Small-scale Column Experiments Research Articles

About the Role of Porosity and Surface Chemistry of Phosphorus-Containing Activated Carbons in the Removal of Micropollutants

The preparation of phosphorus-containing activated carbons and the effect of their surface chemistry and porosity on the performance as adsorbents of paracetamol are herein reported. A parent activated carbon is prepared by chemical activation of olive stones with phosphoric acid at 500 ºC and impregnation weight ratio of 3:1. This carbon is thermal treated in inert atmosphere at 900 ºC, producing porosity shrinkage, loss of 20% of surface area and less oxidized phosphorus groups. In addition, our knowledge about the redox behavior of P-containing groups has allowed the controlled gasification of the parent activated carbon in diluted air atmosphere, developing wide micropores and mesopores, increasing 40% the specific surface area and producing more oxidized phosphorus groups. Adsorption of a model micropollutant, paracetamol, has been conducted over these activated carbons using diluted aqueous solutions (<10 mg L-1). Batch and small-scale column experiments confirmed that the presence of narrow microporosity and surface chemistry compatible with paracetamol improves the adsorption capacity, at the point of overcoming the potential effect of additional microporosity development. Moreover, the presence of a well-developed micro- and mesoporisity combined with a low surface acidity (that increases the affinity of the activated carbon surface and paracetamol) enhances the mass transfer rate of the adsorbent, improving the small-scale column performance parameters. These results also confirm that controlled gasification at high temperatures of P-containing activated carbons is an useful method for improving their behavior in micropollutant abatement.

Predicting the propagation of concentration and saturation fronts in fixed-bed filters

The phenomenon of adsorption is widely exploited across a range of industries to remove contaminants from gases and liquids. Much recent research has focused on identifying low-cost adsorbents which have the potential to be used as alternatives to expensive industry standards like activated carbons. Evaluating these emerging adsorbents entails a considerable amount of labor intensive and costly testing and analysis. This study proposes a simple, low-cost method to rapidly assess the potential of novel media for potential use in large-scale adsorption filters. The filter media investigated in this study were low-cost adsorbents which have been found to be capable of removing dissolved phosphorus from solution, namely: i) aluminum drinking water treatment residual, and ii) crushed concrete. Data collected from multiple small-scale column tests was used to construct a model capable of describing and predicting the progression of adsorbent saturation and the associated effluent concentration breakthrough curves. This model was used to predict the performance of long-term, large-scale filter columns packed with the same media. The approach proved highly successful, and just 24–36 h of experimental data from the small-scale column experiments were found to provide sufficient information to predict the performance of the large-scale filters for up to three months.

Sorbent materials for rapid remediation of wash water during radiological event relief

Procedures for removing harmful radiation from interior and exterior surfaces of homes and businesses after a nuclear or radiological disaster may generate large volumes of radiologically contaminated waste water. Rather than releasing this waste water to potentially contaminate surrounding areas, it is preferable to treat it onsite. Retention barrels are a viable option because of their simplicity in preparation and availability of possible sorbent materials. This study investigated the use of aluminosilicate clay minerals as sorbent materials to retain 137Cs, 85Sr, and 152Eu. Vermiculite strongly retained 137Cs, though other radionuclides displayed diminished affinity for the surface. Montmorillonite exhibited increased affinity to sorb 85Sr and 152Eu in the presence of higher concentrations of 137Cs. To simulate flow within retention barrels, vermiculite was mixed with sand and used in small-scale column experiments. The GoldSim contaminate fate module was used to model breakthrough and assess the feasibility of using clay minerals as sorbent materials in retention barrels. The modeled radionuclide breakthrough profiles suggest that vermiculite-sand and montmorillonite-sand filled barrels could be used for treatment of contaminated water generated from field operations.

Evaluating the long-term performance of low-cost adsorbents using small-scale adsorption column experiments

This study investigated a novel method of predicting the long-term phosphorus removal performance of large-scale adsorption filters, using data derived from short-term, small-scale column experiments. The filter media investigated were low-cost adsorbents such as aluminum sulfate drinking water treatment residual, ferric sulfate drinking water treatment residual, and fine and coarse crushed concretes. Small-bore adsorption columns were loaded with synthetic wastewater, and treated column effluent volume was plotted against the mass of phosphorus adsorbed per unit mass of filter media. It was observed that the curve described by the data strongly resembled that of a standard adsorption isotherm created from batch adsorption data. Consequently, it was hypothesized that an equation following the form of the Freundlich isotherm would describe the relationship between filter loading and media saturation. Moreover, the relationship between filter loading and effluent concentration could also be derived from this equation. The proposed model was demonstrated to accurately predict the performance of large-scale adsorption filters over a period of up to three months with a very high degree of accuracy. Furthermore, the coefficients necessary to produce said model could be determined from just 24 h of small-scale experimental data.

