properties. The method showed good linearity (0.1–10 μg/L, r > 0.99) with an LOD and LOQ of 0.20 μg/kg and 0.50 μg/kg, respectively. Recoveries at 0.5–15.0 µg/kg spiking levels were 74.9–109% (RSDs 1.24–11.6%). This approach provides rapid, accurate, and high-precision analysis of diazepam in aquatic products, meeting regulatory requirements. Full article

The initial surface reaction of gallium nitride (GaN) grown by atomic layer deposition (GaN-ALD) was investigated using density functional theory (DFT) calculations. Trimethylgallium (TMG) and ammonia (NH₃) were used as gallium (Ga) and nitrogen (N) precursors, respectively. DFT calculations at the B3LYP/6-311+G(2d,p) and 6-31G(d) levels were performed to compute relative energies and optimize chemical structures, respectively. TMG adsorption on Si₁₅H₁₈–(NH₂)₂ and Si₁₅H₂₀=(NH)₂ clusters was modeled, where –NH₂ and =NH surface species served as adsorption sites. The reaction mechanisms in the adsorption and nitridation steps were investigated. The results showed that TMG can adsorb on both surface adsorption sites. In the initial adsorption stage, TMG adsorbs onto =NH- and –NH₂-terminated Si(100) surfaces with activation energies of 1.11 and 2.00 eV, respectively, indicating that the =NH site is more reactive. During subsequent NH3 adsorption, NH₃ adsorbs onto the residual TMG on the =NH- and –NH₂-terminated surfaces with activation energies of approximately 2.00 ± 0.02 eV. The reaction pathways indicate that NH₃ adsorbs via similar mechanisms on both surfaces, resulting in comparable nitridation kinetics. Furthermore, this study suggests that highly reactive NH₂⁻ species generated in the gas phase from ionized NH₃ may help reduce the process temperature in the GaN-ALD process. Full article

Zeolite adsorption followed by NaCl-NaClO regeneration is an effective method for the on-site treatment of ammonia in initial stormwater. However, the formation and toxicity of chlorine species during the zeolite regeneration process need to be investigated. In this study, under intermittent and continuous operations, zeolites adsorbed NH₄Cl + HA (humic acid) and actual stormwater, then regenerated with NaCl-NaClO (0.5 g/L NaCl, ClO⁻:N molar ratio of 1.8, pH = 10). This technology was assessed from the following three aspects: adsorption and regeneration, chlorine species formation, and toxicity. The results showed that zeolites exhibited a greater adsorption capacity for HA in stormwater compared to that in an NH4Cl + HA solution, and the presence of ammonia had a minimal impact on this process. During zeolite regeneration, ammonia had a competitive advantage over HA for ClO⁻. ClO₃⁻ was inevitably formed in regeneration. The formation of chlorinated organic compounds (COPs) increased over time. The order of chlorine species toxicity in zeolite regeneration solution was free chlorine > COPs > ClO₃⁻. Controlled regeneration time was required to minimize the formation and toxicity of chlorine species. During the 10 cycles of regeneration, chlorine species continued to form and caused high toxicity hazards. Full article

To address severe ammonia gas and dust pollution coupled with resource waste in exhaust gases from urea prilling towers, a production process for gasified biochar-based slow-release fertilizer is proposed to achieve resource recovery of exhaust pollutants. Through phosphoric acid impregnation modification applied to gasified biochar, its ammonia gas adsorption capacity was significantly enhanced, with saturated adsorption capacity increasing from 0.61 mg/g (unmodified) to 32 mg/g. Coupled with the tower-top bag filter, the modified biochar combines with ammonia gas and urea dust in exhaust gases, subsequently forming biochar-based slow-release fertilizer through dehydration and granulation processes. Material balance analysis demonstrates that a single 400,000-ton/year urea prilling tower achieves a daily fertilizer production capacity of 55 tons, with 18% active ingredient content. The nitrogen content can be upgraded to national standards through urea supplementation. Economic analysis demonstrates a total capital investment of USD1.2 million, with an annual net profit of USD0.88 million and a static payback period of 1.36 years. This process not only achieves ammonia gas emission reduction but also converts waste biochar into high-value fertilizer. It displays dual advantages of environmental benefits and economic feasibility and provides an innovative solution for resource utilization of the exhaust gases from the urea prilling process. Full article

