Transcript Chemistry for Changing Times 11th Edition Hill and Kolb

Chemistry for Changing Times
12th Edition
Hill and Kolb
Chapter 14
Water: Rivers of Life;
Seas of Sorrow
John Singer
Jackson Community College, Jackson, MI
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Water: Some Unique Properties
Expands when it freezes.
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Water: Some Unique Properties
High Heat of Vaporization
Water has a very high heat of vaporization for a
liquid.
Therefore, a large amount of heat is required to
vaporize a small amount of water.
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Water: Some Unique Properties
High Specific Heat
Specific heat is the amount of heat energy
necessary to raise the temperature of 1 gram of
water 1 oC.
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Water in Nature
75% of Earth’s surface is covered with water.
Nearly 98% of that is seawater.
About 2% of Earth’s water is frozen in the polar
ice caps.
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The Water Cycle and Natural
Contaminants
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The Water Cycle and Natural
Contaminants
Natural contaminants in water include:
• Gases including radon, nonmetal oxides, and
others.
• Dissolved minerals including cations and
anions. Calcium, magnesium, and iron salts
cause hard water.
• Organic Matter: Bacteria, microorganisms,
and animal wastes are all potential
contaminants of natural waters.
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The Water Cycle and Natural
Contaminants
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Chemical and Biological
Contamination
Waterborne Disease
Contamination of water by pathogenic
organisms was a serious problem. The EPA
estimates that 30 million people in the U.S. are
threatened by bacterial contamination of water
supplies. It is estimated that 80% of all illness in
the world is caused by water contamination.
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Chemical and Biological
Contamination
Acid Rain
Sulfur and nitrogen oxides (SOx and NOx) are
deposited as acid rain. Acidic precipitation
damages the environment by lowering the pH of
soil and lakes and streams. Acid rain also can
corrode metals and dissolve limestone and
marble.
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Chemical and Biological
Contamination
Sewage and Dying Lakes
The release of sewage into waterways increases
the biochemical oxygen demand (BOD), and
leads to eutrophication (aging) of a lake.
Organic matter can undergo either aerobic or
anaerobic decay.
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Chemical and Biological
Contamination
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The Water Cycle and Natural
Contaminants
Sewage and Dying Lakes
Eutrophication is a natural process that is
accelerated by the presence of human waste
and runoff from farms, lawns, and other human
activity.
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Industrial Water Use
Manufacturing processes produce waste
products and use water resources.
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Groundwater Contamination
Approximately one-half of the U.S. population
gets its drinking water from groundwater
sources. Groundwater sources in many parts of
the country are contaminated. Groundwater is
easy to contaminate and difficult, as well as
expensive, to clean up.
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Groundwater Contamination
Nitrates
Nitrate contamination of groundwater is
particularly a problem in rural areas. Agricultural
activity contributes fertilizers and animal wastes
to water sources. Nitrates are very soluble. They
are therefore difficult to remove from water
supplies. Nitrates are a problem with infants
usually less than one year old. They metabolize
nitrate to nitrite. Nitrite ions then complex heme
and the baby can turn blue and die. This
condition is known as methemoglobinemia
(blue baby syndrome).
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Groundwater Contamination
Nitrates
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Groundwater Contamination
Volatile Organic Chemicals (VOCs)
VOCs can contaminate groundwater and add
undesirable odor to drinking water. Also, many
are carcinogenic. Sources include: industrial
activity, oil and brine wells, landfills, leaking
underground storage tanks, and illegal dumping
of organic wastes.
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Making Water Fit to Drink
More than 170,000 public water systems exist in
the United States. The per capita use of water in
the U.S. is almost 2 million liters per year. This
includes water used for industrial, agricultural,
and personal purposes. This use exceeds the
per capital use of other nations.
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Making Water Fit to Drink
The United States Safe Drinking Water Act was
first passed in 1974. It was amended in 1986
and 1996. The act authorizes the EPA to set,
monitor, and enforce national health-based
standards for contaminants in municipal water
supplies.
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Making Water Fit to Drink
The United States Safe Drinking Water Act
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Making Water Fit to Drink
Parts per Million (ppm)
1 ppm = 1 g solute
106 g solution
Parts per Billion (ppb)
1 ppb = 1 g solute
109 g solution
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Water Treatment Plants
In most urban areas, water is treated at a water
treatment plant before it is distributed to homes
for consumption.
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Water Treatment Plants
The first step in water treatment is to add slaked
lime and alum to the water:
The slaked lime and alum form the gelatinous
aluminum hydroxide, which coagulates colloidal
particles with bacteria. These are then removed by
filtering through sand and gravel filters. Charcoal is
often present in the filtering process to remove
odors and the water is aerated to improve taste.
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Water Treatment Plants
Chemical Disinfection
Chlorine is added to kill any remaining bacteria.
Municipal drinking water often contains residual
chlorine so that the water can be free from
bacteria at any point in the distribution system.
Ozone can also be used for bacterial
disinfection and has the added advantage of
killing many viruses.
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Water Treatment Plants
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Water Treatment Plants
Other Technologies
Ultraviolet light (UV) can also be used to
disinfect water. It is most effective in small-scale
applications. One disadvantage is that it does
not offer the residual protection that chlorine or
ozone does.
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Water Treatment Plants
Fluorides
Many municipal water supplies have fluoride
added to help prevent tooth decay.
Tooth enamel is composed of a calcium
phosphate complex called hydroxyapatite.
Fluoride ions replace some of the hydroxide ions,
making the enamel harder and less affected by
acids:
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Water Treatment Plants
Fluorides
Water is fluoridated by adding H2SiF6 or Na2SiF6
to a concentration 0.7-1.0 ppm. Early studies
showed a 50% to 70% reduction in dental caries
(cavities) in populations using fluoridated
drinking water.
Fluoridation of drinking water is not without
controversy. Some people object to the
fluoridation of drinking water.
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Wastewater Treatment
Before wastewater can be returned to the
environment, it should be treated to remove
harmful contaminants. Municipal wastewater
treatment is considered to involve up to three
levels of processing.
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Wastewater Treatment
Primary sewage treatment involves holding the
sewage in settling ponds to allow heavier solids
to precipitate out as sludge.
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Wastewater Treatment
Secondary sewage treatment involves passing
the effluent from the primary treatment through
sand and gravel filters. During this process,
aerobic bacteria can break down much of the
organic matter.
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Wastewater Treatment
Another form of secondary treatment is called
the activated sludge method. The sewage is
placed into tanks and aerated with large
blowers.
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Wastewater Treatment
Tertiary treatment involves further treating the
sewage, such as charcoal filtration to absorb
organic molecules, reverse osmosis, further
filtration, distillation, etc.
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Wastewater Treatment
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The Newest Soft Drink: Bottled
Water
Bottled water is the fastest growing and most
profitable segment of the beverage industry. Per
capita consumption is 90 liters per year and
growing. Many people think that drinking bottled
water is better for one’s health than drinking tap
water. In many cases, bottled water is someone
else's tap water.
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Alternative Sewage Treatment
Systems
Sludge from municipal sewage treatment
systems can be used as fertilizer.
A number of communities allow primary
treatment in settling ponds. The effluent is then
allowed to flow into marshes that filter the
sewage and use the nutrients.
Toilets have been developed that compost
wastes. Composting toilets use no energy or
water.
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We Are the Solution to Water
Pollution
Water is essential to our
quality of life. We must
do what we can to
maintain the quality of
our water sources.
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