Ammonia Nitrogen In Wastewater Research Articles

Resource Utilization of Rare-Earth-Rich Biomass and Ammonia Nitrogen Effluent from Mining

The post-treatment of heavy metal-enriched plants in mining areas and the purification of ammonia and nitrogen pollution in water bodies are significant for the ecological environment of ionic rare earth mining areas. Herein, we focused on the biochar production potential of Dicranopteris pedata, characterizing biochar prepared by an oxidative modification process and an iron modification process. We conducted adsorption experiments to comparatively investigate the adsorption performance of biochar on NH4+ and studied the fertilizer application and migration toxicity of the adsorbed biochar for rare earth elements (REEs). Results indicated that ~332.09 g of biochar could be produced per unit area of D. pedata under 100% clipping conditions. The Brunauer–Emmett–Teller (BET) specific surface area of oxidized biochar (H2O2BC) increased, and the pore size of iron-modified biochar increased. The adsorption behavior of biochar toward NH4+ was well represented by the pseudo-second-order and Langmuir models. H2O2BC demonstrated the strongest adsorption of NH4+ with maximum theoretical equilibrium adsorption of 43.40 mg·g−1, 37.14% higher than that of pristine biochar. The adsorption process of NH4+ on biochar is influenced by various physicochemical mechanisms, including pore absorption, electrostatic attraction, and functional group complexation. Furthermore, the metal ions in the biochar did not precipitate during the reaction process. The adsorbed NH4+ biochar promoted the growth of honey pomelo without risking REE pollution to the environment. Therefore, it can be applied as a nitrogen-carrying rare earth fertilizer in low rare earth areas. This study provides a theoretical basis and technical support for the phytoremediation post-treatment of rare earth mining areas and the improvement of ammonia nitrogen wastewater management pathways in mining areas.

Efficient removal of ammonia from aqueous solution using coal-based carbon membrane via electrochemical oxidation in the present of chloride ion

To tackle the escalating issue of ammonia nitrogen water pollution, developing efficient removal technologies holds paramount significance. In this work, an electrochemical membrane reactor (EMR) was constructed for the decontamination of ammonia nitrogen wastewater using the coal-based carbon membrane (CCM) as the flow-through anode. The removal efficiency and degradation mechanism of ammonia nitrogen by EMR during the treatment were investigated. It was found that, under applied voltage and in the presence of chloride ions, the CCM exhibited excellent chlorine evolution performance, and as a result, the EMR had excellent ammonia nitrogen removal efficiency. The removal of ammonia nitrogen by the flow-through EMR was following the pseudo-first-order kinetics. Analysis revealed that various operating parameters, including applied voltage, chloride ion concentration, flow rate, pH value, and initial ammonia concentration, all significantly influenced the ammonia nitrogen treatment performance of EMR. At optimal operation conditions (feed concentration of 30mg/L, applied voltage of 2.8V, NaCl concentration of 0.1mol/L and flow rate of 2ml/min), the EMR achieved a removal rate of 100% for ammonia nitrogen with a low energy consumption (EC) of 0.0380kW•h/g-NH4-N. The degradation mechanism analysis revealed that the primary means of ammonia removal relied on indirect oxidation mediated by OCl·, which was generated by the oxidation of Cl- on the surface of CCM within the solution under the influence of the electric field. Furthermore, the EMR demonstrated good applicability across various water matrices. In conclusion, the EMR holds considerable potential for the decontamination of ammonia nitrogen-containing wastewater.

Performance of single PN/A reactor under wide fluctuation of nitrogen load.

Partial nitritation-anammox (PN/A) is a cost-effective technology in high ammonia-nitrogen wastewater treatment. However, PN/A is prone to instability as the ammonia-nitrogen sharply fluctuates. In this study, a packed bed reactor is employed to construct a single-stage PN/A system to investigate the operational characteristics and explore the denitrification mechanism. The effluent NH4+-N concentration, ammonia nitrogen removal rate (ARE), and total nitrogen removal rate (TNR) could be sustained at about 60mg/L, 80%, and over 70%, respectively, when the influent nitrogen load rate (NLR) is changed from 0.733 to 0.879kg-N/m3/day. Both ARE and TNR are decreased when NLR continues increasing to 1.026kg-N/m3/day. The influent NLR decreases from 0.879 to 0.147kg-N/m3/day, and ARE and TNR reached 98% and 85.4%, respectively. Therefore, the denitrification effect of the reactor could be recovered, and the excellent nitrogen removal capacity could be obtained within a wide range of influent NLR. Moreover, the high-throughput sequencing and metagenomic testing indicate that the Proteobacteria and Planctomycetes that the PN/A functional strains (i.e., ammonia-oxidizing bacteria (AOB) and anammox bacteria (AnAOB)) account for 38.8% in the sludge. The relative abundance of Nitrospira containing the nitrite-oxidizing bacteria (NOB) has dropped to 0.01%, and the functional gene nxr of the nitrite oxidation process is also inhibited. The relative expression of the functional gene is dominated by the short-range nitritation and anammox oxidation, which demonstrates that the nitrogen removal is mainly dominated by nitritation-anammox.

