Carbon Dioxide

 

 

Information on Carbon Dioxide Amounts and Water Quality

 

  1. What is it?

    Carbon dioxide is a poisonous gas. A molecule of carbon dioxide is made up of 1 part carbon and 2 parts oxygen. Therefore, its chemical formula is CO2.

 

  1. Where is it found?

    1. In our atmosphere. About 0.03% of our air is carbon dioxide.
    2. In solution, (mixed in) the water of lakes, ponds, streams and oceans.


  2. Where does it come from?

    1. It is produced by almost all living organisms (both plant and animal).
    2. It is given off, (exhaled) into the air every time we breathe.
    3. Even organisms without lungs or gills release carbon dioxide into the environment. This includes insects, plants, bacteria, etc.
    4. Plants give off carbon dioxide mostly at night.
    5. All aquatic organisms release this gas into the water. Some of it bubbles to the surface, some of it dissolves (mixes in) with the water, but most of the carbon dioxide found in the water is produced by organisms (bacteria mostly) that carry on decomposition of dead material.







  3. Carbon dioxide and plants - a nest relationship

    1. Most of the plant material in an aquatic environment is made up of algae.
    2. During daylight all plants use carbon dioxide and give off oxygen. This process is called photosynthesis - it requires light.
    3. At night, the opposite is true. Plants use oxygen and give off carbon dioxide. This process is called respiration.
    4. All dead plants will use up a lot of oxygen and give off a lot of carbon dioxide as they rot and decay.


  4. Carbon dioxide and animals - another exciting relationship!

    1. All animals use oxygen and give off carbon dioxide.
    2. Dead animals continue to use oxygen and give off carbon dioxide as they rot and decay.


  5. Carbon dioxide and other chemical factors?

    1. Because oxygen is used up as carbon dioxide is produced, the quantities of these gases are usually opposite in quantities. This means if there is a high carbon dioxide amount there is going to be a low oxygen amount.
    2. High levels of carbon dioxide will make the pH more acidic.


  6. Other important facts about carbon dioxide.

    1. A high level of carbon dioxide usually indicates that there is a lot of dead material undergoing decomposition. This may occur naturally, but could be the result of different types of water pollution or water treatment.
    2. The carbon dioxide in a lake is not constant; it changes. Below are some diagrams and explanation of some of those changes and fluctuations that occur in the amounts of carbon dioxide.
      1. Top/bottom - Dead organisms usually sink. As a result, the carbon dioxide level caused by their decomposition is usually greater near the bottom of the lake.


        2. Day/night - The carbon dioxide level will be greater at night because plants will be using oxygen and producing carbon dioxide at the time.

         

        3. Spring/Fall - The carbon dioxide level will be greater in the fall as a result of dead algae plants and animals that have died over the winter and are now decaying.

         

        4. New/old - In terms of succession, an older lake will have more carbon dioxide because of more decay due to more organisms.

       

 

 

Carbon Dioxide (CO2) in Water

Free (CO2) Carbon Dioxide in water exists in varying amounts naturally. Most well waters will contain less than 50 ppm of Carbon Dioxide in drinking water. A large amount of Carbon Dioxide in water creates an acidic water conditions. When carbon dioxide dissolves in water it creates the following; Water (H2O) plus carbon dioxide (CO2) yields carbonic acid (H2CO3). The dissociation of carbonic acid yields hydrogen (H+) and bicarbonate alkalinity (HCO3). The carbon dioxide in water ph value will drop as the concentration of carbon dioxide increases, and conversely will increase as the bicarbonate alkalinity content increases. Carbon dioxide in water equation is as follows; H2O + CO2 <====>H2CO3<====> H+ + HCO3- Carbon dioxide in Water with a pH of 3.5 or below generally, contains mineral acids such as sulfuric or hydrochloric acid. Carbon Dioxide can exist in waters with pH values from 3.6 to 8.4, but will never be present in waters having a pH of 8.5 or above. The pH value is not a measurement of the amount of carbon dioxide in the water, but rather the relationship of carbon dioxide and bicarbonate alkalinity.

 

 



CO2 - Carbon Dioxide Water Treatment

Free CO2 in water, can be easily dissipated by aeration. A two column deionizer (consisting of a hydrogen form strong acid cation and a hydroxide form strong base anion) will also remove the carbon dioxide from drinking water. The cation exchanger adds the hydrogen ion (H+) which shifts the above equation to the left in favor of water and carbon dioxide release. The anion resin removes the carbon dioxide by actually removing the bicarbonate ion. A forced draft degasifier placed between the cation and anion will serve to blow off the CO2 before it reaches the anion bed, thus reducing the capacity requirements for the anion resin. Another CO2 carbon dioxide water treatment option can be eliminated by raising the pH to 8.5 or above with a soda ash or caustic soda chemical feed system.

 

 

 

Testing Procedures