This master's thesis considers the feasibility of municipal sludge lime treatment witch is carried out before centrifuge dewatering. At lime treatment the digested sludge soluble phosphorus sequestration to sludge could be manage, either sludge thickening or reject water treatment context. Reject waters and digested sludge were taken from three different wastewater treatment plant Suomenoja, Ali-Juhakkala and Kariniemi. All wastewater treatment plants sewage treatment process is a bio-chemical and phosphorous precipitation has been carried out using ferrous sulfate.Lime treatment was carried out on a laboratory scale mixers to one liter batch test by raising the pH to about 9 using slaked (Ca(OH)2) or quick lime (CaO). Lime treatment precipitated the soluble phosphorus, when the reject water or digested sludge phosphorus concentration was over the residual concentration of lime phosphorus precipitation. However, the lime treatment also released the sludge bound phosphorus in to soluble form. Phosphorus release of a soluble form thought to be due i.a. the formed iron hydroxide of phosphorus chemical precipitation. The phosphate will release from the solid phase when iron hydroxide phosphate oxide surface sorption capacity decreases when the pH rises.Due to the low phosphate concentration the precipitation of the phosphorous was low in the reject water and digested sludge of Suomenoja and Ali-Juhakkala samples. In these samples the phosphate concentration even increased slightly because of lime treatment. The reject water and digested sludge of Kariniemi the phosphate reduction was good with reject water up to 60 % and the digested sludge up to 50 %. Lime treatment especially after the digested sludge phosphate release from the solid fraction back into a soluble form was strong. 24 hours after the lime precipitation of the digested sludge the phosphate concentration was increased even over the original level. At reject water the phosphate release after the lime treatment was low. The effect of lime treatment was also examined to ammonium nitrogen concentration, alkalinity and CODCr. Also the reject water and digested sludge settle ability of suspended solids and hygienic quality where examined. However, the addition of lime the Suomenoja flotated digested sludge was settled at the tests.Sludge lime treatment can potentially gain an advantage over the use of sludge in agriculture promotion point of view. Lime precipitation of phosphorus achieved from reject water and digested sludge. The release of phosphate after the sludge lime treatment should be evaluated for follow-up studies, after that the conclusions can be drawn to method feasibility on sludge gravity thickening. According to the results of this thesis lime treatment can be only recommended for use in wastewater treatment plants which reject water containing plenty of phosphorous. Lime treatment of reject water can significantly reduce the internal phosphorus loading of the wastewater treatment plant.
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