Removal Process Research Articles

Thermodynamics and Kinetic Study for Removal of Orange-G Dye from Aqueous Solution by Nano Composite

In this study, where graphene oxide was prepared by Hummer method, while copper oxide was prepared in the green way using (capparies spinosa) plant extract as a reducing agent, these oxides were diagnosed as well as the binary nanocomposite by several techniques including Fourier Transform Infrared Spectroscopy (FTIR), X-rays diffraction , and field Emission scanning electron microscopy (FESEM), after that the superimposed (GO/CuO) was used to adsorbent the orange G dye ( Orange - G) from its aqueous solutions, A number of factors affecting adsorption were studied (equilibrium time, surface weight, pH, concentration effect, temperature). The results showed that the ideal time for adsorption of the orange dye (orange-G) on the surface of the nanocomposite (GO/CuO) was (30min), the best ideal weight for dye removal was (0.05gm), the best concentration was (20ppm), and the best acid function was (pH=2). After that, the adsorption kinetics were also studied by applying the pseudo first and second order of adsorption. The results showed that the adsorption process follows the false second-order kinetics. The thermodynamic functions of the removal process were also studied, and it was found that the value of (DH) is negative for the surface of the composite (GO/CuO) with dye. Meaning the adsorption process is exothermic, and that the DG0 has negative value, meaning that the adsorption processes occur spontaneously. positive DS0 values indicate that the molecules are becoming less bound

Enhanced tetracycline removal in sequencing batch reactors by bioaugmentation using tetX-carrying strains: Efficiency and mechanisms

Tetracyclines antibiotics (TCs) pose notable environmental challenges due to their persistence in the effluent of wastewater treatment systems. Bioaugmentation offers a promising strategy for their removal, yet information is still very limited. This study aimed to assess the efficacy of bioaugmentation using wild-type (Sphingobacterium sp. WM1) and engineered tetX-carrying (PUC-tetX) strains for enhancing tetracycline (TC) removal in sequencing batch reactors (SBRs). Bioaugmentation mitigated TC's inhibitory effects on denitrification and phosphorus removal processes within SBR systems. Specifically, strain WM1 outperformed strain PUC-tetX in removing TC from sludge and maintained a longer viability. TC addition (500 μg/L, at an environmentally relevant concentration) and bioaugmentation did not significantly impact overall microbial community diversity. Notably, the introduction of these exogenous bacteria markedly increased the abundance of the tetX gene, correlating with the increase in TC degradation. Interestingly, MAGs associated with the Chloroflexi phylum in bioaugmented reactors showed the transfer of the tetX gene to autochthonous bacterial species, promoting TC removal capability. These findings underscored the potential of bioaugmentation to enhance antibiotic removal and provided insights into the dynamics of ARGs and tetX gene within activated sludge systems.

Poly(A)-Specific Ribonuclease Deficiency Leads to Deregulated Expression of Genes Involved in Sex Determination and Gonadal Maturation in Zebrafish

Abstract Background Deadenylation, the process of removal of poly (A) tail of messenger ribonucleic acids (mRNAs), is a rate-limiting step in mRNA stability, and poly(A)-specific ribonuclease (PARN) is the most important exonuclease involved in this process. Besides mRNA stability, PARN is also involved in several other processes including telomere maintenance, noncoding RNA maturation, ribosome biogenesis, and TP53 function. Previously, we have shown that zebrafish PARN null mutants are viable and fertile but turn out to only develop into males, indicating a role in oogenesis. The present study was focused on analyzing the expression of genes involved in sex determination and gonadal development in PARN mutant zebrafish. Materials and Methods Total RNA was extracted and quantitative real-time polymerase chain reaction was performed to determine the expression level of genes involved in gonad development in PARN mutant embryos (4 days postfertilization [dpf]) and adults (120 dpf) in comparison to their wild-type siblings. The expression levels were estimated by the ΔΔCT relative quantification method. Results At 4 dpf, the expression of germ cell-specific genes did not show any significant difference in the null mutants compared to the heterozygous and their wild-type siblings, suggesting no effect on germ cell differentiation due to the loss of PARN. However, the majority of the ovary-associated genes analyzed showed an increased expression in PARN null and heterozygous mutants compared to the wild-type siblings. Intriguingly, the expression of testis-associated genes showed decreased expression in the mutants compared to their wild-type siblings at 4 dpf. In adult stages, as expected, the expression of genes that jointly regulate the proper formation and function of ovaries and testes showed decreased expression in PARN null mutants. Interestingly, the expression of genes involved in the differentiation of testes, despite showing a decreased expression in the mutants, was comparable between the null and heterozygous mutants. Conclusion Taken together, these results suggest that the loss of PARN does not affect germ cell differentiation but affects the sexual differentiation that happens at later stages of development, particularly the process of oogenesis, in zebrafish.