Rapid small-scale column tests for Cr(VI) removal by granular magnetite

This study evaluates the possibility of using magnetite as an adsorbent for the removal of Cr(VI) in a bed column setup under continuous flow conditions. For this purpose, granular magnetite was synthesized on a large scale and tested in both batch and rapid small-scale column experiments using reliable conditions of drinking water treatment. Column tests, which were designed to scale-down larger adsorption systems in terms of size, time and water flow, indicate a higher removal capacity compared to that observed during batch experiments with magnetite powder, reaching 9.2 mg/g at pH 6.4 before residual Cr(VI) exceeds 10 μg/L. The main parameters of this process, including pH, contact time and granular size, were also examined under similar column tests suggesting the improvement of the overall effectiveness and operation time at lower water pH, higher empty bed contact times and larger particle dimensions.

Enhanced U(VI) removal from drinking water by nanostructured binary Fe/Mn oxy-hydroxides

This study demonstrates the hexavalent uranium U(VI) adsorption capacity of innovative binary iron–manganese oxy-hydroxides (FMHO) as compared with the corresponding capacity of the conventional iron oxy-hydroxides (FHO). The experimental results showed that the synthesis conditions strongly influence the adsorption efficiency of the materials. For both FMHO and FHO oxy-hydroxides, those prepared at synthesis pH 5.5, showed the highest adsorptive performance and therefore were selected as qualified materials for further evaluation at NSF water matrix. The maximum U(VI) uptake of qualified FMHO at 20°C was 133mg/g, achieved at pH values between 6 and 7. This value is 25% higher than the corresponding 106mg/g of FHO. The improved U(VI) sorption efficiency of FMHO is mainly attributed to the higher specific surface area (261m2/g) as compared to qualified FHO (155m2/g). Kinetic studies showed that 95% of total uptake on FMHO was accomplished within 4h and reached equilibrium within 8h. The respective thermodynamic data indicated that U(VI) uptake onto both FMHO (ΔΗ0=13,2kJ/mol) and FHO (ΔΗ0=10.3kJ/mol) is physisorption of spontaneous and endothermic nature. Rapid small-scale column experiments showed that FMHO can successfully remove U(VI) to concentrations below the WHO recommended maximum permitted concentration in drinking water of 30μg/L, achieving the adsorption capacity of 4mg/g at 30μg/L equilibrium concentration. This value is considered adequate given that higher loadings would cause handling, transportation and disposal issues due to uranium radioactivity.

Bimetallic oxide-coated sand filter for simultaneous removal of bacteria, Fe(II), and Mn(II) in small- and pilot-scale column experiments

The aim of this study was to examine the simultaneous removal of bacteria, Fe(II), and Mn(II) by iron-manganese bimetallic oxide-coated sand (IMCS) using small-scale (length = 20 cm, inner diameter = 2.5 cm) and pilot-scale (length = 140 cm, height of filter media = 100 cm, inner diameter = 20 cm) column experiments. Small-scale column experiments showed that the Mn(II) removal capacity of IMCS (qeq = 0.027 mg g−1) was greater than that of iron oxide-coated sand (ICS) (qeq = 0.020g g−1), manganese oxide-coated sand (MCS, qeq = 0.012 mg g−1), and dual media containing ICS and MCS (qeq = 0.015 mg g−1). The Fe(II) removal capacity of IMCS (qeq = 0.034 mg g−1) was similar to that of ICS (qeq = 0.035 mg g−1), MCS (qeq = 0.035 mg g−1), and ICS/MCS (qeq = 0.034 mg g−1). Simultaneous removal experiments in small columns indicated that the bacterial removal capacity of IMCS (qeq = 7.158 mg g−1) in solution containing Fe(II) and bacteria was greater than that in solution with Mn(II) and bacteria (qeq = 4.031 mg g−1). For solutions with Fe(II), Mn(II), and bacteria, the bacterial removal capacity of IMCS was 6.636 mg g−1, which was greater than that in samples with Mn(II) and bacteria. These results indicated that bacterial removal capacity was improved in the presence of Fe(II). Pilot-scale column experiments (46-day operation) showed that the removal capacities of IMCS for Fe(II), Mn(II), and bacteria were 0.059, 0.068, and 1.187 mg g−1, respectively. The long-term experiments demonstrated that IMCS was effective as an adsorptive filter medium for the simultaneous removal of Fe(II) and bacteria. However, chemical additions might be necessary for Mn(II) removal to meet the water quality limit.

The performance of a fixed-bed treatment system packed with layered textiles for their filtration/adsorption potential for salt and organic pollutant

The main contribution of the research work presented here was to select and investigate a few commercially available textiles to study their filtration/adsorption potential for salt and total organic carbon (TOC) reduction during wastewater treatment. First, several physical–mechanical properties, such as tensile strength, thickness, weight, density and structural aspect of two woven (polyamide and polyester) and two nonwoven (polypropylene [PP] and PP/polyethylene [PE]) textiles, were determined. Also, the void amount and total void area percentage of textiles were measured, which influence the wastewater flow (clog) and filtration efficiency. With the intention of examining the adsorption ability of the selected textiles, kinetic experiments were carried out in shake-flasks using three commonly-used salts. Afterwards, small-scale column experiments were conducted in a continuous-flow operation to assess the TOC and salt reduction. It was found that both nonwoven textiles (either made from PP or from bicomponent PP/PE) with the more complex structures and a higher total void area were more suitable for the removal of salt and TOC in comparison to the efficiency of a column packed with sand/woven fabrics, regarding the type and concentration of salt as well as the contact time.

