AbstractAddition of powdered activated carbon (PAC) significantly improved treatment of a chemical waste landfill leachate in sequencing batch bioreactors (SBRs). Concentrations for many of the monitored halogenated organic compounds in the effluent were below their respective detection limits. Excellent treatment efficiency was achieved under a variety of operating conditions: wastewater composition, feed rate, hydraulic retention time, organic loading, PAC dosages, biomass and PAC concentrations in the bioreactors. The PAC‐SBR performance was unaffected when wastewater feeding was suspended during weekends and holidays. The PAC‐SBR treatment cost is much lower than either that of the conventional granular activated carbon adsorption technology or the two‐stage process of biodegradation and carbon trea