Enhancement of cold-adapted heterotrophic nitrification and denitrification in Pseudomonas sp. NY1 by cupric ions: Performance and mechanism

Cupric ions can restrain biological nitrogen removal processes, which comprise nitrite reductase and nitric oxide reductase. Here, Pseudomonas sp. NY1 can efficiently perform heterotrophic nitrification and aerobic denitrification with cupric ions at 15 °C. At optimal culturing conditions, low cupric ion levels accelerated nitrogen degradation, and ammonium and nitrite removal efficiencies increased by 2.33%–4.85% and 6.76%–12.30%, respectively. Moreover, the maximum elimination rates for ammonium and nitrite increased from 9.48 to 10.26 mg/L/h and 6.20 to 6.80 mg/L/h upon adding 0.05 mg/L cupric ions. Additionally, low cupric ion concentrations promoted electron transport system activity (ETSA), especially for nitrite reduction. However, high concentrations of cupric ions decreased the ETSA during nitrogen conversion processes. The crucial enzymes ammonia monooxygenase, nitrate reductase, and nitrite reductase possessed similarly trends as ETSA upon exposure to cupric ion. These findings deepen the understanding for the effect of cupric ions on nitrogen consumption and bioremediation in nitrogen-polluted waters.

Operando Freezing Cryogenic Electron Microscopy of Active Battery Materials.

Understanding structural and chemical evolution of battery materials during operation is critical to achieving safe, efficient, and long-lasting energy storage. Cryogenic electron microscopy (cryo-EM) has become a valuable tool in battery characterization, leveraging low temperatures to improve stability of sensitive materials under electron beam irradiation. However, typical cryo-EM sample preparations leave extended time between the electrochemical point of interest and ex situ freezing of samples, during which active structures may relax, degrade, or otherwise evolve. Here, we detail a method for operando freezing cryo-EM to preserve and characterize native electrode and interfacial structures that arise during battery cycling, based on an operando plunge freezer and cold sample removal process. We validate the method on multiple electrode materials and quantify and discuss the freezing rate achieved. Operando freezing cryo-EM can be used to directly visualize transient features that arise at active electrochemical interfaces, to enable deeper understanding of structural evolution and interfacial chemistry in batteries and other electrochemical systems.

Typical Heterotrophic and Autotrophic Nitrogen Removal Process Coupled with Membrane Bioreactor: Comparison of Fouling Behavior and Characterization.

There is limited research on the relationship between membrane fouling and microbial metabolites in the nitrogen removal process coupled with membrane bioreactors (MBRs). In this study, we compared anoxic-oxic (AO) and partial nitritation-anammox (PNA), which were selected as representative heterotrophic and autotrophic biological nitrogen removal-coupled MBR processes for their fouling behavior. At the same nitrogen loading rate of 100 mg/L and mixed liquor suspended solids (MLSS) concentration of 4000 mg/L, PNA-MBR exhibited more severe membrane fouling compared to AO-MBR, as evidenced by monitoring changes in transmembrane pressure (TMP). In the autotrophic nitrogen removal process, without added organic carbon, the supernatant of PNA-MBR had higher concentrations of protein, polysaccharides, and low-molecular-weight humic substances, leading to a rapid flux decline. Extracellular polymeric substances (EPS) extracted from suspended sludge and cake sludge in PNA-MBR also contributed to more severe membrane fouling than in AO-MBR. The EPS subfractions of PNA-MBR exhibited looser secondary structures in protein and stronger surface hydrophobicity, particularly in the cake sludge, which contained higher contents of humic substances with lower molecular weights. The higher abundances of Candidatus Brocadia and Chloroflexi in PNA-MBR could lead to the production of more hydrophobic organics and humic substances. Hydrophobic metabolism products as well as anammox bacteria were deposited on the hydrophobic membrane surface and formed serious fouling. Therefore, hydrophilic membrane modification is more urgently needed to mitigate membrane fouling when running PNA-MBR than AO-MBR.

