Helen P. Grigoropoulou

Equilibrium and kinetic ion exchange studies of Pb2+, Cr3+, Fe3+ and Cu2+ on natural clinoptilolite

In the present study ion exchange of Pb2+, Cu2+, Fe3+ and Cr3+ on natural clinoptilolite is examined at 27 +/- 1 degree C and initial concentration of 10 meq/dm3. Equilibrium is favorable for Pb2+, unfavorable for Cu2+ and sigmoid for Cr3+ and Fe3+. Selectivity series deduced from equilibrium isotherms is Pb2+ > Cr3+ > Fe3+ > Cu2+, while when maximum exchange levels (MELs) are considered, selectivity series is Pb2+ > Cr3+ approximately = Cu2+ > or = Fe3+. Cu2+ manifests the higher value of diffusion coefficient in the clinoptilolite particles among the metals studied, equal to 1.40 x 10(-9) cm2/s. According to the fixed bed experiments the upflow rate (5-15 Bed Volumes (BV)) is influencing the breakthrough point for all metals studied. The breakthrough point varies between 12.3 BV for Pb2+ and 1.18 for Cu2+. Flow rate is also influencing the operating capacity, giving values between 0.433 meq/g(clinoptilolite) for Pb2+ and 0.053 for Fe3+. Breakthrough point values confirm the selectivity order deduced from the equilibrium isotherms, while operating capacity values confirm the selectivity order deduced from MEL experiments.

Ion exchange of Pb2+, Cu2+, Fe3+, and Cr3+ on natural clinoptilolite: selectivity determination and influence of acidity on metal uptake

In the present study ion exchange of Pb(2+), Cu(2+), Fe(3+), and Cr(3+) on natural Greek clinoptilolite was examined in terms of selectivity toward the above heavy metals in single- and multicomponent solutions in batch systems. Also examined are the influence of clinoptilolite on solution acidity and the effect of acidity on the ion exchange process. Clinoptilolite increases solution acidity due to the exchange of H(+) cations with the cations initially present in its structure. H(+) cations should be considered as competitive ones in ion exchange processes, and consequently ion exchange of metals is favored at high acidity values. Cu(2+) and Cr(3+) are the most sensitive cations with respect to acidity. Selectivity determination demonstrates that the selectivity at total concentration 0.01 N and acidity 2 in both single- and multicomponent solutions is following the order Pb(2+)>Fe(3+)>Cr(3+) > or =Cu(2+). This order is set since the first days of equilibration. However, Cu(2+) shows remarkable changes in selectivity and generally its uptake and selectivity are increasing with time. On the other hand selectivity in single metal solutions where acidity is not adjusted is following the order Pb(2+)>Cr(3+)>Fe(3+) congruent with Cu(2+).

Modeling of ion exchange of Pb2+ in fixed beds of clinoptilolite

Abstract Ion exchange of Pb 2+ on natural clinoptilolite in fixed bed and batch operations has been studied and simple models on experimental data have been applied. The operations are conducted at ambient temperature, an initial concentration of 0.01 N and at pH 4. Paterson’s model is used to describe batch kinetics, the Langmuir isotherm is used to correlate equilibrium data and a solid diffusion controlled process is used to describe the fixed bed operation. The evaluated operating capacity is in the range of 0.21–1 meq/g and the diffusion coefficient is in the range of (0.07–5.4) × 10 −12 m 2 /s. The experimental results obtained put the basic theory under question. According to these experiments, the capacity and diffusion coefficient in fixed bed systems are flow dependent and different from those measured in the batch-reactor systems. This could be explained if the type of experimental setup influenced both the equilibrium isotherm and the system behavior.

Pretreatment of natural clinoptilolite in a laboratory-scale ion exchange packed bed

The impact of the operational and chemical conditions of pretreatment upon the effective capacity of clinoptilolite has been investigated. Pretreatment tests have been performed in an ion exchange packed bed. The parameters examined for the pretreatment solution were the volumetric flow rate, the concentration, the total volume and the pH; and for washing after pretreatment the volume of washing water used. An optimal flow rate and a minimum concentration were determined, for a pretreatment that leads to a high effective capacity of the material, while pH adjustment did not result in a higher effective capacity and one washing (10 bed volumes) after pretreatment was found to be sufficient. Furthermore, the water quality (use of tap water) as well as the surface dust of the original material (about 5% w/w) did not alter its effective capacity.

