Ozgur Ozdemir

Color removal from textile dyebath effluents in a zeolite fixed bed reactor: Determination of optimum process conditions using Taguchi method

Taguchi method was applied as an experimental design to determine optimum conditions for color removal from textile dyebath house effluents in a zeolite fixed bed reactor. After the parameters were determined to treat real textile wastewater, adsorption experiments were carried out. The breakthrough curves for adsorption studies were constructed under different conditions by plotting the normalized effluent color intensity (C/C(0)) versus time (min) or bed volumes (BV). The chosen experimental parameters and their ranges are: HTAB concentration (C(htab)), 1-7.5 gL(-1); HTAB feeding flowrate (Q(htab)), 0.015-0.075 L min(-1); textile wastewater flowrate (Q(dye)), 0.025-0.050 L min(-1) and zeolite bed height (H(bed)), 25-50 cm, respectively. Mixed orthogonal array L(16) (4(2)x2(2)) for experimental plan and the larger the better response category were selected to determine the optimum conditions. The optimum conditions were found to be as follows: HTAB concentration (C(htab))=1g L(-1), HTAB feeding flowrate (Q(htab))=0.015 L min(-1), textile wastewater flowrate (Q(dye))=0.025 L min(-1) and bed height (H(bed))=50 cm. Under these conditions, the treated wastewater volume reached a maximum while the bed volumes (BV) were about 217. While HTAB concentration, gL(-1) (A); zeolite bed height, cm (D) and wastewater flowrate, L min(-1) (C) were found to be significant parameters, respectively, whereas, HTAB flowrate, L min(-1) (B) was found to be an insignificant parameter.

Feasibility analysis of color removal from textile dyeing wastewater in a fixed-bed column system by surfactant-modified zeolite (SMZ)

In this study, the ability of surfactant-modified zeolite (SMZ) to remove color from real textile wastewater was investigated. Tests were performed in a fixed-bed column reactor and the surface of natural zeolite was modified with a quaternary amine surfactant hexadecyltrimethylammonium bromide (HTAB). The zeolite bed that was modified at 1 g L(-1) HTAB concentration and HTAB flow rate of 0.015 L min(-1) showed good performance in removing color. Effects of wastewater color intensity, flow rates and bed heights were also studied. Wastewater was diluted several times in the ratios of 25%, 50% and 75% in order to assess the influence of wastewater strength. The breakthrough curves of the original and diluted wastewaters are dispersed due to the fact that breakthrough came late at lower color intensities and saturation of the bed appeared faster at higher color intensities. The column had a 3-cm diameter and four different bed heights of 12.5, 25, 37.5 and 50 cm, which treated 5.25, 19.50, 35.25 and 51 L original textile wastewater, respectively, at the breakthrough time at a flow rate of 0.025 L min(-1). The theoretical service times evaluated from bed depth service time (BDST) approach for different column variables. The calculated and theoretical values of the exchange zone height were found with a difference of 27%. The various design parameters obtained from fixed-bed experimental studies showed good correlation with corresponding theoretical values, under different bed heights. The regeneration of the SMZ was also evaluated using a solution consisting of 30 g L(-1) NaCl and 1.5 g L(-1) NaOH at pH 12 and temperature 30 degrees C. Twice-regenerated SMZ showed the best performance compared with the others while first- and thrice-regenerated perform lower than the original SMZ.

3-D Imaging of Inhomogeneous Materials Loaded in a Rectangular Waveguide

A Newton-type method for the reconstruction of inhomogeneous 3-D complex permittivity variation of arbitrary shaped materials loaded in a rectangular waveguide is presented. The problem is first formulated as a system of integral equations consist of the well-known data and object equations, which contain the dyadic Greens function of an empty rectangular waveguide. Two unknowns of this system are solved in an iterative fashion by linearizing one of them, i.e., the data equation in the sense of the Newton method, which corresponds to a first-order Taylor expansion of the related integral operator. Since the problem is severely ill posed by nature, a regularization in the sense of Tikhonov is applied to the data equation. A detailed numerical implementation of the method, together with some numerical examples are also given to show the capabilities and validation limits of the method.

Higher Order Inhomogeneous Impedance Boundary Conditions for Perfectly Conducting Objects

A new, simple, and fast method for the solution of electromagnetic scattering problems for perfectly conducting objects of arbitrary shape is presented. The method is based on an equivalent representation of the conducting object in terms of a circular one having a higher order impedance boundary condition on its surface. As a first result, a new universal relation between the higher order surface impedances and the shape of the object is obtained. Then, by taking advantage of this relationship, the scattering problem related to a conducting object is recast as the solution of a matrix equation whose coefficients are determined from the higher order impedances. Numerical simulations show that the method yields to accurate results, and that, it is computationally effective

A Newton method for the reconstruction of perfectly conducting slightly rough surface profiles

A new method for the reconstruction of a one-dimensional profile of a perfectly conducting rough surface illuminated by a plane wave at a fixed frequency is addressed. By a special representation of the scattered electric field, the total field in the half-space over the surface is obtained from the measured data, which leads to a nonlinear equation with a surface function as unknown. The nonlinear equation is solved iteratively via the Newton method and a regularization in the least square sense. Numerical simulations show that the method yields satisfactory reconstructions for slightly rough surface profiles.

