Adsorptive removal of Drimarine Red HF-3D dye from aqueous solution using low-cost agricultural waste: batch and column study

This study involves the utilisation of peanut husk for the removal of Drimarine Red HF-3D dye from aqueous solutions. Batch study experiments were conducted with native, HNO₃-treated and Na-alginate-immobilised peanut husk biomass. Maximum dye removal (95.24 mg/g) was obtained with HNO₃-treated biomass. The experimental data were successfully explained with a pseudo-second-order kinetic model for all types of biosorbents. The equilibrium data fitted well to the Freundlich adsorption isotherm model. A thermodynamic study was also carried out to check the nature of the adsorption process. A fixed-bed column study for Drimarine Red HF-3D was carried out to optimise the effect of bed height, flow rate and initial dye concentration using peanut husk biomass. The column study showed that biosorption capacity increased with the increase in initial dye concentration and bed height, but decreased with increased flow rate. Data for Drimarine Red HF-3D were in very good agreement with the bed depth service time model. Fourier transform infrared analysis demonstrated the involvement of different functional groups in dye biosorption. These results showed that peanut husk biomass possessed good potential for the removal of Drimarine Red HF-3D from aqueous solution.     

Removal of Novacron Golden Yellow dye from aqueous solutions by low-cost agricultural waste: Batch and fixed bed study

The present work describes the removal of Novacron Golden Yellow (NGY) dye from aqueous solutions using peanut hulls. The experiments were performed with native, pretreated and immobilised forms of peanut hulls. The effect of various operational parameters (pH, biosorbent dose, initial dye concentration and temperature etc.) was explored during batch study. NGY showed maximum removal at low pH and low biosorbent dose. High initial dye concentration facilitated the biosorption process. Maximum dye removal with native, pretreated and immobilised biomass was found to be 35.7, 36.4 and 15.02 mg/g respectively. The experimental data were subjected to different kinetic and equilibrium models. The kinetic data confirmed the fitness of pseudo-second-order rate law for NGY biosorption. The equilibrium modelling was carried out by Freundlich, Langmuir and Temkin models. The isothermal data of NGY removal were best described by Freundlich adsorption isotherm. Negative values of Free energy change (Δ G⁰) for NGY with native and pretreated biomass depicted the spontaneous nature of biosorption process. In column mode, the effects of bed height, flow rate and initial dye concentrations were optimised. Maximum NGY biosorption (7.28 mg/g) was observed with high bed height, low flow rate and high initial concentration in continuous mode. Bohart–Adams model best fitted to the data obtained from column studies. The results indicated that the peanut hulls could be used effectively for the removal of dyes containing wastewater.     

Fixed-bed column sorption of borate onto pomegranate seed powder-PVA beads: a response surface methodology approach

Pomegranate seed powder (PS) was functionalized with polyvinyl alcohol (PVA) and utilized for boron removal from the aqueous system. Results of Brunauer--Emmett--Teller (BET) surface area analysis and Boehm titration indicated notable decrease in total surface area and increase in acidic surface functional groups of PS after PVA modification. Enhanced sorption is indicative of complex formation between diol groups of the pomegranate seed powder--polyvinyl alcohol (PS–PVA) and borate ions. Under column test, the saturated sorption capacity of boron was noted to be dependent on flow rate and bed height. The developed central composite design (CCD) was adequate to elucidate the sorption mechanism. Mathematical modeling of the column data was conducted, and a modified-dose-response model was the most suitable to describe the breakthrough curve and observed to be consistent with CCD analysis. This is further supported by extensive error analyses conducted between the model predicted and experimental data.     

