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

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Abstract
A rise in pHw of three mineral soils was obtained with Al precipitated sludge due to the decrease in exchangeable Al content. The content of organic matter complexed (AAA-EDTA extractable) Al increased in the soils. The sludges precipitated with Fe had no effect on soil pHw and exchangeable Al in comparison to the no sludge treatment. Ca sludge as well as lime stabilized sludges elevated soil pHw by 0.5–1.5 units. The increase in soil organic matter content obtained with sludges was only slight, Fe+Al sludges resulting in the highest increases. Extractable P content of soils treated with Al sludge was lower than that of soils treated with Fe+Al or Fe sludges. In limed soils (pHw 6.5) the P contents did not deviate. The greatest increase in soil extractable P content was obtained with Ca sludge.