CE 326 Principles of Environmental Engineering
IOWA STATE UNIVERSITY
Dr. S.K. Ong
WATER QUALITY CONCEPTS
INTRODUCTION
The quality of water is important as it defines the different uses or activities associated with the water such
as drinking water, industrial water, water-based recreation, aquatic life, and aesthetic enjoyment. Drinking water, the
highest beneficial use of water, must be free of health hazards such as pathogens, toxins, and carcinogens. Aesthetic
factors such as clarity, taste and odor, and chemical balance are also important. The water quality standards for
drinking water are found in the Safe Drinking Water Act (pages 159 - 168 of Davis and Cornwell book)
In this laboratory, several common water quality parameters will be determined using simple chemical and
biological techniques. The purpose of this laboratory is to provide a general introduction of the quality of various
sources of water. The water quality parameters to be tested include pH, alkalinity, hardness, turbidity, color and
total coliform (bacteria).
pH is a term used universally to express the intensity of the acid or the alkaline condition of a solution. It is
a way of expressing the hydrogen-ion concentration, or more precisely, the hydrogen-ion activity. In almost every
phase of environmental engineering practice, pH plays an important role - from chemical coagulation, disinfection,
corrosion control and biological treatment of waste.
Alkalinity of a water is a measure of its capacity to neutralize acids. The alkalinity of natural waters is due
primarily to the salts of weak acids with bicarbonates representing the major form of alkalinity in natural waters.
Hardness of water is a property caused by the presence of polyvalent metal cations. Hardness cations react
with certain anions (eg., SO42-and CO32- ) to form scales in hot water lines. The hardness of natural waters is largely
due to Ca2+ and Mg2+ ions.
Turbidity may be caused by a wide variety of materials - from colloidal and extremely fine dispersions to
coarse materials. Much of the material is inorganic but considerable amounts of organic matter may be included.
Many surface waters are colored to the extent that they are not acceptable for domestic or industrial uses.
Color in water may result from the presence of natural metallic ions (iron and manganese), humus and peat
materials, and industrial waste. Platimum-cobalt colors are used as standard unit of color. Solutions of potassium
chloroplatinate (K2PtCl6) tinted with small amounts of cobalt chloride yield colors which are very much like the
natural colors.
Public water supplies are tested using indicator organisms whose presence is evidence that the water has
been polluted with feces of humans or warm-blooded animals. The indicator organism used is the coliform bacteria
which reside in the human intestinal tract and are excreted in large numbers in feces. One of the accepted analytical
methods is the membrane filtration method.
EQUIPMENT AND MATERIALS
Tests
pH
Alkalinity
Hardness
Turbidity and color
Total Coliform
Equipment and Materials
water samples (coke and Ames tap water), pH meter
water samples (Ames groundwater and Lake Laverne)
0.02 N H2SO4 , burette, pipette, flasks, methyl-orange indicator, pH meter
water samples (Ames groundwater, Ames drinking water)
0.01 N EDTA solution, EBT indicator, CaCO3 standard
water samples (Ames tap water and Lake LaVerne)
Nessler tubes, Hach turbidimeter, color standards
water samples (Ames tap water and Lake LaVerne)
dilution bottles, pipettes, graduated cylinders, culture medium (M-endo), petri-dishes,
filtration units, membrane filter, forceps, incubator (35o C), colonies counter
Four stations will be set up. Divide into four groups. When you are done with one station, move to the next.
Station 1
Station 3
pH and Turbidity and color
alkalinity
Station 2
Station 4
Hardness
Bacteria (coliform) count
EXPERIMENTAL PROCEDURES
1.
2.
pH and alkalinity
i.
Measure the pH of the two samples:
pH of fresh Coke ____pH of Ames Water _________
Turbidity and Color
i.
Turbidity - Pour sample (Ames tap water or Lake Laverne water) in a turbidimeter tube. Read
readings on the turbidimeter. Note turbidimeter will be calibrated by TAs.
ii.
Color - Fill a matched Nessler tube to the 50 mL mark with Ames tap water or Lake Laverne
water. Observe sample color and compare with the standards. If turbidity is present and not
removed, report results as apparent color. Report color as follows:
Color units = A x 50/B
where A = estimated color of diluted samples, B = mL sample taken for dilution
3.
Hardness
i.
Add 25 mL of water sample (Ames Groundwater or tap water) to a 125 mL erlenmeyer flask,
dilute to 50 mL using distilled water
ii.
