Differential Column Batch Reactor Research Articles

Congo red adsorption with cellulose-graphene nanoplatelets beads by differential column batch reactor

Cellulose beads loaded with graphene nanoplatelets (GNP) were prepared by a physical gelation method, which was feasible under mild conditions. The phases spontaneously separate when the cellulosic solution is dropped into an acid solution, maintaining semi-spherical shapes with diameter between 3.4 and 3.9 mm, which is desirable for continuous-flow systems. Beads were tested for the removal of Congo red dye using a differential column batch reactor. Langmuir isotherm described the adsorption equilibrium, with maximum adsorption capacities of 98.1 and 139.6 mg/g for cellulose and cellulose-GNP beads. GNP increased the number of binding sites in the adsorbent. Removal efficiencies were higher than 90% within a broad range of initial concentration and sorbent loading. Static batch experiments evidenced slow kinetics for both sorbents, reaching equilibrium after 400 min. Hence, mass transfer was enhanced using a differential column batch reactor. The mass transfer coefficient, kL increased from 3.16 × 10−4 to 6.94 × 10−4 L/mg min, reaching equilibrium in half of the static adsorption time. External mass transfer resistance was minimized as turbulent flow is developed around the sorbent particles, allowing to obtain adsorption efficiencies close to 100% in a reasonably low time of 100 min. GNP promoted faster kinetics, as kL was 7.58 × 10−4 L/mg min. A model was developed to describe the adsorption dynamics based on the equilibrium. Although desorption was not favorable, cellulose-GNP beads’ direct disposal is attractive due to the sorbent’s hydrogel-like nature. A future work perspective is to evaluate these adsorbents under continuous fixed-bed operation.

Kinetic, mechanism and mass transfer impact on electrochemical oxidation of MIT using Ti-enhanced nanotube arrays/SnO2-Sb anode

In this study, a novel Ti-enhanced nanotube arrays/SnO2-Sb electrode was prepared by the sol-gel method on enhanced TiO2 nanotube arrays (ENTA). The characterization, degradation performance, oxidation mechanism and mass transfer impact of the novel electrode was investigated. Compared with the conventional Ti/SnO2-Sb electrode, our novel electrode has higher oxygen evolution potential and electrochemical stability, due to the fabrication of ENTA structure. Its application for the destruction of a common biocide of MIT (2-methyl-4-isothiazolin-3-one), the first-order rate constants were determined from 0.01 min−1 to 0.505 min−1 during the electrochemical process. The radical oxidation and non-radical oxidation of the MIT degradation contribution were quantitatively identified as 87.8% and 12.1%, respectively. Furthermore, the second-rate constant between hydroxyl radical and MIT was estimated at 3.72×109M−1S−1. The mass transfer impact was investigated with a differential column batch reactor (DCBR) under the conditions of various electrode spacing and fluid velocities. It indicated that reducing the electrode spacing and increasing the fluid velocity would enhance the mass transfer process and increase the overall oxidation rate. Meanwhile, the EE/O decreased from 17.7 kWh m−3 to 9.7 kWh m−3, and the mass transfer coefficients increased dramatically from 0.52 × 10−6 m s−1 to 2.48 × 10−6 m s−1.

Electrochemical degradation of ciprofloxacin on BDD anode using a differential column batch reactor: mechanisms, kinetics and pathways.

