Introduction to Desalination. Louis Theodore

that are toxic, noxious, or otherwise harmful to fish, man, or other animals.

       Water purification – Any process in which water is treated in such a way as to remove or reduce undesirable impurities.

       Water quality – The chemical, physical, or biological characteristics of water with respect to its suitability for a particular purpose.

       Water quality criteria – The specific levels of water quality that, if reached, are expected to render a body of water suitable for its designated beneficial use.

       Water quality standards – The state-adopted, EPA-approved, allowable numeric ambient water quality concentrations for surface water bodies defined for each beneficial use.

       Water recycling – Reuse of water for the same application for which it was originally used.

       Water reuse – Using treated wastewater (reclaimed water) for some beneficial purpose rather than discharging it to surface water; the deliberate use of reclaimed wastewater must be in compliance with applicable rules for a beneficial purpose (landscape irrigation, agricultural irrigation, aesthetic uses, ground water recharge, industrial uses, or fire protection).

       Water rights – The rights acquired under the law to use surface or groundwater for a specified purpose, in a given manner, and usually within the limits of a given period.

       Water softening – A treatment process designed to completely or partially remove hardness-producing ions, Ca2+ or Mg2+, from a potable water.

       Water solubility – A measure of the maximum concentration of a chemical compound that can result when it is dissolved in water.

       Water supplier – A person who owns or operates a water supply system; they can be public or private.

       Water supply system – The collection, treatment, storage, and distribution of potable water from source to consumer.

       Water surcharge – Imposition of an increased cost due to excessive water use.

       Water table – The upper level of the groundwater below which the ground is saturated with water.

       Water treatment – The purification of water to make it suitable for drinking or other beneficial uses.

       Waterlog – Occurs when water is added to land faster than it can drain.

       Watershed – The area surrounding a stream that supplies it with runoff.

       Waterway – Any body of water, other than the open sea, that is or can be employed by boats as a means of travel.

       Well – A bored, drilled, or driven shaft, or a dug hole, whose depth is greater than the largest surface dimension and whose purpose is to reach underground water supplies, or to store or bury fluids below ground.

       Wetland – An area covered or saturated permanently, occasionally, or periodically by fresh or salt water.

       WHO – World Health Organization of the United Nations, based in Geneva (www.who.int).

      Reference

      1 Theodore, L., Reynolds, J., and Morris, K. (1997). Concise Dictionary of Environmental Terms. Amsterdam, The Netherlands: Gordon and Breach Science Publishers.

3 Engineering Principles

      3.1 Introduction

      This chapter introduces the reader to the general subject of engineering principles. Seven topics are addressed in the chapter that include: the metric system, SI multiples and prefixes, conversion constants, dimensional analysis, flow diagrams, significant figures and approximate numbers, and generic problem-solving techniques. A series of illustrative examples are provided to highlight concepts presented throughout the chapter.

      3.2 The Metric System

      The need for a single worldwide coordinated measurement system was recognized over 300 years ago. Gabriel Mouton, Vicar of St. Paul in Lyons, proposed a comprehensive decimal measurement system in 1670 based on the length of one minute of arc of a great circle of the Earth. In 1671 Jean Picard, a French astronomer, proposed the length of a pendulum beating seconds as the unit of length. (Such a pendulum would have been easily reproducible, thus facilitating the widespread distribution of uniform standards). Other proposals were made, but over a century elapsed before any action was taken.

In 1790, in the midst of the French Revolution, the National Assembly of France requested the French Academy of Sciences to “deduce an invariable standard for all the measures and weights.” The Commission appointed by the Academy created a system that was, at once, simple and scientific. The unit of length was to be a portion of the Earth’s circumference. Measures for capacity (volume) and mass (weight) were to be derived from the unit of length, thus relating the basic units of the system to each other and to nature. Furthermore, the larger and smaller versions of each unit were to be created by multiplying or dividing the basic units by 10 and its multiples. This feature provided great convenience to users of the system by eliminating the need for such calculations and divisions by 16 (to convert ounces to pounds) and by 12 (to convert inches to feet). Similar calculations in the metric system could be performed simply by shifting the decimal point. Thus, the metric system is a base-10 or decimal system.

      The Commission assigned the name metre (which is now spelled meter) to the unit of length. This name was derived from the Greek word metron meaning “a measure.” The physical standard representing the meter was to be constructed so that it would equal one ten-millionth of the distance from the north pole to the Equator along the meridian of the Earth running near Dunkirk in France and Barcelona in Spain.

      The metric unit of mass, called the gram, was defined as the mass of one cubic centimeter (a cube that is 1/100 of a meter on each side) of water at its temperature of maximum density. The cubic decimeter (a cube 1/10 of a meter on each side) was chosen as the unit of fluid capacity. This measure was given the name liter.

      Although the metric system was not accepted with enthusiasm at first, adoption by other nations occurred steadily after France made its use compulsory is 1840. The standardized character and decimal features of the metric system made it well suited to scientific and engineering work. Consequently, it is not surprising that the rapid spread of the system coincided with an age of rapid technological development. In the United States, by Act of Congress in 1866, it was made “lawful throughout the United States of America to employ the weights and measures of the metric system in all contracts, dealings, or court proceedings.”

      By the late 1860s, even better metric standards were needed to keep pace with scientific advances. In 1875, the international “Treaty of the Meter,” set up well-defined metric standards for length and mass and established permanent machinery to recommend and adopt further refinements in the metric system. This treaty, known as the Metric Convention, was signed by 17 countries, including the United States. Because of the Treaty, metric standards were constructed and distributed to each nation that ratified the Convention. Since 1893, the internationally agreed-to metric standards have served as the fundamental weights and measures standards of the United States.

A total of 35 nations – including the major nations of continental Europe and most of South America – had officially accepted the metric system by 1900. Today, except for the United States and a few small countries, the entire world is using predominantly the metric system or is committed to its use. In 1971 the Secretary of Commerce, in transmitting to Congress the results of a 3-year study authorized by the Metric Study Act of 1968, recommended a program that the United States change to predominant use of the metric system through a coordinated national program.

      The International Bureau of Weights and Measures (located at Sevres France) serves as a permanent secretariat for the