Disinfection Return to Process Page

What is disinfection and why is it done?   After completing the tertiary settling stage, the wastewater is almost ready to be returned back into the environment.  Up to this point, the main thrust of treatment has been with removing pollutants like solids, ammonia, and oxygen demand that can cause harm to the aquatic life downstream.  Since the treatment process uses naturally occurring bacteria to aid in the treatment there have been no steps taken to eliminate those bacteria.  The disinfection process is the final treatment stage whose sole purpose is to eliminate the bacteria that we have depended upon so far.  The bacteria that live in wastewater, if left to go into the environment, can cause illness and in remote cases death.  There are several different methods of disinfecting the wastewater, but the most commonly used method is chlorine.  The same chlorine that is used to disinfect our drinking water supplies and pools is also used to disinfect the wastewater.  At the LaPorte Wastewater Facility, we receive the chlorine in a compressed, liquid form.  The chlorine comes out of the cylinder as a gas at room temperature and is then mixed with the wastewater at a high enough level to kill the bacteria in the water.  The effect is the same as adding chlorine to a swimming pool.  Once the chlorine has been added, the wastewater flows through another tank called a contact chamber to allow the chlorine time to work on the bacteria.  By the time the water has reached the end of the contact chamber it is disinfected, however it is now also toxic to aquatic life if it were to be released back into the environment.  In order to eliminate the toxicity from the chlorine, we apply sulfur dioxide to the water which will remove the excess chlorine.  With this final step, the wastewater has now been cleaned and sanitized and is ready to be recycled back into the environment.