Method for treating sludge from wastewater treatment
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United States of America Patent
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Apr 17, 2001
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N/A
app pub date -
Sep 14, 1999
filing date -
Mar 14, 1997
priority date (Note) -
Expired
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Abstract
A method for treating sludge from wastewater purification is described. In the method, a sludge is treated, which contains phosphorus and at least one metal which originates from precipitation chemicals and which is selected among divalent iron and aluminum, the pH of the sludge being adjusted to below 4, preferably below 2, for dissolving the content of the phosphorus and said metal in the sludge; the remaining sludge is separated; the solution relieved of sludge and containing phosphorus and said metal is treated for precipitation of the phosphorus content of the solution as FePO.sub.4 at a pH of 2-3; and precipitated FePO.sub.4 is separated. The method is characterized in that the solution which remains after separation of FePO.sub.4 and which contains said metal from the precipitation chemicals, is recycled to the wastewater purification. The phosphorus content of the solution is precipitated as FePO.sub.4 by adding an at least equivalent amount of Fe.sup.3-.
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