The electrochemical reduction of nitrate to ammonia offers a promising solution for both alleviating nitrate pollution in wastewater and providing a sustainable ammonia source for agriculture use. This review focuses on the role of carbon-based catalysts in electrochemical nitrate reduction to ammonia, emphasizing their potential in addressing environmental pollution and supporting sustainable ammonia production. Carbon materials, known for their abundance, affordability, and eco-friendly properties, are central to this process. The review highlights key strategies for enhancing catalytic performance, including heteroatom doping, the development of porous structures, and the integration of metal/metal oxide nanoparticles. Additionally, it addresses significant challenges such as weak nitrate adsorption, slow reaction kinetics, and competition with the hydrogen evolution reaction. Through the integration of advanced material design, mechanistic insights, and innovative engineering strategies, this review provides valuable guidance for the future design of carbon-based catalysts, paving the way for significant advancements in both nitrate removal and sustainable ammonia synthesis. Full article

The recirculating aquaculture system (RAS) has been rapidly adopted worldwide in recent years due to its high productivity, good stability, and good environmental controllability (and therefore friendliness to environment and ecology). Nevertheless, the effluent from seawater RAS contains a high level of ammonia nitrogen which is toxic to fish, so it is necessary to overcome the salinity conditions to achieve rapid and efficient nitrification for recycling. The moving bed biofilm reactor (MBBR) has been widely applied often by using PE fillers for efficient wastewater treatment. However, the start-up of MBBR in seawater environments has remained a challenge due to salinity stress and harsh inoculation conditions. This study investigated a new PE-filler surface modification method towards the enhanced start-up of mariculture MBBR by combining liquid-phase oxidation and maifanstone powder. The aim was to obtain a higher porous surface and roughness and a strong adsorption and alkalinity adjustment for the MBBR PE filler. The hydrophilic properties, surface morphology, and chemical structure of a raw polyethylene filler (an unmodified PE filler), liquid-phase oxidation modified filler (LO-PE), and liquid-phase oxidation combined with a coating of a maifanstone-powder-surface-modified filler (LO-SCPE) were first investigated and compared. The results showed that the contact angle was reduced to 45.5° after the optimal liquid-phase oxidation modification for LO-PE, 49.8% lower than that before modification, while SEM showed increased roughness and surface area by modification. Moreover, EDS presented the relative content of carbon (22.75%) and oxygen (42.36%) on the LO-SCPE surface with an O/C ratio of 186.10%, which is 177.7% higher than that of the unmodified filler. The start-up experiment on MBBRs treating simulated marine RAS wastewater (HRT = 24 h) showed that the start-up period was shortened by 10 days for LO-SCPE compared to the PE reactor, with better ammonia nitrogen removal observed for LO-SCPE (95.8%) than the PE reactor (91.7%). Meanwhile, the bacterial community composition showed that the LO-SCPE reactor had a more diverse and abundant AOB and NOB. The Nitrospira has a more significant impact on nitrification because it would directly oxidize NH₄⁺-N to NO₃⁻-N (comammox pathway) as mediated by AOB and NOB. Further, the LO-SCPE reactor showed a higher NH₄⁺-N removal rate (>99%), less NO₂⁻-N accumulation, and a shorter adaption period than the PE reactor. Eventually, the NH₄⁺-N concentrations of the three reactors (R1, R2, and R3) reached <0.1 mg/L within 3 days, and their NH₄⁺-N removal efficiencies achieved 99.53%, 99.61%, and 99.69%, respectively, under ammonia shock load. Hence, the LO-SCPE media have a higher marine wastewater treatment efficiency. Full article

This study focuses on the chemical synthesis of nano-titanium dioxide (nano-TiO₂) via ammonium fluorotitanate ((NH₄)₂TiF₆) precipitation with ammonia solution, aiming to elucidate the effects of experimental parameters—including reaction temperature, duration, molar ratio of (NH₄)₂TiF₆ to ammonia, and (NH₄)₂TiF₆ concentration—on the particle size of synthesized nanoparticles, as well as the correlation between particle size and photocatalytic performance. The synthesized nanoparticles predominantly exhibited spindle-shaped morphology. Direct TEM imaging revealed the crystallization and growth mechanisms during synthesis: higher molar ratios, combined with lower temperatures and shorter durations, facilitated the formation of ultrafine particles, whereas lower molar ratios, with elevated temperatures and prolonged reaction times, yielded larger particles. Notably, nanorod structures emerged under low-temperature conditions with F⁻ ion adsorption. To investigate the relationship between particle size and photocatalytic performance, a Taguchi method-inspired experimental design was employed to evaluate the positive or negative impacts of particle size on photocatalytic activity. An experimental matrix was constructed using coded values for each factor, and regression coefficients were calculated to quantify input-output correlations. Results demonstrate that titanium dioxide catalysts with a particle size range of 50–75 nm exhibit optimal photocatalytic efficiency. Full article

