Effect of Phosphorus Precipitation Chemicals on Characteristics and Agricultural Value of Municipal Sewage Sludges

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Abstract
The precipitation of P from municipal waste waters with Ca, Al or Fe chemicals increased the content of these elements in sewage sludge. The total P content of Al sludges was the highest (30 g kg−1 DM) and that of Ca sludge the lowest (12 g kg−1 DM). About 1% of the total P was extractable in 0.5 M acid (pH 4.65) ammonium acetate, Ca sludge being an exception with about 30% amount of extractable P. The extractable fraction of total Ca (7–172 g kg−1 DM) varied between 39 and 98%. Acid (pH 4.65) ammonium acetate-EDTA extractable fraction of total Al (10–65 g kg−1 DM) varied between one and 23%, and that of total Fe (13–89 g kg−1 DM) between eleven and 23% in different sludges. Maximal Al extractable in 1 M KCl amounted to 0.2% of the total Al.

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