Modelling of water flow through typical Bavarian soils: 1. Estimation of hydraulic characteristics of the unsaturated zone

Over an eight-year period (1984–1991), seven experimental lysimeters filled with different soil materials from the State of Bavaria (quartz and tertiary sands, quartz and fluvioglacial gravels) were used to study water flow and tracer transport through the unsaturated zone under natural atmospheric conditions. The experiments were performed in the input—output mode using weekly water flow and tracer contents (environmental deuterium) in the precipitation and in the outflow in order to estimate the unsaturated hydraulic and transport parameters of the soils with limited measured data. This paper (Part 1) presents the evaluation of soil hydraulic parameters for tested soils, while the second paper (Part 2) is concerned with the estimation of transport parameters (dispersion, water content and possible zones with stagnant water). The estimation of the soil physical characteristics, i.e. the relationship between water pressure head and water content, performed by applying the van Genuchten model, showed a satisfactory accuracy against the measured data. Determination of the hydraulic conductivity as a function of water content using the van Genuchten-Mualem conductivity model did not yield good results, due to the fact that the theoretical water flow model based on such soil parameters was not able to fit the measured values of water content at the upper 20 cm and the cumulative water outflow simultaneously. To estimate the conductivity—water content characteristics, the inverse modelling technique was used for each lysimeter. The cumulative outflow curves were fitted to the observed outflow data by a trial-and-error procedure using the conductivity—water content relationship as the fitting function. It was shown that this method of estimating the soil characteristics yields parameters which are closer to the true values compared to those found in small-scale column experiments. The soil characteristics obtained in this part of the study were further used for modelling environmental deuterium transport through the soils (Part 2).

Evaluation of Migration of Cesium-137 Adsorbed on Fine Soil Particles through Natural Aerated Soil Layer

In order to evaluate migration of 137Cs adsorbed on fine soil particles in natural aerated soil layers, filtration constants of fine soil particles between soil and pore water were determined by the inverse analysis of the results of a large scale indoor migration test (STEM) using the soil layer samples collected from the natural aerated soil layers of Tokai and Rokkasho-mura without any disturbance. The amounts of 13,Cs which migrated through the soil layer samples with the movement of fine soil particles were also determined by the inverse analysis. The filtration constant for a loamy soil layer was larger than that for a sandy soil layer and the dependence of the filtration constant on mean diameter was the same as that obtained in small scale column experiments. On the other hand, the amount of 137Cs which migrated through the soil layer sample with the movement of fine soil particles was 0.15~6.5% of introduced 137Cs and dependent on size distribution and solidification degree of the soil layer sample. Therefore, it seems that the amount of 137Cs which migrates to a long distance with the movement of fine soil particles is small in the case of a fine and solidified soil layer. A trial evaluation of the migration of 137Cs adsorbed on fine soil particles using the result of the analysis showed that the concentration decreasing effect of Rokkasho's soil layer including the loamy soil layer was larger than that of Tokai's sandy soil layer.

Evaluation of migration of cesium-137 adsorbed on fine soil particles through natural aerated soil layer.

In order to evaluate migration of 137Cs adsorbed on fine soil particles in natural aerated soil layers, filtration constants of fine soil particles between soil and pore water were determined by the inverse analysis of the results of a large scale indoor migration test (STEM) using the soil layer samples collected from the natural aerated soil layers of Tokai and Rokkasho-mura without any disturbance. The amounts of 13,Cs which migrated through the soil layer samples with the movement of fine soil particles were also determined by the inverse analysis. The filtration constant for a loamy soil layer was larger than that for a sandy soil layer and the dependence of the filtration constant on mean diameter was the same as that obtained in small scale column experiments. On the other hand, the amount of 137Cs which migrated through the soil layer sample with the movement of fine soil particles was 0.15~6.5% of introduced 137Cs and dependent on size distribution and solidification degree of the soil layer samp...

Experimental and computational studies on propane-propylene separation by adsorption and variable-temperature stepwise desorption

An experimental adsorption and desorption study was carried out using propane-propylene gas mixtures adsorbed onto 13X molecular sieves in order to obtain a better understanding of a variable-temperature stepwise desorption (VTSD) method that has been found to have potential for industrial separations. The experimental conditions used were based on estimates of possible industrial importance. Both desorption rates and desorption equilibrium data were obtained at one atmosphere with no dilution gases, in small U-tube columns (0.012 m diameter). The desorption rates appeared to be relatively rapid and not an important factor in pilot-scale desorption in comparison with heat transfer rates. A computational method has been developed in order to calculate the composition and amounts of gases that are desorbed during variable-temperature stepwise desorption. The computed predictions ofa pilot-scale system, based on equilibrium data from small scale column experiments, were compared with pilot-scale (0.04 m diameter × 1.8 m length) experimental results and were found to provide reasonable approximations.