Mixed Adsorbents Research Articles

H and CO Co-Induced Roughening of Cu Surface in CO2 Electroreduction Conditions.

The dynamic restructuring of Cu has been observed under electrochemical conditions, and it has been hypothesized to underlie the unique reactivity of Cu toward CO2 electroreduction. Roughening is one of the key surface phenomena for Cu activation, whereby numerous atomic vacancies and adatoms form. However, the atomic structure of such surface motifs in the presence of relevant adsorbates has remained elusive. Here, we explore the chemical space of Cu surface restructuring under coverage of CO and H in realistic electroreduction conditions, by combining grand canonical DFT and global optimization techniques, from which we construct a potential-dependent grand canonical ensemble representation. The regime of intermediate and mixed CO and H coverage─where structures exhibit some elevated surface Cu─is thermodynamically unfavorable yet kinetically inevitable. Therefore, we develop a quasi-kinetic Monte Carlo simulation to track the system's evolution during a simulated cathodic scan. We reveal the evolution path of the system across coverage space and identify the accessible metastable structures formed along the way. Chemical bonding analysis is performed on the metastable structures with elevated Cu*CO species to understand their formation mechanism. By molecular dynamics simulations and free energy calculations, the surface chemistry of the Cu*CO species is explored, and we identify plausible mechanisms via which the Cu*CO species may diffuse or dimerize. This work provides rich atomistic insights into the phenomenon of surface roughening and the structure of involved species. It also features generalizable methods to explore the chemical space of restructuring surfaces with mixed adsorbates and their nonequilibrium evolution.

Effect of “black carbon” on antimony accumulation in traffic-loaded topsoil

Traffic-loaded areas have been of increasing concern due to the potential risk of carcinogenic pollutants, including antimony (Sb), which accumulates mostly in atmospheric particles (PM) and can interact with soil organic matter (Corg). The stability of Sb in topsoils was studied via the adsorption mechanism using standard soils and Corg-reach vehicle-produced particles as the unique source of “traffic” Sb. The mixed adsorbents were prepared from loamy sand and clay standard soils, and braking abrasion dust and diesel engine soot as Sb sources in atmospheric PM. Whereas the black carbon (BC), as part of Corg, disposes of exceptional adsorption properties compared to the other Corg, all adsorption experiments were performed identically on the adsorbents prepared from the original standard soils and Sb source materials and on the adsorbents prepared from the same materials annealed at 375 °C to ensure only BC participation in adsorption processes. The concentration of the Sb model solution corresponded to the average Sb content in rainwater from traffic-loaded localities. In addition to Sb, the Corg and iron (Fe) were monitored. The sorbability of Sb on the loamy sand soil mixtures increased up to 90% compared with the pure soil due to new active surface sites for Sb binding created due to the Corg added with the source material. The clay soil mixture containing 10 times more Corg compared with the loamy sand soil accumulated the Corg from the source material, which resulted in blocking active sites and a decline in Sb sorbability by up to 20%. The processes performed identically with original and annealed materials showed the same trends and confirmed the key role of BC and soil quality in the accumulation and stability of Sb in traffic-loaded topsoils. The participation of Fe in Sb surface interactions was not observed.

Comparison of cadmium and copper removal by maize cobs and mixed adsorbent from industrial effluents

