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What is the Effect of Chlorine Concentrations on Carbon Filter Performance?

Researched by Steven P.


The purpose of this experiment was to determine whether the efficiency of a carbon filter decreases faster at higher concentrations of chlorine.

I became interested in this idea because I love engineering.  This experiment uses engineering techniques to measure the chlorine content in the water.  Engineers also use carbon filters at water treatment plants to remove chlorine.

The information gained from this experiment will help society because people will know how well a carbon filter works at removing different amounts of chlorine in the water and when the filter fails to remove the chlorine.



My hypothesis is that the chlorine removal efficiency of an activated carbon filter will decrease more rapidly at higher concentrations of chlorine, and that the rate of failure will also be faster than at lower concentrations.

I base my hypothesis on previous experiments that show the chlorine removal efficiency of activated carbon filters.  The American Water Works Association states these results in Water Quality and Treatment - A Handbook of Community Water Supplies.



The constants in this study were:
The type of carbon filter
    The type of water
    The brand of chlorine
    The LaMotte test kit
    The temperature of the water
    The test set-up
    The procedures used

The manipulated variable was the amount of chlorine used in the concentrations. The concentration levels were:
    10 milligrams of chlorine per liter of water
    22 milligrams of chlorine per liter of water
    30 milligrams of chlorine per liter of water
    42 milligrams of chlorine per liter of water

The responding variable was the concentration of chlorine measured in parts per million flowing out of the filter.

To measure the responding variable I used a LaMotte chlorine test kit.   The kit uses reagents to measure free and total chlorine in parts per million.




Quantity Item Description
2 20 liter buckets
1 1 meter hose
1 Faucet filter attachment
1 Screw hose clamp
1 Faucet adapter with washer
1 Hose connector
1 PVC coupling
2 Washers
5 Granular activated carbon replacement filters
1 1000-milliliter graduated cylinder
1 50-milliliter graduated cylinder
1 10-milliliter graduated cylinder
Bulb pipette
Chlorine test kit
200  DPD 1 tablets
200 DPD 3 tablets
As Needed  Tap water
As Needed  Distilled water
Bottle of bleach (3.79 liters)
Paint stirring stick
Camera with film
As Needed Paper






1.    Attach a 1-meter hose with couplings from the 20-liter input bucket to the faucet attachment.
2.    Put a new carbon filter into the faucet attachment.
3.    Turn the faucet attachment to the ìoffî position.
4.    Pour 15 liters of water into the input bucket.
5.    Add the calculated concentration of chlorine to the 15 liters of water.
6.    Thoroughly mix the chlorine into the water.
7.    Place the 20-liter output bucket underneath the filter.
8.    Turn the faucet filter attachment to the ìonî position.
9.    Allow all of the 15 liters of water to run through the filter from the input bucket.
10.  Measure 10 milliliters of water as it flows out of the filter into a 10-milliliter test tube every 15, 30, or 60 liters (depending on the concentration).
11.    Put a DPD 1 tablet into the 10 milliliters of water. the tablet dissolve, then wait 30 seconds.  Take the free chlorine reading by comparing the color of the water in the test tube to the known amounts of chlorine and colors on the Lamotte test kit.
13. Put in a DPD 3 tablet into the 10 milliliters of water.
14. Let the tablet dissolve, then wait 30 seconds.  Take the reading for the amount of total chlorine, as in step 12.
15. If the readings are getting to be 4.0 or higher, you need to make a 10 to 1 dilution or a 20 to 1 dilution of the sample in order to get a more accurate reading with the LaMotte test scale.
16. Turn the faucet filter attachment to the ìoffî position, empty the output bucket and put it back underneath the filter.
17. Repeat steps 4 through 16 until the carbon filter output has reached the failure point (input concentration).
18. Repeat steps 2 through 17 for each concentration level.



The original purpose of this experiment was to determine whether the efficiency of a carbon filter decreases faster at higher concentrations of chlorine.

In my test, I defined failure as when the outlet concentration of chlorine was at or near the inlet concentration.  At some concentrations it was difficult to reach failure, so I stopped the test when there would be no more changes in the test.

