The spent caustic wastewater from petroleum refinery contains high concentration sulfide

phenol and oil pollutants.A novel two stage circulating biological aerated filter (CBAF) was used to treat the wastewater after dilution by water and neutralization by H2SO4.The factors of dissolved oxygen (DO) concentration

hydraulic retention time (HRT)

nutrient

pH value

temperature and backwashing cycle

which affected the treatment efficiency of spent caustic wastewater were investigated.The experimental results showed that the average removal percentages of COD

sulfide

volatile phenol and oil pollutants were 89.3%，99.8%，93.6% and 85.7%， respectively under feasible conditions.The average removal loading rates of COD and sulfide pollutants were 8.37 kg·m-3·d-1 and 4.44 kg·m-3·d-1

respectively.The experimental results also showed that the CBAF process was a kind of high loading rate

high treatment efficiency

long backwashing cycle and low cost treatment process with a good application prospect for the treatment of spent caustic wastewater from petroleum refinery.