Ammonium removal using a calcined natural zeolite modified with sodium nitrate

Zeolites in wastewater treatment: A comprehensive review on scientometric analysis, adsorption mechanisms, and future prospects

Zeolites possess a microporous crystalline structure, a large surface area, and a uniform pore size. Natural or synthetic zeolites are commonly utilized for adsorbing organic and inorganic compounds from wastewater because of their unique physicochemical properties and cost-effectiveness. The present review work comprehensively revealed the application of zeolites in removing a diverse range of wastewater contaminates, such as dyes, heavy metal ions, and phenolic compounds, within the framework of contemporary research. The present review work offers a summary of the existing literature about the chemical composition of zeolites and their synthesis by different methods. Subsequently, the article provides a wide range of factors to examine the adsorption mechanisms of both inorganic and organic pollutants using natural zeolites and modified zeolites. This review explores the different mechanisms through which zeolites effectively eliminate pollutants from aquatic matrices. Additionally, this review explores that the Langmuir and pseudo-second-order models are the predominant models used in investigating isothermal and kinetic adsorption and also evaluates the research gap on zeolite through scientometric analysis. The prospective efficacy of zeolite materials in future wastewater treatment may be assessed by a comparative analysis of their capacity to adsorb toxic inorganic and organic contaminates from wastewater, with other adsorbents.

Molten Alkali-Assisted Formation of Silicate Gels and Its Application for Preparing Zeolites

Fly ash was used as raw material to prepare zeolites through silicate gels, assisted by the hydrothermal method. The silicate gels could be effectively formed in a few minutes in a molten alkali environment. The zeolites could be prepared by using these silicate gels through the hydrothermal method, which realizes the transformation from useless materials to highly valuable materials. The obtained zeolites were applied to the removal of ammonium in water, achieving the highvalue utilization of fly ash. The synthesized zeolites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrum (EDS), thermogravimetric (TG), and Fourier transform infrared (FTIR) spectroscopy. The study on the adsorption and removal of ammonium in water shows that the adsorption of ammonium is more in line with pseudo first-order kinetics, and the adsorption mainly occurs in the first 20 min. The adsorption can reach equilibrium in 30 min, and the maximum adsorption capacity can reach 49.1 mg/g. The adsorption capacity of ammonium has the best performance at pH = 5. Furthermore, within a certain range, an increase in temperature is beneficial for the removal of ammonium.

Reducing nitrogen loss from farmland by layered double hydroxide-supported carbon dots-enhanced ammonium immobilization

It remains a significant challenge to develop a kind of cost-effective and eco-friendly adsorbent with strong immobilization capabilities for ammonium in farmland. In this work, we employed Ca/Al layered double hydroxide-supported carbon dots (CDs@Ca/Al-LDHs) as a novel and efficient adsorbent for ammonium immobilization both in aqueous and soil environments. Such a composite could exhibit a high adsorption capacity towards ammonium in solution, which was four times higher than zeolite and three times higher than biochar under the same conditions. The mechanism investigations revealed that electrostatic interactions between the negatively charged CDs and the positively charged ammonium played a key role in the adsorption. In 30-day leaching experiments, the fabricated composite cumulatively reduced ammonium and nitrate by 6.3% and 9.7%, respectively at a dosage of 0.1% (w/w). Incubation experiments further confirmed that the developed composite could effectively inhibit ammonia volatilization and nitrification by immobilizing the ammonium within soil matrices. Our results demonstrated that CDs@Ca/Al-LDHs represented a promising candidate for cost-effective and eco-friendly immobilization of excess ammonium from over-fertilized farmland.

