Thermal Conversion of Municipal Wastewater Sludge, Phase II: Study of Heavy Metal Emissions

摘要

The object of this work was to compare and analyze heavy metal emissions associated with the thermal conversion (incineration) processes which can be conducted in a multiple-hearth furnace to dry municipal wastewater (sewage) sludge and reduce its volume by forming an ash or char. Sludge for this project was obtained from Jersey City, New Jersey. It contains about 8 percent solids which were increased to between 40 and 50 percent solid by adding polymer as a filter aid and filtering it in a 4 ft x 4 ft pilot filter press having expandable rubber diaphragm plates. A pilot scale multiple-hearth furnace, .91 m (36 inch) 10 x 6 hearth was used for the thermal conversion process. Sludge was subjected to thermal conversion at the conditions: (1) Incineration at 900C (1625F); (2) Low Temperature Conversion at 700C (1290F) (starved air combustion or pyrolysis); (3) High Temperature Conversion at 900C (1290F) (starved air combustion or pyrolysis). Results indicated that the low temperature conversion substantially retained cadmium, lead, and beryllium in the ash or char when compared to incineration. However, the ash retained far more silver during incineration than it did during high or low temperature conversion.