Abstract: A pilot scale eco-pond system, consisting of facultative pond, aerobic pond and hydrophyte pond, was used to test the efficiency and influence factors of tail water deep treatment of petrochemical wastewater. The results indicate that COD concentration in effluent ranges from 40 mg/L to 50 mg/L, equivalent to COD reduction rate of 25%-50%, and reaches the A level of class 1 standard for COD in“Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant” (GB 18918-2002), except the concentration index of petroleum substances, which is slightly overweight. Among influence factors, the temperature is the main one. The treatment efficiency changes with seasons. The influence of higher temperature on TN removal is higher than that on COD and TP, while the effect of illumination on COD, TP and TN removal is relatively similar. The highest removal rates for three pollutants occur at about 16:00 pm, and the removal rates decline in a certain degree at night.

Key words: eco-pond, facultative pond, aerobic pond, petrochemical wastewater, tail water