In general, I found filter performance did vary with different concentrations of chlorine.  Lower concentrations of chlorine took more water to reach failure.  Higher concentrations took less water and the rate of failure was faster.  The filters were more efficient at lower concentrations than at higher concentrations.  I found it interesting that the filter did a better job of removing chlorine after it sat over night.

More detailed results are chown on the following tables and graphs. The results are:

  •  In every graph the 42 mg/l test failed first, and the 10 mg/l failed last.
  •  When I looked at filter efficiency, the efficiency decreased at a slower rate at lower concentrations.
  •  The first graph shows the amount of chlorine captured by the filter.  Except for the 42 mg/l test, the filter failed at about the same amount of chlorine in each test.
  •  The second graph shows the total amount of chlorine that has gone through the filter.  The performance of the filters was similar, but they still worked better at lower concentrations.
  •  The third graph also shows the total amount of chlorine that has gone through the filter.  At lower concentrations I was able to get more chlorine through the filter before the test was complete.
  •  The fourth graph shows the total liters of water through the filter.  The second graph, the filter efficiency was better at lower concentrations.  I could put more water through the filter at lower concentrations such as 10 mg/l to get the same efficiency.
  •  The last graph also shows the total number of water through the filter.  There was a big difference in the amount of water for each concentrations of chlorine.  It shows that the rate of failure (how fast the outlet concentration went up) was much greater at higher concentrations.

Click here to see my graphs



My hypothesis was that the chlorine removal efficiency of an activated carbon filter will decrease more rapidly at higher concentrations of chlorine, and that the rate of failure will also be faster than at lower concentrations.

The results indicate that my hypothesis should be mostly accepted because the filters did fail faster at higher chlorine concentrations.  Also, since the filters regenerated themselves, the rate of failure in the higher concentrations wasnít always faster than the lower concentrations.  At lower concentrations the filter should last longer than at higher concentrations.

Because of the results of this experiment, I wonder if I were to run chlorinated water through the filter non-stop, if the filter wouldnít regenerate and the test results would be more consistent.  I also thought that the filters should hold about the same amount of chlorine from test to test.  Because the amount of chlorine captured by the filters was different, I wonder if the water flowed evenly through the filter, or if the carbon could more easily adsorb lower concentrations of chlorine.

If I were to conduct this project again, I would make sure my chlorine test method was more accurate because it was hard to compare colors to get good test readings.  I would also find a quicker way to fill my bucket.




The topics in this report are carbon, granular activated carbon, carbon filters, and chlorine.  It also includes information on adsorption, filtration, and people who have studied and helped us understand carbon or chlorine.  I hope you learn a little more about carbon and chlorine.


Carbon is in group 14 on the periodic table (Iva).  The symbol for carbon is C.  The electron configuration is 2-4, which means there are 2 electrons close to the nucleus and 4 electrons are a little farther away.  The atomic number for carbon is 6, which is the total number of electrons.  The atomic weight of carbon is 12.011. The most common isotope of carbon is carbon-12.  In 1961, carbon-12 was chosen to take the place of carbon-16 as the standard for atomic weight.

Carbon is important to all living things.  On Earth there are three forms of pure carbon.  These three forms are diamond, graphite, and amorphous carbon. The physical properties of the three forms of carbon are very different from each other because of their different structures.

Diamond is the hardest material known to man because each atom is linked to four other atoms making a three-dimensional framework.

Graphite is made of weakly bonded layers with the atoms arranged in a hexagon shape. These layers slide over each other easily, making it a good lubricant.

Amorphous carbon has a low degree of crystalinity.  Amorphous has no particular pattern or shape.  Pure amorphous carbon can be made by cooking purified sugar at 100º Celsius in a vacuum.

Carbon has the ability to link to other carbon atoms to form complex chains and rings.  This allows it to make an almost infinite number of carbon compounds.  The most common of the compounds contain carbon and hydrogen.  The first carbon compounds were found in living things in the beginning of the Nineteenth century.  Because carbon was first found in living things, the study of carbon is called organic chemistry.