Reconstruction of the Electromagnetic Field in Layered Media Using the Concept of Approximate Transmission Conditions

We propose a fast and stable method to reconstruct the electromagnetic field in layered media from overdetermined data on the outer boundary. This procedure can be used for instance as a data pre-processing in inversion algorithms to accurately image buried objects under known stratified structures. Our method is based on successive use of so-called approximate transmission conditions that provide accurate reconstructions for layers with sufficiently small width. The feasibility and efficiency of the proposed method are demonstrated by numerical experiments.

Electromagnetic Imaging of Closely Spaced Objects Using Matching Pursuit Based Approaches

In this letter, sparse signal recovery framework is applied for the reconstruction of two closely placed point-like objects from measured scattered electromagnetic field. Greedy matching pursuit-based algorithms are investigated as the sparsity promoting method. The performances of the matching pursuit algorithms are compared against convex relaxation methods. Orthogonal matching pursuit algorithm implemented with a flexible tree structure is shown to improve the resolution for the inverse scattering problem.

Imaging of Dielectric Objects Buried under an Arbitrary Rough Surface

A method for the reconstruction of cylindrical bodies buried in a half-space having a locally rough interface is addressed. Through the Greens function of the two-half spaces medium with rough interface the problem is reduced to the solution of a Fredholm integral equation of the first kind involving the object function related to the unknown bodies. The integral equation is solved via an application of MoM by the use of Tikhonov regularization. The method yields quite satisfactory results in the case of multi-incidence and for the objects having relatively small sizes. I. INTRODUCTION Imaging of objects buried in a layered medium constitutes an important class of problems in electromagnetic theory due to the fact that the results of such investigations have various applications in practice in the areas of detection and location of dielectric mines, non-destructive testing, determination of underground tunnels and pipelines etc. Although during the last two decades several techniques have been developed, most of them are deals with the layered backgrounds with planar boundaries (1,2). Whereas in most of the real applications the bodies are buried in layered media having rough interfaces and the roughness has a strong effect on the scattering phenomena as well as inversion algorithms. For instance, in the case of bodies buried underground the roughness of the earth surface can potentially modify object scattering returns from those with a flat interface. For that reason the problem has to be considered in its actual conditions. The main objective of this paper is to give a method to solve the inverse scattering problem related to the inhomogeneous cylindrical bodies buried in a half-space with rough interface in the case of plane wave illumination. The scattered field measurements are assumed to be performed at the far field region in the half-space not containing the bodies. For the sake of simplicity only the surfaces having one-dimensional profiles are considered. The material of the bodies are assumed to be inhomogeneous, i.e: their dielectric permittivities and con- ductivities are functions of the location. Through the Greens function of the back-ground medium with rough interface the problem is first reduced to the solution of a Fredholm integral equation of the first kind for an unknown function which is multiple of the object function and the total field. On the other hand the determination of the Greens function constitutes a separate and difficult problem. In the open literature not much work has been done in that direction except (3), which is valid only for the slightly rough surfaces. Here we give a new and general method which is based on buried object approach (BOA) given in (4), where the perturbations of the rough surface from the flat one are assumed to be buried objects in a two-part space with planar interface. The inverse scattering problem is then solved by an application of MoM to the resulting Fredholm integral equation for the object function. Since the integral equation has a continuous kernel, it is severely ill-posed and a regularization in the sense of Tikhonov is applied. The reconstructions obtained for a number of illuminations show that the method yields quite satisfactory results for the objects having relatively small sizes.

Cauchy Data Contrast Source Inversion Method

This letter introduces a computationally efficient inversion algorithm based on the contrast source inversion method for two-layered media applications. The proposed algorithm employs Cauchy data to derive an integral representation of the electromagnetic field inside the homogeneous neighborhood of the target. This representation yields a Lippmann-Schwinger-type integral equation that does not involve the background Greens function. Therefore, it provides a significant improvement in computational efficiency. Numerical experiments are provided to demonstrate the performance of the method.

Hard thresholding based compressed sensing approach for thermoacoustic tomography

In this paper we present a reconstruction method based on compressed sensing for thermoacoustic tomography. The proposed method combines hard thresholding algorithm with conjugate gradient method to solve the inverse source problem of thermoacoustic tomography. Within the compressed sensing approach, the method is applied to thermoacoustic tomography. Numerical results for two different scenarios verify that the proposed method improves the image reconstruction quality with under-sampled data.