Synthetic wastewater was used in all experiments. The synthetic wastewater was fed and discharged by a set of two peristaltic pumps. Fine air bubbles were supplied by diffusers which were placed at the bottom at a volumetric flow rate of 0.24 m3 h-1(2.0 cm s-1 superficial air flow velocity) during the time for aeration. The effluent was discharged through the outlet ports which had a volumetric exchange ratio (VER) of 50% and located at the middle height in the glass column. The sludge retention time (SRT) was determined by the discharge of total suspended solids (TSS) with the effluent. The working temperatures for the bioreactors were controlled at 30 ± 1, 40 ± 1 and 50 ± 1 °C using water bath sleeves and a thermostat without controlling the dissolved oxygen and pH level. The bioreactors are referred to as SBR30, SBR40 and SBR50.