Effect of the main components in gasification wastewater on the surface properties of coal water slurry

AbstractCoal water slurry is an advanced and efficient clean coal technology; using gasification wastewater to prepare coal water slurry can recycle wastewater and improve energy utilization efficiency. As the complex substances in wastewater have a great influence on the slurry properties, the effects of organic matter, metal ions, and ammonia nitrogen in gasification wastewater on the surface properties of coal water slurry are studied in this paper in order to provide new ideas for slurry mechanism of coal water slurry prepared from wastewater. Results show the following: (a) Compared with ordinary coal water slurry, the concentration of coal water slurry prepared from wastewater with high organic content increased by 2.9%, while the concentration of coal water slurry prepared from wastewater with high ammonia nitrogen content decreased by 2.1%. (b) The contact angles of coal water slurry prepared with phenols, alcohols, and urethane are reduced by 2.8°, 6.3°, and 1.5°, respectively, so organic matter can change the hydrophilicity of coal particles and affect slurryability. (c) Mg2+ and Ca2+ have basically no effect on slurry. Fe3+ reduces the absolute value of Zeta potential by 33.1, and Cu3+ increases that by 22.8, as they affect the slurryability by changing the surface potential of coal particles and the absorption of additives. (d) Ammonia nitrogen influences the slurryability by changing the pH value of the slurry. The conclusion of the influence mechanism of organic matter, metal ions, and ammonia nitrogen in wastewater on slurryability can provide a technical reference for the selection of suitable wastewater to prepare coal water slurry.

Effect of CeO2 on the preparation of functional ceramsite and the adsorption effect of ammonia-nitrogen wastewater treatment

This study investigates the effect of rare earth oxide CeO2 on the physical properties of ceramsite and its efficiency in treating ammonia-nitrogen wastewater. Ceramsite was prepared from solid waste with 10% coal gangue added as a pore-forming agent. Ceramsite sample I with CeO2 and sample II without CeO2 were prepared using pure reagents. The process parameters for both samples were optimized using an orthogonal test. Additionally, the effects of CeO2 on ceramsite performance and the treatment of ammonia-nitrogen wastewater were studied, and the adsorption mechanism of CeO2 on ammonia-nitrogen wastewater was clarified. The process parameters for preparing ceramsite sample Ⅰ were: preheating for 30 min at 600 °C, followed by roasting for 20 min at 1090 °C. The parameters for preparing ceramsite sample Ⅱ were: preheating for 30 min at 600 °C, followed by roasting time for 15 min at 1090 °C. The presence of CeO2 increased the porosity of the ceramsite by 0.89% and the specific surface area by 0.66 m2/g. Under neutral environmental conditions of water samples, CeO2 increased the removal rate of ammonia nitrogen by 1.85%. Ceramsite has a high porosity and specific surface area, indicating that it has abundant internal pores, a large contact area with ammonia-nitrogen, a strong ability to remove ammonia nitrogen, and resistance to erosion and water flow shear, which are conducive to the treatment of ammonia-nitrogen wastewater.

