ABSTRACT
This investigation was performed on the biological removal of nitrogen from refinery's wastewater by the nitrification and denitrification process. In a petroleum refinery, removing of hydrocarbons is the main concern and nitrogen content is supposed to be negligible. The aim of this work was to search for nitrogen in Tehran Refinery wastewater and employing a biological technology to reduce this pollutant. Samplings were done in different points of wastewater treatment plant; influent to aeration unit, effluent of aeration unit and effluent of clarifiers. The results showed that despite of a high average removal efficiency of COD > 93%, the nitrogen removal during conventional activated sludge process was not efficient and sludge rising due to denitrification was observed within the clarifier. The analysis conducted in laboratory scale showed that a simultaneous nitrification and denitrification [SND] process could easily be realized in the same activated sludge plant by using the flocculating sludge and control of dissolved oxygen concentration. It was found that the higher MLSS value [10.0 g/L] and mixing rate [300 rpm] is effective in improving total nitrogen removal and overall SND performance. Our experimental results indicated that the SND process is very efficient for nitrogen removal from industrial wastewater