Modification of natural zeolites and their applications for heavy metal removal from polluted environments: Challenges, recent advances, and perspectives

In recent decades, environmental pollution has become a significant problem for human health and environmental impact. The high accumulation of heavy metals in waters and soils from different sources was conducted by finding efficient and environmentally friendly treatment methods and materials for their removal. Natural zeolites have found wide-ranging applications in environmental remediation and protection, considering various treatment and modification methods designed to enhance the natural zeolites' adsorptive or ion-exchange capabilities for increased efficiency. This paper briefly consolidates the recent scientific literature related to the main characteristics of natural and modified zeolites, the advantages and limitations of their environmental remediation application, and summarizes the methodologies applied to natural zeolites in order to improve their properties. Their application for removing heavy metals from water systems and soils is also comprehensively discussed. This review highlights the excellent potential of natural zeolites to be used after specific treatment or modification as a sustainable and green material to solve numerous environmental pollution issues.

High adsorption capacity of ammonia nitrogen on hexagonal porous aluminosilicate derived from solid-waste bagasse bottom ash

This study investigates the use of a hexagonal-porous aluminosilicate (HAS) adsorbent derived from bagasse bottom ash (BBA), an agricultural solid waste, for the adsorption of ammonia nitrogen (NH3-N)-a key water pollutant from agricultural and farming activities. Sodium silicate derived from BBA via the alkaline fusion method was employed, resulting in energy savings due to a synthesis temperature 1.53 times lower than that of commercial sodium silicate synthesis. The sol-gel method was utilized to successfully synthesize HAS featuring a high surface area and porosity using the sodium silicate prepared from BBA. However, an increase in aluminum content resulted in a decrease in surface area and hexagonal porosity. In performance tests, the HAS(5) adsorbent exhibited the most efficient NH3-N removal, outperforming other adsorbents by 4.54-25.19 times across all initial concentrations. This enhanced efficiency can be attributed to its numerous acidic surface sites, enabling the bonding of NH3-N molecules through monolayer adsorption on the HAS surface.

Performance and mechanism of simultaneous nitrification and denitrification in zeolite spheres internal loop airlift reactor

An internal loop airlift reactor was constructed with zeolite spheres as biofilm carriers (ZS-ALR), and the performance and mechanism of nitrogen removal were investigated. The results indicated that the TN, NH₄⁺-N and TOC removal efficiencies of ZS-ALR reached 96.12%, 100% and 94.54% under appropriate conditions (HRT of 6-8 h, aeration rates of 80-120 mL/min, C/N ratios of 4-6), and the highest TN removal rate constant was 0.01156 min^-1. Further investigating the influence of ammonia-N concentrations on nitrogen removal and biofilm stability revealed that catabolism was important in TN removal, and the prominent genera for nitrogen removal included Sphaerotilus (42.20%), Flavobacterium (17.47%) and Fusibacter (6.14%). Meanwhile, the abundance of amoA, napA, narG and nosZ genes was markedly influenced by ammonia-N concentrations. The nitrogen removal of ZS-ALR was mainly through ammonia-N adsorption by zeolite spheres and simultaneous nitrification and denitrification by biofilm.

Synthesis of NaA zeolite from foundry dust and its adsorption capacity of ammonia

Eutrophication of water bodies due to excess ammonia nitrogen (NH₄⁺-N) is harmful to aquatic organisms and human health. In this study, foundry dust (FD) from foundry industry was used to synthesize NaA zeolite to use as an adsorbent to remove NH₄⁺-N from wastewater. Results demonstrate that FD could be successfully synthesized to form a foundry dust-based NaA zeolite (FZA) through adjustment of the silica-alumina ratio of n (SiO₂)/n (Al₂O₃) at 2 at 95 °C. Specific surface area, total pore volume, and cation exchange capacity (CEC), and maximum adsorption NH₄⁺-N of FZA was respectively 43.185 cm²/g, 0.0364 cm³/g, 212.35 mmol/100 g and 37.81 mg/g, which was 4.74, 1.54, 1.52 and 1.62 times as much as the NaA zeolite (SZA). FZA with higher adsorption NH₄⁺-N capacity was related to higher specific surface area and CEC. The NH₄⁺-N adsorption amount of 28.57 mg/g by FZA was obtained after the fourth regeneration, which was notably higher than that of SZA (23.27 mg/g). The desorption rate of NH₄⁺-N from FZA was 87% by the fourth regeneration. FZA effectively removed NH₄⁺-N from swine wastewater containing 153.32 mg/L NH₄⁺-N. Results suggest that FZA could be used as absorbent to removal NH₄⁺-N from wastewater.