Firmicutes and Bacteroidetes as the dominant microorganisms for ammonium nitrogen wastewater treatment with a low C/N ratio in BCOR

Improving nitrogen removal is a significant concern in the biological treatment of ammonium nitrogen (NH4+-N) wastewater with low chemical oxygen demand (COD)/NH4+-N (C/N) ratio, and microorganisms are the critical factor affecting nitrogen removal. In this study, a laboratory-scale biological contact oxidation reactor (BCOR) system was successfully started up (day 1 to day 47) and stabilized (day 48 to day 320). A 16S rRNA gene sequencing analysis showed that the phyla Firmicutes and Bacteroidetes were first observed as the dominant microorganisms in the BCOR for the ammonium nitrogen wastewater treatment with a low C/N ratio. The genera Bacteroides (phylum Bacteroidetes), Porphyromonas (phylum Bacteroidetes), Dialister (phylum Firmicutes), and Anaerococcus (phylum Firmicutes) also became the main microorganisms in this system for the first time. These microbial communities enabled the system to achieve an average ammonium nitrogen removal efficiency and total nitrogen removal efficiency of 95.8 % and 88.1 %, respectively, during the operational period. It indicated that these dominant microorganisms in the BCOR system played an essential role in improving the performance of biological nitrogen removal. This conclusion will play a critical role in promoting the microbial mechanism research and technology engineering application of the BCOR system for treating ammonium nitrogen wastewater with a low C/N ratio.

Characteristics of Novel Heterotrophic Nitrification–Aerobic Denitrification Bacteria Bacillus subtilis F4 and Alcaligenes faecalis P4 Isolated from Landfill Leachate Biochemical Treatment System

Heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria are the key functional microorganisms needed to achieve simultaneous nitrification and denitrification (SND). In this study, 25 strains of HN-AD bacteria were successfully isolated from a stable landfill leachate biochemical treatment system, of which 10 strains belonged to Firmicutes and 15 strains belonged to Proteobacteria. Bacillus subtilis F4 and Alcaligenes faecalis P4 displayed good tolerance at a wide range of ammonia nitrogen (NH4+-N) concentrations. When the C/N ratio was 20, the removal rates of ammonia nitrogen were 90.1% and 89.5%, and the chemical oxygen demand (COD) removal rates were 92.4% and 93.9%, respectively. The napA gene encoding periplasmic nitrate reductase (Nap) and the nirS gene encoding nitrite reductase (Nir) were detected, and nitrogen balance showed assimilation and HN-AD was the main nitrogen metabolism mode in both strains. The use of immobilization materials could increase removal rate of ammonia nitrogen by 21.1% and 29.6%, respectively. The research results of this work can provide theoretical basis and technical support for the practical application of HN-AD bacteria to enhance the treatment of high ammonia nitrogen wastewater with high efficiency and low consumption.

In situ electro-generated Ni(OH)2 synergistic with Cu cathode to promote direct ammonia oxidation to nitrogen.

To solve the problem of low removal rate and poor N2 selectivity in direct electrochemical ammonia oxidation (EAO), commercial Ni foam and Cu foam were used as anode and cathode of the EAO system, respectively. The coupling effect between the cathode and anode promoted nitrogen cycling during the reaction process, which improved N2 selectivity of the reaction system and promoted it to achieve a high ammonia removal rate. This study showed that the thin Ni(OH)2 with oxygen vacancy formed on the surface of Ni foam anode played an effective role in the dimerization of intermediate products in ammonia oxidation to form N2. This electrochemical system was used to treat real goose wastewater containing 422.5 mg/L NH4+-N and 94.5 mg/L total organic carbon (TOC). After treatment, this electrochemical system achieved good performance with an ammonia removal rate of 87%, N2 selectivity of 77%, and TOC removal rate of 72%. Therefore, this simple and efficient system with Ni foam anode and Cu foam cathode is a promising method for treating ammonia nitrogen wastewater.

Influence of aeration modes and DO on simultaneous nitrification and denitrification in treatment of hypersaline high-strength nitrogen wastewater using sequencing batch biofilm reactor (SBBR)

