Treatment method for waste water sludge comprising phoshorous, heavy metals and at least one metal
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United States of America Patent
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Feb 24, 1998
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N/A
app pub date -
May 31, 1996
filing date -
Aug 26, 1993
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Abstract
Waste water sludge which contains phosphorous, heavy metals and at least one metal originating from a waste water treatment coagulant, is treated in order to recover the phosphorous and the at least one metal, and to discharge the heavy metals. The at least one metal includes iron. The treatment method includes the steps of acidifying the sludge to dissolve metals contained therein; subjecting the acidified sludge to liquid-liquid extraction to thereby provide an aqueous phase or raffinate, and recovering at least a portion of the at least one metal; treating the raffinate, during a first precipitation stage, with an effective amount of chemicals to provide a precipitate including heavy metals, and a solution having a decreased content of heavy metals; discharging the precipitate including heavy metals; treating the solution having a decreased content of heavy metals, in a second precipitation stage, with an effective amount of chemicals to provide a precipitate including phosphorous; and recovering phosphorous from the precipitate including phosphorous.
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