Zeolite Composite Materials from Fly Ash: An Assessment of Physicochemical and Adsorption Properties

Waste fly ash, with both low (with the addition of vermiculite) and high contents of unburned coal, were subjected to hydrothermal syntheses aiming to obtain zeolite composite materials-zeolite + vermiculite (NaX-Ver) and zeolite + unburned carbon (NaX-C). The composites were compared with parent zeolite obtained from waste fly ash with a low content of unburned carbon (NaX-FA). In this study, the physicochemical characteristics of the obtained materials were evaluated. The potential application of the investigated zeolites for the adsorption of ammonium ions from aqueous solutions was determined. Composite NaX-Ver and parent zeolite NaX-FA were characterized by comparable adsorption capacities toward ammonium ions of 38.46 and 40.00 mg (NH₄⁺) g^-1, respectively. The nearly 2-fold lower adsorption capacity of composite NaX-C (21.05 mg (NH₄⁺) g^-1) was probably a result of the lower availability of ion exchange sites within the material. Adsorbents were also regenerated using 1 M NaCl solution at a pH of 10 and subjected to 3 cycles of adsorption-desorption experiments, which proved only a small reduction in adsorption properties. This study follows the current trend of waste utilization (fly ash) and the removal of pollutants from aqueous solutions with respect to their reuse, which remains in line with the goals of the circular economy.

Removal of Ammonium Ions from Aqueous Solutions Using Alkali-Activated Analcime as Sorbent

Five alkali-activated analcime (ANA) sorbents (ANA-MK 1, ANA 2, ANA 3, ANA-MK 4, and ANA-MK 5) were developed for ammonium (NH4+) ion removal. Acid treatment and calcination were used as pre-treatments for analcime, and metakaolin (MK) was used as a blending agent in three sorbents. Sorption experiments were performed to evaluate the effects of sorbent dosage (1–20 g L−1), initial NH4+ ion concentration (5–1000 g L−1), and contact time (1 min–24 h). ANA-MK 1, ANA 2, and ANA-MK 4 were the most efficient sorbents for NH4+ ion removal, with a maximum experimental sorption uptake of 29.79, 26.00, and 22.24 mg g−1, respectively. ANA 3 and ANA-MK 5 demonstrated lower sorption capacities at 7.18 and 12.65 mg g−1, respectively. The results for the sorption of NH4+ ions onto the alkali-activated analcime surfaces were modeled using several isotherms. The Langmuir, Freundlich, Sips, and Bi-Langmuir isotherms were the best isotherm models to represent the studied systems. The results of the kinetic studies showed the maximum NH4+ ion removal percentage of the sorbents was ~80%, except for ANA-MK 5, which had a ~70% removal. Moreover, the pseudo-first-order, pseudo-second-order, and Elovich models were applied to the experimental data. The results showed that the sorption process for ANA-MK 1, ANA 2, ANA 3, and ANA-MK 4 followed the Elovich model, whereas the pseudo-second-order model provided the best correlation for ANA-MK 5.

