Wastewater generated from olive processing comes either from olive oil or edible olive producing industries. Both types of wastewater constitute a major environmental concern since they are characterized by high organic content and are generated in large quantities for a specific period of the year. Furthermore, they contain compounds such as polyphenols, that are toxic to plants and/or soil microbes when discarded to soil receptors. This study aims at investigating the potential for biological treatment of a green olive debittering wastewater (GOW). The performance of a separate anaerobic, aerobic and a combined anaerobic-aerobic process was evaluated. Anaerobic digestion of GOW reached a 49% maximum efficiency of organic matter removal with a polyphenolic reduction of about 12%. The process seemed to be severely influenced by an inhibitory factor as suggested by the limited chemical oxygen demand (COD) removal, volatile fatty acids accumulation and low biogas production. The aerobic biotreatment of the GOW was more efficient than its anaerobic counterpart, resulting in a degradation efficiency of 71.6-75.9%. However, it hardly affected the polyphenolic compounds, with the additional disadvantages of the requirement for pH correction of the influent and the high production of biomass. On the other hand, aerobic treatment of the anaerobic effluent achieved a COD and polyphenolics reduction by 74 and 19.6% resulting in an overall reduction by 83.5 and 28%, respectively. Furthermore, the combined anaerobic-aerobic treatment results in a smaller amount of aerobic sludge and does not require a pH correction of the anaerobic or the aerobic influent.