lesson 1_ introduction to water treatment
TRANSCRIPT
-
7/28/2019 Lesson 1_ Introduction to Water Treatment
1/6
Lesson 1:
Introduction to Water Treatment
Objective
In this lesson we will learn about the following concepts:
The hydrologic cycle and how it is like nature's way of treating water
An introduction to water treatment
Reading Assignment
Along with the online lesson, read Chapter 1: Water Treatment Plant Operator, in
your textbook Operation of Water Treatment PlantsVolume I.
Lecture
Hydrologic Cycle
Hello, I'm Rosa Cooke from Mountain Empire Community College. I would like to
introduce you to a subject called water and wastewater treatment. In water and
wastewater, there are many concepts to learn so I thought I would start out with the
way nature treats water - thehydrologic cycle.
The hydrologic cycle follows water as it evaporates from the earth's surface, forms
clouds, and then falls back to the earth's surface as rain. The diagram below shows an
overview of the process.
-
7/28/2019 Lesson 1_ Introduction to Water Treatment
2/6
Since the cycle is continuous, there is no actual beginning or end, so you can begin
anywhere. However, there are five basic processes that make up the hydrologic
cycle:Condensation,precipitation,infiltration, runoff, andevapotranspiration.
Water vapor condenses to form clouds, which result in precipitation when the
conditions are suitable. Precipitation falls to the surface and infiltrates the soil or flows
to the ocean as runoff. Surface water evaporates, returning moisture to the
atmosphere, while plants return water to the atmosphere by transpiration.
Condensation is the process of water changing from a vapor to a liquid. Water vapor
in the air rises mostly by convection. This means that warm, humid air will rise, while
cooler air will flow downward. As the warmer air rises, the water vapor will lose
energy, causing its temperature to drop. The water vapor then has a change of state
into liquid or ice. You can see condensation in action whenever you take a cold soda
from the refrigerator and set it in a room. Notice how the outside of the soda can
"sweats"? The water doesn't come from inside the can, it comes from the water vapor
in the air. As the air cools around the can water droplets form.
Precipitation is water being released from clouds as rain, sleet, snow, or hail.
Precipitation begins after water vapor, which has condensed in the atmosphere,
becomes too heavy to remain in atmospheric air currents and falls. Under some
circumstances precipitation actually evaporates before it reaches the surface. More
often, though, precipitation reaches the Earth's surface, adding to the surface water in
streams and lakes, or infiltrating the soil to become groundwater.
A portion of the precipitation that reaches the Earth's surface seeps into the ground
through the process calledinfiltration. The amount of water that infiltrates the soil
-
7/28/2019 Lesson 1_ Introduction to Water Treatment
3/6
varies with the degree of land slope, the amount and type of vegetation, soil type and
rock type, and whether the soil is already saturated by water. The more openings in
the surface (cracks, pores, joints) the more infiltration occurs. Water that doesn't
infiltrate the soil flows on the surface as runoff.
Precipitation that reaches the surface of the Earth but does not infiltrate the soil is
called runoff. Runoff can also come from melted snow and ice. When there is a lot of
precipitation, soils become saturated with water. Additional rainfall can no longer
enter it. Runoff will eventually drain into creeks, streams, and rivers, adding a large
amount of water to the flow. Surface water always travels towards the lowest point
possible, usually the oceans. Along the way some water evaporates, percolates into
the ground, or is used for agricultural, residential, or industrial purposes.
Evapotranspiration is water evaporating from the ground and transpiration by
plants. Evapotranspiration is also the way water vapor re-enters the atmosphere.
Evaporation occurs when radiant energy from the sun heats water causing the water
molecules to become so active that some of them rise into the atmosphere as vapor.
Transpiration occurs when plants take in water through the roots and release itthrough the leaves, a process that can clean water by removing contaminants and
pollution.
As you can see, many processes are at work to give you the water you need. And
these processes are always at work. Just because Antarctica is frozen doesn't mean
that evaporation is not taking place (ice can turn directly to water vapor by a process
called sublimation). And because the Sahara Desert is so dry doesn't mean that
precipitation is not happening (it evaporates before it makes it to the ground).
