Filtration is a fundamental unit operation that, within the context of this volume, separates suspended particle matter from water. Although industrial applications of this operation vary significantly, all filtration equipment operate by passing the solution or suspension through a porous membrane or medium, upon which the solid particles are retained on the medium's surface or within the pores of the medium, while the fluid, referred to as the filtrate, passes through. In a very general sense, the operation is performed for one or both of the following reasons. It can be used for the recovery of valuable products (either the suspended solids or the fluid), or it may be applied to purify the liquid stream, thereby improving product quality, or both. Examples of various processes that rely on filtration include adsorption, chromatography, operations involving the flow of suspensions through packed columns, ion exchange, and various reactor engineering applications. In petroleum engineering, filtration principles are applied to the displacement of oil with gas (i.e., liquid-liquid separations), in the separation of water and miscible solvents (including solutions of surface-active agents), and in reservoir flow applications. In hydrology, interest is in the movement of trace pollutants in water systems, the purification of water for drinking and irrigation, and to prevent saltwater encroachment into freshwater reservoirs. In soil physics, applications are in the movement of water, nutrients and pollutants into plants. In biophysics, the subject of flow through a porous media touches upon life processes such as the flow of fluids in the lungs and the kidney. Although there are numerous industry-specific applications of filtration, waster treatment has historically and continues to be the largest general application of this unit operation. The objective of this chapter is to provide an overview of filtration terminology and basic engineering principles, as well as calculation methods that describe the filtration process in a generalized way. The basis equations describing the generalized process of filtration have been around for nearly 100 years, and with few refinements, continue to be applied to modern design practices. At the end of this chapter you will find four annexes. The first is a list of important terms and their definitions. These terms will help to orient you to discussions in later chapters. Next you will find a Nomenclature section that defines all the mathematical terms used in this chapter. Following this is a list of suggested references along with a critique and general synopsis of the references. This will tell you what each of the references covers and the level of coverage, along with the price of the textbook. Finally, there is a section on Questions for Thinking and Discussing to challenge you. Remember to refer to the Glossary at the end of the book if you run across any terms that are unfamiliar to you.
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