Download Chapter 13

Chemistry for Changing Times
11th Edition
Hill and Kolb
Chapter 13
Chemistry
John Singer
Jackson Community College, Jackson, MI
© 2007 Prentice Hall
Water: Some Unique Properties
Expands when it freezes.
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.
Water: Some Unique Properties
High Specific Heat
Specific heat is the amount of heat energy to necessary
to raise the temperature of 1 gram of water 1 oC.
Water, Water Everywhere
75% of the Earth’s surface is covered
with water. Nearly 98% of that is
seawater.
The Water Cycle and Natural
Contaminants
The Water Cycle and Natural
Contaminants
Natural contaminants in water include;
Gases including as 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.
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.
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.
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 and
anaerobic decay.
Chemical and Biological
Contamination
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.
Industrial Pollution
Manufacturing processes produce waste
products and use water resources.
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.
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).
Groundwater Contamination
Nitrates
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.
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.
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.
Making Water Fit to Drink
The United States Safe Drinking Water Act
Making Water Fit to Drink
Parts per Million (ppm)
1 ppm = 1 g solute
106 g solution
Parts per Billion (ppb)
1 ppm = 1 g solute
109 g solution
Water Treatment Plants
In most urban areas, water is treated
at a water treatment plant before it is
distributed to homes for consumption.
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.
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.
Water Treatment Plants
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.
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:
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.
From Wastewater to Drinking Water
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.
From Wastewater to Drinking Water
Primary sewage treatment involves holding the sewage
in settling ponds to allow heavier solids to precipitate out
as sludge.
From Wastewater to Drinking Water
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.
From Wastewater to Drinking Water
Another form of secondary treatment is called the
activated sludge method. The sewage is placed into
tanks and aerated with large blowers.
From Wastewater to Drinking Water
Tertiary treatment involves further treating
the sewage, such as charcoal filtration to
absorb organic molecules, reverse
osmosis, further filtration, distillation, etc.
From Wastewater to Drinking Water
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.
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.
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.