The adsorbent studies with agricultural adsorbent (maize) and commercially purchased activated charcoal and bone charcoal (1:1 ratio) were carried out for the removal of copper and cadmium. The Mixed adsorbent was prepared by mixing activated charcoal and bone charcoal in 1:1 ratio for the batch studies. The activated charcoal prepared from maize cob was used as an adsorbent in order to evaluate its potential for the removal of copper and cadmium from electroplating industries. The characterization studies were performed which includes BET analysis, XRD analysis, Proximate and Ultimate analysis, pore size distribution, evaluation of particle size of the mixed adsorbent and maize cob. Adsorption studies were performed by batch experiments as a function of process parameters such as pH varying from 2, 4, 6 and 8, metal ion concentration of 50 ppm, adsorbent dosage of 0.5–5 g/L, equilibrium time varying from 150 to 180 min, and at fixed agitation rate of 180 rpm. Comparison studies were made for the mixed adsorbent and maize cobs for the removal of copper and cadmium in terms of % removal, and adsorption capacity for the process parameters pH, adsorbent dosage and contact time. In comparison with the maize cobs, the highest % removal was obtained for mixed adsorbent (Activated Charcoal + Bone Charcoal) due to the high surface area of the activated charcoal as well as negative charge from the bone charcoal which induces the synergistic effect (of the mixed adsorbent) as well as less particle size and more pore volume that enhances the % removal for three parameters that were studied in this paper. The adsorption parameters such as metal ion concentration of copper and cadmium was fixed at 50 ppm, constant agitation rate of 180 rpm, and constant temperature of 25 °C were maintained throughout study. All the findings and experimental results were discussed in detailed and presented in this paper.

Unveiling the non-equilibrium process in multilayer mixture adsorption

The Brunauer–Emmett–Teller (BET) theory [S. Brunauer et al., “Adsorption of gases in multimolecular layers,” J. Am. Chem. Soc. 60, 309–319 (1938)] constitutes a cornerstone in gas-adsorption physics. Recently, the kinetic BET equation of single-kind adsorbate has been proposed [H. Yu and X. Zhang, “Molecular-kinetic study of multilayers gas-adsorption in a rarefied gas environment,” Phys. Fluids 34, 123106 (2022)], while its counterpart of mixed adsorbates is currently unknown. Gas mixtures are commonly found in both natural and artificial systems. To address this limitation, we have proposed a kinetic BET theory for adsorbate mixtures in this paper. Moreover, we gave an analytical solution addressing low gas pressure conditions. In this condition, we predicted the “over-adsorption” of one species in the mixture with a higher desorption rate over time, and the “inertia effect” during the crowed-out process of the fast-desorbing species. Further, we also simulated the reciprocal influence of multilayer gas adsorption on the non-equilibrium fluids. Our findings provide valuable insights into gas-adsorption experiments and can facilitate technological advancements.

Pilot-Scale Experimental Investigation on Dry Capture of Mercury and SO3 in Smelting Gas of Acid Making.

In this study, a novel dry capture process utilizing a mixed adsorbent of ZnO and CuS was proposed for the simultaneous removal of Hg0 and SO3 in flue gas from zinc smelting, addressing severe mercury pollution and high SO3 concentrations. The experimental results showed that flue gas cooling caused the SO3 to transform into sulfuric acid mist, which changed the reaction mechanism from a gas-solid to a liquid-solid reaction and helped to improve the SO3 removal efficiency. Additionally, properly increasing the absorbent/SO3 molar ratio significantly improved the SO3 removal performance. However, excessive absorbent injection could cause aggregation and uneven dispersion of the absorbent particles in the flue gas, therefore impairing the effectiveness of SO3 capture. Under typical operating conditions (flue gas flow rate of 3500 m3/h, flue gas temperature of 180 °C, ZnO/SO3 molar ratio of 0.74, and residence time of 0.5 s), using a mixed absorbent of ZnO and CuS achieved an SO3 removal efficiency of up to 32.6%, and a total mercury capture at 43.2%, of which the Hg0 removal attained a remarkable 76.3%. These results preliminarily confirm the feasibility of the dry capture technology for simultaneous removal of SO3 and mercury, laying the foundation for further application and promotion.

In-situ immobilization of arsenic and antimony containing acid mine drainage through chemically forming layered double hydroxides

