Patent ID: 7048859

Claim:
A process consisting essentially of contacting a substantially aqueous stream, which comprises biosolids having anionic surface charges, with (a) an anionic inorganic colloid and (b) an organic polymer to produce flocculated biosolids under a condition effective to reduce the chemical oxygen demand of said stream; and optionally removing said flocculated biosolids from said stream; before said contacting, the pH of said stream is reduced with an acid to a pH of from 4.5 to less than 7; said inorganic colloid is present in said stream in the concentration of from about 20 to about 2000 ppm by weight and is selected from the group consisting of polysilicic acid, polysilicic acid microgel, acidic polyaluminosilicate, acid-stabilized polysilicate microgel, colloidal silica, colloidal tin oxide, aluminum modified colloidal silica, clay, and combinations of two or more thereof; and said organic polymer is present in said stream in the concentration of from about 1 to about 2500 ppm by weight, has a number average molecular weight greater than 1,000,000 and is selected from the group consisting of polyacrylamide, guar gum, and combinations thereof.