Coarse bubble mixing in anoxic zone greatly stimulates nitrous oxide emissions from biological nitrogen removal process

The biological nitrogen removal process in wastewater treatment inevitably produces nitrous oxide (N2O), a potent greenhouse gas. Coarse bubble mixing is widely employed in wastewater treatment processes to mix anoxic tanks; however, its impacts on N2O emissions are rarely reported. This study investigates the effects of coarse bubble mixing on N2O emissions in a pilot-scale mainstream nitrite shunt reactor over a 50-day steady-state period. Online and offline N2O monitoring campaigns show that coarse bubble mixing in the anoxic zones significantly elevates N2O emissions, yielding an extremely high emission factor of 15.5 ± 3.5 %. Intensive sampling and isotopic analyses suggest that the elevated emissions are primarily due to the inhibition of the N2O denitrification process by oxygen in the anoxic phase introduced by coarse bubbling. Substituting coarse bubble mixing with submersible pump mixing resulted in a substantial reduction of N2O emissions, decreasing the emission factor by an order of magnitude to 1.2 ± 0.8 %. The findings reveal that a previously overlooked factor, coarse bubble mixing, can significantly stimulate N2O emissions. The use of coarse bubble mixing in anoxic tanks of biological nitrogen removal warrants caution.

Transient behavior of the DYNASWIRL® phase separator during cryogenics tank-to-tank transfer operations

In order to separate gas and liquid from a two-phase mixture in space or earth applications, one can generate a strong artificial acceleration field instead of relying on gravity. This can be achieved by generating a swirl flow in a separator. The DYNASWIRL® phase separator is such a passive device, which had been demonstrated in air/water mixtures in the laboratory and on five reduced gravity NASA parabolic flights. In this work, extensive laboratory testing and numerical simulations are conducted to demonstrate the validity of the DYNASWIRL for phase separation with cryogenics. Liquid nitrogen (LN2) is used for extensive testing involving unsteady tank-to-tank transfer with quenching of separator and piping, liquid boil-off and vaporization, phase separation and recovery. This paper describes the separator and testing setups used. It examines the effects of the liquid (water and LN2), geometric parameters, and their effects on the separation and on the pressure loss across the separator, and analyzes the flow dynamics of the gas removal process. Validated numerical simulations support the experimental results and help explain the effects of the design parameters on the results.

Effect of magnetic powder (Fe3O4) on heterotrophic-sulfur autotrophic denitrification efficiency and electron transport system activity for marine recirculating aquacultural wastewater treatment

As an efficient nitrogen removal process, heterotrophic-sulfur autotrophic denitrification (HSAD) has attracted extensive attention in wastewater treatment. However, the effects of magnetic powder (Fe3O4) on the electron transport activity in HSAD process remain unclear. Therefore, in this study, a heterotrophic-sulfur autotrophic denitrification system was established to remove nitrogen from marine recirculating aquacultural wastewater for evaluating the effects of Fe3O4. At the optimal Fe3O4 concentration of 50 mg/L, the nitrogen removal efficiency reached 100% with lower sulfate accumulation, and the start-up time was shortened. The assays of denitrifying enzymes and electron transport system activity showed that Fe3O4 improved the activities of nitrate and nitrite reductases, and increased the efficiency of electron transport. Microbial community analysis revealed that Fe3O4 enriched heterotrophic denitrifier Thauera and sulfur autotrophic denitrifier Canditatus Thiobios, and thus enhanced denitrification efficiencies. This study demonstrated that Fe3O4 is an efficient denitrification accelerator in HSAD for treating marine recirculating aquacultural wastewater.

