Properties of sewage sludge and of the thermally processed sewage sludge ash

The sludge collected in 1 German-and 5 Polish sewage treatment plants contained similar to50% mineral substances in its dry mass. TG showed wt. losses of 71.5, 32 and 52% up to 233, 405 (diffuse exo) and 457degreesC (sharp exothermal effect). The contents of N, C, and H were 5.3-5.8, 38.5-39.4, 5.1-5.2% (dry basis), resp. The heat of combustion of dry sludge was 16-16.8 MJ/kg. The PO43- and Ca determined in the ash were 11-19 and 2-12%, resp. Heavy metals (Zn, Pb, Cu, Ni, Cr, Cd, Co) ranged from several ppm (Cd. similar to20 ppm) to a few tenths (Cr. 0.2-0.3%) or even a few % (Zn, 6.9%). X-rays disclosed SiO2, Fe2O3, CaSO4 and Ca9FeH(PO4)(tau) (minor peaks) as amorphous, and quartz, calcite and albite as crystalline phases in the ash.