lesson 11_ laboratory procedures

7/11/2014 Lesson 11: Laboratory Procedures

http://water.me.vccs.edu/courses/ENV110/Lesson11_print.htm 1/6

Lesson 11: Laboratory Procedures

Objective

In this lesson we will learn the following:

What laboratory procedures need to be done in the water plant.

Reading Assignment

Along with the online lesson, read Chapter 11: Laboratory Procedures, in your textbook Operation

of Water Treatment Plants Volume I .

Lecture

A laboratory is a place for precise work to determine appropriate treatment of raw water and the

quality of the finished water. It must be kept organized, well maintained, and clean. All instruments

must be kept clean and routinely calibrated with proper records. A number of lab tests are neededdaily, quarterly, semiannually, annually, and at other specified intervals to monitor the water quality

before, during, and after the treatment. A test is not better than the sample, and the sample is not

better than the manner in which it is collected.

Sampling

Valid testing starts with an adequate and representative sampling. A sample is either a grab or a

composite. A grab sample, as the name indicates, is a specific volume collected at one site at one

time. These samples indicate the quality of water at that time and at that site. Grab samples are

taken for bacteriological and disinfection residual tests. A composite sample is a mixture of a

number of portions taken at the specific intervals. This reduces the number of tests. Each portion

can be proportionate to the flow or volume. For each test operators should follow the prescribed

sampling size, collecting, and preserving procedure given in the Standard Methods for theExamination of Water and Waste Water. Testing must be done as soon as possible and not later

than the specified holding time.



Tests

Various regularly performed common tests by the operating staff are for tastes and odor, turbidity,

jar test, pH, alkalinity, hardness, disinfection residual, coliform bacteria, and the heterotrophic plate

count. All other tests are run either by highly trained chemists and microbiologists of the lab or by

certified contract laboratories.

Tastes and Odors

Testing for taste and odor is important because of aesthetic value. The majority of water quality

complaints are of this type. Most of the organic and some inorganic chemicals cause tastes and

odors. These chemicals come from the decaying organic matter, runoffs, industrial wastes, andmunicipal sewage discharges. Geosmin and methyl-isobarneol (MIB) are the serious odor-causing

chemicals; they are produced by bacteria, particularly actinomycetes, while decomposing deadorganic matter at the bottom of the water bodies. Even a very low concentration of these chemicals

can cause earthy-musty odors. The odors are common in spring and fall due to the turn over of thelakes and reservoirs. In the groundwater, the tastes and odors can be due to iron, manganese, and

hydrogen sulfide (H2S).

These are general classes of odors:

Aromatic (spicy)Balsamic (flowery)Chemical

DisagreeableEarthy

MustyGrassy

Vegetable

These are called the reference odor in the water samples.

Turbidity

Turbidity is the murkiness in the water caused by colloidal (1 to 100 nanometer particles) and othersuspended particles, such as clay, sand, silt, organic matter of plant and animal origin, planktons,



and other microscopic organisms. Turbidity particles can be waterborne pathogens or particles

harboring them. The lower the turbidity, the less is the amount of the particulate matter. It meansthere is less probability of the presence of waterborne pathogens, and the water is safer. Therefore,

turbidity is one of the primary standards for the drinking water. The finished water turbidity is testedat least every four hours.

Turbidity is measured as the amount of scattered light by the suspended particles in the sample.Turbidity of the finished water should be equal to or less than 0.3 nephalometric turbidity unit

(NTU) in 95 percent of the samples/month.

Jar Testing

Jar testing is a useful tool to determine the practical optimum dose of a chemical under the simulatedplant conditions. It uses a range of increasing dose of a particular chemical in a series of six jars

with a stirring and illumination mechanism.

