Municipal wastewater sludges frequently contain undesirably high concentrations of heavy metals and/or organic pollutants which interfere with beneficial use of sludge on farmland and with some disposal practices such as ocean disposal. Centrifugal classification is a low-cost procedure that has been demonstrated in the study to concentrate contaminants into the centrate stream, thus reducing the contaminants in the centrifuge cake and upgrading it for beneficial use. Experiments with a small solid-bowl continuous decanter centrifuge were conducted to show the effects of machine and process variables (e.g., centrifuge speed, flow rate) on separation of heavy metals. Recovery factors varied from day to day, no doubt as a result of changes in the sludge. Results from a full-scale installation at a Los Angeles County plant showed similar recovery factors, differing in some details. Examination of three years of Los Angeles' operational data showed consistent separation with no marked trends. Los Angeles data also showed substantial concentration of organic pollutants into the centrate solids.