Christakis A. Paraskeva

Purification of olive mill wastewater phenols through membrane filtration and resin adsorption/desorption

Olive tree cultivation has a long history in the Mediterranean countries, and even today consists an important cultural, economic, and environmental aspect of the area. The production of olive oil through 3-phase extraction systems, leads to the co-production of large quantities of olive mill wastewater (OMW), with toxic compounds that inhibit its biodegradation. Membrane filtration has been used for the exploitation of this byproduct, through the isolation of valuable phenolic compounds. In the current work, a fraction of the waste occurring from a membrane process was used. More specifically the reverse osmosis concentrate, after a nanofiltration, containing the low-molecular-weight compounds, was further treated with resin adsorption/desorption. The non ionic XAD4, XAD16, and XAD7HP resins were implemented, for the recovery of phenols and their separation from carbohydrates. The recovered phenolic compounds were concentrated through vacuum evaporation reaching a final concentration of 378 g/L in gallic acid equivalents containing 84.8 g/L hydroxytyrosol.

Three-dimensional trajectory analysis and network simulation of deep bed filtration

Abstract A three-dimensional simulator of deep bed filtration in granular porous media is developed. The void space of the porous medium is modeled as a network of unit cells of the constricted-tube type with mouth and constriction diameters distributed according to prescribed size distributions. The rate of deposition in each cell is determined using the particle trajectory analysis which requires determination of the flow field in the unit cell and of all the forces and torques acting on the particle. The overall rate of deposition, expressed in terms of the filter coefficient, is determined through a detailed numerical procedure that involves simultaneous solution of the local deposition rate equations, the mass balance equation at the nodes of the network, and the equations of perfect mixing of outgoing streams at pore intersections (nodes). Numerical results agree with the experimental observation that deposition in oblique flow channels contributes substantially to the overall rate of deposition. It is found that substitution of even a few relatively large unit cells (weak collectors) into a network of otherwise uniformly sized unit cells increases the flow rate of lateral streams and leads to higher filter coefficients thanks to high impacted fractions in transverse pores.

THREE-DIMENSIONAL TRAJECTORY ANALYSIS OF PARTICLE DEPOSITION IN CONSTRICTED TUBES

A 3-D trajectory analysis of particle deposition in unit cells of the constricted-tube type is developed. Creeping newtonian How of the suspension through the unit cells is assumed, and the flow field in each unit cell is computed using the collocation solution provided by Tilton and Payatakes (1984). Particle trajectory equations are developed for the three-dimensional case, taking into account the hydrodynamic forces and torques, gravity, the London-van der Waals force, and the double ionic layer force. The one-step trajectory approach is used to predict the rate and pattern of deposition in a unit cell of arbitrary orientation. Numerical results agree with the experimental observation that deposition in oblique flow channels contributes substantially to the overall rate of deposition. Particle size and pore geometry effects on the rate of deposition are thoroughly studied and shown to be important for various cell orientations. This method can be used in a 3-D network analysis to estimate the overall f...

Adsorption of atrazine from aqueous electrolyte solutions on humic acid and silica

The adsorption of, the still widely used, herbicide atrazine on model soil components, such as humic acid and humic acid-silica gel mixtures, was investigated in a series of batch experiments, under different experimental conditions (ionic strength, temperature, and pH). The investigation aimed at obtaining an estimate of the contribution of each of the soil components on the adsorption of atrazine from aqueous solutions. The kinetics of atrazine adsorption on humic acid showed two steps: a fast step, of a few hours duration, and a second slow step, which continued for weeks. The kinetics of adsorption data gave a satisfactory fit to the Elovich equation. Τhe adsorption of atrazine on the test substrates was found to be reversible in all cases. The atrazine uptake data on the test substrates were fitted best with the Freundlich adsorption isotherm. The ionic strength of the atrazine aqueous solutions did affect the amount of the atrazine adsorbed on the test substrates, suggesting that electrostatic forces between atrazine molecules and soil play a significant role in the adsorption process. An increase of temperature resulted in a decrease of atrazine adsorption on humic acid at low atrazine equilibrium concentrations. However, for higher levels of equilibrium concentrations (≥3 mg/L) the amount of atrazine adsorbed onto the test substrate increased as temperature increased. The calculated isosteric enthalpies of adsorption ranged between slightly exothermic at low atrazine uptake and slightly endothermic at high atrazine uptake, all values being in the range of physisorption.

High-Added Value Materials Production from OMW: A Technical and Economical Optimization

The extraction of olive oil generates huge quantities of solids and of high organic wastewaters with toxic constituents that have a great impact on land and water environments. Based on a membrane process, authors proposed an alternative method for treatment of olive mill wastewaters (OMWs). In the present paper, a technoeconomic analysis for the implementation of the proposed method in the entire Region of Western Greece (RWG) is presented. This paper takes into account fixed and operational costs, costs for the infrastructure, equipment, land, maintenance, and so forth, considering the treatment of 50,000 tons per harvesting period in the area of RWG. The study showed that the establishment of only one central treatment manufacture could reduce the uncontrolled disposal of OMW. Exploitation of the isolated fractions as manure in fertilizers (nutrients components) or as components in ecological herbicides (phenolics) can depreciate the total cost in a period of about five years.