Introduction to Water Treatment
Now that you know how nature treats water, let's see how it's done in the water plant
before we consume it in a glass of water.
Water treatment in a typical water treatment plant is shown in the picture below.
Based on the characteristics of the raw water and on other factors, this treatmentprocess may vary considerably from place to place.
-
7/28/2019 Lesson 1_ Introduction to Water Treatment
4/6
As water is pumped from the source (a well, spring, river, or lake) it is screened to
remove debris. Then, at the water plant, various characteristics of the raw water are
tested.
The water may be prechlorinated to kill microorganisms, control odors and taste, and
aid in coagulation and setttling. The water may also be aerated, which removes carbon
dioxide (CO2) and raises pH, oxidizes iron (Fe) and manganese (Mn), removes
hydrogen sulfide (H2S), and removes organic contaminants. Potassium permanganate
(KmnO4) may be added to the water in the collection tray of the aerator in order to
remove iron and manganese from the water. Ozone may be added to the water totreat iron and manganese, remove algae, neutralize hydrogen sulfide (H2S), and aid in
flocculation. Many of these are dependent upon the plant and the amount of water
being distributed daily.
In most cases, the water then enters a flash mix chamber. Here, various chemicals are
added and are mixed into the water. Coagulants cause fine particles to clump together
into larger particles. Alkali are added to adjust the pH as well as to oxidize iron and
manganese. Hexametaphosphate may be added to prevent corrosion of pipes.
-
7/28/2019 Lesson 1_ Introduction to Water Treatment
5/6
After flowing out of the flash mix chamber, the water goes through a chamber which
causes coagulation and flocculation to occur. Here, the fine particles of contaminants
gather together into large clumps called floc. When the water flows into the
sedimentation basin, some of the floc settles out of the water and is removed. Next,
the water is passed through filters which remove particles too small to settle out in the
sedimentation basin.
Finally, chlorine is added to the water. The water may also be fluoridated to reduce
tooth decay in the consumers. The water is left in the clear well for a period of time to
allow the chlorine to kill bacteria in the water and to oxidize hydrogen sulfide. The
water is now treated and ready to be distributed.
That was a quick overview of the water treatment process and what happens to water
as it goes through the plant step by step. We will get into greater detail in later lessons
so that you will understand each step of the process, why it is done and how to make
sure each step is being done efficiently.
Review
Nature treats water in its own way through the hydrologic cycle, though we still need
to treat the water before we drink it due to all the pollution and bacteria in the
environment. The hydrologic cycle provides the supply of water for us to use for
consumption, continuously cycling through over and over. The five basic processes
that make up the hydrologic cycle are condensation, precipitation, infiltration, runoff,
and evapotranspiration.
In the water treatment plant the water comes in from the source, is aerated and the
addition of chemicals to aid in coagulation and flocculation occurs in the flash mix
chamber, it is then allowed to go through coagulation and flocculation, and settle out in
the sedimentation basin. The water will pass through a filtration system after the
sedimentation basin, removing partilces that were too small to settle out. Chlorine is
added as the final step and then the water is stored until it is distributed to the
consumer.
Assignments
Work the followingcrossword puzzle that comes from definitions in your textbook.
You may either print the puzzle out, complete it and mail or fax back to the instructor
or you may send an email with the correct answers numbered accordingly.
http://water.me.vccs.edu/courses/env110/crosswords/lesson1.pdf -
7/28/2019 Lesson 1_ Introduction to Water Treatment
6/6
Quiz
Answer the questions in the Pre-Quiz and the Lesson 1 quiz. When you have gotten
all the answers correct, print the page and either mail or fax it to the instructor. You
may also take the quiz online and submit your grade directly into the database for
grading purposes.
http://water.me.vccs.edu/courses/env110/quiz1.htmhttp://water.me.vccs.edu/courses/env110/quiz0.htm