Add 1 - 2 mL buffer solution. The pH should be 10.0 ± 0.1
iii.
Add 1 - 2 drops of Erichrome Black T (EBT) indicator.
iv.
Titrate to a blue color (or the disappearance of the last reddish tinge in the solution) with standard
0.01 M ethylenediaminetetraacetic (EDTA) acid solution. Titration should be conducted within 5
minutes. Record volume (A) of titrant used. Repeat for the other water sample.
Ames Groundwater
Ames tap water
v.
4.
End volume (mL):
End volume (mL):
Hardness (mg/L as CaC03) = A x B x 1000/(mL of Sample),
where B is equal to 1 mg CaCO3 for 1.00 mL EDTA titrant
Alkalinity
i.
Add 50 mL of water sample (Ames groundwater or Lake LaVerne water) to an erlenmeyer flask.
ii.
Add 2 drops of methyl orange indicator
iii.
Read the initial volume of the standard 0.02 N acid. Titrate flask with acid until color changes
from yellow-orange to red or pH 4.5. Read final volume of standard acid. Record volume of
titrant used. Repeat for the other water
Ames Groundwater
Lake Laverne water
V.
4.
Start volume (mL):
Start volume (mL):
Start volume (mL):
Start volume (mL):
End volume (mL):
End volume (mL):
Total Alkalinity (as mg/L as CaCO3)
= mL acid used x Normality of Acid x 50,000/Vol. of Sample
Total Coliform (Bacteria) Count
i.
Prepare 100 mL of Ames water or Lake LaVerne water.
ii.
Place a sterile membrane filter over the porous plate of the receptacle with forceps. Carefully
match funnel unit over receptacle and lock it in place. Filter sample under partial vacuum. With
filter in place, rinse funnel by filtering three 20 - 30 mL portions of sterile dilution water. Upon
completion, unlock and remove the funnel, remove membrane filter, and place filter on medium.
iii.
Invert petri dish and place dish in incubator for 24 hr at 35˚ C. Appoint a member of your group
to return the next day to count the bacteria formed.
iv.
Typical coliform colony has a pink to dark-red color with a metallic surface sheen. Count sheen
colonies with the aid of a dissecting microscope. Use only membrane filters with 20 to 80 colonies
and not more than 200.
v.
Report results as: Total Coliform colonies/100 mL
= coliform colonies counted x 100/mL of sample filtered
LABORATORY REPORT FORMAT
Introduction
Describe the purpose of experiments and summarize the theoretical background.
You need to expand on the information that is already presented in this handout.
Procedure
Describe the experimental procedures
Results
Report all results in an organized table
Discussion
Answer the following questions.
A.
pH and Turbidity and color
1.
What are the pHs of coke and Ames Water? Comment on a likely source of
acidity in the coke.
2.
What are the turbidities and colors of Ames drinking water and Lake LaVerne water?
3.
What is the difference between turbidity and color?
4.
Why is it important to remove turbidity from water for drinking purposes?
B.
Hardness
1.
What are the hardness of Ames ground water (before treatment) and Ames Drinking
water (after treatment)? Is Ames drinking water hard or soft?
2.
What is meant by total hardness, carbonate hardness and temporary hardness.
3.
Why are people concerned with hardness?
C.
Alkalinity
1.
Comment and contrast the concentrations of alkalinity taken from two sources (surface
water – lake Laverne and groundwater – Ames groundwater)1.
2.
What are the major chemical components that make up alkalinity in natural waters?
What are the sources of alkalinity in natural waters?
2.
Air pollutants such as the oxides of sulfur and nitrogen cause acid rain - what is the
approximate pH you would expect in acid rain? What would such rainfall do to the
alkalinity of natural waters such as lakes.
D.
Total Coliform (Bacteria)
1.
What are the total coliform for Ames tap water and Lake LaVerne water?
2.
What is the difference between total coliform and fecal coliform?
3.
What is the Drinking Water Standards for total coliform? Comment on
whether the drinking water standard has been met for Ames drinking water or
Lake Laverne.
Conclusions
REFERENCES
Sawyer and McCarthy, Chemistry for Environmental Engineering, 3rd ed. McGraw Hill, 1978.
APHA- AWWA-WPCF, Standard Methods for the Examination of Water and Wastewater, 17th Edition, 1989.