A growing number of electrochemical oxidation system was employed for the degradation of refractory contaminants. In this study, a boron-doped diamond (BDD) anode/Ti cathode equipped in the differential column batch reactor (DCBR) was utilized for electrochemical oxidation of ciprofloxacin (CIP). The feed solution within the DCBR system was confirmed as a uniform flow state through a computational fluid dynamics (CFD) simulation analysis. The results showed that the BDD anode/Ti cathode electrochemical system was with a high efficiency oxidation performance when treating the CIP contaminant. The CIP was completely degraded within 20 min, and over 50% DOC removed after 120 min. Therefore, two-stage electrochemical oxidation mechanism was proposed. Four major factors, the initial concentration, current density, pH, and electrolyte concentration, on the CIP degradation efficiency were systematically investigated. The CIP degradation curve followed pseudo first-order degradation kinetics. The electric efficiency per order (EE/O) of the electrochemical oxidation system was calculated to determine an optimal operation condition. Moreover, the oxidation intermediates were identified with a mass spectrometry (LC/MS/MS) and the degradation pathways were proposed in this study. The destruction of quinolone moiety and piperazine ring and fluorine substitution were the three possible degradation pathways during BDD anode oxidation process.

Electrochemical oxidation of ofloxacin using a TiO2-based SnO2-Sb/polytetrafluoroethylene resin-PbO2 electrode: Reaction kinetics and mass transfer impact

Electrochemical oxidation has been proposed for the destruction of organic contaminants; however, this process is hampered by low oxidation efficiency and high energy cost. Accordingly, we developed a TiO2-based SnO2-Sb/polytetrafluroethylene resin (FR)-PbO2 electrode that was based on TiO2 nanotubes. We tested the performance of the electrode on an antibiotic, ofloxacin, and identified the major pathway of ofloxacin oxidation. We found growing TiO2 nanotubes on Ti material increased current efficiency, and the electrical efficiency per order (EE/O, kWh/m3) for oxidation was decreased by 16.2%. Our electrode requires a large overpotential before electrons flow, which minimizes oxygen evolution, reduces hydrogen peroxide and ozone generation, and favors hydroxyl radicals (HO) production. We found the electron efficiency (EE) during oxidation was as high as 88.45%. In other words, 88.45% of the electrons that flow out of the electrode cause oxidation. The effects of current density, initial concentration, pH value and electrolyte concentration were investigated. A differential column batch reactor (DCBR) was used to simulate the performance of continuous plug flow reactor and we found that the destruction of ofloxacin followed pseudo-first order model. We also evaluated the impact of mass transfer on electrochemical performance. The effects of fluid velocity and electrode spacing on oxidation rate were evaluated by determining the mass transfer coefficient and the effectiveness factor Ω (between 0 and 1). Our experiments and calculations indicated that the mass transfer reduced oxidation rate by more than 55% (Ω<0.45) for an electrode spacing of 1cm at a fluid velocity of 0.033m/s. Unlike studies carried out using completely mixed batch reactor, the DCBR can simulate the flow conditions in pilot or full scale reactors; consequently, observed pseudo-first order rate constants in the DCBR can be used for preliminary design.

Adsorption Kinetics of Fluroxypyr Herbicide in Aqueous Solution onto Granular Activated Carbon

Fluroxypyr is a widely used herbicide whose presence in natural waters has prompted research into its removal by adsorption. This article reports a kinetics study of fluroxypyr adsorption on a commercial activated carbon. The experimental study used a micro differential column batch reactor operated at three solution flow rates and two initial fluroxypyr concentrations, establishing a differential regime in order to obtain correct experimental data. Initial rates at zero coverage permitted the external transfer coefficient k L to be calculated. Internal surface diffusion coefficients D S were determined by using the Homogeneous Surface Diffusion Model running the FAST software and taking advantage of tabulated user-oriented solutions. This model satisfactorily fits the experimental data. D S values were 2.5 × 10−14 and 4.2 × 10−14 m2 s−1 for initial concentrations of 30 and 50 mg/L, respectively. These values were confirmed by experiments in a widely used shaken batch reactor with a determined k L value.

