Pilot-scale studies dealing with the use of recirculating-slurry solids-contact clarifiers in treating activated sludge plant effluent were studied. Evaluation of all available materials led to selection of Darco S-51 activated powdered carbon and Purifloc C-32 polyelectrolyte flocculating agent, with 6 to 7 mg/l of polyelectrolyte required at a carbon feed rate of up to 140 mg/l. 30% greater carbon efficiency, as opposed to a single stage conventional unit, was achieved with a single slurry unit, while results for two series clarifiers were comparable to that of two conventional counter-current adsorption systems requiring multiple agitated tanks, clarifiers, and filters. Estimated costs for a 10 mgd plant with 240 mg/l and 8 mg/l dosages of carbon and polyelectrolytes respectively are $0.15/1000 gal for a 10 mgd plant, and $0.12.7/1000 gal for a 100 mgd plant. Further cost reductions could be possible in the event that effluent quality restrictions would allow a decrease in the carbon dosages. (WRSIC abstract)