Abstract: A multi-stage contact oxidation system was used in a bench-scale experiment study to treat the automobile painting wastewater， which has poor biodegradability and contains high concentration of COD (chemical oxygen demand). The wastewater used for this experiment is the actual painting wastewater which has been pretreated by the physic-chemical treatment process in the paint shop of some automobile factory， and its BOD₅/COD is less than 0.1， COD mass concentration is 800~1500mg/L. The results shown that the multi-stage contact oxidation system can efficiently degrade the COD of the painting wastewater. After the experimental system keeping running stably， the total COD removal rate is more than 80% with the hydraulic retention time (HRT) of 8 hours. Meanwhile， this system has a strong impact resistance capacity. The COD mass concentration of final treated wastewater is less than 500mg/L， which can reach the factory discharge requirement for the paint shop. Besides， this system with simple structure can efficiently reduce the excess sludge production and can keep running stably， which can greatly reduce the treatment cost for the painting wastewater.

Key words: multi-stage contact oxidation, painting wastewater, chemical oxygen demand, excess sludge, hydraulic retention time