Acid mine drainage (AMD) rich in arsenic (As) and antimony (Sb) is considered as a significant environmental challenge internationally. However, simultaneous removal of As and Sb from AMD is still inadequately studied. In this study, a highly effective and simple approach was proposed for mitigating As and Sb-rich AMD, which involves in-situ formation of layered double hydroxides (LDHs). Following the treatment, the residual concentrations of iron (Fe), magnesium (Mg), sulfate, As and Sb in field AMD were decreased from their initial concentrations of 1690, 1524, 2055, 7.8 and 10.6 mg L−1, respectively, to 1.3, 12.4, 623, 0.006 and 0.004 mg L−1, respectively. Chemical formula of the resulting As and Sb-loaded LDHs can be identified as Mg4.226Fe2.024OH2SO4AsSb0.006∙mH2O. The dissolution rates of metal(loid)s in As and Sb-loaded LDH were lower than 1% under strongly acidic and alkaline environments. In presence of the mixed adsorbates, the As immobilization capacity by LDHs was significantly decreased, with an apparent intervention from Sb. However, As did not have a significant effect on the immobilization of Sb by LDH. As was immobilized by LDHs through anion exchange and complexation with —OH groups, while Sb was captured by anion exchange and complexation with MgH2O62+. Density functional theory (DFT) calculations further proved the above conclusions. This novel approach is effective and can be applied for in-situ AMD treatment from abandoned mines.

Novel cetyltrimethylammonium bromide modified mixed adsorbent for efficient treatment of dyeing and printing wastewater

The treatment of dyeing and printing wastewater is a formidable challenge due to its high chemical oxygen demand (COD) and chromaticity, which pose severe threats to both the environment and human health. In this study, a composite modified adsorption material was prepared based on the applicability and feasibility in practical engineering applications. A novel mixed modified adsorbent was developed by incorporating activated carbon and activated clay as the foundation materials, followed by the addition of cetyltrimethylammonium bromide (CTAB) for modification. The performance of the composite adsorbent was evaluated via adsorption experiments of bromophenol blue (BPB) solution and dyeing and printing wastewater. The results demonstrated that the mixed modified adsorbent achieved a remarkable removal rate of 99% for BPB and 99.3% for chromaticity, under the optimal adsorption conditions. Furthermore, the regeneration performance of the mixed modified adsorbent was found to be exceptional. The adsorption process of BPB by the composite adsorbent was governed by the quasi-second-order kinetic model and Freundlich isotherm model, as evidenced by adsorption kinetics and isotherm analyses. The straightforward preparation method, coupled with the superior adsorption performance, underlines the promising potential of the proposed composite adsorbent for practical applications.

Accumulation of toxic Pb(II) ions by the iron-containing minerals in the presence of ionic polyacrylamide soil conditioner

The aim of this research was to determine the adsorption–desorption, surface, electrokinetic, and stability properties of aqueous suspensions of iron-containing minerals in the presence of anionic polyacrylamide (AN PAM) and lead(II) ions. Three minerals found in the soil environment, akaganeite, goethite, and magnetite, were synthesized based on the precipitation method. The interaction mechanism of heavy metal ions with polymer flocculant, which are adsorbed on the soil mineral particles, was proposed. It was shown that the best affinity to the AN PAM or/and Pb(II), adsorbed both from single and mixed solution, shows akageneite (characterized by the highly developed specific surface area). Polymer-metal complexes formed in the mixed adsorbate systems are rather stable, evidence of which is reduced desorption and consequently limited bioavailability of toxic lead ions for organisms and plants in soil environment.

Study on electrical double layer nanostructure on zeolitic materials’ surface in the presence of impurities of different nature

The aim of the research was to compare the adsorption mechanisms of heavy metal ions (Pb(II) and Zn(II)), as well as organic substances [diclofenac molecules and pol(acrylic acid) macromolecules on the surfaces of Na-X and Na-P1 synthetic zeolites as well their Na-X© and Na-P1© carbon composites]. The single and mixed adsorbate systems were considered. The more probable structures of the formed adsorption layers were proposed based on the results of the solid surface charge density and zeta potential experiments. The great applicability of the analysis of the parameters characterizing the electrical double layer in determination of the binding mechanism of simple inorganic ions and more complex organic molecules on the surface of the examined solids from the one- and two-component solutions was proved. Moreover, the changes of the surface and electrokinetic factors after the addition of the organic molecules enable specification of drug molecule orientation as well as the polymeric chain conformation at the solid/liquid interface.

