Method for Processing Sludge

Abstract

This invention relates to a method for processing sludge involving the addition of a lime-based basic agent to a sludge having a first pH value in order to raise the pH to a second value higher than the first one, adding at least one anionic organic flocculating agent that is active at the second pH value, flocculating the sludge, and separating the flocculated sludge between dehydrated sludge and a liquid phase.

1 . Sludge treatment method, comprising
 addition, to a sludge having a first pH value below 9, of a basic agent based on lime, with a view to raising the pH to a second value higher than the first,   addition of at least one anionic organic flocculant, active at the said second pH value wherein said anionic organic flocculant is an anionic polymer having a mean molecular weight greater than 500,000 Da,   flocculation of the sludge, and   separation in the flocculated sludge between dewatered sludge and a liquid phase; and   characterized in that the basic agent based on lime to add to the sludge having said first pH value below 9 requires, in order to reach a pH of 12 by introducing said basic agent into an aqueous solution of NH 4 Cl/(NH 4 )2HPO 4  having an initial pH of 7.5, a time t pH12  equal to or less than 90 seconds, in order to cause said rise in pH of the sludge up to the aforementioned said second value in less than 5 minutes, wherein said second value is equal to or greater than 11, and wherein said basic agent based on lime is accelerated basicity lime selected from the group consisting of partially slaked quicklime, limes formed by particles having a d 50  equal to or less than 30 μm and high reactivity quick lime.   
     
     
         2 . Method according to  claim 1 , characterized in that the said rise in pH lasts for less than 3 minutes. 
     
     
         3 . Method according to  claim 1 , characterized in that the addition of the basic agent based on lime and the addition of the said at least one anionic organic flocculant take place simultaneously. 
     
     
         4 . Method according to  claim 1 , characterized in that the lime contains a proportion >0 and <10% of alkali metal hydroxide by weight. 
     
     
         5 . Method according to  claim 1 , characterized in that the said at least one organic flocculant is chosen from the group consisting of polyelectrolytes based on polymers of copolymers of acrylic acid, acrylate, acrylamide and mixtures thereof. 
     
     
         6 . Method according to  claim 1 , in which the said anionic organic flocculant is an anionic polymer having a mean molecular weight greater than 1,000,000 Da. 
     
     
         7 . Method according to  claim 1 , in which the said anionic organic flocculant is an anionic polymer having a mean molecular weight between 5.10 6  and 35.10 6  Da. 
     
     
         8 . Method according to  claim 1 , in which the said anionic organic flocculant is an anionic polymer having a mean molecular weight between 15.10 6  and 30.10 6  Da. 
     
     
         9 . Method according to  claim 1 , characterized in that the said second pH value is equal to or greater than 12. 
     
     
         10 . Method according to  claim 1 , characterized in that the said rise in pH lasts for less than 2 minutes. 
     
     
         11 . Method according to  claim 1 , characterized in that the said rise in pH lasts for less than 1 minute. 
     
     
         12 . Method according to  claim 1 , characterized in that the addition of the basic agent based on lime and the addition of the said at least one anionic organic flocculant take place separate in time.