Application of zeolites in permeable reactive barriers (PRBs) for in-situ groundwater remediation: A critical review

Permeable reactive barrier (PRB) is one of the most promising in-situ groundwater remediation technologies due to its low costs and wide immobilization suitability for multiple contaminants. Reactive medium is a key component of PRBs and their selection needs to consider removal effectiveness as well as permeability. Zeolites have been extensively reported as reactive media owing to their high adsorption capacity, diverse pore structure and high stability. Moreover, the application of zeolites can reduce the PRBs fouling and clogging compared to reductants like zero-valence iron (ZVI) due to no formation of secondary precipitates, such as iron monosulfide, in spite of their reactivity to remove organics. This study gives a detailed review of lab-scale applications of zeolites in PRBs in terms of sorption characteristics, mechanisms, column performance and desorption features, as well as their field-scale applications to point out their application tendency in PRBs for contaminated groundwater remediation. On this basis, future prospects and suggestions for using zeolites in PRBs for groundwater remediation were put forward. This study provides a comprehensive and critical review of the lab-scale and field-scale applications of zeolites in PRBs and is expected to guide the future design and applications of adsorbents-based PRBs for groundwater remediation.

Thermally Modified Palygorskite Usage as Adsorbent in Fixed-Bed Reactor for High Concentration NH4+-N Removal and Further Application as N-Fertilizer in Hydroponic Cultivation

Palygorskite sample (Pal) underwent thermal treatment at 400 °C (T-Pal) to be used as adsorbent for the removal of 200 mg NH₄⁺-N/L from artificial solution. After thermal treatment, the sample was characterized via X-ray diffraction (XRD) and scanning electron microscopy (SEM). For NH₄⁺-N removal, T-Pal was added as a bed matrix in fixed-bed reactor experiments and the effect of flow rate was determined. It was indicated that with the flow rate increase from 10 mL/min to 50 mL/min, fewer liters of the solution were purified, rendering a longer residual time of interactions, which is optimal for NH₄⁺-N removal from T-Pal. The maximum removed amount was calculated at 978 mg NH₄⁺-N (q_total), suggesting T-Pal is a promising ammonium adsorbent. The data of kinetic experiments were applied to Clark, Yoon-Nelson, and Thomas kinetic models, with Clark having the best fit, highlighting a heterogenous adsorption. At the end of kinetic experiments, T-Pal applied in hydroponic cultivations and presented a sufficient release rate, which was found utilizable for saturated T-Pal usage as N fertilizer that satisfactory results were deemed concerning lettuces characteristics and growth.

Enhanced removal of ammonia nitrogen from rare earth wastewater by NaCl modified vermiculite: Performance and mechanism

Wastewater from rare earth mining (WREM) is very harmful to environment and human health due to its high concentration of ammonia nitrogen (NH₃-N). It is therefore necessary and urgent to find a low-cost and convenient technique to remove high concentration of NH₃-N from WREM. In this study, Natural powdered vermiculite (NV) was modified with seven sodium chloride (NaCl) solutions, and seven kinds of sodium chloride modified vermiculite (Na-V) were obtained. The NH₃-N adsorption performance of Na-V is greatly improved compared with NV. Among them, vermiculite modified with 180 g/L NaCl yielded the highest ammonium adsorption capacity (Q_m, 11.569 mg/g), which was 63.43% higher than NZ (Q_m, 7.079 mg/g). The characterizations of 180-Na-V confirmed the removal mechanism of NH₃-N that the improved capacity of modified vermiculite was attributed to its higher mesoporous volume and ion-exchange capacity, which are the result of sodium-ion exchange and Interlayer effect from high concentration of NaCl. The adsorption isotherms and kinetics were respectively best consistent with Langmuir model and the pseudo-second-order (PSO) model. The adsorption capacity (3.808 mg/g) of vermiculite after 5 cycles could still maintain 75.09% of the initial adsorption capacity (5.071 mg/g). A large amount of Na-V had little effect on pH of water, which meet the requirements of practical application. Including pH, dosage, coexisting ions, the effects of other factors on ammonium adsorption were also determined. This study provides a new method for vermiculite to remove high concentration of NH₃-N.