Sequencing batch biofilm reactor (SBBR) has the potential to treat hypersaline high-strength nitrogen wastewater by simultaneous nitrification-denitrification (SND). Dissolved oxygen (DO) and aeration modes are major factors affecting pollutant removal. Low DO (0.35–3.5 mg/L) and alternative anoxic/aerobic (A/O) mode are commonly used for municipal wastewater treatment, however, the appropriate DO concentration and operation mode are still unknown under hypersaline environment because of the restricted oxygen transfer in denser extracellular polymeric substances (EPS) barrier and the decreased carbon source consumption during the anoxic phase. Herein, two SBBRs (R1, fully aerobic mode; R2, A/O mode) were used for the treatment of hypersaline high-strength nitrogen wastewater (200 mg/L NH4+-N, COD/N of 3 and 3% salinity). The results showed that the relatively low DO (2 mg/L) could not realize effective nitrification, while high DO (4.5 mg/L) evidently increased nitrification efficiency by enhancing oxygen transfer in denser biofilm that was stimulated by high salinity. A stable SND was reached 16 days faster with a ∼10% increase of TN removal under A/O mode. Mechanism analysis found that denser biofilm with coccus and bacillus were present in A/O mode instead of filamentous microorganisms, with the secretion of more EPS. Corynebacterium and Halomonas were the dominant genera in both SBBRs, and HN-AD process might assist partial nitrification-denitrification (PND) for highly efficient TN removal in biofilm systems. By using the appropriate operation mode and parameters, the average NH4+-N and TN removal efficiency could respectively reach 100% and 70.8% under the NLR of 0.2 kg N·m−3·d−1 (COD/N of 3), which was the highest among the published works using SND-based SBBRs in treatment of saline high-strength ammonia nitrogen (low COD/N) wastewater. This study provided new insights in biofilm under hypersaline stress and provided a solution for the treatment of hypersaline high-strength nitrogen (low COD/N) water.

A hydrogel-modified electrochemical biosensor for the rapid detection of ammonia‑nitrogen-resistant bacteria

Ammonia‑nitrogen wastewater is one of the main pollutants in the current environment. Rapid detection of microorganisms resistant to ammonia‑nitrogen provides a basis for bioremediation of ammonia‑nitrogen contaminated sites. This study uses electrochemical analysis for efficiently detecting of ammonia-resistant bacteria, utilizing a commercially available, low-cost screen-printed electrode (SPE) modified with agarose-based hydrogel (gel) or graphene oxide (GO). At the same time, the study employed electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV) to monitor bacterial growth, revealing Escherichia coli (E. coli) inhibition upon ammonia‑nitrogen addition, while Raoultella terrigena (RN1) and Pseudomonas (RN2) exhibit tolerance. The method provides sensitivity results in <45 min, which is significantly faster than traditional methods. RN1 and RN2 exhibit promising ammonia‑nitrogen removal rates, reaching up to 81 % and 92 %, respectively. This study aimed to develop an effective electrochemical method for rapidly detecting the sensitivity of microorganisms to ammonia‑nitrogen. The method offers advantages such as high speed, efficiency, and cost-effectiveness, potentially providing valuable microbial resources for mitigating ammonia nitrogen wastewater pollution.

Preparation of a novel ZnFe2O4 /oyster shell powder composite photocatalyst for visible-light-driven photocatalytic degradation of ammonia nitrogen wastewater

In this study, ZnFe2O4/oyster shell powder (ZF-OSP) composite photocatalyst was successfully synthesized via sol-gel method for the purpose of removing ammonia nitrogen (NH4+-N) from wastewater. The NH4+-N degradation rate by ZF at pH of 6.2 in 210 min was observed to be 19.5%. To improve the NH4+-N treatment efficiency of ZF, a high pH level of 11 was required by adding NaOH. In comparison, the ZF-OSP composite photocatalyst with a mass ratio of 1:1 achieved an impressive 91.8% elimination of NH4+-N at pH of 6.2 in 210 min without the requirement for additional pH adjustment and pH was stably maintained at 9.5–10.0. In addition, NO3--N and NO2--N were barely accumulated during the NH4+-N degradation process. Quenching experiments demonstrated that the degradation of NH4+-N in wastewater was significantly mediated by the participation of h+, •OH and •O2-. Moreover, NH4+-N removal rate of recovered ZF-OSP/1:1 composite photocatalyst by magnetic force after the first reuse cycle remained above 80.8%. Overall, the ZF-OSP/1:1 composite photocatalyst could not only address the challenge of recovery for non-magnetic powder photocatalysts, but also reduce the use of NaOH and offer a potentially effective and environmentally friendly solution for water treatment.