This study evaluated the odor mitigation potential of rice husk biochar in a simulated dairy bedded pack over 21 days. Biochar was incorporated into a dairy manure–sawdust mixture at 5% and 10% dry weight. Emissions of key odorous compounds—ammonia (NH₃), sulfur compounds, volatile fatty acids, phenol, p-cresol, and indole—were evaluated. Odor units were assessed to determine perceived odor reduction. Biochar significantly reduced NH₃ and dimethyl sulfide (DMS) emissions: NH₃ by 27% and 43%, and DMS by 53% and 75%, at 5% and 10% application, respectively. The NH₃ reduction was attributed to ammoniacal nitrogen adsorption, while the DMS reduction likely resulted from enhanced air permeability suppressing anaerobic bacterial activity. The 5% biochar treatment, achieving 63% and 70% of the NH₃ and DMS reductions attained by the 10% treatment, respectively, offers a more practical and cost-effective option. Other odorous compounds were not significantly affected. A temporary reduction in odor units was observed on day 7. Rice husk biochar contains 14.5% atomic Si, primarily as silica, which supports structural stability but hinders pore development, reducing adsorption efficiency. These findings demonstrate the importance of biochar’s physicochemical properties in odor mitigation. Future research should evaluate long-term field performance, microbial interactions, and silica modification strategies. Full article

This review assesses biochar’s potential to mitigate nitrogen (N) losses when co-applied with N fertilizers, emphasizing mechanisms linked to its measurable physicochemical properties. The mitigation of ammonia (NH₃) volatilization shows variable effects from its cation exchange capacity (−21.7% to 20.4%) and specific surface area (SSA; −23.8% to 39.1%). However, the biochar pH (influencing mitigation from −45.0% to −9.0%) and application rate are key factors, with clayey soils exhibiting the greatest mitigation (−52.2%), potentially due to their high bulk density. High SSA biochar, often from high pyrolysis temperatures, reduces nitrate-N (NO₃⁻-N) leaching (up to −26.6%) by improving the soil’s water-holding capacity. A co-application with organic fertilizers shows a pronounced mitigation (up to −39.0%) due to a slower N release coupled with biochar adsorption. A high SSA also plays an important role in mitigating nitrous oxide (N₂O) emissions (up to −25.9%). A higher biochar C/N ratio promotes microbial N immobilization, contributing to N₂O reductions (+1.5% to −34.2%). Mitigation is greater in sandy/loamy soils (−18.7% to −7.9%) than in clayey soils, where emissions might increase (+18.0%). Overall, biochar applications demonstrate significant potential to mitigate N losses and improve N use efficiency, thereby supporting sustainable agriculture; however, its effectiveness is optimized when biochar properties (e.g., high SSA and appropriate C/N ratio) and application strategies are tailored to specific soil types and N sources. Full article

The excessive input of nitrogen and phosphorus pollutants into surface water bodies poses a serious threat to the aquatic ecosystem. As an efficient porous adsorbent material, ceramsite shows remarkable potential in the field of simultaneous nitrogen and phosphorus removal. In this study, Fe₂O₃ catalyzed the decomposition of K₂CO₃ to generate CO and CO₂ gases, leading to the formation of a large number of pore structures in the composite ceramsite. Subsequently, adsorption experiments were conducted on the obtained ceramsite. The regulatory mechanisms of the ceramsite dosage and solution pH on its adsorption performance were revealed. The experiments show that as the ceramsite dosage increased from 2.1 g/L to 9.6 g/L, the adsorption capacities of ammonia–nitrogen and phosphorus decreased from 0.4521 mg/g and 0.4280 mg/g to 0.1430 mg/g and 0.1819 mg/g, respectively, while the removal rates increased to 68.66% and 58.22%, respectively. This indicates that the competition between the utilization efficiency of adsorption sites and the mass-transfer limitation between particles dominates this process. An analysis of the pH effect reveals that the adsorption of ammonia–nitrogen reached a peak at pH = 10 (adsorption capacity of 0.4429 mg/g and removal rate of 81.58%), while the optimal adsorption of phosphorus occurred at pH = 7 (adsorption capacity of 0.3446 mg/g and removal rate of 86.40%). This phenomenon is closely related to the interaction between the existing forms of pollutants and the surface charge. Kinetic and thermodynamic studies show that the pseudo-second-order kinetic model (R² > 0.99) and the Langmuir isothermal model can accurately describe the adsorption behavior of the ceramsite for ammonia–nitrogen and phosphorus, confirming that the adsorption is dominated by a monolayer chemical adsorption mechanism. This study explores the dosage–efficiency relationship and pH response mechanism of Fe₂O₃-catalyzed porous ceramsite for nitrogen and phosphorus adsorption, revealing the interface reaction pathway dominated by Fe₂O₃ catalysis and chemical adsorption. It provides theoretical support for the construction of porous ceramsite and the development of an efficient technology system for the synergistic removal of nitrogen and phosphorus. Full article