Organics and nutrient recovery from anaerobic digester residues

Abstract

Sludge from an anaerobic digester is treated to recover one or more of fibers, or solids or liquids with a high nutrient content. The solids or liquids can be used as a fertilizer. The fibers can be used in a plant growing medium. Solids are separated from liquids in the sludge and dried. The solids may be dried to produce a flake or pellet. Ammonia in the liquids is recovered and used to produce a concentrated acidic ammonium salt solution. This solution may be mixed with the solids to produce a nitrogen enhanced solid. The fibers and solids or liquids can also be used in combination to produce an enhanced plant growing medium. A device and process for removing ammonia from a liquid can be used in the system or separately.

We claim: 
     
         1 . An apparatus for treating sludge comprising,
 (a) one or more of a mechanical dewatering device and a dryer configured to receive the sludge and to output a solids fraction and a liquid fraction;   (b) an ammonia recovery system to receive the liquid fraction and output an acidic ammonium salt solution;   (c) a pellet making machine to receive the solids fraction and the acidic ammonium salt solution and to combine them into pellets.   
     
     
         2 . The apparatus of  claim 1  further comprising an air flow drier to receive and dry the pellets. 
     
     
         3 . The apparatus of  claim 1  wherein the ammonia recovery system comprises one or more of a steam based ammonia stripper and ii) a vacuum induced ammonia gas extractor. 
     
     
         4 . The apparatus of  claim 3  wherein the ammonia recovery system further comprises an ammonium salt solution concentrator. 
     
     
         5 . The apparatus of  claim 1  further comprising an anaerobic digester to produce the sludge. 
     
     
         6 . A process of making a fertilizer pellet comprising combining dried solids extracted from anaerobic digester sludge with an acidified liquid comprising ammonia previously removed from the anaerobic digester sludge. 
     
     
         7 . The process of  claim 6  further comprising drying the pellet by way of a flow of air at 90 degrees Celsius or less. 
     
     
         8 . A process comprising steps of a) recovering fibers and a filtrate from an anaerobic digester sludge; b) recovering solids and a liquid from the filtrate; and, c) recovering ammonia from the liquid. 
     
     
         9 . The process of  claim 8  wherein the fibers are used in a plant growing medium. 
     
     
         10 . The process of  claim 9  wherein at least some of the solid or liquids are added to the plant growing medium. 
     
     
         11 . The process of  claim 8  wherein at least some of the solids or liquids are converted into a granule or flake form.