Hybrid growth microorganisms in sequencing batch reactors have proven effective for treating the toxic compound phenol, but the toxicity effect under different toxicity conditions has rarely been discussed. Therefore, the performance of the HG-SBR under toxic, acute and chronic organic loading can provide the overall operating conditions of the system. Toxic organic loading (TOL) was monitored during the first 7 hr while introducing 50 mg/L phenol to the system. The system was adversely affected with the sudden introduction of phenol to the virgin activated sludge, which caused a low degradation rate and high dissolved oxygen consumption during TOL. Acute organic loading (AOL) had significant effects at high phenol concentrations (600, 800 1000 mg/L). The specific oxygen uptake rate (SOUR) gradually decreased to 4.9 mg O2/(g MLVSS·hr) at 1000 mg/L of phenol compared to 12.74 mg O2/(g MLVSS·hr) for 200 mg/L of phenol. The HG-SBR was further monitored during chronic organic loading (COL) over 67 days. The effects of organic loading were more apparent at 800 mg/L and 1000 mg/L phenol concentrations, as the removal range was between 22%–30% and 18%–46% respectively, which indicated the severe effects of COL.
