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Introduction to the A/O treatment project example of synthetic ammonia production wastewater 1 Introduction my country is a country with a large population and a large agricultural country. Agricultural production is inseparable from chemical fertilizers, which account for about 40% of the increase in agricultural production. Therefore, chemical fertilizers have always played a very important role in the development of the national economy. After 20 years of rapid development of reform and opening up, my country's chemical fertilizer industry has now reached a considerable scale. The output of chemical fertilizers ranks third in the world after the United States, and the output of nitrogen fertilizer ranks first in the world. The raw material route of the nitrogen fertilizer industry adopts a route in which oil and coke are mainly used (accounting for about 64% to 67%) and oil and gas coexist, and natural gas only accounts for 19% to 20%. Different raw material routes have different production processes, and the same raw material routes also have different production processes. Different processes have different sources of wastewater. The production processes and wastewater sources of the main products of synthetic ammonia and nitrogen fertilizer are described below:: 1.1 Synthetic ammonia production process and wastewater sources: (1) Wastewater from the process of producing synthetic ammonia from coal coke gas mainly comes from three parts: ①Desulfurization wastewater generated from gasification process ； ②Desulfurization wastewater generated from desulfurization process ； ③Ammonia-containing wastewater generated from the copper washing process. (2) Wastewater for ammonia production from oil and gas production mainly comes from carbon black wastewater and cyanide-containing wastewater produced in the carbon removal process. ； Desulfurization wastewater generated from desulfurization process ； As well as the low-pressure shift condensate and methanation condensate produced during the removal of organic sulfur, that is, ammonia-containing wastewater. (3) The wastewater from the gas-to-gas ammonia synthesis process is mainly the desulfurization wastewater produced by the desulfurization process and the ammonia-containing wastewater produced by the copper washing process, as well as the condensate produced during the removal of organic sulfur, that is, ammonia synthesis wastewater. 1.2 The production process of the main products of nitrogen fertilizer and the source of wastewater. The wastewater in the production of ammonia carbonate is the fluorine-containing wastewater produced by the tail gas scrubber. ； The wastewater in urea production is mainly the desorption liquid produced by the distillation and evaporation process and the synthetic ammonia wastewater produced by the vacuum evaporation process. To sum up, the nitrogen fertilizer industrial wastewater can be divided into oxygenated wastewater from media generation, carbon black wastewater from oil gas generation, self-sulfur wastewater and ammonia-containing wastewater according to its properties. Among them, gas production wastewater and self-ammonia wastewater have the greatest impact on the water environment. Table 1 Gas-making wastewater quality and discharge standard pollutants Water temperature °C Suspended solids mg/l Cyanide mg/l Sulfide mg/L Volatile phenol mg/l Ammonia nitrogen mg/l pH CODcr mg/L Gas-making wastewater (before treatment) 45-55 50-500 10-30 0.1-10 0.01-3 40-100 6-9 30-200 Water requirements for process production <32 <50 <5 <1.0 Trace amount - 6-9 - Comprehensive wastewater discharge standard GB8978-1996 Level I - 70 0.5 1.0 0.5 15 6-9 100 Level II - 200 0.5 1.0 0.5 50 6-9 150 Synthetic ammonia industry water pollutant discharge standard GWPB4-1999 (medium) Level I-- 100 1.0 1.0 0.20 60 6-9 150 Level II-- 100 1.0 1.0 0.20 100 6-9 150 2 Process Principle A/O method biological removal of ammonia nitrogen: The ammonia nitrogen in the sewage is nitrified into nitrate nitrogen by nitrifying bacteria under oxygenated conditions (section O), and a large amount of nitrate nitrogen flows back to section A. Under anoxic conditions, through the action of facultative anaerobic denitrifying bacteria, the organic matter in the sewage is used as an electron donor, and nitrate nitrogen is used as an electron acceptor, so that the nitrate nitrogen wave is reduced to pollution-free nitrogen, which escapes into the atmosphere to achieve final denitrification. nitrification reaction: NH4+＋2O2→NO3－＋2H++H2O reverse digestion reaction: 6NO3-＋5CH3OH (organic matter)→5CO2↑＋7H2O＋6OH-+3N2↑ 3 Project Example 3.1 -----Comprehensive wastewater treatment project of the group company's sewage treatment plant 3.1.1 Project overview------The design scale of the group company's wastewater treatment project is a daily treatment volume of 240,000 m3/d. Among them, domestic sewage is 59,000 m3/d, nitrogen-containing wastewater is 37,000 mWd, and chemical production wastewater is 144,000 m3/d. The actual daily water treatment volume is 180,000 m3/d. The concentration of main pollutants in the incoming water and the designed water quality parameters of the effluent in this wastewater treatment project are shown in Table 2. The discharge standard of this wastewater project complies with the GB8978--1996 secondary standard. Table 2 Inlet and outlet water quality table items of Jilin sewage treatment project Raw water concentration Outlet water concentration CODcr/(mg/L) 365 120 BOD5/(mg/L) 156 30 NH3-NN/(mg/L) 78 25 pH value>7.5 6-9 Color (dilution factor) 83 83 SS/(mg/L) 250 70 3.1.2 Process flow and brief description (1) Process flow file:///E:/DOCUME~1/zzjjaa/LOCALS~1/Temp/ksohtml/wps_clip_image1.png (2) Brief description of the process flow. The chemical wastewater is lifted by a pump and enters the homogeneous reaction tank, where alkali is added to neutralize it and then enters the sedimentation ground to settle. After the sedimentation sludge is concentrated, it is dehydrated and transported externally. The sedimentation effluent enters the steady flow tank, then enters the aeration sedimentation ground, and then enters the sedimentation tank and enters the A/O (nitrification and denitrification) biochemical treatment system together with the domestic sewage treated by aeration and sedimentation. Finally, the wastewater is discharged after contact disinfection. 