Effective removal of host cell-derived nucleic acids bound to hepatitis B core antigen virus-like particles by heparin chromatography.

Virus-like particles (VLPs) show considerable potential for a wide array of therapeutic applications, spanning from vaccines targeting infectious diseases to applications in cancer immunotherapy and drug delivery. In the context of hepatitis B core antigen (HBcAg) VLPs, a promising candidate for gene delivery approaches, the naturally occurring nucleic acid (NA) binding region is commonly utilized for effective binding of various types of therapeutic nucleic acids (NAther). During formation of the HBcAg VLPs, host cell-derived nucleic acids (NAhc) might be associated to the NA binding region, and are thus encapsulated into the VLPs. Following a VLP harvest, the NAhc need to be removed effectively before loading the VLP with NAther. Various techniques reported in literature for this NAhc removal, including enzymatic treatments, alkaline treatment, and lithium chloride precipitation, lack quantitative evidence of sufficient NAhc removal accompanied by a subsequent high VLP protein recovery. In this study, we present a novel heparin chromatography-based process for effective NAhc removal from HBcAg VLPs. Six HBcAg VLP constructs with varying lengths of the NA binding region and diverse NAhc loadings were subjected to evaluation. Process performance was thoroughly examined through NAhc removal and VLP protein recovery analyses. Hereby, reversed phase chromatography combined with UV/Vis spectroscopy, as well as silica spin column-based chromatography coupled with dye-based fluorescence assay were employed. Additionally, alternative process variants, comprising sulfate chromatography and additional nuclease treatments, were investigated. Comparative analyses were conducted with LiCl precipitation and alkaline treatment procedures to ascertain the efficacy of the newly developed chromatography-based methods. Results revealed the superior performance of the heparin chromatography procedure in achieving high NAhc removal and concurrent VLP protein recovery. Furthermore, nuanced relationships between NA binding region length and NAhc removal efficiency were elucidated. Hereby, the construct Cp157 surpassed the other constructs in the heparin process by demonstrating high NAhc removal and VLP protein recovery. Among the other process variants minimal performance variations were observed for the selected constructs Cp157 and Cp183. However, the heparin chromatography-based process consistently outperformed other methods, underscoring its superiority in NAhc removal and VLP protein recovery.

Comammox rather than AOB dominated the efficient autotrophic nitrification-denitrification process in an extremely oxygen-limited environment

The discovery of complete ammonia oxidizer (comammox) has challenged the traditional understanding of the two-step nitrification process. However, their functions in the oxygen-limited autotrophic nitrification-denitrification (OLAND) process remain unclear. In this study, OLAND was achieved using comammox-dominated nitrifying bacteria in an extremely oxygen-limited environment with a dissolved oxygen concentrations of 0.05 mg/L. The ammonia removal efficiency exceeded 97 %, and the total nitrogen removal efficiency reached 71 % when sodium bicarbonate was used as the carbon source. The pseudo-first- and second-order models were found to best fit the ammonia removal processes under low and high loads, respectively, suggesting distinct ammonia removal pathways. Full-length 16S rRNA gene sequencing and metagenomic results revealed that comammox-dominated under different oxygen levels, in conjunction with anammox and heterotrophic denitrifiers. The abundance of enzymes involved in energy metabolism indicates the coexistence of anammox and autotrophic nitrification-heterotrophic denitrification pathways. The binning results showed that comammox bacteria engaged in horizontal gene transfer with nitrifiers, anammox bacteria, and denitrifiers to adapt to an obligate environments. Therefore, this study demonstrated that comammox, anammox, and heterotrophic denitrifiers play important roles in the OLAND process and provide a reference for further reducing aeration energy in the autotrophic nitrogen removal process.

