Method for treating wastewater sludge

Abstract

A method of decontaminating wastewater sludge to a level that meets or exceeds USEPA Process to Further Reduce Pathogens standards, wherein lime or kiln dust and/or other alkaline materials are mixed with wastewater sludge in sufficient quantity to raise the pH of the mixture to 12 and above for a predetermined time and drying the resulting mixture.

We claim:  
     
       1. A method of treating wastewater sludge to provide a fertilizer for agricultural lands which can be applied directly to the lands which consists essentially of the following steps: 
       mixing said sludge with at least one alkaline material; wherein , the amount of added material mixed with said sludge being sufficient to raise the pH of said mixture to at least 12 and to hold the pH of greater than 12 for at least 7 days , ; and  
       actively drying said mixture for at least 30 days and until a minimum solids concentration of 65% solids is reached, the amount of added material being also sufficient to maintain the pH above 12 until the sludge solids achieve at least 60% solids by weight,  
       the amount of added material mixed with said sludge and the length of time of drying being sufficient to reduce significantly offensive odor of the sludge to a level that is tolerable ; , to reduce animal viruses therein to less than one plaque forming unit per 100 ml of said sludge; , to reduce pathogenic bacteria therein to less than three colony forming units per 100 ml of said sludge ; , to reduce parasites therein to less than one viable egg per 100 ml of said sludge ;  , to reduce vector attraction to said sludge ;  and to prevent significant regrowth of the pathogenic microorganisms, while being insufficient to eliminate all beneficial non-pathogenic microorganisms from the sludge.  
     
     
       2. The method set forth in  claim 1  wherein the added material comprises kiln dust and the amount of added material comprises about 35% by weight of the sludge to reduce the odor to a level that is tolerable in a closed room even though the pH may drop below 9 during the drying, and maintain that odor control indefinitely even though said mixture is exposed to climatic conditions. 
     
     
       3. The method set forth in  claim 1  wherein the amount of added material mixed with said sludge and the length of time of drying is sufficient to reduce the odor to a level that is tolerable in a closed room even though the pH may drop below 9 during the drying, and maintain that odor control indefinitely even though said mixture is exposed to climatic conditions. 
     
     
       4. The method set forth in  claim 1  wherein the alkaline material is selected from the group consisting of lime, cement kiln dust and lime kiln dust to form a mixture. 
     
     
       5. A method of treating wastewater sludge to provide a fertilizer for agricultural lands which can be applied directly to the lands which consists essentially of the following steps: 
       mixing said sludge with at least one alkaline material; wherein , the amount of added material mixed with said sludge being sufficient to raise the pH of said mixture to at least 12 for at least 72 hours , ; 
       concurrently with the high pH pH, heating the mixture to at least 50° C., but not at a temperature sufficient to cause sterilization, the amount of heat being sufficient that the sludge stored in a static condition will be maintained at a temperature of at least 50° C. for at least 12 hours , ; and 
       actively drying said mixture until a minimum solids concentration of  50 %  solids is reached, 
       the amount of added material mixed with said sludge, the heating, and the length of time of drying being sufficient to reduce significantly offensive odor of the sludge to a level that is tolerable ; , to reduce animal viruses therein to less than one plaque forming unit per 100 ml of said sludge ; , to reduce pathogenic bacteria therein to less than three colony forming units per 100 ml of said sludge ; , to reduce parasites therein to less than one viable egg per 100 ml of said sludge ; , to reduce vector attraction to said sludge ;  and to prevent significant regrowth of the pathogenic microoganisms, while being insufficient to eliminate all beneficial non-pathogenic microorganisms from the sludge. 
     
     
       6. The method set forth in  claim 5  wherein the added material comprises kiln dust and the amount of added material comprises about 35% by weight of the sludge to reduce the odor to a level that is tolerable in a closed room even though the pH may drop below 9 during the drying, and maintain that odor control indefinitely even though said mixture is exposed to climatic conditions. 
     
     
       7. The method set forth in  claim 6  wherein the amount of added material mixed with said sludge and the length of time of drying is sufficient to reduce the odor to a level that is tolerable in a closed room even though the pH may drop below 9 during the drying, and maintain that odor control indefinitely even though said mixture is exposed to climatic conditions. 
     
     
       8. The method set forth in  claim 5  wherein the alkaline material is selected from the group consisting of lime, cement kiln dust and lime kiln dust to form a mixture.