CK-12 Engineering: An Introduction for High School
Page 6
unintended consequences
When we use water we decrease its quality
increase its quality
do not affect its quality
improve its quality
Review Answers
To Engineer Is Human
b
a,b,c,d
b
a
d
b,c
a,b,c,d
a,d
d
a
Water and Disease: A Case Study
Do you ever wonder how diseases spread? Water serves as a carrier or transmitter of many diseases. In fact, many of the world’s diseases are dependent on water for their transmission. These diseases often occur in large epidemics and can be quite catastrophic. A large part of water engineering is maintaining water quality so the water that we receive when we turn on our kitchen faucets is potable. In addition to making water safe for drinking, water engineering is also about transporting water from its source into our homes and to the areas where we live.
In this section we will investigate cholera, a waterborne disease; we will learn about the scientific problem solving that verified that cholera was transmitted by water. We will then begin to investigate how engineers help society manage our water supply. This topic will be expanded in later sections.
Background Information: Cholera
Figure 3.4
Microscopic view of cholera bacteria.
Cholera is an acute intestinal infection caused by ingestion of contaminated water or food. The infection is caused by the Vibrio cholerae bacterium (Figure 4). This bacterium typically travels through water that is contaminated by human or animal feces. Human beings can contract cholera by ingesting water or food contaminated by the V. cholerae bacterium. Symptoms of cholera include diarrhea, abdominal cramps, nausea, vomiting, and dehydration. As the human body does not produce lasting immunity against the cholera bacterium, it is possible that the disease can be contracted more than once. When people die from cholera, it is generally due to severe dehydration caused by the illness. When left untreated cholera generally has a high mortality rate. A cholera outbreak can be widespread, causing a large scale epidemic in which hundreds or thousands of people die.
Activity
Research and review resources on cholera epidemics on the World Wide Web. Refer to encyclopedias from your school library or local library. Prepare a short list of answers that do no exceed words for each of the following questions. You might use some of these suggested phrases for searching on the Internet: cholera, epidemics, cholera and water, water-borne diseases, water contamination sources, water quality, water purification.
What were some of the major cholera epidemics of the past?
What are some of the major cholera epidemics of the present?
Where and under what conditions did the cholera epidemics occur?
What role did water play in these cholera epidemics?
How can the quality of water be maintained so the water does not get contaminated from bacteria such as the cholera bacterium?
The 1854 Case of Cholera in London
In 1854, hundreds of people living in London died during a cholera epidemic. At that time, very little was known about how the disease was transmitted. Many believed that people could contract diseases such as cholera by breathing bad or foul air. It is estimated that 616 people died during this epidemic. If not for the intervention of Dr. John Snow (b. 1813–d. 1858), who carefully mapped the number of deaths that occurred around water sources, primarily the Broad Street pump, and then worked with other officials to remove its handle, the cholera epidemic of 1854 in London would have been more widespread. It was later discovered that sewage was contaminating the water source for the Broad Street pump. Preventing people from using this pump stopped the use of water from that source. This action has been credited with greatly reducing the number of deaths during this epidemic.
Dr. Snow created the map in Figure 5. The Snow map depicted the area around the Broad Street pump where the number of deaths is indicated by dark blocks at the homes and establishments around the pump.
During an earlier cholera epidemic in London in 1848 and 1849, Snow had proposed the unusual idea that cholera was caused by something that was ingested orally, rather than by inhaling foul air. During the cholera epidemic of 1854 in London, Snow collected data by carefully interviewing people around Broad Street who had not been infected by the water they had been drinking. Others would cite, after Snow’s death in 1858, that the data he had collected supporting his theory that cholera was primarily spread by sewage-contaminated water. Dr. Snow’s research into the spread of cholera locally around the Broad Street pump is an important lesson taught even today to epidemiology students as a model of scientific reasoning. Dr. Snow authored a report about the cholera outbreak in the Parish of St. James, Westminster, during the Autumn of 1854; this as well as his other works are available online at the John Snow Archive and Research Companion website.
Figure 3.5
Number of deaths at 40 Broad Street. Deaths at homes are indicated by dark lines.
Today most of us know that unclean water carries bacteria that cause disease. We value clean water. However, in the 1800s, the idea that water could carry disease was frightening to many. During that time many people believed that catastrophic diseases such as cholera were visitation of retribution for sinful living of the poor. Dr. Snow had to work hard to convince the local authorities to remove the handle of the Broad Street pump. Now, people know that cholera infection can be avoided by drinking clean water. During the twentieth century, in the western hemisphere, incidences of cholera in the recent past are almost nonexistent. However, it is estimated by the World Health Organization (WHO) that in developing nations only % of the population have access to clean water.