Numerical simulation and experimental investigation on thermal regeneration of spent activated carbon: Thermal desorption of mixed organic adsorbates in porous media

In the thermal regeneration of spent activated carbon, the thermal desorption of the adsorbate is the key process. In the actual desorption process, traditional models lead to inaccurate simulation results due to the presence of residual adsorbent. In this paper, a multi-phase porous media heat and mass transfer model is developed, which can calculate the thermal desorption characteristics of mixed adsorbates in spent activated carbon and reflect the presence of residual adsorbates, with a significant improvement in accuracy compared to the traditional model. The feasibility of the application of the model is verified by comparing the computational simulation results with the experimental results. Based on the simulations and theoretical analysis, it was concluded that the temperature rise and liquid phase content of the spent activated carbon samples under constant heating conditions were characterized by "fast-slow-fast" and "slow-fast-slow", respectively; the fluid flow inside the thermally regenerated samples was dominated by vapor flow The fluid flow within the thermally regenerated samples is dominated by vapor flow, with 90% of the vapor flow being viscous and the liquid flow being driven mainly by Darcy friction. In addition, the design and comparison of column and barrel shaped regeneration samples resulted in savings of up to 24.4% in thermal regeneration time for spent activated carbon at the same external temperature.

Interparticle diffusion and thermodynamic modeling studies for the removal of heavy metals using mixed adsorbents in industrial effluents

AbstractPollution of water, air, and soil by industrial effluents is a major problem nowadays. A variety of contaminants are too responsible for changing the physicochemical properties of the receiving body. There are practical treatment solutions available to clean up contaminants from various resources. The term “adsorption” refers to one of them. The purpose of the research work is to remove heavy metals from industrial effluent. Mixed adsorbents prepared from activated charcoal and bone charcoals were used to remove the copper and cadmium ions. The experiment carried out in a batch operation and modeling of these data for intraparticle diffusion and thermodynamic calculations were reported in this research work. At optimum operating condition pH 6; metal ion concentration 50 mg/L; dose 5 g/L; agitation 180 rpm and temperature 40°C maximum 99.41% copper ions and 88.12% cadmium ion removal was achieved. Cadmium ions were well fitted in the thermodynamic model compared to copper ions, as demonstrated by the higher correlation coefficient R2 (0.9824) value. Intra particle diffusion demonstrated that film diffusion was a rate‐limiting step at the start of the reaction, while microporous intraparticle diffusion was the rate‐determining phase later on. A Fourier transformation infrared spectroscopy, X‐ray diffraction, and scanning electron micrography analysis confirmed the suitability of mixed adsorbents for the removal of cadmium and copper metal ions.

Interaction mechanism of heavy metal ions with the nanostructured zeolites surface – Adsorption, electrokinetic and XPS studies

The aim of the research was to compare the mechanisms of heavy metal ions (Pb(II) and Zn(II)) adsorption on the surfaces of nanostructured synthetic zeolites: Na-X, Na-P1, their carbon composites: Na-X (C), Na-P1 (C) and the precursor of these structures - high-carbon fly ash (HC FA). The research was carried out in single and mixed adsorbate systems. Heavy metals were selected on the basis of their toxicity and their occurrence in the natural environment. The adsorption–desorption and electrokinetic data were obtained by means of inductively coupled plasma-optical emission spectrometry, potentiometric titrations and zeta potential determination. Additionally, the X-ray photoelectron spectroscopy (XPS) was applied to specify the elemental composition of the solids surfaces and the chemical forms of adsorbed metals.

Dispersive solid-phase extraction combined with high-performance liquid chromatography for determination of seven anesthetics in aquatic products

