Patent ID: 7285222

Claim:
A method for recycling sludge during waste-water treatment, comprising the steps of: chemical coagulation for production of a sludge including copper ions; sulfuric acid leaching wherein said sludge is leached in sulfuric acid of concentration 1-2N, a copper-rich solution and residues are separated, said solution having a copper content attaining 18-39 g/L; and refrigeration and crystallization for transforming said solution into copper sulfate crystals; wherein said sludge is recycled to produce said copper sulfate crystals, and said residues are reused as a coagulant in said step of chemical coagulation, achieving a goal of zero sludge production; and wherein said step of chemical coagulation further comprises the steps of: (1) waste-water equalizing in a waste-water equalization tank for storing raw waste-water and for adjusting the variable effect of concentration on said waste-water; (2) mixing said waste-water with a coagulant including said residues in a coagulation tank for increasing the concentration of metallic ions; (3) adjusting the pH value of said waste-water in a pH adjustment tank for making said waste-water basic, thereby facilitating the formation of metallic hydroxides; (4) adding a polymer flocculating agent to said waste-water in a flocculated tank for accelerating the precipitation of said metallic hydroxides; (5) separating said metallic hydroxides and upper-layer waste-water in a precipitation tank; (6) filtering out impurities and materials that deteriorate water quality within said upper-layer waste-water in a filtering unit; (7) adjusting the pH value of said upper-layer waste-water in a neutralization and effluent tank so that said upper-layer waste-water satisfies a standard of effluent water; (8) sending a solid sludge to a sludge thicken tank, guiding metallic hydroxides precipitated at a bottom of said precipitation tank into said sludge thicken tank for enrichment, sending liquid induced in said step of sludge thicken back to said waste-water equalization tank to mix said raw waste-water therein; and (9) dehydrating said sludge from said sludge thicken tank in a sludge hydro-extractor; to produce said sludge including copper ions.