Nitrogen recovery system and method using heated air as stripping gas

Abstract

A process for the recovery of nitrogen from anaerobically digested liquid waste and for the collection of the nitrogen as nitrate compounds that can be used to produce fertilizer and compost, includes stripping ammonia from anaerobically digested liquid waste, and converting the ammonia into nitrates via nitrification. The stripping gas is heated above ambient atmospheric temperature to improve nitrogen recovery. The heat can be reclaimed by burning gases generated during the anaerobic digestion process.

1 . A method for recovering nitrogen from liquid waste, comprising: 
 (a) anaerobically digesting liquid waste into digested liquid waste containing ammonia;    (b) stripping said ammonia from said digested liquid waste to produce gas containing ammonia; and    (c) converting stripped ammonia into nitrogen-containing compounds in a biofilter.    
   
   
       2 . The method of  claim 1 , further comprising separating solids from the digested liquid waste prior to stripping.  
   
   
       3 . The method of  claim 1 , further comprising raising the pH of the digested liquid waste.  
   
   
       4 . The method of  claim 1 , further comprising raising the temperature of the digested liquid waste.  
   
   
       5 . The method of  claim 1 , wherein ammonia is stripped by contacting the digested liquid waste with air.  
   
   
       6 . The method of  claim 1 , further comprising collecting organic biomass containing nitrogen.  
   
   
       7 . The method of  claim 1 , wherein the pH of the digested liquid waste is about 7 to about 8.  
   
   
       8 . The method of  claim 1 , wherein the pH of the digested liquid waste is about 8 to about 9.  
   
   
       9 . The method of  claim 2 , wherein the separated solids are recycled to anaerobic digestion.  
   
   
       10 . A method for recovering nitrogen from anaerobically digested liquid waste, comprising: 
 (a) stripping ammonia from anaerobically digested liquid waste to produce gas containing ammonia; and    (b) converting stripped ammonia into nitrogen-containing compounds in a biofilter.    
   
   
       11 . The method of  claim 10 , further comprising raising the pH of the digested liquid waste.  
   
   
       12 . The method of  claim 10 , further comprising raising the temperature of the digested liquid waste.  
   
   
       13 . The method of  claim 10 , wherein ammonia is stripped by contacting the digested liquid waste with air.  
   
   
       14 . The method of  claim 10 , further comprising collecting organic biomass containing nitrogen.  
   
   
       15 . The method of  claim 10 , wherein the pH of the digested liquid waste is about 7 to about 8.  
   
   
       16 . The method of  claim 10 , wherein the pH of the digested liquid waste is about 8 to about 9.  
   
   
       17 . A method for making fertilizer from liquid waste containing manure, comprising: 
 (a) anaerobically digesting liquid waste containing manure into digested liquid waste containing ammonia;    (b) stripping said ammonia from said digested liquid waste to produce gas containing ammonia; and    (c) converting stripped ammonia into nitrogen-containing compounds in a biofilter.    
   
   
       18 . The method of  claim 17 , further comprising separating solids from the digested liquid waste prior to stripping.  
   
   
       19 . The method of  claim 17 , further comprising raising the pH of the digested liquid waste.  
   
   
       20 . The method of  claim 17 , further comprising raising the temperature of the digested liquid waste.  
   
   
       21 . The method of  claim 17 , wherein ammonia is stripped by contacting the digested liquid waste with air.  
   
   
       22 . The method of  claim 17 , further comprising collecting organic biomass containing nitrogen.  
   
   
       23 . The method of  claim 17 , wherein the pH of the digested liquid waste is about 7 to about 8.  
   
   
       24 . The method of  claim 17 , wherein the pH of the digested liquid waste is about 8 to about 9.  
   
   
       25 . The method of  claim 17 , wherein the separated solids are recycled to anaerobic digestion.