Characteristics of coking wastewater:
Coking wastewater contains pollutants including phenols, polycyclic aromatic compounds, and heterocyclic compounds containing nitrogen, oxygen, and sulfur. It is a typical industrial wastewater containing refractory organic compounds. The easily degradable organic matters in coking wastewater are mainly phenolic compounds and benzene compounds, and pyrrole, naphthalene, furan, and oxazole are degradable organic compounds. Refractory organics are mainly pyridine, carbazole, biphenyl and terphenyl. The water quality of coking wastewater varies greatly depending on the process and production operation of each plant. The quality of ammonia water from the coking plant is as follows: CODcr3000-3800mg / L, phenol 600-900mg / L, cyanide 10mg / L, oil 50-70mg / L, and ammonia nitrogen 300mg / L.
Coking wastewater treatment:
The pre-treatment methods before biological treatment are usually physical and chemical methods, such as air floatation, blow-off, coagulation and sedimentation, and breakpoint chlorination. The main purpose is to make the water in the secondary biochemical treatment process biodegradable Range. In the pretreatment process, the stripping method is mainly used for steaming ammonia, and the air flotation method is used for biological treatment of oil removal.
The SDN process SDN (Enhanced Denitrification / Nitrification) process is a biological treatment process in which advanced biological denitrification technology is applied to the field of coking wastewater treatment, so that the removal rate of ammonia nitrogen and COD reaches more than 90 to 96%. Compared with previous treatment processes, SDN has the characteristics of strong system adaptability, stable operation, simple operation, low cost, and wide range of pollutant removal. The wastewater is treated and reused for coke quenching and coal washing, which greatly reduces the amount of fresh water, which not only reduces the total amount of pollutants discharged, but also saves water, which has obvious economic benefits.
The SDN coking wastewater treatment process consists of four sections of pretreatment, biological treatment, advanced treatment, and sludge treatment. The functional division is clear and easy to operate and manage. Among them, the biochemical treatment section uses the SDN process composed of two parts, intensified hypoxia and aerobic. The removal rate of ammonia nitrogen and COD in this process reaches more than 90 to 96%, which completely solves the problems of low removal rate of ammonia nitrogen and COD in traditional treatment processes, unstable biochemical systems, and high investment and operating costs.
HSB Process HSB (High Solution Bacteria) is the English abbreviation of high-decomposing bacteria. It is a highly effective microbial flora composed of more than 100 species of bacteria. deal with. According to different wastewater water quality, screening and domestication of microorganisms, targeted selection of a variety of microorganisms and planting them in the wastewater treatment tank, through the metabolic process of continuous growth of microorganisms, decomposition of different pollutants to form each other The dependent biological chain and decomposition chain break through the restriction that conventional bacteria can only decompose certain pollutants to a certain intermediate stage and cannot proceed. The final products are CO, H2O, N2, etc., which achieve the purpose of harmless wastewater. This technology has the following advantages:
Ⅰ. HSB technology has good degradation performance for COD, NH 3-N, etc. After adding HSB strains, not only COD and NH3-N can reach the standard emission, but also phenol, cyanide, etc. can be greatly degraded;
Ⅱ. Low investment costs. Because HSB high-efficiency strains can effectively treat high-concentration COD and NH3-N, the air-float deoiled water from the original activated sludge process can be directly entered into the HSB treatment device, and no dilution water is added. Not only reduce the volume of processing facilities and footprint, but also save a lot of water resources;
III. Lower operating costs. When the process is running normally, only a small amount of phosphate is added as a bacterial agent in the aerobic tank. Generally, the screwdriver is: C: N: P = 200: 5: 1. Significantly reduce the amount of carbon sources added;
Ⅳ. Less residual sludge. According to preliminary estimates, only 0.05 kg of sludge is produced per I kg of COD, which is much less than the amount of sludge produced by the A0 process and A2O process, which can save or greatly reduce the cost of sludge treatment equipment and operation.
At present, the main standards for domestic coking wastewater treatment are "Integrated Wastewater Discharge Standard" (GB8978-1996), the first-class COD standard is 100mg / L, and the ammonia nitrogen is 25mg / L. With the improvement of national water quality standards, after the secondary biochemical treatment of urban domestic sewage and industrial wastewater by the mainstream process AO and its deformation process, there may still be a long way for the effluent to reach the reuse standard, especially the removal rate of COD needs to be further Improvement requires deep processing. In the advanced treatment process, advanced oxidation has the advantages of fast reaction time, thorough removal of pollutants, and complete recycling of treated wastewater. Experts expect that it will soon be used in the advanced treatment of various wastewaters, especially in the field of high-concentration industrial wastewater. . In addition, membrane treatment technology also has its own advantages, such as efficient separation process, low energy consumption, etc., and with the maturity of membrane technology, it is believed that it will also be used in the advanced treatment of wastewater.
Of course, there are also some problems with membrane treatment and advanced oxidation technology for the advanced treatment of coking wastewater, mainly including:
(1) If the membrane treatment technology is used for advanced treatment, there is a secondary water treatment process. After the membrane separates the secondary effluent, the water will form two parts: one is the water that can be directly reused after treatment, accounting for the total amount of water. 75% of the total; the other part is concentrated sewage, COD and salt content is relatively high, accounting for 25% of the total water, this part of water needs to be treated twice. Experts suggest that activated carbon adsorption can be used to remove COD in this part of the sewage, but there are problems with activated carbon adsorption such as regeneration of activated carbon. Some scholars have suggested that this part of wastewater can be returned to the secondary treatment, which avoids subsequent treatment. The impact of water quality needs further research and demonstration.