Experimental and modeling approach to study sorption of dissolved hydrophobic organic contaminants to microbial biofilms

A biofilm reactor was developed to investigate the sorption of polycyclic aromatic hydrocarbons (PAH) as model compounds for hydrophobic organic contaminants (HOC) to intact microbial biofilms at environmentally realistic concentrations. When operated as a differential column batch reactor, the system can be used to study the thermodynamics as well as the kinetics of the exchange of HOC between an aqueous phase and microbial biofilms. Organic carbon normalized partition coefficients ( K oc) for phenanthrene, fluoranthene and pyrene were at the lower end of those known for other organic sorbents. Intra-biofilm diffusion coefficients ( D) were calculated from decrease in solute concentration over time using a model for diffusion through a plane sheet and ranged from 0.23 to 0.45×10 −9 cm 2 s −1 for the three PAH. These diffusion coefficients are about four orders of magnitude lower than those reported in literature for free aqueous solution. These data and the experimental approach presented here are useful to assess the importance of microbial biofilms for exchange processes of HOC in heterogeneous systems such as water distribution systems, membranes and aquifers, sewer systems or surface soils.

Removal of Arsenite and Arsenate Using Hydrous Ferric Oxide Incorporated into Naturally Occurring Porous Diatomite

In this study, a simplified and effective method was tried to immobilize iron oxide onto a naturally occurring porous diatomite. Experimental resultsfor several physicochemical properties and arsenic edges revealed that iron oxide incorporated into diatomite was amorphous hydrous ferric oxide (HFO). Sorption trends of Fe (25%)-diatomite for both arsenite and arsenate were similar to those of HFO, reported by Dixit and Hering (Environ. Sci. Technol. 2003, 37, 4182-4189). The pH at which arsenite and arsenate are equally sorbed was 7.5, which corresponds to the value reported for HFO. Judging from the number of moles of iron incorporated into diatomite, the arsenic sorption capacities of Fe (25%)-diatomite were comparable to or higher than those of the reference HFO. Furthermore, the surface complexation modeling showed that the constants of [triple bond]SHAsO4- or [triple bond]SAsO4(2-) species for Fe (25%)-diatomite were larger than those reference values for HFO or goethite. Larger differences in constants of arsenate surface species might be attributed to aluminum hydroxyl ([triple bond]Al-OH) groups that can work better for arsenate removal. The pH-controlled differential column batch reactor (DCBR) and small-scale column tests demonstrated that Fe (25%)-diatomite had high sorption speeds and high sorption capacities compared to those of a conventional sorbent (AAFS-50) that is known to be the first preference for arsenic removal performance in Bangladesh. These results could be explained by the fact that Fe (25%)-diatomite contained well-dispersed HFO having a great affinity for arsenic species and well-developed macropores as shown by scanning electron microscopy (SEM) and pore size distribution (PSD) analyses.

Intraparticle diffusion and adsorption of arsenate onto granular ferric hydroxide (GFH).

Porous iron oxides are being evaluated and selected for arsenic removal in potable water systems. Granular ferric hydroxide, a typical porous iron adsorbent, is commercially available and frequently considered in evaluation of arsenic removal methods. GFH is a highly porous (micropore volume approximately 0.0394+/-0.0056 cm(3)g(-1), mesopore volume approximately 0.0995+/-0.0096 cm(3)g(-1)) adsorbent with a BET surface area of 235+/-8 m(2)g(-1). The purpose of this paper is to quantify arsenate adsorption kinetics on GFH and to determine if intraparticle diffusion is a rate-limiting step for arsenic removal in packed-bed treatment systems. Data from bottle-point isotherm and differential column batch reactor (DCBR) experiments were used to estimate Freundlich isotherm parameters (K and 1/n) as well as kinetic parameters describing mass transfer resistances due to film diffusion (k(f)) and intraparticle surface diffusion (D(s)). The pseudo-equilibrium (18 days of contact time) arsenate adsorption density at pH 7 was 8 microg As/mg dry GFH at a liquid phase arsenate concentration of 10 microg As/L. The homogeneous surface diffusion model (HSDM) was used to describe the DCBR data. A non-linear relationship (D(S)=3.0(-9) x R(p)(1.4)) was observed between D(s) and GFH particle radius (R(P)) with D(s) values ranging from 2.98 x 10(-12) cm(2)s(-1) for the smallest GFH mesh size (100 x 140) to 64 x 10(-11) cm(2)s(-1) for the largest GFH mesh size (10 x 30). The rate-limiting process of intraparticle surface diffusion for arsenate adsorption by porous iron oxides appears analogous to organic compound adsorption by activated carbon despite differences in adsorption mechanisms (inner-sphere complexes for As versus hydrophobic interactions for organic contaminants). The findings are discussed in the context of intraparticle surface diffusion affecting packed-bed treatment system design and application of rapid small-scale column tests (RSSCTs) to simulate the performance of pilot- or full-scale systems at the bench-scale.