According to the WHO, the current response to cholera outbreaks tends to mostly in the form of emergency response whenever there is an outbreak. While emergency response is very important and prevents many deaths, it does not help prevent causes of cholera. Therefore, one cannot emphasize enough the importance of long-term cholera prevention. Key to the prevention of cholera and other waterborne diseases is closely related to the prevention of water contamination and water purification. Separating sewage water from natural water sources, treatment of sewage water, treatment of water resources, and purification of water for storage and delivery for human consumption are key elements of such a strategy that involve engineering solutions. In addition, medical research, personal hygiene, and public health education will play a key role in the prevention of cholera epidemics.
Water Engineering and Management
Figure 3.6
Water towers such as this one help distribute clean water to surrounding communities.
One of our significant challenges today is to obtain water for people and for food production, look after critical ecosystems and habitats, and deal with the variability and uncertainty of water on our earth. Water engineers and managers need to understand the complexity of water use and water resources management. Water for human consumption includes engineering solutions related to water supply and sanitation; management of water treatment and distribution systems (Figure 6); storm water, domestic wastewater, and urban drainage; and sustainable management of water for urban and rural areas. Water for food production includes the use of water for agricultural purposes which necessitates engineering solutions related to planning, design, implementation, operation, and maintenance of irrigation and drainage projects. Water for energy production includes the use of engineering solutions such as dams for hydroelectric power. Water management is also related to engineering solutions for uncertain events such as flooding caused by natural and human activities.
Review Questions
The following questions will help you assess your understanding of this section. There may be one, two, three, or even four correct answers to each question. To demonstrate your understanding, you should
find all of the correct answers.
Water engineers are concerned with ensuring that water is drinkable
drinking eight glasses of water a day
transporting water to our homes
marketing bottled water
An example of a disease caused by contaminated water is a cold
colessus
Cholera
colitis
We can prevent waterborne diseases by washing our hands
public health education
vaccinations
visits to the doctor
Water engineers look for solutions to mitigate overfishing the oceans
natural flooding
building ships
human caused flooding
Review Answers
Water and Disease: A Case Study
a,c
c
b
b,d
Reflection Questions
Why do North Americans not have to worry about cholera?
When we travel abroad to some countries, we are advised to receive a cholera vaccination. Why is it necessary to receive a cholera vaccination?
Further Reading
Johnson, Steven. The Ghost Map (The Story of London’s Most Terrifying Epidemic and How It Changed Science, Cities, and the Modern World). Riverhead Books, New York, 2006.
Tuthill, Kathleen. “John Snow and the Broad Street Pump: On the Trail of an Epidemic.” Cricket, 31 (2003): 23–31. Available on the web at
http://www.ph.ucla.edu/epi/snow/snowcricketarticle.html
Water and Engineering
Many of the great engineering achievements beginning at the earliest times through the present have been associated with providing a reliable water supply and with disposing of wastewater. The Roman aqueducts that supplied Rome and other cities with drinking water between and are one example of this. The sewer system in London developed during the late 1800s is another example. Because of these engineering accomplishments, most people in the developed world have access to safe drinking water.
In this section, we investigate the relationship between engineering and water. We first describe the concept of water quality standards and how drinking water should meet these standards. We then describe the techniques engineers have developed to provide potable water and to treat wastewater so that it does not unduly pollute the environment.
Water Quality Standards
Most of us know that the water we receive from our local municipalities is treated. The treatment of water has to follow water quality standards. In the United States, the development of water quality standards began in the early twentieth century. Over time, these water quality standards have evolved and have become more rigorous. Laws and regulations such as the Clean Water Act govern water quality standards in the United States. The US Environmental Protection Agency (EPA) has the mission of protecting human health and the environment. The EPA has created water quality standards that define the goals for a body of water and specify its uses. They establish criteria to protect those water uses. They also establish requirements to protect water from pollutants.
In general, a water quality standard consists of four basic elements (EPA):
Designated uses of the water body (e.g., recreation, water supply, aquatic life, agriculture).
Water quality criteria to protect designated uses (numeric pollutant concentrations and narrative requirements).
An antidegradation policy to maintain and protect existing uses and high-quality waters.
General policies addressing implementation issues (e.g., low flows, variances, mixing zones).
