Abstract: Waste water discharged from FCC LoTOx unit has the characteristics of highly saline and total nitrogen (TN). TN value exceeds the maximum emission standard limit, but the problem is difficult to be solved because the saline wastewater could shock wastewater treatment system. As a result, exploring a kind of economical & proven technology has significant meaning for setting a demonstration to other enterprises encountering similar problems. Based on analyzing and summing up the wastewater quality, biological filter technology with three-stage process (AOO) is proven useful for bio-denitrification. As a point, salt tolerance of biofilm depends on microbial cultivation and acclimation but not using commercial engineering bacteria. According to the experimental results, the average NO3-N removal rate is up to 94.8% when the wastewater is diluted one time for treating. Industrial unit with acapacity of 20 m3/h was built, which could remove 70% TN from the wastewater. All water quality parameters of unit outlet are coming up to the effluent permit limits from "Emission standard of pollutants for petroleum refining industry". The developed process is cost-effective because the operation costs as low as 0.54 CNY/t of wastewater treated. In conclusion, the successful experience could be copied to similar enterprises.

Key words: flue gas desulfurization and denitrification, wastewater, ozone oxidation, notrogen, biological filter