Patent ID: 7166227

Claim:
A method of treating, in wastewater purification, sludge containing organic matter, divalent iron and phosphorus, comprising: treating the sludge so that it contains dissolved iron and phosphorus at a molar ratio Fe:P of above 1:1; treating the sludge at 0–100° C. with an acid, wherein a pH of 1–5 is achieved for dissolution of divalent iron and phosphorus from the sludge; supplying the sludge with an oxidizer or mixture of oxidizers selected from hydrogen peroxide and percompounds, whereby divalent iron is oxidized by Fenton's reaction to trivalent iron; and (i) trivalent iron is precipitated as trivalent iron phosphate particles to promote improved dewatering of the sludge; (ii) free radicals with a deodorisation and sanitation effect are formed by Fenton's reaction; dewatering the sludge at a pH of at most 7; and recirculating the aqueous solution obtained in dewatering to the wastewater purification.