An immobilized cell bioreactor with granular activated carbon as the inert material inoculated two species, Pseudomonas sp1 and Pseudomonas sp2, to degrade chemical oxygen demand (COD) and benzene, naphthalene, phenanthrene, pyridine, quinoline, and isoquinoline in the wastewater discharging from a biomass gasification power-generation plant. The results indicated that these toxic compounds were removed efficiently. The course of the 66-d experiment was divided into three phases mainly in accordance with different influent COD concentrations: microbial adaptation and proliferation phase (from 1 to 23 d), stable metabolic phase (from 24 to 57 d), and high efficient reaction phase (from 58 to 66 d). The high removal rates of COD and some toxic compounds with a 24-h hydraulic retention time were accomplished.