State governments are required to identify the appropriate uses for water bodies. These uses are identified by taking into consideration the value of the water body for various uses. The uses for a water body can include any of the following: public water supply, protection of fish, shellfish, and wildlife, recreation, agriculture, industry, and navigation. In making these designations, the appropriate authorities must examine whether the water body is suitable for the intended use. This determination is made based on the physical, chemical, and biological characteristics of the water body, its geographical setting and scenic qualities, and economic considerations.
Drinking Water
Figure 3.7
The city of New York monitors its drinking water to ensure that it is safe. This sign marks the location of a station where the drinking water is sampled.
The quality of drinking water differs from one location to another. Quality is dependent on the condition of the water source and the treatment. Each local community water supplier is required to provide an annual report, sometimes known as a “consumer confidence report” to the public. This report usually provides information on the quality of the local drinking water, its source, and the contaminants found in the water (Figure 7).
Scientists report the contaminants in water as contaminants in parts per million (ppm), parts per billion (ppb), and parts per trillion. When water contaminant measurements are reported in this manner, you may wonder: How can amounts of contaminants that seem so very small cause health problems? Scientific research has shown that, for example, lead concentrations as small as 15 ppb can be harmful to infants and children. The smell of petroleum products in water can be detected by humans even when the amount of petroleum in water is as low as 10 ppb.
It is very important to note that there is no such thing as naturally pure water. All water in nature contains some sort of impurities. Since water is a good solvent, as it flows through various layers of soil and over rocks, it dissolves minerals. These minerals in the water may get the taste (good or bad). However, if these minerals are above a certain level, they could be harmful.
Have you ever thought about where your drinking water comes from? Many of us take the drinking water we get when we turn on our kitchen faucet for granted. The water in many urban areas comes from surface sources such as lakes, rivers, and reservoirs. These sources can be near the urban areas or far away. Water suppliers procure and treat the water they provide. It is important to consider the entire watershed that provides the water. A watershed is the land from which precipitation (usually rain or snow) flows into the river, lake, or reservoir.
In many urban and rural areas, water also comes from ground water that is pumped from a well. Wells provide water from aquifers, which are natural water reservoirs under the earth’s surface. Aquifers may lie under parts of several states or may only be a few miles wide. Thus, water quality is affected not only by the water source such as a river or well that we can see, but also by activities that occur many miles away.
Before the water is delivered to our homes, the water is treated. The treatment of drinking water that is most common is disinfection. Water suppliers add chlorine or another disinfectant to kill bacteria and germs in the water. This commonplace drinking water treatment is considered to be one of the most important scientific advancements of the twentieth century.
Activity
Common water treatment methods: Before we examine a water treatment plant, list and describe some common ways to treat water or purify water for drinking that you can do at home or during emergencies.
Materials needed: Internet-accessible computer, science textbooks.
Suggested phrases for searching on the Internet: Water purification at home, Water purification during emergencies, Common water purification methods.
Directions: Working alone or in a group, brainstorm a list of ways in which drinking water might be bad. From your list, identify problems that might need to be treated. Brainstorm a second list of ways to obtain good drinking water in your home. Do any of these solve the problems identified on your first list?
Using the Internet, research news stories related to water supply and water problems in your local community. How do the results of your research compare to your first list of potential problems with water? Are there problems that you did not anticipate?
Research information on water purif
ication techniques that can be used at home. Discuss in small groups what you learned from your research. Prepare a chart with a brief description of common water problems and the treatment/purification methods appropriate to each problem; include a list of materials you would need for each treatment method and illustrate each method by making your own drawing.
Hints: Filtration, Boiling, Distillation, Water Softeners, Reverse Osmosis
Extensions: What will be the cost of implementing these home-based water purification techniques if you were to need clean water for a family of four? How would you go about determining the amount of water that you will need? What is the most effective method in terms of removing impurities for the quantity of water you need for a family for four for drinking/food purposes?
Water Treatment Basics
Municipalities must perform two types of water treatment: treatment of water before it is used for drinking and other purposes, and treatment of wastewater such as sewage so that it is safe to return to the environment. Typically, drinking water is treated based on the quality of the source water. Ground water, for instance, usually requires less treatment than surface water from a river or a lake. Thus, the quality of the water that enters your community water treatment plant determines how the water will be treated prior to distribution.
Wastewater includes sewage as well as water used in industrial and agricultural processes. It flows out of homes and neighborhoods through sewage pipes to a wastewater treatment plant. Here, the wastewater is treated to remove solids and contaminants. The treated wastewater may be re-used for irrigation and landscaping. The treated wastewater is also returned to streams, rivers, and oceans, which can also be a source of pollution.