Effects of pretreatment on physical and ion exchange properties of natural clinoptilolite.

Four pretreatment procedures have been applied to natural clinoptilolite to establish the influence of the pretreatment process on the properties of the material under investigation. Modification of material properties is imposed for its use in wastewater treatment via ion exchange processes. Batch pretreatment procedures as well as continuous flow column have been studied by using sodium chloride, sodium hydroxide and nitric acid solutions in deionized water. Measurements of the effective capacity, the diffusion coefficient in the solid state and examination of the crystal structure have been employed to assess the effect of each specific pretreatment on the material under test. The effective capacity is improved in all cases, by a factor of 2.4 to 3.6, while the diffusion coefficient values depend strongly on the type of pretreatment used and fall in the range of 0.03−1.37×10−8 cm2s−2 at 20°C. The crystal structure remains unaltered as evidenced by XRD measurements.

Liquid holdup and flow dispersion in zeolite packed beds

Abstract A simple tracing method, based on residence time distribution measurements, is presented for the evaluation of the liquid holdup and dispersion in zeolite packed beds. Two tracers and two different materials, one porous (zeolite clinoptilolite) and one non-porous (SiC), were used in experiments on seven packed beds of different dimensions, operating under downflow or upflow condition, in the range of superficial velocities from 0.04 to 0.61×10 −2 m / s . The corresponding superficial Reynolds number is between 0.6 and 8.50. Drainage and tracing methods are experimentally compared. The tracing techniques tested are reliable and applicable for the determination of liquid holdup and dispersion in clinoptilolite beds. Liquid holdup, as % of void volume of the bed, is 90±10% for upflow condition, independent of the superficial velocity. For downflow condition it reaches 80% for superficial velocities greater than 0.4×10 −2 m / s . Peclet numbers were determined, giving different trends for upflow and downflow conditions. For superficial velocity near 0.4×10 −2 m / s (Reynolds number near 4) and greater, Peclet numbers are identical and in the vicinity of 0.12. A discussion is conducted in order to clarify this observation. Approximate correlations are proposed for liquid holdup and Peclet number in zeolite packed beds.

COAGULATION FOR TREATMENT OF PAINT INDUSTRY WASTEWATER

ABSTRACT In the present study, the coagulation of paint industry wastewater was examined. Ferrous and aluminum sulphate and polyaluminum chloride (PACl) were used as coagulation agents and the influence of the coagulant dose and effective pH on the quality of treated wastewater was investigated. Optimum pH for FeSO4 addition was near 9.7, the required coagulant dose was about 2 g/L and average process efficiency varied between 30 and 80% in COD and between 70 and 99% in turbidity terms, for a wide spectrum of wastewater batches. In the case of Al2(SO4)3, no pH adjustment was needed and process efficiency varied between 70 and 95% in COD and between 90 and 99% in turbidity terms, for an effective dose of 2.5 g/L. Further improvement of process efficiency was possible by raising the pH of the supernatant liquid after alum-sludge sedimentation to 10. In the case of PACl optimum pH was around 7 and process efficiency was about 98% based on both quality parameters, for an effective dose of 4 g/L. Cationic polyelectrolytes were proved to have a higher potential vs. coagulation than anionic ones when acting as primary coagulants. Combination of Al2(SO4)3 or PACl with polyelectrolytes resulted in high process efficiencies, while maintaining liquid pH values at acceptable limits.

Acetaldehyde Yield and Reaction Products in the Catalytic Destruction of Gaseous Ethanol

The catalytic destruction of ethanol (0.5% v/v) over a typical three-way catalyst (Pt/Rh/Ce) and two base catalysts (1% CuO and 10% CuO on γ-Al2O3) was studied in a continuous flow reactor, under atmospheric pressure. The effect of the temperature (100--500 °C) and of the oxygen concentration (0--10% v/v) on the operation of the tested catalysts and on the product profiles is presented. The formation of acetaldehyde during the catalytic destruction of ethanol, the main concern of ethanol addition to fuels, was extremely dependent on the oxygen concentration. It is noteworthy that more acetaldehyde was produced during the oxidation of ethanol in oxygen deficit conditions than during its decomposition in the absence of oxygen. Copper addition on γ-Al2O3 enhanced acetaldehyde formation, while less acetaldehyde amounts were produced over the noble metal catalyst.