Chromium (VI) biosorption by immobilized Aspergillus niger in continuous flow system with special reference to FTIR analysis

Aspergillus niger was treated with acid and immobilized in calcium alginate matrix. The dynamic removal of Cr (VI) ion was studied using continuously fed column packed with immobilized biosorbent beads. Column experiments were carried out to study the effect of various bed heights (20, 30, 40 cm) under different flow rates (5, 7.5, 10 ml min(-1)) on efficiency of biosorption. The maximum time (1020 minutes; 17 hr) before breakthrough point was observed in case of 40 cm bed height with flow rate of 5ml min(-1). FTIR analysis of acid treated immobilized A. niger was used fora qualitative and preliminary analysis of chemical functional groups present on its cell wall which provided the information on nature of cell wall and Cr (VI) interaction during the process of biosorption. The IR spectra of biosorbent recorded before and after chromium biosorption had shown some changes in the band patterns, which were finally analyzed and was found that chemical interaction such as ion-exchange between carboxyl (-COOH), hydroxyl (-OH) and amine (-NH2) group of biosorbent and Chromium ion were mainlyinvolved in biosorption of Cr (VI) onto A. niger cell wall surface. The biosorbed metal was eluted from biosorbent by using 0.1 M H2SO4 as eluant. Immobilized biosorbent could be reused for five consecutive biosorption and desorption cycles without apparent loss of efficiency after its reconditioning. Considering all above factors together this paper discusses the efficient chromium biosorption process carried out by immobilized A. niger biosorbent.     

A novel polyacrylonitrile–zeolite nanocomposite to clean Cs and Sr from radioactive waste

Radioactive wastes containing Cs⁺ and Sr²⁺ are among the most dangerous environmental pollutants. Therefore, removing Cs⁺ and Sr²⁺ from environmental media is needed. Removal can be done by nanocrystalline ion exchangers. Nanocrystalline ion exchangers are studied in depth for the treatment of nuclear wastes because these exchangers have high exchange capacity and fast kinetics. However, operating the columns of these exchangers is very difficult. This issue may be overcome by the preparation and use of nanocomposites. Here, we prepared a novel polyacrylonitrile–zeolite nanocomposite for the removal of Cs⁺ and Sr²⁺ in a fixed-bed column operation. We studied the effect of influent flow rate, nanocomposite bed height and initial concentrations. Experimental data were analysed using the Thomas model and the bed-depth service time model. The results reveal that total adsorbed ion and bed capacity increased with increasing initial ions concentration and bed height; and decreased with increasing influent flow rate. The maximum bed capacity was 0.085 meq/g for Cs⁺ and 0.128 meq/g for Sr²⁺. The critical bed height (Z ₀) was 4.35 cm for Cs⁺ and 2.89 cm for Sr²⁺. These findings demonstrate that the new nanocomposite is suitable for removal of Cs⁺ and Sr²⁺.     

D201树脂对双组分萘系化合物的吸附分离

用D201强碱性阴离子交换树脂自双组分水溶液中选择吸附分离1-氨基-2-萘酚-4-磺酸(1,2,4-酸)和2-萘酚,考察了溶液pH值、浓度、温度、树脂床高及流速等因素对吸附和分离系数的影响.结果表明,在pH 3—6时,树脂对1,2,4-酸有较高的吸附量及吸附选择性,利于1,2,4-酸与2-萘酚的选择性吸附分离.温度对吸附的影响较小,等温吸附规律符合Freundlich模型.动态吸附表明,至1,2,4-酸的泄漏点时,吸附流出液中几乎只含2-萘酚,1,2,4-酸被吸附于树脂上.随着树脂床层的增长或初始浓度和流速的减小,都使泄漏点推迟及分离系数提高.载酚酸的树脂柱可用15%质量比的NH4Cl和20%体积比的乙醇混合液定量洗脱1,2,4-酸.     

固体聚硅硫酸铁混凝剂的表面形貌及混凝效能

以水玻璃、硫酸亚铁及氯酸钠为原料,采用共聚法制备不同Si/Fe摩尔比的聚硅硫酸铁(PFSS)混凝剂,通过两种方式固化:(1)将未稀释的PFSS经自然干燥制成凝胶状样品;(2)将不同聚合反应时间的PFSS稀释后干燥制成粉末状样品.用扫描电镜及X射线衍射仪对其表面形貌及成分进行观察和分析,对比粉末状固体PFSS与液体PFSS的混凝性能.结果表明,两种固化手段制备的PFSS表面形貌完全不同,其中凝胶状样品没有孔隙、连接紧密,而粉末状样品是松散的片状或晶须状结构,Si/Fe摩尔比对样品的表面形貌有很大影响.PFSS不是原料的简单复配,而是"硅铁反应的共聚物".反应时间对固体PFSS混凝性能的影响小于对液体PFSS的影响,制备液体和固体混凝剂需要不同的反应时间.与液体PFSS相比,固体PFSS的除浊性能随Si/Fe摩尔比的增加逐渐下降,而除UV254的性能却逐渐升高.延长沉淀时间有利于固体PFSS混凝性能的提高.     