Most of the problems in the source water, particulary in the surface water, quality are due to

seasonal variations or other unusual circumstances, such as drought, heavy rains, unexpecteddischarge of raw sewage, or runoffs from farm land. These problems can be solved by this test,

which is important for coagulation, softening, sedimentation, removal of synthetic organics, and for

tastes and odor control. It makes the water treatment more effective, easy, and economical.



pH

pH, hydronium ion index, is the measurement of acidity (H+). Acidity in water is usually due tocarbon dioxide (CO2) from rain water, mineral acids, chlorine, and heavy metal salts, such as alum.

pH is an important parameter in the water utility. It is used to determine the condition of water forproper coagulation, softening, and stabilization.

Alkalinity

Alkalinity of water is its capacity to neutralize acidity. Carbonates, bicarbonates, and hydroxides

are the most common forms of alkalinity in natural waters. These chemicals are mostly compoundsof calcium and magnesium coming from mineral deposits such as limestone and dolomite. Industrial

discharges can also cause alkalinity. Bicarbonate alkalinity is present between pH 4.3 and 8.3.

Carbonate and bicarbonate alkalinity is present between pH 8.3 and 9.4, and carbonates andhydroxides are present between pH 9.4 and 14. Alkalinity does not exist below pH 4.3. Alkalinity

test is important to determine proper coagulation and the stability of water.

Disinfection Residual

Chlorine is one of the most effective disinfectants and is quite commonly used for water disinfection.Chlorine, combined with ammonia, forms chloramines, which are called combined residual chlorine.

Total residual chlorine is the sum of the free residual chlorine and combined residual chlorine.

Coliform Bacteria Tests

Bacteriological quality of water is important to determine the degree of disinfection and possiblepresence of waterborne pathogens. Bacteria, being small, are present almost everywhere, such as

in air, water, and on lab equipment. Therefore, all equipment and handling is done in a sterile

environment to ensure the accuracty of data.

Media are the food for the bacteria to culture them in the laboratory. Different bacteria have

different food requirements; therefore, each medium will allow certain types of bacteria to grow.



Media are either liquid, known as broths, or semisolid (gelatinous), which are called agars.

To ensure the absence of waterborne pathogens, the water is tested for coliform bacteria. Coliformbacteria are present in human wastes and in soil contaminated with human wastes. These bacteria in

human wastes are known as fecal coliform bacteria. Those in the soil are called nonfecal

coliforms. Both fecal and nonfecal coliforms are called the total coliform group. This group is used

as an indicator of the presence of human wastes in water and the possible presence of waterbornepathogens. The two most common techniques for testing coliform bacteria are the membrane filter

technique and the multiple tube fermentation/most probable number technique.

Heterotrophic or Standard Plate Count (HPC)

This test gives the total count of almost all types of bacteria in the water sample that can grow on ageneral medium called the standard plate count agar or nutrient agar. A count less than 500

colonies/mL of the sample means that the water is properly disinfected, and vice versa.

Furthermore, a count of higher than 500 colonies/mL interferes with the growth of total coliformbacteria.

Review

A number of lab tests are needed daily, quarterly, semiannually, annually, and at other specified

intervals to monitor the water quality before, during, and after the treatment. A sample is either a

grab or a composite. A grab sample, as the name indicates, is a specific volume collected at one

site at one time. These samples indicate the quality of water at that time and at that site. Grabsamples are taken for bacteriological and disinfection residual tests. A composite sample is a

mixture of a number of portions taken at the specific intervals. This reduces the number of tests.

Each portion can be proportionate to the flow or volume.

Various regularly performed common tests by the operating staff are for tastes and odor, turbidity,

jar test, pH, alkalinity, hardness, disinfection residual, coliform bacteria, and the heterotrophic plate

count. All other tests are run either by highly trained chemists and microbiologists of the lab or by

certified contract laboratories.



Assignment

Work the following crossword 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

Quiz

Answer the questions in the Lesson 11 quiz . When you have gotten all the answers correct, print

the page and either mail or fax it to the instructor.

http://water.me.vccs.edu/courses/ENV110/crosswords/lesson11.pdf

http://water.me.vccs.edu/courses/ENV110/quiz11.htm

lesson 11_ laboratory procedures

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