Using raw and thermally modified fibrous clay minerals as low concentration NH4+-N adsorbents

Raw and modified fibrous clay minerals palygorskite (Pal) and sepiolite (Sep) were tested for their ability to remove ammonium from ammonium polluted water. Palygorskite and sepiolite underwent thermal treatment at 400°C (T-Pal and T-Sep respectively). Raw and thermally treated samples were characterized using XRD, SEM, BET, FTIR, TGA, zeta potential, and XRF. The techniques verified the effect of thermal treatment on sample structures and the enhancement of negative charge. Both raw and thermally activated materials were applied in batch kinetic experiments, and found to be efficient adsorbents in their raw forms, since Pal and Sep achieved 60 and 80% NH₄⁺-N removal respectively within 20 min of contact for initial NH₄⁺-N concentration of 4 mg/L. Similar removal rates were gained for other concentrations representative of contaminated aquifers that were examined, ranging from 1 to 8 mg/L. Results for the modified T-Pal and T-Sep minerals showed up to 20% higher removal rate. Saturation tests indicated the positive effect of thermal treatment on the minerals since T-Pal and T-Sep removal efficiency reached 85% and remained stable for 24 h. However, competitive ions in real water samples can influence the NH₄⁺-N removal efficiency of the examined samples. At almost all the examined samples, the nonlinear Freundlich isotherm and linear pseudo-second kinetic models showed better fitted all examined samples thus indicating heterogeneous chemisorption.

An Investigation into the Adsorption of Ammonium by Zeolite-Magnetite Composites

The discharging of ammonium from industrial, domestic, and livestock sewage has caused eutrophication of the water environment. The objectives of this study are to synthesize magnetic zeolite (M-Zeo) by an eco-friendly, economical, and easy procedure and to investigate its suitability as an adsorbent to remove ammonium from an aqueous solution. Based on characterization from XRD, BET, and SEM-EDS, Fe3O4 was proved to successfully load on natural zeolite. The effect of pH, temperatures, reacting times, initial ammonium concentrations, and regeneration cycles on ammonium adsorption was examined by batch experiments. The ammonium adsorption process can be best described by the Freundlich isotherm and the maximum adsorptive capacity of 172.41 mg/g was obtained. Kinetic analysis demonstrated that the pseudo-second-order kinetic model gave the best description on the adsorption. The value of pH is a key factor and the maximum adsorption capacity was obtained at pH 8. By using a rapid sodium chloride regeneration method, the regeneration ratio was up to 97.03% after five regeneration cycles, suggesting that M-Zeo can be recycled and magnetically recovered. Thus, the economic-efficient, great ammonium affinity, and excellent regeneration characteristics of M-Zeo had an extensively promising utilization on ammonium treatment from liquid.

Zeolite Application in Wastewater Treatment

As a scarce natural resource, the preservation of water quality is of fundamental importance to guarantee its availability for future generations. Due to the increasing industrial activity, effluents are generated with a series of chemical compounds, such as nitrogenous, phosphoric, and organic compounds, heavy metals, and dyes which, if improperly disposed of, contribute to contamination, followed by significant environmental impacts, in addition to the damage to human health. The adsorption technique is an effective approach for removing contaminants from effluents, showing high versatility, due to the use of various materials as adsorbents. Belonging to a wide variety of materials, zeolites reveal to be a promising adsorbent. Zeolites are minerals found in nature or which can be synthesized from industrial residues, standing out in the treatment of contaminated effluents. Zeolite removal efficiency depends on the contaminant to be removed and can reach up to 96% for heavy metals, 90% for phosphoric compounds, 96% for dyes, 80% for nitrogen compounds, and 89% for organics. Aiming at the identification of the more relevant findings and research gaps to advance the use of zeolites in the large-scale treatment of industrial effluents, a review on the recent application of zeolites is needed. This paper presents a global view of zeolites, and a review is conducted on several recent studies using zeolites as adsorbents for the contaminants considered, indicating the main characteristics of the various adsorption systems, demonstrating the particularities of each process, and aiming to reveal useful information to provide future research, in addition to identifying points that need further investigation.