Steady Shallow-Water Current and Solute Transport around a Semi-Conical Headland

Laboratory experiments have been carried out to investigate the effects of a sloping wall headland on the flow characteristics and the associated concentration distributions from a point source around the headland. A semi-conical headland with a slope of 1:2 was set up in a flow basin, 4.8 m long and 3.8 m wide. In this paper, the experimental results of a steady shallow-water current are reported. Three dimensional flow velocities in the basin were measured using Sontek-ADV instrument. The dye concentration levels in the basin were measured by two fluorometers. The experimental results showed a large-scale re-circulation region behind the semi-conical headland. The peak turbulence energy, at about 53% of the local kinetic flow energy, coincides with the region of high velocity gradient. Significant vertical flows were observed around the area near the downhill slope of the headland, with a maximum ratio of vertical to horizontal velocities being about 22%. Such relatively significant vertical scouring velocities, coupled with strong turbulence energy and high horizontal velocity gradients in the same region, could cause severe bed erosion. The experimental results have also been compared with the predicted results of a depth-averaged numerical model. The predicted eddy structure and the concentration distribution in the re-circulation area were found to compare favourably with the experimental results. However, the discrepancies in the flow velocities and the concentration levels near the headland were apparent. It was observed that the dye concentration continued to spread in the cross-stream direction after passing the headland, whereas only a limited extent of the lateral spreading was predicted by the numerical model further downstream of the headland.     

改性天然沸石的除氟性能研究

高效除氟材料的应用能降低饮用水中的氟质量浓度.采用静态吸附实验,比较了天然沸石和实验室制得的氢氧化铝、硫酸铝、聚合硫酸铁(PFS)改性天然沸石的除氟性能.结果表明,PFS改性的天然沸石具有良好的除氟效果,静态除氟容量可达25 mg·g~(-1).通过动态吸附试验,进一步探讨了饮用水的氟质量浓度、流速、停留时间、床层高度等因素对PFS改性天然沸石除氟性能的影响.研究发现,原水氟质量浓度越低,最佳除氟停留时间越短,PFS改性天然沸石滤柱床层高度越小.当停留时间为68 s,滤柱床层高度为47 mm时,含氟为5.8 mg·L~(-1)的模拟水样经吸附滤柱后,其氟质量浓度降到0.95 mg·L~(-1),低于国家生活饮用水标准的上限值1 mg·L~(-1).当含氟为4.14 mg·L~(-1)时,停留时间缩短为58 s,最小床层高度为40 mm;含氟为2.5 mg·L~(-1)时.停留时间为47 s,最小床层高度为32 mm,出水即可符合国家生活饮用水标准.因此,可根据不同高氟水地区的氟质量浓度来确定停留时间和床层高度,从而确定材料的适宜用量和流量.     

Cleaning of water contaminated by heavy metals using beetroot fibers as biofilter

We report for the first time the use of beetroot fibers to eliminate heavy metals from polluted water. This biomass is used to remove lead, copper and zinc ions. The kinetics and beetroot fibers fixation capacities of lead, zinc and copper according to various physico‐chemical parameters such as pH, and the concentration of metal solutions were studied. The experiments were carried out in a laboratory column with fixed bed. For kinetic studies, samples of metal solutions were taken at regular intervals and measured by atomic absorption spectrometry. pH at 6.6 shows a maximum retention of the above cited metals by beetroot fibers (98%, 92%, 90% respectively). Quantity of cations retained by this biomass in simple and mixture solution is respectively estimated to be 23.6, 14.02 and 14.64 mg/g. Results indicate the usefulness of this biomass in the remediation of water contaminated by heavy metals by a rapid, practical and efficient method.     