随着麻醉剂广泛用于渔业生产过程和水产品运输等领域,建立水产品中麻醉剂残留的检测方法具有重要意义。由于水产品基质复杂且麻醉剂残留水平低,因此需要合适的前处理方法以提高检测灵敏度。该研究基于分散固相萃取-高效液相色谱,建立了一种同时检测水产品中普鲁卡因、丁氧卡因、三卡因、丁香酚、甲基丁香酚、异丁香酚、甲基异丁香酚7种麻醉剂的分析方法。前处理采用分散固相萃取;确定了1.0%甲酸乙腈为提取溶剂,20 mg苯乙烯-甲基丙烯酸缩水甘油酯聚合物微球(PS-GMA)、50 mg N-丙基乙二胺(PSA)和10 mg C18混合吸附剂为净化剂,二甲基亚砜(DMSO)辅助氮吹的前处理方法;优化了提取时间和DMSO用量等条件。7种麻醉剂采用Welch welchrom C18色谱柱(250 mm×4.6 mm, 5 μm)进行分离,以甲醇和0.05%甲酸-5 mmol/L乙酸铵水溶液为流动相进行梯度洗脱,检测波长为235、260和290 nm,以鱼肉和对虾两种基质匹配标准曲线进行定量分析。实验结果表明,在优化的实验条件下,7种目标麻醉剂在各自的浓度范围内具有良好的线性关系(相关系数R2>0.999),检出限(LOD)为0.011~0.043 mg/kg。在鱼肉样品中,3个水平的平均加标回收率为79.7%~109%,相对标准偏差(RSD)低于7.2%;在对虾样品中,平均回收率为78.0%~99.9%, RSD低于8.3%。该方法具有快捷简便、操作简单、灵敏度高等优点,可应用于水产品中3种氨基苯甲酸酯类和4种丁香酚类麻醉剂的检测。

Simultaneous removal of Pb and MTBE by mixed zeolites in fixed-bed column tests

The co-contamination of metals and organic pollutants, such as Pb and methyl tert-butyl ether (MTBE), in groundwater, has become a common and major phenomenon in many contaminated sites. This study evaluated the feasibility of their simultaneous removal with permeable reactive barrier (PRB) packed with mixed zeolites (clinoptilolite and ZSM-5) using fixed-bed column tests and breakthrough curve modeling. The effect of grain size on the permeability of PRB and removal efficacy was also assessed by granular and power clinoptilolite. The replacement of granular clinoptilolite by powder clinoptilolite largely reduced the breakthrough time but increased the saturation time nearly fourfold. The column adsorption capacity of clinoptilolite powders almost tripled that of clinoptilolite granules (130.6 mg/g versus 45.3 mg/g) due to higher specific surface areas. The minimum thickness and corresponding longevity of PRB were calculated as 7.12 cm and 321.5 min when 5% of granular clinoptilolite was mixed with 5% ZSM-5 and 90% sand as mixed PRB reactive media compared with 10.86 cm and 1230.2 min for the application of powder clinoptilolite. This study is expected to provide theoretical support and guidance for the practical application of mixed adsorbents in PRBs.

Development of humic acid based adsorbents for fast and efficient removal of ammonia and organic nitrogen from super magnetic separation treated wastewater

Although super magnetic separation technology (SMS) displayed great potential in removing pollutants from wastewater, the effluent was failed to meet wastewater discharge standard due to relatively high ammonia (AN) and organic nitrogen (ON). In this study, the carbonated and sulfonated humic acid (SCHA) adsorbent was optimally prepared for removing AN from wastewater. Then, based on the carbonated HA with iron loading (CHA-Fe) in our previous study, HA based mixed adsorbent, combining SCHA with CHA-Fe was directly used to simultaneously adsorb AN and ON in wastewater. The optimally prepared SCHA showed fast and efficient adsorption of AN with removal efficiency of around 60% within 40 min, which was ascribed to the function of strong electrostatic interaction by the successfully introduced –SO3-, but cations like Ca2+, Mg2+ and Al3+ significantly reduced AN adsorption. The adsorption data were adjacent with the Langmuir adsorption model with monolayer coverage and pseudo-second-order kinetic model. The calculated maximum adsorption capacity on AN was 12.84 mg/g at 298 K, which was higher than most of the other forms of materials. The thermodynamics of AN adsorption was found to be a spontaneous and exothermic process. In addition, the mixed adsorbent could simultaneously and efficiently adsorb AN and ON from wastewater with the removal efficiency of more than 75% under a wide pH range from 6 to10. It was mainly because the mixed adsorbent could automatically regulate solution pH to neutral range, in which electrostatic adsorption of AN by SCHA and coordinated adsorption of ON by CHA-Fe was intensified. When applied in treating actual wastewater after SMS, the mixed adsorbent could fast and effectively make the wastewater meet the discharge standard (level A) in China (GB18918-2002) through regulating mixed adsorbent dosage. This work provided theoretical and technical basis for physicochemical wastewater treatment processes and developed a new strategy for treating wastewater containing AN and various organics.

