People need clean water to be healthy, to grow crops and for many industrial purposes. Plants and animals need unpolluted water, too. To reduce the possibility of polluting the water with household or industrial waste, most communities have sewage treatment plants. Individual homes may have septic tanks, and many industrial plants have their own water treatment facilities.

Most water treatment processes start with a simple filtration process. A series of screens is used to filter out large items, such as sticks, stones and rags. The water is then held in a settling tank for a period of time to allow suspended solids to sink to the bottom. The settled solids are called sludge.

After the sludge has settled out, the water is usually treated with chlorine to kill bacteria, then it is discharged into a river, lake or the ocean. This mechanical separation with the addition of chlorine to kill bacteria (chlorination) is called primary sewage treatment.

A similar process is used in household septic tanks. In a septic tank system, the water flows to a tank in which the solids settle to the bottom and the greases and oils float to the top/ The water is carried through pipes to perforated pipes into a drain field where it flows out over and through gravel. The gravel and microorganisms living in the soil remove many contaminants from the water.

Many communities have a more advanced sewage treatment system called secondary sewage treatment. In secondary treatment, the water from the settling tank is aerated by one of several ways. The aeration encourages the growth of bacteria and other microorganisms that remove many organic chemicals and suspended solids from the water. After additional time in a settling tank or pond, the water is chlorinated and released.

Even secondary treatment does not remove all pollutants. Many salts, pesticides, phosphates and other pollutants remain in secondary treated water. To remove the remaining chemicals is an expensive operation, but a few communities have invested in tertiary treatment facilities. Tertiary water treatment involves different processes, many of them chemical, to remove different pollutants. Many tertiary treatment plants claim that the water they release is potable, or safe to drink.

OBJECTIVES: This laboratory will acquaint you with two exercises. In the first, you will learn a modified method of testing for the presence of coliform bacteria in water. Coliform organisms are used by sanitation departments as indicator organisms for the amount of microbial pollution of water. (This experiment will be started today, and results will be observed in the next class period.) In the second exercise, you and your team will design and test the effectiveness a simple water filtering system.

EXERCISE 1

INTRODUCTION: Coliform bacteria are a group of many types of bacteria found in human and animal feces. Their presence in numbers above an acceptable limit in water supplies is an indication of contamination. In the first exercise today, you will test water samples which you have collected and brought into the lab. Tabulation of coliform bacteria will be made in the next class period, following a 48 hour incubation period to allow the bacteria to grow. The equipment includes a specially treated petri plate, to be used with the Coliscan agar; the agar will not solidify if any other petri plate is used.

EQUIPMENT:

(Equipment for this exercise is per every two students)

Screwcap vial (given to you in class) with water that you have collected
1 Coliscan petri dish
1 vial Coliscan media
1 sterile calibrated disposable pipet
Marking pen

PROCEDURE:

Note: Activity must be done as soon as possible in the lab, as the agar requires 40-45 minutes to solidify.

1. Without opening petri plate, turn it upside down and write your names and the date in a very small area on the surface. (You do not want to use a lot of spaces, because you will have to "read" the cultures through the transparent plate.)

2. Carefully remove the sterile pipet from its wrapper, being careful not to touch anything with it.

3. Using the calibrated markings on the pipet, collect the following amounts of water from your collected sample:

1.0 ml, if you brought in tap or clear water
0.5 ml, if you brought in "contaminated" water

4. Carefully take cap off of "Coliscan" media vial; expel sample into the vial.
5. Replace cap and gently swirl the media and water sample together.
6. Carefully remove the lid of the petri plate and pour entire contents of Ciliscan media vial into the bottom of the petri plate.
7. Replace lid immediately, and gently swirl the media all over the bottom of the plate several times. Do not use so much force as to spill any of the media over the sides.
8. Set the plate aside, in an area where it will not be disturbed for at least 40 minutes (the end of the lab)
9. At the end of the lab, when the media is solidified, invert the plate and give it to your instructor or place it where you are instructed. (The plates will be incubated for 48 hours at 28- 35 degrees Celsius, then refrigerated to inhibit any further growth.)
10. Dispose of all pipettes and vials in biohazard collection bags placed in the labs.

