Efficient treatment of saline wastewaters, particularly those containing inhibitory and toxic compounds, has been a challenge in recent years This study proposed and investigated an efficient option for treating such streams. An MgO nanocrystal mesoporous powder was prepared from natural magnesite, and its potential to serve as a catalyst for degradation and chemical oxygen demand (COD) removal of phenol from saline wastewater was evaluated The influence of several parameters including pH, close of MgO nanocrystals, and NaCl concentration was investigated on the catalytic zonation process (COP) of phenol in saline wastewater The concentration of NaCl had no adverse influences on the phenol degradation The results indicated that 96% of the phenol and 70% of the COD were removed in the COP (initial phenol concentration was 1100 mg/L and initial COD was 2500 mg/L) under optimum experimental conditions of pH 7 and a 4 g/L catalyst dose after an 80 min reaction time. A synergistic influence of about 39% was observed for phenol degradation in the COP. The effluent from the COP obtained from the aforementioned conditions was efficiently post-treated in a batch biological reactor, such that after 10 h of aeration, the COD was reduced to around 20 mg/L. In contrast, it took 50h for reduction of COD to below 100 mg/L when adding raw phenol wastewater into the bioreactor. Therefore, the prepared powder was found to be an efficient and promising catalyst for zonation. and coupling the developed COP with a biological process might be an attractive treatment option for saline wastewaters containing high concentrations of toxic compounds (C) 2010 Elsevier B V. All rights reserved