Carbon has very high melting points and cannot be dissolved at ordinary temperatures. At high temperatures carbon reacts with metals to make carbides and it also reacts with oxygen to form carbon monoxide (CO) and carbon dioxide (CO2).  Carbon in the form of coke is used to remove oxygen from metal oxide to make pure metal.  Carbon can form compounds with most non-metallic elements.  Some of these compounds, such as carbon tetrachloride (CCI4), must be formed indirectly.  Carbon is a widely distributed element and makes up 0.025 percent of the earthís crust.  The carbon in the crust is mostly in forms of carbonates.

Carbon dioxide is an important part of the Earthís atmosphere and is the main source of carbon incorporated into living things.  During photosynthesis in plants, carbon dioxide is changed into organic compounds which are eaten by humans and other living things.  Amorphous carbon can be found in varying degrees of purity in charcoal, coal, coke, carbon black, and lampblack.  Lampblack, sometimes wrongly called carbon black, is made by burning liquid hydrocarbons such as kerosene with an insufficient supply of air, which creates a smoky flame.  The smoke and soot is gathered in a separate chamber and was used for inks and paints.  Lampblack has been replaced with carbon black, which has finer particles.  Carbon black is made by incomplete combustion of gas.  Carbon black is mainly used as a reinforcing agent for rubber.

In 1985, scientists vaporized graphite to make a stable form of a carbon molecule consisting of 60 carbon atoms in a roughly spherical shape looking like a soccer ball. The molecule was named buckminsterfullerene, or ìbuckyballî for short, in honor of R. Buckminster Fuller who invented the geodesic dome. The first synthetic diamond was made by General Electric in 1955.  Minute synthetic diamonds are often used as abrasives today.  Diamond coatings can be synthetically made by heating carbon dioxide over a metal surface with lasers.  Diamond coatings can extend the life of tools such as precision dies, drills, and saw blades by 1000 times.

Granular Activated Carbon

There are a few important dates in the history of carbon adsorption.  In 1773 Carl Wilhelm Scheele described his experiments on gasses exposed to carbon.   In 1785, Lowitz observed that charcoal would decolorize many liquids.  This is the earliest documented use of carbon for the removal of impurities in solutions.  In the 1860ís, charcoal was first used in England to remove tastes and odors from water supplies.  During the last 50 years there has been an improvement in the efficiency of charcoal through the process of activation.

In my experiment I am using granular activated carbon filters.  These filters use a process called adsorption, which is the removal of material from water.  Adsorption is one of the most efficient organic removal processes for an engineer.  Activated carbon is very porous and has a large surface area for its size.  It has a surface area of 500 to 1400 square meters for every gram.  Carbon granules can also act as a filter because larger particles in the water are trapped between the carbon granules.  Activated carbon can also remove non-biodegradable materials, which could have returned to the environment.

Activated carbon is made from carbonaceous materials such as wood, coal, peat, nut shells, sawdust, and petroleum residues.  Activated carbon is made in two separate processes.  The first one is carbonization, which is the dehydration and the conversion of organic materials to primary carbon.  The second one is activation, which is the burn-off of decomposition products created during carbonization and enlargement of the pores in the carbon materials.

The following are the important steps in making Granular Activated Carbon:
 1.  Dry the raw material at temperatures up to 170º Celsius.
2.  Heat the dried material above 170º Celsius so it is broken down and gasses such as carbon monoxide, carbon dioxide and acetic acid are released.
 3.  The material is then heated further and decomposed at temperatures of 270º to 280º Celsius.
4.  The carbonization process is then completed at 400º to 600º Celsius to produce approximately 80% primary carbon.
 5.  In the activation process the carbonized product is then treated with an activating agent such as steam or carbon dioxide.  Steam is most widely used because at 750º to 950º Celsius it burns off by-products and increases the pore size.

An important consideration in the performance of and activated carbon filter is how long the contact time is between the carbon and the chlorine.  Contact time is the term engineers use to describe how long the water is in contact with the carbon.


