The potential of the anaerobic, expanded-bed, granular activated carbon (GAC) reactor in treating a high-strength waste containing RCRA semivolatile organic compounds was studied. Six semivolatiles, orthochlorophenol, nitrobenzene, naphthalene, para-nitrophenol, lindane, and dibutyl phthalate, were fed to the reactor in a high-strength matrix of background solvents consisting of acetate, acetone, and methanol. Performance was evaluated over a period of 530 days. The reactor was found to effect complete removals of all the semivolatile compounds with the exception of orthochlorophenol. Removal of orthochlorophenol ranged from 77 percent to 99 percent. Removal of all the semivolatiles was elucidated relative to adsorption and biodegradation. With the exception of naphthalene, which was found to be completely removed by adsorption, all the other semivolatiles were removed primarily by biodegradation. COD removals in excess of 90 percent were also observed throughout the study. (Copyright (c) 1992 Water Environment Federation.)