Removal of chromium and Iron using mixed adsorbent for synthetic and industrial samples in a continuous column reactor

he results of the experiments showed that bed weight, flow rate, and initial metal ion concentration all play a role in the removal of Cr (III) and Fe (II). The optimized break through curve was obtained at 36cm bed height and 10ml/min for chromium where 97.5 to 100% removal was observed at a saturation time of 500-600 min. With the increase in bed height from 12cm to 36cm, both the breakthrough and saturation times for Cr (III) increased. The break through time at 12cm, 24cm, 36cm and 10ml/min for Cr (III) were 70 min, 105 min, and 35 min respectively. The saturation time for Cr (III) at 12cm, 24cm, 36cm and 10ml/min were 460 min, 490 min, and 500 min respectively. Similarly, the break through time for Fe (II) at 12cm, 24cm, 36cm and 10ml/min were 70 min, 80 min, and 100 min respectively. At 12cm, 24cm, 36cm, and 10ml/min, the saturation time for Fe (III) was 340 minutes, 360 minutes, and 430 minutes, respectively. Overall in the column performance comparison between synthetic solution and industrial effluents for chromium, synthetic solution performance was more superior at fixed volumetric flow rates of 10 ml/min and bed heights ranging from 12 cm to 36 cm But the reverse trend was observed in case of fixed bed heights of 36 cm (150 g) and variation of volumetric flow rates from 10ml/min to 30ml/min which indicates that industrial effluent performance was superior when compared to synthetic solution for heavy metal removal.

Model sorption of industrial wastewater containing Cu2+, Cd2+, and Pb2+ using individual and mixed rice husk biochar

Few studies have used biochar mixtures to remove potentially toxic elements from industrial wastewater. The present batch studies compare the adsorption of Cu 2 + , Cd 2 + , and Pb 2 + by single and mixed sorbents using rice husk feedstock (RH), rice husk biochar (RHB), ethylene-diamine-tetra-acetic acid-modified biochar (EDTA-RHB), and a mixture (MB) of these biosorbents. Metal sorption studies were carried out by varying the adsorbents, metal ion concentrations, contact time, and solution pH in a synthetic industrial wastewater. In all experiments, RHB, EDTA-RHB, and MB removed up to 98% of the metal ions within 60 min at pH 4. Kinetic studies showed that first- and second-order models gave the best fit for MB; whereas, the Freundlich model gave the best fit for the isotherm data. Results indicate that MB and EDTA-RHB treatments were more effective for adsorbing the studied heavy metals than RH or RHB. Such biosorbents could be useful in the treatment of co-existing potentially toxic elements from wastewater. • Individual and mixed biosorbents efficiently removed the heavy metals. • Double Gompertz model best fitted to the metal removal, vs. logistic, 2x logistic, or Gompertz. • Adsorption by mixed adsorbents best fitted with Freundlich compared to Langmuir model. • Mixed adsorbents had higher adsorption of Cu 2+ , Cd 2+ , and Pb 2+ in a mixture solution.

