Systems and Methods for Achieving Partial Nitrification in a Biological Nitrogen Removal Reactor

Abstract

Methods of controlling a nitrification reaction in a biological nitrogen removal reactor to favor partial nitrification of ammonia to nitrite instead of complete oxidation of ammonia to nitrate are disclosed. In some embodiments, the methods include the following: maintaining a pH in the reactor within a range that promotes growth of ammonia oxidizing bacteria; maintaining a concentration of dissolved oxygen in the reactor within a range that limits the ammonia oxidizing bacteria from completing nitrification; selecting an operational solids retention time within a range suitable for maintaining increasing concentrations of the ammonia oxidizing bacteria in the reactor while reducing concentrations of nitrite oxidizing bacteria in the reactor; and increasing a concentration of free ammonia in the reactor thereby inhibiting growth of the nitrite oxidizing bacteria in the reactor.

What is claimed is: 
     
         1 . A method of controlling conditions in a biological nitrogen removal reactor to favor partial nitrification of ammonia to nitrite, said method comprising:
 controlling conditions within said biological nitrogen removal reactor to promote growth of ammonia oxidizing bacteria;   increasing a concentration of free ammonia in said reactor thereby inhibiting growth of said nitrite oxidizing bacteria in said reactor; and   maintaining a concentration of dissolved oxygen in said reactor within a range that limits said ammonia oxidizing bacteria from completing nitrification.   
     
     
         2 . The method according to  claim 1 , wherein said step of controlling further comprises:
 includes maintaining a pH in said reactor within a range that promotes the growth of ammonia oxidizing bacteria; and   selecting an operational solids retention time within a range suitable for maintaining increasing concentrations of said ammonia oxidizing bacteria in said reactor while reducing concentrations of nitrite oxidizing bacteria in said reactor.   
     
     
         3 . The method according to  claim 2 , wherein said pH is about 7.4 to 7.6. 
     
     
         4 . The method according to  claim 1 , wherein said dissolved oxygen in said reactor is about 0.6 to 2.5 mg O2/L. 
     
     
         5 . The method according to  claim 2 , wherein said solids retention time is about 2.5 to 3.5 days. 
     
     
         6 . The method according to  claim 1 , wherein said reactor is operated at a temperature that is substantially the ambient temperature. 
     
     
         7 . The method according to  claim 1 , wherein a portion of said ammonia oxidizing bacteria in said reactor is  Nitrosomonas europaea.    
     
     
         8 . A system for achieving partial nitrification in a biological nitrogen removal reactor, said system comprising:
 a control module for controlling conditions within said biological nitrogen removal reactor to promote growth of ammonia oxidizing bacteria; and   a dissolved oxygen control module for maintaining dissolved oxygen in said reactor within a range that prevents ammonia oxidizing bacteria from completing nitrification;   wherein said system increases a concentration of free ammonia in said reactor thereby inhibiting growth of said nitrite oxidizing bacteria in said reactor.   
     
     
         9 . The system according to  claim 8 , wherein said control module comprises:
 testing apparatus for measuring pH, dissolved oxygen, and solids retention time in said reactor;   a pH control module for maintaining pH in said reactor within a range that promotes growth of ammonia oxidizing bacteria; and   a solids retention time control module for maintaining operational solids retention time in said reactor within a range suitable for maintaining increasing concentrations of said ammonia oxidizing bacteria in said reactor while reducing concentrations of nitrite oxidizing bacteria in said reactor.   
     
     
         10 . The system according to  claim 9 , wherein said pH control module is effective to adjust the pH in said reactor so that it is within a predetermined range. 
     
     
         11 . The system according to  claim 10 , wherein said predetermined range for pH in said reactor is about 7.4 to 7.6. 
     
     
         12 . The system according to  claim 10 , wherein said pH control module includes apparatus for adding sodium bicarbonate to said reactor to adjust pH. 
     
     
         13 . The system according to  claim 8 , wherein said dissolved oxygen control module is effective to adjust the dissolved oxygen in said reactor so that it is within a predetermined range. 
     
     
         14 . The system according to  claim 13 , wherein said predetermined range for dissolved oxygen in said reactor is about 0.6 to 2.5 mg O2/L. 
     
     
         15 . The system according to  claim 13 , wherein said dissolved oxygen module includes apparatus for injecting a mixture of air and ammonium into said reactor to adjust dissolved oxygen. 
     
     
         16 . The system according to  claim 9 , wherein said operational solids retention time control module is effective to adjust the operational solids retention time in said reactor so that it is within a predetermined range. 
     
     
         17 . The system according to  claim 16 , wherein said predetermined range for solids retention time is about 2.5 to 3.5 days. 
     
     
         18 . The system according to  claim 8 , wherein said reactor is operated at a temperature that is substantially the ambient temperature. 
     
     
         19 . The system according to  claim 8 , wherein said system is configured to operate automatically and in real time. 
     
     
         20 . The system according to  claim 8 , wherein a portion of said ammonia oxidizing bacteria in said reactor is  Nitrosomonas europaea.