Photocatalytic oxidation degradability of ammonia–nitrogen and Ni/Co ammonia complexes in ternary precursor wastewater by constructing MoS2/g-C3N4 heterojunction: Performance and mechanism

In this study, MoS2/g-C3N4 heterojunction photocatalysts were fabricated in order to treat ammonia–nitrogen wastewater resulting from the production of ternary cathode material precursors used in the manufacture of lithium-ion batteries. The catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), N2 adsorption–desorption test, UV–Vis diffuse reflectance spectra (UV–Vis DRS), Fourier-transform infrared spectroscopy (FT-IR Nicolet 6700), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The catalytic efficiency of the catalysts on ammonia–nitrogen and Ni/Co ammonia complexes in the wastewater was investigated by varying MoS2 doping, catalyst dose, adsorption duration, and photocatalysis duration. The results showed 2.0 g/L of MoS2/g-C3N4-1 wt% (photocatalyst with a content of 1 wt% MoS2) has the best photocatalytic efficiency. A degradation efficiency of 87.52 % for ammonia–nitrogen, 98.34 % for nickel and 97.80 % for cobalt was reached after one hour of dark adsorption and four hours of illumination. EDS and XPS analysis revealed that Ni2+/Ni3+ and Co2+/Co3+ were adsorbed from the solution onto the catalyst surface, and that NH4+/NH3 was converted into NO3− and N2.

Micro-oxygen supply combined with applied voltage enhance ammonium oxidation and denitrification in a single-chamber microbial electrolysis cell: Performance and mechanism

Anodic ammonium oxidation catalyzed by microorganisms holds great potential as an effective anaerobic approach for ammonium and total nitrogen removal. However, the application of this approach is constrained by a low rate of ammonium oxidation, limiting the efficiency of total nitrogen removal. To overcome this limitation, a small amount of oxygen was introduced into a single-chamber microbial electrolysis cell to initiate the production of hydroxylamine through ammonium oxidation. Enhanced efficiency of overall nitrogen removal was obtained by the combined regulation of micro-oxygen and microbial electrode catalysis for ammonium oxidation and denitrification. According to the ammonium oxidation amount, the total oxidized nitrogen removal efficiency reached 67.87 ± 0.25 % and total nitrogen removal amount was 202.9 ± 0.5 mg/L, showing a high performance for treating high ammonium-contained wastewater. The oxidation peaks of hydroxylamine were determined at 0.43 V (vs. Ag/AgCl) for revealing the possible process of anodic hydroxylamine oxidation coupling to cathodic denitrification. In addition, microbial community analysis revealed that increasing the applied voltage regulated the abundance of nitrifying and denitrifying functional microbial communities both in the solution and on electrodes, and the key functional genes including hydroxylamine oxidation (hao), nitrate reduction (narG, narH, narI, napA, napB), nitrite reduce (nirK, nirS), and nitric oxide reduce (norB, norC), increased significantly at the applied voltage of 0.9 V, which accompanied by an obvious enhancement of enzyme activity compared to anaerobic and open circuit voltage. This work revealed the enhanced performance and mechanism on synergistic regulation by micro-oxygen and applied voltage for ammonium oxidation and denitrification, and provided new insights and feasible enhancing measures for treating high ammonium-nitrogen wastewater with low C/N ratio.

Efficient removal of ammonia nitrogen via a coupled system of Ni1Cu0.2-Se-T/CP anode and copper foam cathode

Direct electrochemical oxidation is a green, clean and promising process for the treatment of ammonia nitrogen (NH4+-N) wastewater. Nevertheless, drawbacks of slow reaction kinetics and large overpotential greatly limit the ammonia oxidation reaction. To address the issue, Ni1Cu0.2-Se-T/CP was synthesized by the combination of heteroatom doping and in situ electrochemical oxidation (ISEO). Physical characterization shows that there are homogeneous and dense microscopic nanosphere particles on the electrode surface, which provide good attachment sites for the adsorption of reactants. Electrochemical tests further show that this catalytic electrode exhibits not only a high current density (37.17 mA·cm−2) at 0.65 V vs.Hg/HgO but also has the low Tafel slope (92.25 mV·dec−1) to ammonia oxidation reaction. Then, Ni1Cu0.2-Se-T/CP was applied as anode with copper as cathode to construct a coupled system. The area ratio of cathode/anode was optimized to improve the removal effect of ammonia nitrogen. The NH4+-N conversion efficiency of 100% was obtained at a constant anode potential of 0.65 V vs.Hg/HgO for 15 h when the cathode/anode area was 1:4. The system N2 selectivity up to 77.55%. This work provides a promising process for the green and efficient degradation of ammonia nitrogen wastewater.