Urea formation from carbon dioxide and ammonia at atmospheric pressure

Urea synthesis, currently the largest use of carbon dioxide in organic synthesis, is conventionally operated at high pressure and high temperature. Here, we report for the first time that urea forms at atmosphere and ambient temperatures by negative corona discharge in gas phase. The conversion of CO₂ and yields of a solid mixture of urea and ammonium carbamate, which was identified by the ¹³C NMR spectrum, rise with reducing temperatures and increasing molar ratios of NH₃/CO₂ and discharge frequencies. The conversion of carbon dioxide was found to be 82.16?% at 20?°C and 1?atm with a molar flow ratio of n(NH₃)/n(CO₂) of 2.5. High pressure and high temperature as energy inputs are not necessary.     

Hydrodynamics and bed stability of open channel flows with submerged foliaged plants

In this work we investigate experimentally and numerically the flow structure around foliaged plants deployed in a channel with gravels on the bed under submerged and barely submerged conditions. Velocity and Reynolds stress were measured by using a NORTEK Vectrino profiler. Visual observation shows that the initial motion of gravels is easier to be triggered under the condition of flow with barely submerged vegetation. This is confirmed by the measured velocity, Reynolds stress and total kinetic energy (TKE) profiles. The velocity exhibits a speed up in the near-bed region, and the associated Reynolds stress and TKE increase there. A 3D numerical model is then verified against the experiments and used to investigate systematically the effect of degree of submergence of foliaged plants on the channel bed shear stress. The results show that the maximum bed shear stress occurs when the foliage is situated slightly below the water surface, which can enhance channel bed instability.     

Pier scour within long contraction in cohesive sediment bed

In the present study, an attempt has been made to study the bridge pier scour embedded long contraction for the bed sediment prepared by a mixture of clay and fine sand with varying proportions having a specific range of antecedent moisture content. Results particularly focused on the clay–sand mixed cohesive bed at varying clay fractions of the sediment bed, approach flow velocity, contraction ratio and different pier shapes, on maximum equilibrium scour depth for pier scour within long contraction. Further, regression based equations for the estimation of non-dimensional maximum scour depth for piers within long contraction in clay–sand mixed cohesive bed embedded were proposed.     

Hydrodynamics and contaminant transport on a degraded bed at a 90-degree channel confluence

Channel confluences at which two channels merge have an important effect on momentum exchange and contaminant diffusion in both natural rivers and artificial canals. In this study, a three-dimensional numerical model, which is based on the Reynolds Averaged Navier–Stokes equations and Reynolds Stress Turbulence model, is applied to simulate and compare flow patterns and contaminant transport processes for different bed morphologies. The results clearly show that the distribution of contaminant concentrations is mainly controlled by the shear layer and two counter-rotating helical cells, which in turn are affected by the discharge ratio and the bed morphology. As the discharge ratio increases, the shear flow moves to the outer bank and the counter-clockwise tributary helical cell caused by flow deflection is enlarged, leading the mixing happens near the outer bank and the mixing layer distorted. The bed morphology can induce shrinkage of the separation zone and increase of the clockwise main channel helical cell, which is initiated by the interaction between the tributary helical cell and the main channel flow and strengthened by the deep scour hole. The bed morphology can also affect the distortion direction of the mixing layer. Both a large discharge ratio and the bed morphology could lead to an increase in mixing intensity.     

Electrochemical degradation of Acid Red I dye and its treatment by UV light

Degradation of Acid Red I (ARI) dye by electrochemical treatment and UV light irradiation was studied in this work. The effect of the current density and the concentration of NaCl and dye on the decoloration and degradation efficiency were studied and optimized. The UV irradiation was monitored by UV-Vis spectrophotometry and chemical oxygen demand. The kinetic constants for decoloration and degradation were calculated. Degradation of 86% was achieved in 160?min and the first-order kinetic constant was 0.013?min^?1. Degradation products were identified by gas chromatography/mass spectrometry. The mechanism for the degradation of ARI was proposed.     