Oxygenation par le peroxyde d'hydrogene des biomasses fixees utilisees en traitement biologique des eaux

Because of their advantages as compared to flocculated biomass processes, there is now a revival of interest in fixed biomass processes: no mishaps due to bad flocculation, particularly with filamentous organisms (bulking) compact equipment owing to the ability to obtain greater biomass concentrations (several g l−1), which is impossible in flocculated biomass. In this paper, we will consider mainly bio-discs and submerged fixed bed filters. In bio-disc investigations, Hoehn and Rays (1973), Kornegay and Andrews (1968) now classical results showed that the bacterial film only acts on the surface, over a thickness which, at best, does not exceed 150 μm. At the same time, Bungays (1969) very accurate measurements showed that the film active thickness coincides with the depth where the oxygen concentration in the film is higher than the critical oxygen concentration. In submerged filters, Elmaleh (1976) and Grasmicks (1978) theoretical studies permit one to define a Useful Column Height (UCH) which corresponds to the active part of the reactor and which is superposed on the height where oxygen concentration is higher than the critical oxygen concentration. In classical devices, the UCH is relatively low: approx. 0.50-1 m. In both cases, the system is provided with oxygen through an exchange between the air and the effluent to be treated, at a gas-liquid interface. This procedure limits the O2 concentration to about 9 mg O2 l−1, at the ambient temperature. Therefore, to increase the UCH of a submerged reactor or the active thickness of a bio-disc film by increasing the oxygen penetrating depth, the oxygen partial pressure in the gas phase should be increased by either using pure oxygen or increasing total gas phase pressure. These two methods are somewhat difficult to use and we prefer to use another method: bringing dissolved oxygen directly into the liquid phase without the exchange at the gas-liquid interface. This is feasible by using an oxygen liberating labile chemical reagent i.e. hydrogen peroxide. We consider two types of fixed biomasses: the bio-discs and the submerged filters. Bio-discs. The apparatus used is shown in Fig. 1. The utilization of H2O2 resulted in a very sharp increase in the substrate removal efficiency. It is observed that the substrate removal efficiency (Figs 5 and 6) and the reduced pollution flux (Figs 4 and 7) show a maximum when these are plotted as a function of the ratio: equivalent quantity of O2 given by H2O2/O2 demanded by the effluent and as a function of dissolved oxygen in the liquid phase. Moreover, these curves suggest that oxygen acts as an inhibitor and different attempts at modeling, based on standard models of inhibiting effects, lead to the exponential model giving the lowest deviation (Fig. 8). Submerged packed reactors. The apparatus used is shown in Fig. 3. This unit is fed by urban effluents and the oxygenation in the reactor is carried out by using diluted H2O2 (0.5-1.5 N).

Soluble Phosphorus Removal Through Adsorption on Spent Alum Sludge

In the present study freshly precipitated spent alum sludge [15-75 mg Al l−1] and alum [3-15 mg Al l−1] were tested and compared for their efficiency to remove phosphorus in synthetic wastewater [10mg P l−1, 25°C, pH=6] and it was proven that pure alum is much more efficient at phosphorus removal than the spent alum sludge. The effect of the pH on phosphorus removal efficiency was studied and it was proven that maximum orthophosphate removal is achieved in pH values 5-6 in both cases, alum and spent alum sludge, although alum is efficient in a wider pH range (4-7). The effect of aging [up to two months at 25°C] on the efficiency of the spent sludge to remove phosphorus in synthetic wastewater was studied and it was proven that this efficiency is decreased through aging (up to 20% for 2 months aging). X-ray diffraction was used in order to examine whether this decrease is caused by changes in the structure of adsorbent and a mechanism was proposed to explain the above changes. Kinetics was investigated in the case of fresh and aged spent alum sludge and the pseudo-second-order chemisorption rate equation fits satisfactorily the experimental data [k: 0.286-1.048 g mmol−1 min−1, at 23-26°C]. Finally, equilibrium was studied for fresh and aged spent alum sludge and the Freundlich isotherm fitted best the experimental data suggesting heterogeneous sorption [KF=14.4-19.7, N: 0.13-0.20].