Nitrogen Removal Mechanism and Microbial Community Changes of the MBR Bioaugmented with Two Novel Fungi Pichia kudriavzevii N7 and Candida tropicalis N9

Ammonia nitrogen wastewater causes dissolved oxygen concentrations to decrease and the content of harmful substances to increase. To characterize the application properties of two novel strains of highly efficient ammonium transforming fungi—Pichia kudriavzevii N7 and Candida tropicalis N9—this study used both as compound microbial agents to treat nitrogenous wastewater. Here, we investigated the bioaugmentation effect of compound fungi N7 and N9 in the MBR bioreactor and the effect of N7 and N9 on the fungal and bacterial microbial communities in the system. The results revealed that in the first week after inoculation of N7 and N9, the average removal rate of ammonium in the experimental and control groups were 89.43% and 82.86%, respectively, and the NO3−-N accumulation concentrations were 12.56 mg·L−1 and 17.73 mg·L−1, respectively. The average transformation rate of total nitrogen in the experimental and control groups were 46.32% and 30.6%, respectively. ITS sequencing results indicated that N9 could be a dominant fungus in the complex MBR system. The results of 16S rRNA sequencing showed that the dominant bacterial communities in the system were changed by the inoculation of compound fungi. Therefore, the compound fungi can be applied to strengthen the treatment of nitrogenous wastewater due to its compatibility.

Three-Dimensional Electrochemical Oxidation System with RuO2-IrO2/Ti as the Anode for Ammonia Wastewater Treatment

In this study, a three-dimensional electrochemical oxidation system was constructed to treat ammonia nitrogen wastewater generated from the tail gas absorption of a methionine producer by using a homemade MAC mixed with a GAC at a mass ratio of 1:2 as the particle electrode, with a RuO2-IrO2/Ti polar plate as the anode and a stainless steel plate as the cathode. The effects of current density, initial pH value of wastewater, plate spacing, NaCl concentration and particle filling amount on CODCr and NH4+-N removal were investigated through single-factor experiments, and the removal pathways of CODCr and NH4+-N under the system were initially explored via cyclic voltammetry curves, scanning electron microscopy and tertiary butanol quenching experiments. The experimental results showed that the average removal rate of CODCr was 91.03% and that of NH4+-N was 98.89% after electrolysis for 5 h under the conditions of a current density of 40 mA/cm2, no pH adjustment, the spacing of the electrode plates of 8 cm, the NaCl dosing concentration of 1 g/L, and the particle filling amount of 400 g/L. Under this experimental condition, the removal of CODCr occurred mainly through the indirect oxidation of active chlorine and ·OH, and the removal of NH4+-N mainly through the indirect oxidation of active chlorine.

Research on V2O3 preparation by stepwise catalysis solution-phase hydrogen reduction from shale V-rich solution

Solution-phase hydrogen reduction reaction (SpHR) was introduced to overcome the problems of ammonia nitrogen pollution, high energy consumption, and long production flow of traditional reduction roasting. From φ-pH diagram, the increase of reaction temperature, vanadium concentration and H2 partial pressure is beneficial to the preparation of V2O3. High purity V2O3 could not be prepared by single addition catalysis and synchronous catalysis in SpHR process, and the Ni + NiSO4 stepwise catalysis can effectively eliminate the problem of nickel wrapped in vanadium precipitates during the precipitation process. Under the optimal conditions of Ni + NiSO4 stepwise catalysis of nickel powder dosage 5 g/L, NiSO4 dosage 8 g/L, nickel powder catalytic time 90 min, NiSO4 catalytic time 30 min, the precipitate with nickel content 11.15 % was obtained, and Ni catalyst can be separated by magnetic separation with nickel recovery ratio of 99.52 %. Ni2+ in SpHR precipitates to Ni(OH)2 and then disintegrates and reduces to Ni, and Ni + NiSO4 stepwise catalysis includes two steps of pre-catalysis and secondary catalysis. After fourth cyclic experiment, the vanadium content of V2O3 product obtained was 67.46 % (i.e. 99.21 % V2O3 purity met the requirements of GB 40301–2021), the total recovery was 98.68 %, and the vanadium loss ratio was stable at 1.22 %. The process of SpHR has no ammonia nitrogen wastewater or waste gas discharge, and the price of V2O3 with purity more than 99 % on the market is about 260,000 ¥/t. The stepwise catalysis SpHR has remarkable environmental benefits and economic benefits.

