Illustrating Engineering Concepts With A Household Water Filter Pitcher

Filtration and other methods of treatment of household drinking water supplies have become common in order to prevent the potential health hazards that can be caused by the untreated tap water. Filtration is been done at several stages based on the requirements from the government body, using different types of water filters. The most common small scale water filters used in homes use activated carbon filtration along with an ion exchange resin. In this paper, we discuss several mechanical and materials engineering concepts that can be demonstrated using an inexpensive household water filter pitcher. This experiment is developed for a sophomore level engineering audience. A commercially available filter used in water pitchers is analyzed in this experiment. The filter consists of activated carbon and ion exchange resin enclosed in a cylindrical body. The pitcher and its filter element are used to perform flow rate calculations, particle size measurement and pH calculations. Also, the experiment helps the student to learn about the purification processes and the importance of activated carbon and ion exchange resins in the field of separation and purification. Introduction The use of everyday life experiences serves as a great pedagogical tool for students being exposed to engineering concepts for the first time much like a gourmet chef’s description of the preparation of their favorite dishes with "a little bit of this and little bit of that." 1 . This kind of flexible approach helps the students to develop their critical thinking skills. Pithers and Soden 2 found that college graduates are expected to learn not only the content and methods of a discipline but also to develop 'generic' abilities. These generic abilities include a heavy emphasis on critical thinking skills. Potential employers also place a high priority on critical thinking skills. In a survey of industry experts and faculty, Maricle 3 found that critical thinking was the highest rated competency expected of new college graduates. We describe here a simple but effective experiment targeted at sophomore level engineering students to engage them in critical thinking by the use of active learning methods. A commercially available pitcher-style water filter is used for this experiment. The replaceable filter element or candle consists of activated carbon particles and ion exchange resin particles in a cylindrical plastic container that fits into the clear body of the plastic pitcher. Carbon and resin particles are most widely used in separation and purification purposes. The activated carbon particles work on the adsorption principle, the trapping of impurities by strong physical bonds within the porous structure of carbon A formal definition of adsorption 4 is “The adhesion of the P ge 10714.1 Proceedings of the 2005 American Society for Engineering Education Annual Conference & Exposition Copyright © 2005, American Society for Engineering Education molecules of gases, dissolved substances, or liquids in more or less concentrated form, to the surface of solids or liquids with which they are in contact.” Commercial adsorbent materials such as carbon have enormous internal surfaces. Activated carbon has the highest volume of adsorptive porosity of any material known. Because of its large surface area (1 quart of granules = 6 football fields 5 ), activated carbon has a great ability to adsorb organic molecules of liquids or vapors. Thus, when organic contaminated water is passed through activated carbon, the contaminants are attracted and held to the internal surface walls of the pores (Fig. 1). The contaminants get adsorbed because the attraction force of the carbon surface is stronger than the forces that keep them in solution. Also, large volumes of gases, including most poisonous ones, adhere to the activated carbon particles. Thus, due to its enormous adsorption capabilities, activated carbon is popularly used in many purification applications. Moreover, the activated carbon is very economical and easily available. Various grains and seed husks include rice 6,7 , cotton-seed shell 8 , wheat, sunflower, flaxseed, linseed, corn, soybean cake, jute stalk and grape marc can be pyrolyzed to a char at low temperature. Steam activation then results in activated carbon. The carbon applications is widely used in different industries apart from water purification like food-waste management, anti-nutrients or toxin removal, sugar substitute purification, frying oil treatment, plant cell tissue culture media, enzyme immobilization supports, pharmaceutical antidotes and fermentation process isolations. Fig. 1. Activated carbon granule shown with the adsorbed impurities The ion exchange process percolates water through bead-like spherical resin materials (ionexchange resins). Ions in the water are exchanged for other ions fixed to the beads. The two most common ion-exchange methods are softening and deionization. Softening is used primarily as a pretreatment method to reduce water hardness prior to reverse osmosis (RO) processing. The softeners contain beads that exchange two sodium ions for every calcium or magnesium ion removed from the "softened" water. Deionization (DI) beads exchange either hydrogen ions for cations or hydroxyl ions for anions. The cation exchange resins, made of styrene and divinylbenzene containing sulfonic acid groups, will exchange a hydrogen ion for any cations they encounter (e.g., Na+, Ca++, Al ). Similarly, the anion exchange resins, made of styrene and containing quaternary ammonium groups, will exchange a hydroxyl ion for any anions (e.g., Cl-). The hydrogen ion from the cation exchanger unites with the hydroxyl ion of the anion Carbon particle