Thermodynamic and kinetic models for the removal of copper and cadmium using industrial effluents by mixed adsorbent

The potential of Activated Charcoal and bone Charcoal as a low cost material for the removal of copper and cadmium from synthetic metal solution was studied. A number of experiments were performed in order to determine the potential capacity of the adsorbent in terms of thermo Dynamic equilibrium from the batch data. The Positive values of change in Enthalpy show that the process is endothermic in nature for Cd (II) and the negative values of Change in Enthalpy shows that the process is exothermic in nature for Cu (II). The standard Gibb’s free energy values are positive which means that the process is not spontaneous in nature. The negative values of ΔS show that there is decrease in randomness at the solid/solution interface during the adsorption of copper. The study revealed that mixed adsorbent prepared by blending the activated charcoal and bone charcoal in 1: 1 ratio has more potential to act as an adsorbent for the removal of Cu and Cd from aqueous solution. The optimum temperature was found to be 40°C for both the metals. The higher correlation coefficient R2(0.9824) value shown that cadmium ions were well fitted the thermodynamic model comparing copper ions. The batch adsorption studies have been carried out for 2 hrs considering all the 6 parameters by optimizing each of them. The data obtained for optimized parameters were studied through fitting of kinetic models such as Pseudo-first order and Pseudo second order models for both Copper and Cadmium along with Correlation or regression coefficient (R2) values.

Presence of powdered activated carbon/zeolite layer on the performances of gravity-driven membrane (GDM) system for drinking water treatment: Ammonia removal and flux stabilization

Gravity-driven membrane (GDM) filtration is a promising alternative for decentralized water supply, while its widespread application was hindered by the poor removals of organics and ammonia during long-term operation. In this study, powered activated carbon (PAC) and granular zeolite were selected as typical adsorbents to investigate the impacts of pre-deposited adsorbent layers on contaminant removal and membrane fouling. Results showed that the pre-deposited PAC layers exhibited higher removal of organics than the control, while the zeolites deposited layers exhibited low removal of organics. The presence of PAC only enhanced the NH4+ removal at subsequent stable stage, while zeolites were effective in deal with sudden high NH4+ concentration due to ion exchange. The presence of mixed adsorbents layers had similar organic removal with PAC and NH4+ removal with zeolite. The pre-deposited PAC layers could effectively alleviate membrane fouling in short-term UF tests, while the stable fluxes (5.88–6.54 L/(m2·h)) in long-term GDM operation were slightly lower than the control (6.63 L/(m2·h)). The zeolites deposited layer aggravated membrane fouling in both short-term ultrafiltration and long-term GDM (5.03–3.84 L/(m2·h)), but a higher stable flux (6.10 L/(m2·h)) was observed for GDM using the mixed adsorbents. The pre-deposited adsorbent layers resulted in increased concentrations of biomass, tri-phosphate (ATP) and extracellular polymeric substances (EPS), forming cake layers with a denser structure than the control. Finally, the fouling mechanism for GDM using different adsorbent layers was proposed based on fouling analysis and characteristics of biological fouling layer. The results and conclusion in this study could provide helpful information for the application of GDM with pre-deposited adsorbent layer in treating raw water with organics and/or sudden high ammonia concentration to produce potable water.

Removal of textile azo dyes with mixed biomass of Aspergillus niger and orange peel (Citrus sinensis L. Osbeck)

This study evaluates the removal of textile dyes using mixed adsorbents prepared by the growth of Aspergillus niger in orange peels. The highest azo dye removal efficiency was obtained at pH 2, solid: liquid ratio (1: 4 g·mL-1) and time of equilibrium of 250 minutes for each dye. The concentrations of Remazol Black B (RB) and Remazol Red (RR) in both synthetic textile effluents were between 25 mg·L-1 and 100 mg·L-1. The mixed adsorbent was characterized by X-ray diffraction (XRD), spectroscopy infrared region (FTIR) and scanning electron microscopy (SEM). The results indicated that there was a 100% removal of RB and 94.85% of RR at the concentration of 25 mg·L-1. At the concentration of 100 mg·L-1, the percentages of removal reached 98.87% for RB and 96.37% for RR, respectively. The proposed mixed adsorbent was able to remove the textile dyes, presenting adsorptive capacities of 20.77 mg·g-1 and 19.28 mg·g-1 for the dyes RB and RR. Regarding the adsorption kinetics, the experimental data showed that the pseudo second order model was the one that best explained the adsorptive process. For the equilibrium results, the Langmuir model and the Langmuir-Freundlich model were the ones that best fit the experimental data of RB and RR, respectively. The mixed adsorbent produced is a promising alternative for the treatment of textile effluents.