Important role of Chloroflexi: Improved the cooperation of anammox community under PFOS stress

Perfluorooctane sulfonic acid (PFOS) has received extensive attention in recent years due to its persistence and biotoxicity. As an advanced biological nitrogen removal process, anaerobic ammonium oxidation (anammox) is considered to be the most promising process to replace traditional nitrogen removal technology in the future. However, it is still unclear how PFOS affects microbial community and network structure in anammox system. The study found that PFOS had little influence on the nitrogen removal efficiency. Through microbial community and network analysis, the results showed that the typical anammox bacteria (Candidatus_Kuenenia, Candidatus_Jettenia, and Candidatus_Brocadia) enriched with the increasing concentrations of PFOS. Overall network complexity and proportion of positive links was significantly increased under 10 mg/L PFOS. Especially the subnetwork of Chloroflexi owned 100 % positive links under 10 mg/L PFOS, which accounted for 53.62 % of the corresponding overall network. The genus OLB13 and norank_f__Anaerolineaceae from Chloroflexi could cooperate with anammox bacteria to resist the impact of PFOS and further maintained the stability of anammox system. This study provided new insights into the effects of perfluoroalkyl compounds on anammox system.

Numerical study of proton exchange membrane water electrolyzer performance based on catalyst layer agglomerate model

In this work, a two-dimensional two-phase model of proton exchange membrane water electrolyzer (PEMWE) is developed, in which the catalyst layer (CL) is represented using agglomerate model. The effects of CL composition, porous transport layer (PTL) material properties and operating conditions on PEMWE performance are investigated. The results indicate that small size of catalyst agglomerate around 0.25 μm would benefit PEMWE performance. Appropriate increase of catalyst loading, porosity and ionomer volume fraction in the CL improves PEMWE performance, but their further increment leads to high mass transfer resistance, limiting the improvement of electrolyzer performance. The porosity and ionomer volume fraction of the catalyst layer are suggested to be lower than 0.5 and 0.6, respectively. The catalyst loading should be lower than 1.5 mg cm−2 when the CL porosity is higher than 0.3. The PTLs with high permeability, porosity and low contact angle is beneficial for the gas–liquid two-phase flow and avoiding the overheat and water shortage in the electrolyzer. Increasing the inlet velocity accelerates the bubble removal process, but might results in significant temperature drop, degrading the PEMWE performance. The most suitable temperature of inlet liquid is around 353.15 K. The results provide important guidance for the optimization design of high-performance PEMWE.

Development of an ion exchange process for ammonium removal and recovery from municipal wastewater using a metakaolin K-based geopolymer

Ion exchange represents a promising process for ammonium removal from municipal wastewater (MWW), in order to recover it for fertilizer production. Previous studies on ammonium ion exchange neglected the assessment of process robustness and the optimization the desorption/recovery step. This study aimed at developing a continuous-flow process of ammonium removal/recovery based on a metakaolin K-based geopolymer, named G13. Process robustness was assessed by operating 7 adsorption/desorption cycles with two types of MWW. These tests resulted in satisfactory and constant performances: operating capacity at 40 mgN L-1 in the inlet = 12 mgN gdry sorbent-1, bed volumes of treated MWW at the selected breakpoint = 199 - 226, ammonium adsorption yield = 88 - 91%. Empty bed contact time (EBCT) was decreased from 10 to 5 minutes without any reduction in performances. The NH4+ adsorption process was effectively simulated by the Thomas model, allowing a model-based assessment of the effect of EBCT reductions on process performances. An innovative desorption procedure led to high ammonium recovery yields (86 - 100%) and to a desorbed product composed primarily of KNO3 (54%w) and NH4NO3 (39%w), two salts largely used in commercial fertilizers. The energy consumption of ammonium removal/recovery with G13 resulted 0.027 kWh m-3treated WW, with a relevant reduction in comparison to traditional nitrification/denitrification, whereas the operational cost resulted equal to 60-110% of the cost of the benchmark process. These results show that G13 is a promising material to recover ammonium in a circular economy approach.