3.1.3 Main technical and economic indicators Jilin Chemical Group Corporation sewage treatment plant, with a total project investment of 540 million yuan. The annual operating cost is 54 million yuan/a, including production cost 36 million yuan/a, management cost 1,300 cubic meters/a, and taxes 5 million yuan/a. The cost of sewage treatment is 1.08 yuan/m3 (direct treatment cost calculated based on production cost is 0.65 yuan/m3). 3.2 ------- Fertilizer plant wastewater treatment project 3.2.1 Project overview ------ The chemical fertilizer project has an annual production capacity of 300,000 tons of ammonia and 520,000 tons of urea. The ammonia synthesis unit adopts the Sher residue vaporization process, Lurgi's low-temperature methanol washing process and Kellogg's ammonia synthesis process, and the urea unit uses the Snam gas stripping process. The wastewater treatment device is one of the public facilities supporting the project. Including ash settling unit, chemical treatment unit and biochemical treatment unit. 3.2.2 Process flow and brief description (l) Process flow file:///E:/DOCUME~1/zzjjaa/LOCALS~1/Temp/ksohtml/wps_clip_image2.png (2) Brief description of the process flow. The ash settling unit mainly handles and synthesizes ammonia vaporization part of about 40t/h of carbon black wastewater. After the carbon black wastewater is removed from part of the carbon black through the ash settling tank, about 30t/h is sent to the residual oil vaporization section for reuse. About 10t/h enters the sewage stripping tower to remove NH3 and H2S. It is treated by the chemical treatment unit and dehydrated to remove heavy metals V and Vi before entering the equalization tank. The biochemical treatment unit mainly collects wastewater treated by the chemical unit, CO2 washing water from the ammonia synthesis unit, process condensate from the urea unit, domestic sewage, and polluted rainwater from the tank area. These five wastewaters enter the biochemical treatment unit. This unit adopts the A/O process. 3.3 ------Chemical Group Nitrogen Fertilizer Branch Wastewater Treatment Project 3.3.1 Project Overview The plant currently has a 25,000 tons/year synthetic ammonia production device. The existing supporting wastewater treatment facilities only perform sedimentation treatment on the discharged wastewater, so some pollutants such as cyanide, ammonia nitrogen, sulfide, etc. cannot meet the emission standards. This process adopts A/O processing technology. The design water volume is 1200m3/d. Design inlet water quality CODcr≤230mg/l pH: 7-8 SS≤600mg/l Cyanide≤12.0mg/l Ammonia nitrogen≤460mg/l Volatile phenol≤0.50mg/l Sulfide≤5.58mg/l The treated water quality standard complies with * * The "Water Pollutant Discharge Standard for the Synthetic Ammonia Industry" (GWPB44-1999) implements the secondary emission standards in Table 1. See table for details. 3.3.2 Process flow and brief description (1) Process flow Production wastewater and part of domestic sewage (due to process requirements, production wastewater needs to be treated with part of domestic sewage) are mixed and then enter the regulating tank to adjust the water volume and balance water quality. The mixed sewage is lifted by a water pump. After adding chemicals, it enters a sedimentation tank to settle and remove part of the suspended solids and most of the cyanide, so as to reduce the subsequent treatment load and reduce the inhibitory and toxic effects of cyanide on microorganisms. The effluent and reflux mixed liquid from the first sedimentation tank enters the anoxic tank and undergoes denitrification and denitrification reactions. NO3-N is reduced to N2 and enters the air, while the sewage enters the aerobic tank. In the aerobic tank, degradation and nitrification reactions occur, most of the BOD is degraded, and NH3-N is converted into NO3-N. Most of the effluent from the aerobic tank flows back, and the remaining part enters the secondary sedimentation tank. After the effluent from the secondary sedimentation tank enters the storage tank, it is pumped into the waterscape fountain water distribution system in the office and living areas of the factory. This not only beautifies the factory environment, but also saves water resources. The sludge from the secondary sedimentation tank and the sludge from the primary sedimentation tank enter the sludge concentration tank together. After concentration, they are discharged to the drying field for drying and dehydration, and the supernatant liquid returns to the regulating tank for reprocessing. 3.3.3 Main technical and economic indicators The total investment in the project is 1.35 million yuan, and the water treatment cost per ton is 0.68 yuan. This plan recommends that the factory reuse sewage for production or waterscape fountains. The treated sewage is considered to be reused at a rate of 20%. Each cubic meter of water is calculated at 0.8 yuan, and the reuse benefit per ton of water is: 1×20%×0.8=0.16 yuan/m3·water. 4 Conclusion A/O biological denitrification wastewater treatment technology is a wastewater treatment technology developed in the early 1990s. It can effectively oxidize and degrade the COD components and ammonia nitrogen pollutants in chemical wastewater, so that various pollutant indicators in the wastewater can meet the discharge standards. However, in the past ten years, this wastewater treatment technology with good performance has not been well applied. The A/O biological denitrification wastewater treatment technology is only used in a few large enterprises such as Jilin Chemical Company and Jiujiang Large Fertilizer Plant. This technology needs to be promoted and applied in small and medium-sized fertilizer plants, especially in the nitrogen fertilizer (synthetic ammonia, urea) industry.