AN ECONOMIC-EVALUATION OF BIOLOGICAL REMOVAL OF HEAVY-METALS FROM WASTE-WATER SLUDGE

An economic evaluation was performed for various sludge management practices, including the biological process of metal solubilization for digested and undigested sludges, and the traditional methods of sludge management (landfill, incineration, co-incineration, and the land spreading of liquid or dewatered sludges for agriculture). Biological solubilization (also called bacterial leaching), including lime neutralization and land spreading, was less expensive for undigested than for digested sludge, and was competitive with land spreading of nondecontaminated dewatered sludge for a plant treating 388 000 m3/d of wastewater. These two management practices are approximately equivalent and are less costly than all other options considered. However, for a plant treating 20 000 m3 of wastewater per day, metal solubilization was 43% more costly than the frequently practiced application of dewatered sludge onto agricultural land. For both plants (388 000 and 20 000), decontamination, followed by lime 'stabilization and land spreading, had less of an environmental impact than any of the other management options examined.