Importance of Surface Diffusivities in Pesticide Adsorption Kinetics onto Granular Versus Powdered Activated Carbon: Experimental Determination and Modeling

Three pesticides (atrazine, bromoxynil and diuron) and two granular activated carbons are involved in equilibrium and kinetic adsorption experiments. Equilibrium is represented by Freundlich isotherm law and kinetic is described by the Homogeneous Surface Diffusion Model, based on external mass transfer and intraparticle surface diffusion. Equilibrium and long-term experiments are conducted to compare Powdered Activated Carbon and Granular Activated Carbon. These first investigations show that crushing GAC into PAC improves the accessibility of the adsorption sites without increasing the number of these sites. In a second part, kinetics experiments are carried out using a Differential Column Batch Reactor. Thanks to this experimental device, the external mass transfer coefficient kf is calculated from empirical correlation and the effect of external mass transfer on adsorption is likely to be minimized. In order to obtain the intraparticle surface diffusion coefficient Ds for these pesticides, comparisons between experimental kinetic data and simulations are conducted and the best agreement leads to the Ds coefficient. This procedure appears to be an efficient way to acquire surface diffusion coefficients for the adsorption of pesticides onto GAC. Finally it points out the role of surface diffusivity in the adsorption rate. As a matter of fact, even if the amount of the target-compound that could be potentially adsorbed is really important, its surface diffusion coefficient may be small, so that its adsorption may not have enough contact time to be totally achieved.

Adsorption of Pesticides onto Granular Activated Carbon: Determination of Surface Diffusivities Using Simple Batch Experiments

The Homogeneous Surface Diffusion Model (HSDM) has been successfully used to predict the adsorption kinetics for several chemicals inside batch adsorber vessels. In addition to the adsorption equilibrium, this model is based on external mass transfer and surface diffusion. This paper presents the determination of the surface diffusion coefficient (Ds) using a differential column batch reactor (DCBR). The adsorption kinetics for three pesticides onto granular activated carbon have been established experimentally. Their corresponding three diffusion coefficients were determined by fitting the computer simulations to the experimental concentration-time data. The results show that this original apparatus increases by an order of magnitude the range of reachable diffusion coefficient compared to perfectly mixed contactors. Moreover the computed Ds values are more accurate because of the better assessment of the external mass transfer coefficient (kf) for fixed beds.

Adsorption Behaviour of Low‐Biodegradable Organics on Activated Carbon Surfaces

AbstractAdsorption isotherms of various low‐biodegradable aromatic compounds on two different activated carbons were determined experimentally and described by FREUNDLICH‐type isotherm equations. The equilibrium solid loadings derived from the measurements correlate reasonably well with the adsorbent surface areas and show decreasing values in the order 3‐nitro‐aniline ∼ 4‐chloroaniline &gt; 3.5‐dinitrobenzoic acid &lt; phenylurea. Kinetic experiments in a differential column batch reactor were conducted in order to evaluate liquid‐phase mass transfer and intraparticle diffusion parameters. The homogeneous surface diffusion model could be successfully applied for calculating surface diffusivities and predicting experimental concentration/time profiles.