Answer to Question 1
Answer: The most acute water pollution problems in the world come from wastewater. Wastewater is water that has been used for some purpose and is returned to the environment as a liquid. Wastewater problems are greatest when the volume is large in proportion to the amount of stream flow that is available to dilute it. Wastewater comprises about 15 percent of the flow of U.S. rivers, and so good wastewater treatment is critical.
Rich, industrialized countries like the United States generate more wastewater than do poorer nations, but they also have greater capacity to treat this wastewater. In rich countries, strict legislation requires treatment facilities to be upgraded making their rivers cleaner than a few decades ago. In developing countries, untreated sewage often goes directly into rivers that also supply drinking water. A combination of poor general sanitation, nutrition, and medical care can make drinking this water deadly. Waterborne diseases such as cholera, typhoid, and dysentery are major causes of death in developing countries. Because of improper sanitation, millions of people in Asia, Africa, and South America die each year from waterborne diseases.
As people in these rapidly growing regions crowd into urban areas, drinking water becomes less safe, and waterborne pathogens flourish. In a typical sewage-treatment plant, large solid particles are screened from the water or allowed to settle and the remaining water is oxygenated to allow bacteria to break down organic matter. The water is then discharged to the environment. In advanced systems, some of the products of that breakdown, such as nitrogen and phosphorus, are removed. Most of the world's population living in developed countries is served by some kind of sewage collection and treatment system. In developing countries, however, sewage systems are less common, particularly in rural areas.
Answer to Question 2
Answer: Natural gas is important in many areas as the (relatively) clean-burning fuel of choice for the residential, commercial, and industrial sectors. Gas resources are related to oil resources in that regions that have one tend to have the other, although the quantities vary considerably. Gas is harder to ship across the sea than is oil, so proximity to markets is especially important. Gas production has provided fuel for much of the growth in electricity production that has occurred in the last 30 years.
In Europe, Russia's role in supplying the energy needs of Western Europe has grown dramatically. In recent years, gas production has expanded in the U.S. using a technique called hydrofracking, which allows the extraction of gas from rocks that previously were not considered usable resources. The method is controversial because it may cause contamination of groundwater. However, gas burns cleaner than coal or oil, and it emits less carbon dioxide per unit of heat than other fossil fuels.
World coal reserves are more abundant than oil or gas. Coal plays an important role in providing coal-rich countries such as China and the United States with energy because it is used mainly to produce electricity. Several problems hinder expanded use of coal, including air pollution and land and water impacts. Coal is a major contributor to CO2 emissions and to acid deposition, which occurs when sulfur and nitrogen oxides combine with water to form acidic precipitation. Mining also damages the land from which coal is extracted. Technologies may be developed that will allow us to use coal cleanly, but they will be expensive and may not be fully effective.
Answer to Question 3
Answer: Lithium is a metal with a wide range of uses, but it has received considerable attention in recent years because of its growing importance in batteries used in a wide variety of devices such as cell phones, laptop computers, and hybrid and electric-powered vehicles. Lithium-based batteries are attractive because they are lightweight, and they also are capable of providing relatively high voltages. Commercially valuable lithium deposits are found in several countries.
Chile and Australia each produce about a third of global output, and China and Argentina are also major producers. Bolivia has vast resources that it is only beginning to exploit, and several other countries including the United States have the potential to increase production. At present rates of production the world's reserves would last about 500 years. However, if the market for electric and hybrid vehicles expands dramatically and if those vehicles use lithium-based batteries, prices will rise and production will increase.
Given the speed of technology change and the potential for new deposits to be developed it is unlikely that world supplies of lithium will be severely limited, but it will be a mineral of considerable importance in coming years.
Answer to Question 4
Answer: The world relies heavily on fossil fuels for nearly all its energy needs. This reliance, however, cannot last indefinitely. Fossil fuels are consumed at rates far exceeding the rates at which they are created in nature. Once they are consumed they are not replaced, making them nonrenewable resources.
Wealthy and industrialized countries typically consume large amounts of energy, while poorer ountries usually consume much less. The U.S. imports roughly half of its needs, western European countries more than half, and Japan more than 90 percent. The major producer nations vary according to fuel. Given our dependence on nonrenewable fossil fuels, it is important to know for how long they will be available. Estimates of the amount of fossil fuels remaining carry a large amount of uncertainty because new deposits remain to be discovered and some deposits may be in forms or places that make them too expensive to recover.
However, we do have some idea what is available. The ratio of reserves to annual production (R/P) is an indication of the number of years the known reserves will last. World R/P ratios for oil and gas are currently 51 and 57 years, respectively, while the ratio for coal is 125 years. Thus we appear to have enough fossil fuels to last decades at least, should we choose to use them.
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How to setup and solve a half-life problem using a table of values (Question 1)
How to solve a trigonometric problem involving two right triangles (Question 2)
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