Pyrolysis of sludge from municipal wastewater treatment plants

Abstract

The contribution deals with the pyrolysis of three samples of sludge obtained from municipal wastewater treatment plants under the same process conditions: 0.2 g samples of material were pyrolysed in the nitrogen atmosphere; the final temperature of pyrolysis process was set at 850 °C, and after reaching this value it was kept for the next two hours. The carbon enrichment of pyrolytic coke was the highest in the case of non-limed sludge from the Ostrava Central Wastewater Treatment Plant (CWTP), namely 67.47%, in the case of sludge from the Sviadnov WTP it was 45.99% and in the case of limed sludge from the Ostrava CWTP it was 44.54%; carbon contents in these samples did not differ too much. Pyrolytic gases from the non-limed sludge from the Ostrava CWTP and from the sludge of Sviadnov WTP show similar compositions (H2 forms about 70% and CO2 30% of detected gases). By pyrolysis of limed sludge from the Ostrava CWTP, a gas containing, in addition to hydrogen and carbon dioxide, also carbon monoxide (7% of detected gases) and methane (2.5% of detected gases) was produced. From experiments it is evident that above all the content of volatile organic compounds in sludge and the presence of monoxide calcium, which acts as catalyst in the pyrolysis reaction, in sludge influence the production of gases.