In this work, feasibility of using chemical pretreatment to improve the anaerobic biological degradation of industrial effluents containing high concentrations of phenolic compounds was investigated. For this purpose, chemical pretreatment of the wastewater generated from olive oil production process, namely olive mill effluent (OME), was conducted by means of acid cracking followed by coagulation-flocculation process using one of the coagulating agents such as Al2SO4, FeSO4 and FeCl3, respectively. Biochemical methane potential (BMP) assay was carried out for both crude OME and chemically pretreated OME samples in order to monitor and comparatively evaluate any increase in biogas production as the indicator of improvement in anaerobic biological degradation after chemical pretreatment. The experimental results obtained in this work suggest that pretreatment significantly enhances the biodegradability of OME which was much lower if it was digested alone (without pretreatment). Over 80% increase in biogas production was obtained when digesting OME after chemical pretreatment. It was concluded that among the alternative chemicals, Al2SO4 resulted in highest biogas production from OME, thereby the best results for the enhancement of anaerobic biodegradability of OME were also achieved. It was demonstrated that the biodegradability of OME could be significantly enhanced by chemical pretreatment and therefore anaerobic degradation after a suitable pretreatment could be considered as a safe disposal method for OME. (C) 2007 Elsevier B.V. All rights reserved.