A comparison was made of expanded-bed and packed-bed modes of operation of activated carbon adsorption systems in the direct physico-chemical treatment of raw sewage and primary effluent. The project involved extended field testing of a pilot scale treatment system of chemical clarification followed by adsorption. The expanded-bed and packed-bed modes of operation demonstrated essentially equivalent removal of organic matter from the chemically clarified effluent. When a 24 ft. settled depth of activated carbon was used, both systems consistently produced a clear, treated water with an average organic content of only 3-5 mg/l, measured either as TOC or BOD. The expanded bed mode offered several advantages: (1) it eliminates plugging or fouling with particulate matter and air binding; (2) feed pressure remains constant and maintenance requirements are minimal; and (3) it provides an opportunity for a degree of natural aeration. Estimated cost for treating raw waste water in a 10 MGD plant by this process is about 20 cents per 1000 gal. with a total estimated investment of $4,000,000. (WRSIC abstract)