A Strategy for Quantifying Microplastic Particles in Membrane Filtration Processes using Flow Cytometry

Microplastic (MP) pollution is ubiquitous in the aquatic environment, with significant quantities of MPs originating from municipal wastewater treatment plants. Efforts to evaluate and implement MP removal processes are underway, with membrane technologies often recommended as an "ideal" solution. A key challenge in evaluating these technologies involves efficiently quantifying MP concentrations in samples. Here, flow cytometry (FC) is demonstrated as an effective technique to obtain concentration measurements of plastic microbeads (MBs; 1-5 μm) suspended in water with/without added humic acid. Regardless of solution conditions, MB concentrations were easily quantified via FC. Subsequently, two microfiltration membranes were challenged to these suspensions. As measured via FC, the 0.45 μm membrane demonstrated effective MB rejection (>99%) whereas the 5 μm membrane exhibited a broad range of rejections (40% to >95%) depending on solution conditions and filtration time. Finally, a model was formulated utilizing FC forward light scattering intensity measurements to estimate MB sizes in samples. Using the model, a 33% reduction in median MB size, on average, was noted across the 5 μm membrane when filtering MBs suspended in humic acid solution, affirming a preferential permeation of smaller particles. Overall, this study advances MP quantification techniques towards validating removal processes.

Kinetic study of the simultaneous removal of ibuprofen, carbamazepine, sulfamethoxazole, and diclofenac from water using biochar and activated carbon adsorption, and TiO2 photocatalysis

The growing number of pharmaceuticals released into the environment poses a threat not only to the aquatic environment but also to human health. This work introduces a novel approach for the simultaneous analysis of four pharmaceuticals—ibuprofen, carbamazepine, sulfamethoxazole, and diclofenac—each with distinct chemical structures. The study explores the kinetic behavior of these compounds during their removal from water, employing biochar and activated carbon as adsorbents, as well as titanium dioxide (TiO2) for photocatalytic degradation. This utilizes two distinct approaches incorporating adsorption mechanisms. The concentrations of pharmaceuticals were simultaneously measured using High Performance Liquid Chromatography with Diode Array Detection (HPLC-DAD). In addition to adsorption, photocatalysis with varying dosages of TiO2 was investigated as an alternative method for pharmaceutical removal. The HPLC- DAD analysis enabled the simultaneous monitoring of all four pharmaceuticals in a single analysis. The Langmuir-Hinshelwood model was applied to the photocatalysis data to assess reaction kinetics. The results demonstrate the efficacy of both adsorption methods in removing pharmaceutical contaminants from water. Integrating both adsorption and photocatalysis experiments in one manuscript allows for a comprehensive evaluation of these methods' individual strengths in water treatment applications, providing insights into their combined potential for addressing pharmaceutical contamination in water resources. The calculated removal efficiencies, Langmuir-Hinshelwood kinetics, half-life values, and equilibrium adsorption capacities provide a comprehensive understanding of the efficiency and mechanisms involved in the removal processes, emphasizing the importance of addressing pharmaceutical contamination in water treatment strategies.

Use of Low‐Energy Ultrasonication to Enhance the Purity and Morphology of Cellulose Nanofibers Prepared from Areca Nut Shells

AbstractThe isolation of cellulose nanofibers from areca nut shell has been successfully carried out using a simple alkaline treatment, acid hydrolysis, and followed by a morphological modification using low‐energy sonication method. The alkaline treatment consists of dewaxing and bleaching process to remove lignin, while acid hydrolysis process was carried out to remove hemicellulose. Mechanical fibrillation was carried out via ultrasonication and low‐power homogenization with 100 W cleaner and 3 W homogenizer to obtain fine fibers. Following the scanning electron microscope (SEM) result, the ultrasonicated treatment sample showed better lignin and hemicellulose removal processes and increased dispersity, as well as reduce diameter of cellulose fibers from 710.4 to 451.6 nm. The particle size analyzer (PSA) showed that the colloidal cellulose after sonication provide a frequent diameter of 56 nm. Fourier transform infrared (FTIR) spectroscopy result showed that sonication is an effective removal process of noncellulosic components. X‐ray diffraction (XRD) analysis showed that the crystallinity of nanocellulose decrease following the sonication process. Hence, low‐energy ultrasonication is a viable approach to enhance the morphology and mechanical strength of cellulose nanofiber.

