Analysis of the Variability of the Composition of Sewage Sludge Before and After Drying Treatment – SEM Studies

The aim of the study was to determine the physical and chemical properties of the sewage sludge from “Pomorzany” and “Zdroje” municipal wastewater treatment plants located in Szczecin, Poland. The paper presents the outcomes of SEM observation of dried and stabilized sewage sludge. The research on the obtained materials was conducted using reference methods; the images from a scanning electron microscope were used. The amount of sewage sludge produced with the methods of its management was presented. The technology of sludge management is based on its dehydration up to dry weight content of roughly 20% and then drying in contact dryers up to 90–92% dry weight, separately in both plants. Dried sewage sludge is subsequently burned in mechanical grid boilers at “Pomorzany” WWTP. The analyzed materials were characterized by the pH of 7.90–8.42, dry mass and average organic matter content were 18.949% and 68.903%, respectively. The elements identified in the largest amount on the surface of analyzed materials included calcium, iron, phosphorus, sulphur and silicon. The amount of phosphorus ranging from 1.82 to 3.44% indicates the possibility of using sewage sludge as organic fertilizer product or an alternative source of phosphorus.