Dynamics of the head of gravity currents

The present work experimentally investigates the dynamics of unsteady gravity currents produced by lock-release of a saline mixture into a fresh water tank. Seven different experimental runs were performed by varying the density of the saline mixture in the lock and the bed roughness. Experiments were conducted in a Perspex flume, of horizontal bed and rectangular cross section, and recorded with a CCD camera. An image analysis technique was applied to visualize and characterize the current allowing thus the understanding of its general dynamics and, more specifically, of the current head dynamics. The temporal evolution of both head length and mass shows repeated stretching and breaking cycles: during the stretching phase, the head length and mass grow until reaching a limit, then the head becomes unstable and breaks. In the instants of break, the head aspect ratio shows a limit of 0.2 and the mass of the head is of the order of the initial mass in the lock. The average period of the herein called breaking events is seen to increase with bed roughness and the spatial periodicity of these events is seen to be approximately constant between runs. The rate of growth of the mass at the head is taken as a measure to assess entrainment and it is observed to occur at all stages of the current development. Entrainment rate at the head decreases in time suggesting this as a phenomenon ruled by local buoyancy and the similarity between runs shows independence from the initial reduced gravity and bed roughness.     

Visualization of the internal flow properties and the material exchange interface in an entraining viscous Newtonian gravity current

In order to simulate a simple entraining geophysical flow, a viscous Newtonian gravity current is released from a reservoir by a dam-break and flows along a rigid horizontal bed until it meets a layer of entrainable material of finite depth, identical to the current. The goal is to examine the entrainment mechanisms by observing the interaction between the incoming flow and the loose bed. The sole parameter varied is the initial volume of the gravity current, thus altering its height and velocity. The gravity current plunges or spills into the entrainable bed and the velocity of the flow front becomes linear with time. The bed material is directly affected: motion is generated in the fluid far downstream of, and in that lying beneath the encroaching front. Shear bands are identified, separating horizontal flow downstream from flow with a strong vertical component close to the step. Downstream of the step the flow is horizontal and stratified, with no slip on the bottom boundary and very low shear near the surface. Between these two regions may lie transitional zones with linear velocity profiles, separated by horizontal bands of high shear; the number of transitional zones in the cross-section varies with the initial volume of the dam-break.     

Equilibrium,kinetic, and quantum chemical studies on the adsorption of Congo red using Imperata cylindrica leaf powder activated carbon

Leaf powder of spear grass, otherwise known as Imperata cylindrica (IC), was used to prepare activated carbon. The Imperata cylindrica activated carbon (ICAC) prepared was used for the removal of Congo red (CR) dye from aqueous solution. Operation parameters such as initial dye concentration, contact time, adsorbent dosage, pH, and temperature were studied in batch systems. Equilibrium was attained in 150 and 180?min at lowest and highest concentrations, respectively. Maximum adsorption was observed at pH 3. Quantum chemical studies suggested that the protonation of aniline groups and minimal molecular size at planar geometry coupled with electrostatic interaction enhances the adsorption at low pH. Adsorption data were tested using pseudo-first-order and second-order reaction kinetics; the latter was found to be more suitable with a coefficient of determination of ≥0.99. The adsorption process fits Langmuir isotherm model better than the Freundlich model, with a maximum monolayer coverage of 313?mgg^?1. This study shows that ICAC is effective in removing CR dye from aqueous solutions.     

Equilibrium studies on the adsorption of acid dye into chitin

We report the adsorption isotherm of acid dye on the surface of chitin, a unique solid adsorbent. Adsorption process offers an attractive benefit for a dyeing house treatment. Influences of essential kinetic parameters such as adsorbent particle size, reaction temperature governing the dye adsorption have been investigated. Adsorptions isotherms of dye on chitin were developed and the equilibrium data fitted well to the Langmuir, Freundlich and Redlich Peterson isotherm model. At optimum conditions maximum dye adsorption capacity of chitin estimated with the Langmuir 44.0, 85.0, 104.3 mg/g and 85.0, 114.10, 113.62 mg/g adsorbent. The results showed that chelating polymer of chitin could be considered as potential adsorbents for acid dye removal from dilute solution.