Biochar-alginate beads derived from argan nutshells for effective methylene blue removal: A sustainable approach to wastewater treatment

This study explores the use of biochar derived from Argan Nutshells as a core component in alginate beads for the removal of methylene blue (MB) from aqueous solutions. The characterization of BC/Alg composite was conducted using techniques like Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), and size distribution to assess its structural properties and confirm the strong interaction between both components. The adsorbent exhibited surface functional groups characteristic of both biochar and alginate, and SEM confirmed the spherical morphology of the beads. A response surface methodology (RSM) was used to optimize the adsorption process by evaluating the effects of key parameters including pH, temperature, adsorbent mass, and dye concentration. The results showed that the BC/Alg effectively removed 96.4 % of MB. The pseudo-second order (PSO) kinetic model best described the MB removal process (R2 = 0.9990), while the Langmuir isotherm model accurately represented the adsorption equilibrium (R2 = 0.96879). After four cycles of regeneration trials, BC/Alg retained 82 % MB removal efficiency, indicating high reusability and stability. The remarkable adsorption capability of BC/Alg showed that it may be employed as an economical and environmentally friendly adsorbent in aqueous solutions, strengthening the case for employing Argan nutshells for water treatment.

Mechanism and kinetics of efficient removal of as from a high arsenic-bearing ZnSO4 solution using ultrasound enhanced oxygen

The traditional lime method for arsenic (As) removal from high arsenic-bearing ZnSO4 solution has disadvantages such as high cost, large amount of wet residue, significant secondary hazards, and long process flow. This study developed a new technology for efficient As removal using ultrasound enhanced oxygen. The effects of zinc roasting dust (ZRD) addition, reaction temperature, oxygen flow rate, and ultrasound power on As removal efficiency were investigated. Under the optimal conditions, the removal rate of As reached 97.90 %. The1O2, O2∙- and •OH radicals generated during the ultrasound-enhanced oxygen process significantly enhance the oxidation efficiency of As(III) and Fe2+. Ultrasound can also refine particle size and improve the removal efficiency of As. Compared with traditional lime method, the reaction time and wet residue amount have been reduced by 40 % and 70.37 %, respectively. Field emission scanning electron microscopy (FE-SEM-EDS), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses indicate that As in ZnSO4 solution was primarily removed through by Fe(OH)3 colloidal adsorption and amorphous FeAsO4. Kinetic analysis revealed that the neutralization and As removal process using ZRD under ultrasound and oxygen action conforms to the internal diffusion control model. Ultrasound-enhanced oxygen As removal can reduce the reaction activation energy from 26.94 to 21.02 kJ/mol, effectively lowering the reaction barrier for As removal and demonstrating faster reaction rates under ultrasound conditions. Ultrasound-enhanced oxygen removal of As from high arsenic-bearing ZnSO4 solution provides an efficient and low-cost potential solution for enterprises.

Revisit the role of hydroxylamine in sulfur-driven autotrophic denitrification

Through dedicated batch tests using the enriched sludge dominated by sulfur-oxidizing bacteria (SOB), the potential transformation of hydroxylamine (NH2OH) by SOB and the effects of NH2OH on the rate-limiting sequential reduction processes of sulfur-driven autotrophic denitrification (SDAD) were systematically explored in this study. The results indicated that NH2OH might be first converted to NO by SOB and then participate in the SDAD process, thus accelerating the utilization of S2- and contributing to the formation of N2O. Up to 3.5 mg-N/L NH2OH didn't affect the NO3- or NO2- reduction of SDAD, during which no significant changes were observed for the NH2OH concentration. Comparatively, even though NH2OH had no direct impact on the N2O reduction of SDAD, it could be consumed and therefore affect the depletion of N2O indirectly by regulating the toxic effect and electron supply of S2-. These findings provide novel implications for applying NH2OH to SDAD-based integrated processes for biological nitrogen removal.