Motion and deposition of non-brownian particles in upflow collectors

The motion and deposition of suspended particles in upflow unit cells of sinusoidal shape are studied using a three-dimensional trajectory analysis. Particle stagnation and exclusion regions can develop at the entrance mouth of upflow cells, the extent and distribution of which depend on several parameters including particle size, flow rate, cell geometry, and cell inclination. It is found that the particle exclusion phenomenon can become very significant over a wide range of the preceding parameters and can have significant implications in network-based simulations of upflow or horizontal flow depth filtration. A new definition of the impacted fraction is introduced that is based on the particle entrance velocity and the actual entrance region. Calculations of the deposition rate in sinusoidal collectors indicate that switching from a downflow to an upflow mode results in increased or decreased capture efficiency depending, chiefly, on the inclination of the unit collector.

Computation of light scattering by axisymmetric nonspherical particles and comparison with experimental results

A laboratory prototype of a novel experimental apparatus for the analysis of spherical and axisymmetric nonspherical particles in liquid suspensions has been developed. This apparatus determines shape, volume, and refractive index, and this is the main difference of this apparatus from commercially available particle analyzers. Characterization is based on the scattering of a monochromatic laser beam by particles [which can be inorganic, organic, or biological (such as red blood cells and bacteria)] and on the strong relation between the light-scattering pattern and the morphology and the volume, shape, and refractive index of the particles. To keep things relatively simple, first we focus attention on axisymmetrical particles, in which case hydrodynamic alignment can be used to simplify signal gathering and processing. Fast and reliable characterization is achieved by comparison of certain properly selected characteristics of the scattered-light pattern with the corresponding theoretical values, which are readily derived from theoretical data and are stored in a look-up table. The data in this table were generated with a powerful boundary-element method, which can solve the direct scattering problem for virtually arbitrary shapes. A specially developed fast pattern-recognition technique makes possible the on-line characterization of axisymmetric particles. Successful results with red blood cells and bacteria are presented.

Sand consolidation with calcium phosphate–polyelectrolyte composites

A new method for the consolidation of loose sand formations has been developed. The method involves in situ precipitation of a composite calcium phosphate-polyelectrolyte salt that binds together with loose sand grains, thus resulting to their consolidation. Three different polyelectrolytes (PE) were tested, i.e., polyacrylic acid (PAA), polyallylamine hydrochloride (PAH), and polyethylenimine (PEI). The effect of PE tested on the thermodynamics and the kinetics of precipitation of calcium phosphate salts was investigated. Three types of experiments were done. Investigation of the adsorption of PE on either hydroxyapatite (Ca(5)(PO(4))(3)OH, HAP) crystals or on sand grains. Measurement of the kinetics of heterogeneous nucleation of HAP on the solid substrates and the mechanical properties of the obtained crystals in batch experiments of low and high supersaturation solutions, respectively. Evaluation of the consolidation in sand packs in order to investigate the effectiveness of the method. The crystallization rates, R(p), on HAP crystals in the presence of the PE tested were found in the order R(p)(PAA)>R(p)(PEI)>R(p)(PAH), while nucleation and crystal growth on silicate sand took place only in the absence of adsorbed PE. PAH favored strongly the consolidation process, whereas PEI and PAA resulted in the formation of poorly consolidated grain agglomerates.

Simulation of Downflow and Upflow Depth Filtration of Non-Brownian Particles under Constant Flowrate or Constant Pressure Drop Conditions

The mechanistic simulator of depth filtration of non-Brownian particles in granular bids, which was reported in Burganos et al., 2001, is upgraded and used to investigate the effects of various filter design modes on particle capture efficiency and permeability. The simulation covers all stages of deposition, including extensive pore clogging. The design modes which are examined here are downflow and upflow, in combination with either constant flowrate or constant pressure drop. It is shown that the direction of the macroscopic flow relative to that of gravity has significant effects. Downflow filters clog slower than upflow ones. It is also shown that the modulating functions, which give the effect of the specific deposit on the filtration coefficient and the permeability, dipend on whether the flowrate or the pressure drop is kept constant. During the early stages of deposition, the modulating functions are virtually the same for both modes of operation, but in advanced stages of deposition substantial differences are observed. These differences are attributed to the fact that when the flowrate is kept constant (at the expense of a virtually monotonically increasing pressure drop), the flow is channeled through certain connected pathways which are composed of relatively deposit-free pores. Such pores are kept clean because the local interstitial velocity is high. This phenomenon is much weaker or even absent when the pressure drop is kept constant, in which case the flowrate decreases virtually monotonically. Another interesting new result is that both of the modulating functions depend, weakly but noticeably, on depth.