Oil refinery wastewater (hereafter ORW) is among the most polluted and diffi-cult-to-treat industrial wastewater. Ammonia nitrogen discharge in ORW accounts for 8.45% of that of all industry. However, the efficiency to remove ammonia nitrogen from ORW by using current devices and techniques is considerably low, which generates serious problems for the emission of ORW according to the quality standard of industrial wastewater and the utilization of ORW as a special industrial resource. It finally intensifies the potential tension between oil refinery industry development and environment protection. This study based on the processing techniques of ORW with high ammonia nitrogen and sulfide, and focuses on the pre-treatment techniques in treating wastewater with high ammonia nitrogen and sulfide. Specifically, it explores the main influence mechanism of nitrification performance of ORW system, and sug-gests strategies in real project.
This study developed a new technology of dissolved-air aeration and applied it in the pre-aeration treatment of ORW with high ammonia nitrogen and sulfide. The project study showed that the efficiency of decreasing the volume of the indicators in ORW is significantly improved by following the technical procedure of dissolved-air aeration, compared with traditional craft. The quality of effluent can meet the requirements of the biological treatment stably.
The removal mechanism of sulfide and ammonia nitrogen by dissolved-air aeration is air stripping. Especially when the catalysts exist, the sulfide can be oxidized. The gas-water ratio in dissolved-air aeration is low. In the condition of pH 6-12, gas-water ratio 1-16:1, 96.4%-85.7% of all sulfide can be removed. When treating pretreated acidic water which pH value is adjusted up to 12, the removal rate of ammonia nitrogen is 87.2% with the gas-water ratio 65:1. When treating raw acidic water, the removal rates of ammonia nitrogen and sulfide are 31.7% and 97.7% under the condition of gas-water ratio 19.5:1.
The mechanism of nitrification showed that the main difficulty in removing ammonia nitrogen from ORW is the lethal effect on nitrifying bacteria with high concentration of pollutants in ORW. Therefore, the resolution strategy which ensures the standard of ammonia nitrogen of ORW is to avoid nitrifying bacteria contact with high concentration inffluent. The new technology of dissolved-air aeration in this study can be widely used in the treatment of volatile pollutants in wastewater. The exploration of fundamental reasons and the resolution strategies of removing ammonia nitrogen from ORW will help achieve the standard of ammonia nitrogen of ORW and emission reduction of ammonia nitrogen in the period of The 12th Five Year Plan. It is significant to improve the treatment level of ORW in our country, to promote the standard of ammonia nitrogen of ORW and to use ORW as a special resource.
Key words: Oil refinery wastewater, dissolved-air aeration, ammonia nitrogen, sulfide, acidic water