Factors affecting the fate of heavy metals in the activated sludge process

Abstract

The presence of heavy metals in wastewaters is of interest primarily because of their known toxicity to aquatic organisms at trace concentrations and their potential for economic recovery. In addition, increased volumes of wastewater sludges and the need for envi ronmentally safe reuse or disposal methods has focused attention on heavy metals and other toxic materials associated with these sludges. The sources of heavy metals in municipal wastewaters include industrial dis charges, water distribution system corrosion, and urban stormwater runoff.1 As a result, municipal (and indus trial) wastewater treatment plants are a logical focal point for the control of heavy metals discharged to the aquatic environment. Previous studies of heavy metal removal in waste water treatment plants have demonstrated the wide variability of removal both among different metals and for the same metal.2 ll Generally, about 5 to 20% re moval occurs in the primary sedimentation basin and an additional 10 to 80% removal occurs in the activated sludge process. Because of the wide variability of re moval?but high potential?the activated sludge pro cess was selected for further study.