(2) If the advanced oxidation method is used for advanced treatment, the phenomenon that COD first decreases and then rises may be because the intermediate products produced by advanced oxidation constitute new COD. Experts have suggested that the COD index measured by the potassium dichromate method has certain limitations, and the TOC index may be more suitable.
Experts propose to use the A section of the biochemical treatment process in combination with MBR, and subsequently connect the membrane treatment process such as reverse osmosis / nanofiltration to treat coking wastewater. It is also a good choice. Because MBR is closed and has a small footprint, The plant area can be built beautifully, and the membrane separation technology has a good treatment effect, which is also a promising technical route.
At present, wastewater treatment often focuses on the degradation of pollutants, and ignores the resource recovery and reuse in wastewater, which is not in line with the concept of circular economy. Experts suggest that the development of high-efficiency control integration technology and zero-emission technology throughout the process, and the effective use of ammonia nitrogen and phenol in certain high-concentration wastewater are of great significance to promote the upgrading of wastewater treatment technology.
Juice wastewater treatment equipment, coking wastewater treatment equipment, and sewage treatment equipment provide certain growth and reproduction conditions for activated sludge (microorganisms), that is, various proportions of nutrients, dissolved oxygen, water temperature, etc. The nutrition and survival conditions of activated sludge are : The optimal water temperature is 20 ～ 40 ¡ã C; generally pH 6 ～ 9. Activated sludge has a certain regulation effect on pH. The inlet water pH of the aeration tank is 5.6 ～ 10, and the pH of the secondary sedimentation tank water can still be in the range of 6 ～ 9. Dissolved oxygen is adjusted by controlling the amount of air to control it in the design value range. DO <0.5mg / L, DO is too large, the sludge is easy to self-oxidize; the aeration tank is generally added according to the ratio of BOD5: N: P = 100: 5: 1. The source of nutrients and coking wastewater are complex and depend on the specific water quality. After a certain period of cultivation, live sludge (microorganisms) will grow in large numbers and domesticate microorganisms that can adapt to the needs of coking wastewater. Because of the water quality conditions and lack of nutrition of coking wastewater, the cultivation and domestication of microorganisms are often more difficult. The acclimatization cycle is relatively long, generally 30 to 60 days. The nutritional structure of the Jiao Xiu wastewater often does not correspond to the nutritional ratio required by the microorganisms (that is, the daily BOD5: N: P = 100: 5: 1), so the missing nutrients (such as glucose and urea) need to be added to the coking wastewater. , Sodium phosphate, etc.). A small dose (10mg / L) can be added to glucose, which can strengthen the tricarboxylic acid cycle of microorganisms due to the three carbon compounds (such as pyruvate) produced by the degradation of glucose, thereby improving the removal rate of phenol.
In the aeration tank, put some concentrated sewage sludge or dewatered sludge from other sewage plants (preferably other biological sludge that changes the biochemical treatment of the wastewater of the plant), and at the same time put the nutrient solution required by the microorganisms or the paste prepared with flour. After aeration, stop aeration and drainage after a few hours. If it is the activated sludge method, the supernatant is drained by one third; if it is the contact oxidation method, the water level on the water surface after drainage should not be lower than the filling frame. Then, some aerated coking wastewater began to be placed in the aeration tank, and the amount of water was gradually increased according to the designed water volume of 1/10, 1/8, 1/5, 1/2, and the nutrient solution or paste prepared with flour was added. (COD of incoming water should be controlled at about 300mg / L). After 3 days, test the COD value. If COD "has a 50% removal rate, the COD value in the feed water can be increased to 500mg / L; if the COD removal rate reaches 60% to 70%, if the COD to be treated is 1000mg / L, at this time, the input nutrition or flour paste can be reduced, and the amount of wastewater water is increased, while the influent COD is still controlled at 500-600mg / L; if the COD removal rate is unchanged, then the nutrition or flour paste is reduced again to increase wastewater The amount of water intake began to impact the sludge in the aeration tank, and the MLSS decreased. However, after adaptation, the sludge continued to grow, and the protozoan bellworm, isobranze, cover fiber worm, and roaming worm were very active, until the wastewater entered the exposure The gas tank meets the requirements for setting juice, the process conditions are normally controlled, and the removal rate of various organic matter is stable. After about 1 to 2 months, the sludge domestication is successful. If N or P is missing in the coking wastewater, then it must be replenished daily according to the proportion of water Add investment. Normal operation can be transferred to the end of cultivation.
A large amount of waste water containing toxic, harmful substances such as phenol, cyanide, oil, and ammonia nitrogen was discharged during the coking production process. Coking wastewater mainly comes from coking and gas purification processes and the refining process of chemical products, with the remaining ammonia produced in the process of helium evaporation as the main source.
Distilled ammonia waste water is the waste water discharged after mixing the remaining ammonia water for distillation. Residual ammonia water is the most important phenol cyanide wastewater source of the coking plant. It is high-concentration phenol water containing ammonia, which is discharged by the circulating ammonia water pump in the condensing blast section and sent to the remaining ammonia water storage tank. The remaining ammonia water is mainly composed of three parts: the wet storage water on the surface of the loaded coal, the combined water produced by the carbonization of the loaded coal, and the oily process wastewater added into the gas suction pipe and the collector oxygen circulating water pump. The total amount of remaining ammonia can be calculated as 14% of the coal in the furnace. After the remaining ammonia is mixed in the storage tank with the process wastewater sent by other production equipment, it is called mixed residual ammonia. Where the remaining ammonia is mixed, some are directly steamed, some are dephenolized and then steamed, some are combined with ammonia-rich water to steam ammonia, and some are desulfurized and rich ammonia together with desulfurized rich liquid, and filtered and degreased before deacidifying and steaming ammonia. . The coking plant also contains some other waste water, which accounts for a small proportion and has low pollution indicators, which will not be introduced here.