Treatment of Industrial Wastewater of Samarra Drugs Factory Using Alum

The aim of the present study is to treat the industrials wastewater of Samarra drugs factory (SDF) by using oven dried alum sludge in fixed bed column with down flow, in performing the present study actual wastewater of (SDF) is taken to perform experimental work. It also involve studying the effect of bed depth [50, 60 and 70] cm, flow rate [2, 4 and 6] L/hr and particle size [2.8 and 5] mm. The dried alum sludge packed in Pyrex column with 2.8mm diameter and50cm bed depth then increased the bed depth to become 60 and 70cm with different flow rates[2,4and 6]L/hr for every bed depth ,then used 5mm particle size with 70cm bed depth at different flow rate. The samples were tested by using atomic adsorption apparatus type [shimadzu AA-6200]. The results indicated that the best removal percent of the pollutants [Ca, Zn, Fe, Cu, Cd and pb], at 2.8mm particle size diameter and 70cm bed depth with 2L/hr flow rate. Also the results indicated that the removal percent is directly proportional with bed depth and inversely proportional with flow rate and particle size, and the removal percent different from element to another. Introduction Adsorption is the accumulation of a substance at the interface between two phases. The material adsorbed is called the adsorbate or solute and the adsorbing phase is the adsorbent. In water purification, adsorbents are used to remove organic impurities, particularly those that are nonbiodegradable or associated with taste, odor and color. Although adsorption is applied most often as a tertiary treatment for impurities present in low concentrations, recent physical-chemical processes use adsorption as a primary technique to remove soluble organics from wastewater (Donald, 1979). Adsorption from water on a fixed bed of adsorbent is a process of unsteady state mass transfer between the liquid and solid phase. The concentration of adsorbed substance in both phases is the function of both time and location in bed (Wolborska, 1999). Adsorption is commonly perforated in a packed bed where granular adsorbent is held stationary in a column and the contaminated water is contacted with adsorbent by its continuous passage through the bed. For long passage times, the adsorbent closer to the inlet of the fluid becomes Journal of Kirkuk University –Scientific Studies, vol.6, No.2, 2011 27 saturated with the contaminant at the present influent concentration. This give rise to the concentration front that divides the bed into a contaminated region and intact region. This concentration front, also called the mass transfer zone, continues to travel along the bed as more influent is being pushed into the bed. At the time the leading edge of the concentration front has reached the exit end of the bed, breakthrough is said to have been attained and the first emergence of the contaminant (usually at very low concentration) has just taken place. A breakthrough curve represents the effluent concentration history along the course of the adsorption operation. The point at which breakthrough occurs is called break point (Ruthven, 1984). Adsorption and ion exchange share so many common features in regard to application in batch and fixed-bed processes that they can be grouped together as sorption for a unified treatment. These processes involve the transfer and resulting equilibrium distribution of one or more solute between a fluid phase and particles. The partitioning of a single solute between fluid and sorbed phases or the selectivity of a sorbent towards multiple solutes makes it possible to separate solutes from a bulk fluid phase or from one another. As the processes indicate, fixed-bed operation with the sorbent in granule, bead, or pellet form is the predominant way of conducting sorption separations and purifications. Although the fixed-bed mode is highly useful, its analysis is complex. Therefore, fixed beds including chromatographic separations are given primary attention here with respect to both interpretation and prediction. Adsorption involves, in general, the accumulation (or depletion) of solute molecules at an interface. The accumulation per unit surface area is small; thus, highly porous solids with very large internal area per unit volume are preferred. Adsorbent surfaces are often physically and/or chemically heterogeneous, and bonding energies may vary widely from one site to another. We seek to promote physical adsorption or physisorption, which involves Van der Waals forces (as invapor condensation), and retard chemical adsorption of chemisorption, which involves chemical bonding (and often dissociation, as in catalysis). The former is well suited for a regenerable process, while the latter generally destroys the capacity of the adsorbent. Adsorbents are natural or synthetic materials of amorphous or microcrystalline structure. Those used on a large scale, in order of sales volume, are activated carbon, molecular sieves, silica gel and activated alumina (Keller, 1987). For treating large quantities of liquid, columns packed with adsorbent granules are generally used. The liquid is fed to either the top or bottom of the column and flows through the packing. To avoid excessive pressure drop and minimize losses in handling, the particles for packed columns are Journal of Kirkuk University –Scientific Studies, vol.6, No.2, 2011 27 usually in the range 0.4 to 2.5 mm diameter. Equilibrium between solid and liquid phases is rarely achieved in practical fixed-bed operations. Under non-equilibrium conditions, concentration gradients exist between the bulk fluid surrounding the particle and the fluid inside the particle. The steps in an adsorption process are mass transfer through the external boundary layer, internal diffusion through the porous structure, and adsorption on the interior surface. If one step is much slower than the others under a given concentration gradient, it is called the ratedetermination step or controlling resistance. The transfer of adsorbate from bulk fluid to outer surface of the particle occurs by molecular and convective diffusion. Transport of material through a boundary layer is often referred to as film diffusion. For a given weight of adsorbent, the external surface area is inversely proportional to the diameter of the particles. If film diffusion is the controlling resistance, the rate of adsorption will be inversely proportional to the particle diameter. The transfer of adsorbate from the external surface to the interior of the particle occurs by diffusion in the void space of the pores or by migration along the pore surface. With fluid-phase pore diffusion, mass transfer precedes the adsorptive phase change whereas, with solid-phase pore diffusion, mass transfer occurs after adsorption on the surface. Since solid and pore diffusion occur in parallel, the over all rate of internal transport is the sum of the two processes. The rate equation for transfer of solute from fluid to solid phase depends upon the nature of the interaction between adsorbate and adsorbent. The relative magnitudes of film and internal diffusion are determined by the particular system and conditions. The external mass transfer resistance decreases with increasing fluid velocity over the solid surface. The internal mass transfer resistance decreases with decreasing particle size since the path length for diffusion is lowered. In packed-bed operations, both external and internal mass transfers are often important (Donald, 1979). Effect of Flow rate, bed depth and particle size Flow at low flow rate, the diffusion through the surface film may be the slowest and the rate determining step. If the fluid is agitated, the thickness of the surface layer reduced and the rate of mass transfer will increase. (Weber, 1947) illustrated the effect of flow rate on the solute uptake, based on assumption that film diffusion is rate limiting in early portions of column run. They found that increased flow rate in this region may be expected to result in compression or reduction of surface film, thereby, decreasing external resistance to mass transfer. (Malkoc, 2006) found that when the flow rate was increased the time required for complete Journal of Kirkuk University –Scientific Studies, vol.6, No.2, 2011 27 column saturation decreased shallow breakthrough curve is obtained at the highest flow rate tested. This is due to the decrease in contact time between the adsorbate and the adsorbent at higher linear flow rates. Also they found that the increase in adsorption with the bed height in a fixed bed was due to the increase in adsorbent does in larger beds which provide greater surface area (or adsorption sites). (Al-Bahrani & Martine, 1977) showed that the service life of the adsorbent column increase with increasing bed depth and adsorbent capacity at a break point increases with increasing bed depth; this indicates that for deeper bed the contact time will increase. In case of using an adsorbent particles of much smaller size, that will eliminate interaparticle mass transfer resistance, so that the rate determining step is diffusion through film around each particle. (Furusawa, 1973) showed that the rate of adsorption by small particles is controlled by the rate of mass transfer from the bulk fluid phase to the solid phase, i.e, the film diffusion. The resistance offered by the solid to mass transfer becomes important as the particle size increased. Alum Sludge Alum sludge is an inescapable by-product of the processing of drinking water in water treatment works where aluminum salts is used the coagulant. Aluminum sulphate is arguably the most widely used coagulant in drinking water treatment. When aluminum sulphate is added to raw water, it dissociates into Al 3+ and SO42-. The Al 3+ ions are immediately surrounded by water molecules and hexaaquoaluminum ([Al (H2 O) 6] 3+ ) is rapidly formed. Hexaaquoaluminum formed then undergoes series of rapid hydrolytic reactions to form charged polymeric or oligomeric hydr