Circular economy-driven ammonium recovery from municipal wastewater: State of the art, challenges and solutions forward

In current biological nitrogen removal (BNR) processes, most of ammonium in municipal wastewater is biologically transformed to nitrogen gas, making ammonium recovery impossible. Thus, this article aims to provide a holistic review with in-depth discussions on (i) current BNR processes for municipal wastewater treatment, (ii) environmental and economic costs behind ammonium in municipal wastewater, (iii) state of the art of ammonium recovery from municipal wastewater including anaerobic membrane bioreactor turning municipal wastewater to a liquid fertilizer, capturing ammonium in phototrophic biomass, waste activated sludge for land application, bioelectrochemical systems, biological conversion of ammonium to nitrous oxide as a fuel oxidizer, and adsorption, (iv) feasibility and challenge of adsorption for ammonium recovery from municipal wastewater and (v) innovative municipal wastewater reclamation processes coupled with ammonium recovery. Moving forward, municipal wastewater reclamation and resource recovery should be addressed under the framework of circular economy.

Effect of Exchangeable Ions in Natural and Modified Zeolites on Ag Content, Ag Nanoparticle Formation and Their Antibacterial Activity

To broaden the application of silver nanoparticles (AgNPs), which are well-known antibacterial agents, they are supported on different substrates to prevent aggregation, increase their surface area and antibacterial efficiency, and to be separated from the system more effectively at the end of treatment. To produce nanocomposites that consist of silver nanoparticles on natural and modified zeolites, silver ions (Ag⁺) were loaded onto zeolite (natural, Na-modified, H-modified) and then thermally reduced to AgNPs. The effect of the exchangeable cations in zeolite on Ag⁺ uptake, AgNPs formation, size and morphology was investigated by the TEM, SEM, EDX, XPS, UV-vis, XRD and BET methods. The silver amount in the nanocomposites decreased in the following order Na-modified zeolite > natural zeolite > H-modified zeolite. Microscopic techniques showed formation of AgNPs of 1–14 nm on natural and Na-modified zeolite, while the diameter of metal particles on H-modified zeolite was 12–42 nm. Diffuse reflectance UV-vis and XPS methods revealed the presence of both silver ions and AgNPs in the materials indicating that partial reduction of Ag⁺ ions took place upon heating at 400 °C in air. Additionally, antibacterial properties of the nanocomposites were tested against Escherichia coli, and it was found that Ag–containing composites originating from the Na-modified zeolite demonstrated the highest activity.

Worldwide Research Analysis on Natural Zeolites as Environmental Remediation Materials

Society faces a significant problem in regards to the spread of harmful products in the environment, primarily caused by accelerated growth and resource consumption. Consequently, there is a need for materials to be processed in less harmful ways and to remedy the contaminated sources they generate. Microporous materials have been studied for a long time and are used in waste treatment alternatives. Natural zeolites, on which this study is based, are attractive to the scientific and technological communities, due to their numerous applications as decontaminants and adsorption properties. This study analyzes the intellectual structures of publications related to natural zeolites in environmental remediation, using bibliometric methods to determine their volumes and trends. The methodology comprises of an analysis based on 1582 articles, using VOSviewer software, with data from 1974 to 2020, via the Scopus database. Results reflect a notable increase in publications from the end of the 1990s; the greatest contribution in the area comes from Eurasian countries. The study considers that development in this line of research will continue to increase and serve as a great contribution to preserve the environment in coming years, with themes that focus on water treatment (e.g., drinking water, wastewater, greywater), removal of heavy metals, ammonium, ammonia, and construction.