Chlorine is in group 17 on the periodic table (VIIa).  The symbol for chlorine is Cl.  The electron configuration is 2-8-7, which means there are 2 electrons close to the nucleus, 8 electrons revolving a little bit farther away from the nucleus, and there are 7 electrons very far away from the nucleus.  The atomic number for chlorine is 17, which is the total of all the electrons.  The atomic weight of chlorine is 35.453.  Chlorine is the twentieth most plentiful element in the earthís crust.  Chlorine melts at negative 101º Celsius and boils at negative 34.05º Celsius.

Chlorine is a greenish-yellow gas and has a bad smelling odor.  Chlorine was first identified by Carl Wilhelm Scheele who thought it was a compound.  In 1810, a British chemist named Sir Humphry Davy proved it was an element ant gave it its present name.  Chlorine can be liquefied by putting it under 5170 torr, or 6.8 atmospheres of pressure at a temperature of 20? Celsius.  When chlorine is in a large concentration, it is dangerous and was the first substance used as a poison in World War I.  Chlorine can be made commercially from salt water using a process called electrolysis,  which is running and electric current through the solution.  This produces free chlorine, hydrogen, and sodium hydroxide.  This chlorine is used in the manufacture of bleaching agents for home use and industry.

Chlorine is the most widely used disinfecting agent in local water supplies.  The main benefit of chlorine use is that it is able to completely disinfect throughout the water system.  This means the water is disinfected from the point the chlorine is added to until it reaches your home tap.  The cities of Selah and Yakima use chlorine as a disinfectant.  Selah maintains 0.6 milligrams of chlorine per liter of water in the city water supplies, and they check for a level of 0.4 to 0.8 milligrams of chlorine per liter of water at peopleís homes.  The city of Yakima puts 1.0 milligrams of chlorine per liter of water in the local system.  They measure 0.5 to 1.0 milligrams of chlorine per liter of water at peopleís homes.  They also input 1.0 milligrams of chlorine per liter of water at the Naches Water Treatment Plant.  The goal of most local water systems is to achieve 0.2 milligrams per liter for home use.  My test concentrations were well above this level and the results show that home carbon filters should last a very long time at 0.2 mg/l.

Why Filtration?

The primary reason for using carbon filtration systems is to remove taste and odors from water.  They can also remove impurities, or other organic compounds.  Carbon filters do not remove bacteria, and other microorganisms such as giardia and cryptosporidium.  Bacteria must be removed through biological purification before the water goes through carbon filtration.

U.S. water supplies are probably the safest in the world.  Still, health-conscious people in society are concerned about cancer causing compounds (carcinogens), called trihalomethanes, that are sometimes formed in water when chlorine is added to it.   Although carcinogens are not usually found in high enough concentrations to be harmful, some people still feel they should be removed.  These carcinogens can be removed with carbon filtration.

Industries also want pure water that is taste and odor free to make soft drinks and fruit drinks.  Some people at home also filter water to make their tea and coffee taste better.


I hope you enjoyed my report and learned a little more about carbon chlorine and filtration.  You can continue reading my journal to see how chlorine concentrations effect carbon filter performance.



American Water Works Association, et al.  Water Quality and Treatment ñ A Handbook of Community Water Supplies, New York NY, McGraw-Hill, Inc., 1990.

ìCarbon,î Microsoft Encarta 1998, 1998.

ìChlorine,î Comptonís Reference Collection 1996, 1995.

ìChlorine,î Microsoft Encarta 1998, 1998.

Clorox, Clorox News Line, [Online] Available, 2 December 1998, 13 December 1998.

Environmental Protection Agency, Process Design Manual for Carbon Adsorption, Cincinnati, OH, October 1973.

Omni Filter, Frequently Asked Questions, [Online] Available, 9 December 1998.

Omni Filter, Water News, [Online] Available, 9 December 1998.

Omni Filter, Why Filter Your Water, [Online] Available, 9 December 1998.

Pooler, Theodore W., Professional Engineer.  Huibregtse, Louman Assoc. Inc.,  15 November 1998, 19 February 1999.

ìReagent.î  The Readerís Digest Great Encyclopedia Dictionary.  1966


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