Next Period:

1. Get your sealed Coliscan plate.
2. Place the plate, inverted, against a white background. 3. Count the number of fecal coliform (the indicator organisms) colonies on your plate. They will appear as purple or deep pink colonies, and may be growing on the surface (large colonies) or under the surface, within the solidified media (small colonies.) Other colored colonies (including light pink) are NOT fecal coliform bacteria, and do not need to be counted.

Record here the number of coliform colonies you have: ________________

If you placed 1. ml water in the media before you plated it, this is your FINAL COUNT.
If you used less than 1.0 ml. water, you must calculate the number of colonies, using the following formula:

Number colonies per ml of water = Number of colonies counted divided by amt. of water

EX: You counted 29 purple or pink colonies on your plate, and used 0.3 ml of water:

X = 29/0.3 or 96.67 colonies/ml , rounded off to 97 colonies per ml of water

Interpretation of Results:

Drinking water should contain fewer than 10 colonies/ml
Swimming pool water should have fewer than 100 colonies/ml

EXERCISE 2

INTRODUCTION: In this second activity, you will design and test the effectiveness of various methods of filtering water, which is the first step in primary water treatment. You will make visual observations of the water that has passed through your filter (the filtrate), and then you will evaporate the water to see whether there were dissolved or suspended materials that you did not see.

EQUIPMENT:

(Equipment for this exercise is per team of 3-4 students)

Balance
Two 250 ml beakers
Hot plate
Filter materials: gravel; cotton balls; charcoal briquettes; sand; cloth scraps; soil; styrofoam "popcorn"; paper towels; aluminum foil; *any other items you think might work a a filter that you bring in*
2 liter soda bottle, cut in half
Nylon net (to use as screen material)
Rubber band
"Polluted" water
Data Sheet

PROCEDURE:

****Turn on your hot plate at the beginning of the activitiy, but be very careful to place it in a place where no one will get burned!

1. Construct your filter system in the following manner:
· Take the half of the soda bottle with the neck and opening.
· Place a piece of nylon net, folded a couple of times, over the bottle opening and secure with a rubber band.
· Use a single item or combination up to four items of filter components to build your filter. Place these items in the bottle opening end, as shown to you by your instructor.
· Place the "filter", opening end down into the bottom half of the soda container.

2. Find the mass of a 250 ml. beaker as precisely as possible, using the balance. Record your mass on the Data Sheet in the space indicated.
3. Obtain 250 ml. of the "polluted" water. Record its appearance on your Data Sheet.
4. Pour the "polluted" water carefully through your filter. When all the water has filtered through, transfer this filtrate to your weighed beaker.
5. Observe and describe the filtered water on the Data Sheet.
5. Evaporate the filtrate, as per your instructor’s directions.
6. Find the mass of the beaker and residue remaining after all of the water has evaporated.
7. Find the mass of the residue by subtracting the mass of the beaker from the weight of the beaker plus residue. Record this answer on your Data Sheet.
8. While the water is evaporating, draw a diagram of your filter system on the Data Sheet, labeling all parts and answer the questions. Why did you choose the filtering materials that you used?

DATA SHEET

a. Mass of beaker ______________ gms.

b. Appearance of polluted water:

c. Appearance of filtered water:

d. Mass of residue: _________________ gms.

DIAGRAM OF FILTERING SYSTEM

QUESTIONS

1. Briefly describe primary, secondary and tertiary sewage treatment systems.

2. What are ways that you as an individual can help reduce water pollution produced in your dorm or home?

3. Give three examples of "natural" water filters, i.e., those found in a natural, non-human controlled water system.

Activities based on Coliscan Easygel kits (trademark of Micrology Laboratories, Goshen, IN), and "Water Treatment" in Environmental Science Activities by Michael L. Roa

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