Compact wastewater treatment process based on abiotic nitrogen management achieved high-rate and facile pollutants removal

Chemically enhanced primary treatment (CEPT), ammonium ion exchange and regeneration (AIR) and membrane bioreactor (MBR) were coupled as CAIRM to treat domestic wastewater compactly and efficiently. CAIRM achieved efficient removal of chemical oxygen demand, ammonia nitrogen, total nitrogen (TN) and total phosphorus with total hydraulic retention time of 4.6 h, and obtained 2.3 ± 0.9 mg/L TN in the effluent. CEPT removed phosphate and impurities and prevented AIR from pollution. AIR maintained excellent nitrogen removal with a slight decrease in the exchange capacity of ion exchangers. MBR polished the effluent from AIR, and the larger particle size and better dewaterability of sludge mitigated the membrane fouling. Many heterotrophic genera, such as Rhodobacter and Defluviimonas, were enriched in the oligotrophic MBR. This study demonstrates the viability and stability of CAIRM in efficient wastewater treatment, which will address critical challenges in insufficient nitrogen removal and high land occupancy of current processes.

The Influence of Zeolitic By-Product Containing Ammonium Ions on Properties of Hardened Cement Paste

Fluid catalytic cracking (FCC) catalysts, used in the petroleum industry, are sources of zeolitic by-products. These by-products are often used as sorbents for the removal of ammonium ions from wastewater. After a period of use, the zeolitic by-product loses its sorption properties and is no longer effective. The problem is the use of zeolitic by-product with ammonium ions. In this study, a zeolitic by-product containing ammonium ions and high contents of active SiO2 and Al2O3 was used as a supplementary cementitious material (SCM). Cement pastes containing 0.5%, 1%, 3%, 5%, and 10% of the by-product were prepared, and the compressive strength and density of the pastes were evaluated. Incorporation of the zeolitic by-product increased the cement strength by 17% and 32% after 7 and 28 days of hydration, respectively. Thus, incorporation of the zeolitic by-product with ammonium ions as an SCM has a complex effect on an ordinary Portland cement (OPC) system. Ammonium chloride accelerated cement setting after 7 days of hydration, and the pozzolanic reaction positively affected strength development after 28 days of hydration. The reaction products caused the cement to have a compact microstructure. The zeolitic by-product containing absorbed ammonium ions can be successfully reused to replace ordinary Portland cement in cement pastes.

Non-thermal plasma combined with zeolites to remove ammonia nitrogen from wastewater

In this work, non-thermal plasma combined with zeolites was used to remove inorganic pollutant ammonia nitrogen from wastewater. Ammonia nitrogen elimination performances at various operating parameters were investigated. Roles of active species in the removal of ammonia nitrogen were also discussed. The experimental results showed that 69.97% ammonia nitrogen can be removed from the plasma/zeolites synergistic system after 30 min treatment. The removal efficiency was 16.23% and 61.55% higher than that in sole zeolites adsorption system and that in sole discharge plasma system, respectively. Higher applied voltage, lower initial ammonia nitrogen concentration and weak acidic conditions were favorable for ammonia nitrogen removal. After the addition of zeolites, part of O₃ and H₂O₂ generated in the plasma/zeolites system were decomposed into other oxygen species (•OH and ¹O₂), which improved the oxidation degree of ammonia nitrogen. In addition, the reaction mechanism of ammonia nitrogen in water by plasma/zeolites process was discussed. After repeated use three times, the effect of the zeolites in the plasma/zeolites system remained stable. Characterization of the zeolites after reaction was analyzed through BET, SEM, XRD and FT-IR. The experiments have confirmed the applicability of the plasma/zeolites system for the further treatment of low-concentration ammonia nitrogen wastewater.