Preparation of NaA zeolite molecular sieve based on solid waste fly ash by high-speed dispersion homogenization-assisted alkali fusion-hydrothermal method and its performance of ammonia-nitrogen adsorption

A high-speed dispersion homogenization-assisted alkali fusion-hydrothermal method was successfully developed for the preparation of NaA zeolite molecular sieve with excellent adsorption performance for ammonia nitrogen using solid waste fly ash. The zeolite molecular sieve, prepared at a calcination temperature of 700 °C and a crystallization temperature of 80 °C, was identified as NaA zeolite molecular sieve through XRD and SEM tests, exhibiting a uniform and ordered cubic crystal structure. The result of BET analysis indicates that the NaA zeolite molecular sieve has a specific surface area of 288.219 m2/g and a plentiful pore structure. The effect of pH, adsorption time, and initial concentration of ammonia nitrogen on the adsorption capacity of NaA zeolite molecular sieve was also investigated. The fitting analysis of experimental adsorption data using adsorption kinetics and isotherm models indicates that the kinetic adsorption of ammonia nitrogen solution by zeolite molecular sieve follows the second-order kinetic model more closely. The Langmuir model shows a better correlation than the Freundlich model, suggesting that the adsorption of ammonia nitrogen solution by the zeolite molecular sieve is mainly based on the surface-uniform monolayer physical adsorption process. Under the conditions of pH = 7 and an initial ammonia nitrogen concentration of 100 mg/L, the adsorption capacity of the zeolite molecular sieve for ammonia nitrogen within 60 min can reach 27.5 mg/g, showing excellent adsorption performance. This study establishes a vital research foundation for the utilization of fly ash and the treatment of ammonia nitrogen wastewater, with great ecological and social benefits.

Adsorption Performance of Different Wetland Substrates for Ammonia Nitrogen: An Experimental Study

To investigate the adsorption performance of different substrates for ammonia nitrogen in wastewater, adsorption experiments are conducted on four substrates, namely, zeolite, quartz sand, volcanic rock, and biological ceramsite, and the experimental data are analyzed using adsorption isotherms and three kinetic models. The results show that with the increasing dosage of the substrates, the adsorption capacity gradually decreases, and the removal rate gradually increases. The removal rates all show a rapid increase in the early stage (the first 14 h) and gradually reach a stable state in the later stage (after more than 48 h). The higher the concentration of ammonia nitrogen in the NH4Cl solution, the greater the unit adsorption capacity of ammonia nitrogen by the substrate, the longer the adsorption time required to reach adsorption equilibrium, the lower the total removal rate of ammonia nitrogen, and the longer it takes for the concentration of ammonia nitrogen in the substrate and solution to reach equilibrium. The adsorption capacity of zeolite to ammonia nitrogen is much higher than that of quartz sand, biological ceramsite, and volcanic rock, so zeolite is suitable as the wetland substrate. The adsorption of ammonia nitrogen by the four substrates is principally multi-molecular layer adsorption, and the adsorption phase is heterogeneous.

A novel ammonium-free vanadium precipitation process for the integrated actions of ascorbic acid reduction and enhanced hydrolysis under hydrothermal influence

Vanadium-titanium magnetite is an important source of vanadium, and V2O5 is the main vanadium product. At present, the production of V2O5 is mainly obtained by sodium salt roasting and ammonium salt precipitation, while ammonia nitrogen wastewater and NH3 discharge will cause serious environmental pollution. Calcium and iron salts are mainly intermediate products, and vanadium oxides cannot be obtained directly. Therefore, a clean and sustainable method is proposed to produce V2O5 by ascorbic acid hydrothermal reduction in one step. When the vanadium concentration is 25.48 g/L, under the optimal vanadium precipitation conditions: the ascorbic acid addition ratio is n(ASA): n(V) = 0.1:1, the reaction temperature is 210 °C, the solution pH is 1.25, and the reaction time is 10 h, the precipitation efficiency and V2O5 purity can be 99.60% and 99.12%, respectively. The kinetics and apparent activation energy of the reaction were investigated, and the apparent activation energy was calculated to be 68.80 kJ/mol. The product obtained was characterized by XRD, SEM-EDS, XPS and FTIR, proving that the final product is V2O5. The reaction mechanism of ascorbic acid and vanadium in solution is single electron transfer and recombination, and the formation process of V2O5 is: VO3- → VO2+ → VO2 or V2O3 → V2O5, and ascorbic acid is oxidized to dehydroascorbic acid. In conclusion, the production of V2O5 by hydrothermal reduction of ascorbic acid is environmentally friendly, clean, simple, and efficient.