BACKGROUND: This study is focused on the application of intensified biological systems for the degradation of halogenated organic compounds. The single and combined effects of cometabolism and bioaugmentation with Pseudomonas putida on the aerobic degradation of 4-chlorophenol (4-CP) in sequencing batch reactors was studied. Phenol was added as growth substrate to enhance 4-CP biodegradation through cometabolic transformation. RESULTS: Adaptation of activated sludge by increasing 4-CP loads aimed at a progressive acclimation to that compound, which could be successfully degraded at loading rates below 55 mg g-1 VSS d-1. Using phenol as cosusbtrate allowed almost a threefold decrease of the time required for the exhaustion of 4-CP. The addition of phenol also reduced the toxic effect of 4-CP over P. putida. The bioaugmentation of the SBR with P. putida enhanced the 4-CP removal rate, allowing the SBR to deal with 4-CP loads up to 120 mg g-1 VSS d-1. CONCLUSION: Bioaugmentation of SBR with P. putida improves the capacity of this system to withstand high toxic shocks. Cometabolic degradation of 4-CP with phenol improves the removal rates achieved by the SBR at similar 4-CP loads. Both strategies are more convenient intensification techniques than acclimation for the biological treatment of 4-CP. Copyright (c) 2012 Society of Chemical Industry