Na@La-modified zeolite particles for simultaneous removal of ammonia nitrogen and phosphate from rejected water: performance and mechanism

Rejected water from sludge processing in wastewater treatment plants (WWTPs) is very harmful due to its high concentration of ammonia nitrogen and phosphorus. It is therefore necessary to find a low-cost and convenient technique to simultaneously remove ammonia nitrogen and phosphorus from rejected water. In this study, natural granular zeolite was modified by NaCl and La(OH)₃ to obtain a new material (Na@La-MZP), with several advantages compared with powdered zeolite. Na@La-MZP could remove 92.61% ammonia nitrogen (50 mg/L) and 99.01% phosphate (60 mg/L) at the optimal conditions of dosage 12.5 g/L, initial pH 6.0 and reaction time 12 hours, which enabled the effluent to satisfy the discharge standard (GB 18918-2002) for municipal WWTPs in China. The maximum adsorption capacity of Na@La-MZP was determined as 17.92 mg NH₄⁺-N/g and 9.53 mg P/g by the Langmuir isotherm. Pseudo-second-order kinetics could well illustrate the adsorption process and show that the ammonia nitrogen and phosphate can be degraded by chemical reaction. The characterizations of Na@La-MZP confirmed the removal mechanism of ammonia nitrogen and phosphate. The Na@La-MZP still maintained more than 75% removal efficiency after five reuses. Furthermore, the estimated cost of this treatment method was 0.22 $/m³ rejected water.

Improving Ammonium Sorption of Bayah Natural Zeolites by Hydrothermal Method

Natural zeolites are easily found and abundant in Indonesia. The natural zeolites are low-cost minerals; however, their ammonium sorption is poor. A hydrothermal method was applied to improve the ammonium sorption. Hydrothermal treatment times were varied 8, 24, and 32 h. The parent and hydrothermal treated samples were characterized by using X-ray diffraction (XRD), Field Emission Scanning Electron Microscopes (FE-SEM), Fourier-transform infrared spectroscopy (FTIR), and nitrogen physisorption. Ammonium adsorption was performed using a batch reactor to evaluate the adsorption performance of the prepared zeolite samples. The 8 h hydrothermal (HT 8 h) treated zeolites showed the highest ammonium removal percentage among others. The XRD analysis of HT 8 h shows a higher crystallinity of mordenite and the Brunauer–Emmett–Teller (BET) model shows a surface area of 105 m2/g, much larger as compared to the parent with a surface area of 19 m2/g. Various kinetic and isotherms models were also studied on the parent and HT 8 h samples. The intraparticle equation showed the most accurate model for the kinetic data and the Freundlich equation showed the most accurate model for the isotherm of the experimental data. In terms of ammonium removal efficiency, hydrothermally treated Bayah mordenite compares favorably with treated mordenite from other locations despite that clinoptilolite provides higher removal capacities than mordenite.

Enhanced NO2-Sensing Properties of Au-Loaded Porous In2O3 Gas Sensors at Low Operating Temperatures

NO2-sensing properties of semiconductor gas sensors using porous In2O3 powders loaded with and without 0.5 wt% Au (Au/In2O3 and In2O3 sensors, respectively) were examined in wet air (70% relative humidity at 25 °C). In addition, the effects of Au loading on the increased NO2 response were discussed on the basis of NO2 adsorption/desorption properties on the oxide surface. The NO2 response of the Au/In2O3 sensor monotonically increased with a decrease in the operating temperature, and the Au/In2O3 sensor showed higher NO2 responses than those of the In2O3 sensor at a temperature of 100 °C or lower. In addition, the response time of the Au/In2O3 sensor was much shorter than that of the In2O3 sensor at 30 °C. The analysis based on the Freundlich adsorption mechanism suggested that the Au loading increased the adsorption strength of NO2 on the In2O3 surface. Moreover, the Au loading was also quite effective in decreasing the baseline resistance of the In2O3 sensor in wet air (i.e., increasing the number of free electrons in the In2O3), which resulted in an increase in the number of negatively charged NO2 species on the In2O3 surface. The Au/In2O3 sensor showed high response to the low concentration of NO2 (ratio of resistance in target gas to that in air: ca. 133 to 0.1 ppm) and excellent NO2 selectivity against CO and ethanol, especially at 100 °C.