1. Blow-off method
Under alkaline conditions, a method for separation using the gas-liquid equilibrium relationship between the gas phase concentration and the liquid phase concentration of ammonia nitrogen. It is generally believed that the stripping efficiency is related to temperature, pH and gas-liquid ratio.
The key factors to control the stripping efficiency are temperature, gas-liquid ratio and pH.
When the water temperature is higher than 25 ℃, the gas-liquid ratio is controlled at about 3500, and the pH of the leachate is controlled at about 10.5. For the landfill leachate with an ammonia nitrogen concentration of 2000 to 4000 mg / L, the removal rate can reach more than 90%. The stripping method is not efficient in removing ammonia nitrogen at low temperatures.
Ultrasonic stripping technology was used to treat high-concentration ammonia nitrogen wastewater (for example, 882 mg / L) in a fertilizer plant. The optimum process conditions are pH = 11, ultrasonic stripping time is 40min, and the gas-water ratio is 1000: 1. The test results show that after ultrasonic irradiation of wastewater, the ammonia nitrogen stripping effect is significantly increased. Compared with the traditional stripping technology, ammonia nitrogen stripping The removal rate increased by 17% ~ 164%, more than 90%, and the ammonia nitrogen was within 100mg / L after blowing off.
In order to adjust the pH to alkaline at a lower cost, it is necessary to add a certain amount of calcium hydroxide to the wastewater, but it is easy to scale. At the same time, in order to prevent secondary pollution caused by the stripped ammonia nitrogen, it is necessary to install an ammonia nitrogen absorption device after the stripping tower.
In the treatment of UASB pretreated landfill leachate (2240mg / L), it was found that at a pH of 11.5 and a reaction time of 24h, mechanical agitation was performed only at a speed gradient of 120r / min, and the ammonia nitrogen removal rate could reach 95%. http://euhowblog.com
and deammonia nitrogen by aeration at pH = 12, the pH began to decrease at 17 hours, and the ammonia nitrogen removal rate was only 85%. According to this, it is believed that the main mechanism of nitrogen removal by blow-off method should be mechanical stirring instead of air diffusion stirring.
2. Zeolite adsorption
The cations in zeolite are exchanged with NH4 in wastewater to achieve the purpose of nitrogen removal. Zeolites are generally used to treat low-concentration ammonia-containing wastewater or wastewater containing trace heavy metals. However, Jiang Jianguo et al. Discussed the effect and feasibility of zeolite adsorption to remove ammonia nitrogen from landfill leachate. The results of the pilot study show that each gram of zeolite has the limit potential of adsorbing 15.5 mg of ammonia nitrogen. When the particle size of the zeolite is 30 to 16 mesh, the ammonia nitrogen removal rate reaches 78.5%, and the adsorption time, dosage and zeolite particle size are the same. In the case that the higher the ammonia nitrogen concentration in the feed water is, the higher the adsorption rate is. It is feasible that zeolite is used as an adsorbent to remove ammonia nitrogen from the leachate.
Na-Zeo, Mg-Zeo, Ca-Zeo, and k-Zeo have the best Na-Zeo zeolite effect when zeolite ion exchange method is used to treat pig manure wastewater, followed by Ca-Zeo. Increasing the height of the ion exchange bed can improve the removal rate of ammonia nitrogen. Considering economic reasons and hydraulic conditions, a bed with a height of 18 cm (H / D = 4) and a relative flow rate of less than 7.8 BV / h is a suitable size. The ion exchange method is greatly affected by the concentration of suspended solids.
The application of zeolite deamination method must consider the regeneration of zeolite. Usually there are regeneration liquid method and incineration method. When incineration is used, the ammonia produced must be treated.
3. Membrane separation technology
A method for removing ammonia nitrogen by using the selective permeability of a membrane. This method is easy to operate, has high ammonia nitrogen recovery rate, and has no secondary pollution. Jiang Zhanpeng and others used the electrodialysis method and polypropylene (PP) hollow fiber membrane method to treat high-concentration ammonia nitrogen inorganic wastewater, which can achieve good results. The electrodialysis method can treat 2000 ~ 3000mg / L of ammonia nitrogen wastewater, the removal rate can be above 85%, and 8.9% concentrated ammonia water can be obtained at the same time. The process of this method is simple, does not consume chemicals, and the power consumed during operation is directly proportional to the ammonia nitrogen concentration in the wastewater. The removal efficiency of PP hollow fiber membrane method is> 90%, and the ammonium sulfate concentration recovered at http://euhowblog.com is
about 25%. Alkali needs to be added during operation. The amount of alkali added is directly proportional to the ammonia nitrogen concentration in the wastewater.
Emulsified liquid membrane is a kind of liquid membrane in the form of emulsion with selective permeability, which can be used for liquid-liquid separation. The separation process usually uses an emulsified liquid film (such as a kerosene film) as the separation medium. The NH3 concentration difference and diffusion transmission on both sides of the oil film are used as the driving force to allow NH3 to enter the membrane, thereby achieving the purpose of separation.
4.MAP precipitation method
The following chemical reactions are mainly used:
Mg2 + NH4 + PO43- = MgNH4PO4 ↓
Theoretically, phosphorus and magnesium salts are added to wastewater containing a high concentration of ammonia nitrogen at a certain ratio. When [Mg2 +] [NH4 +] [PO43-]> 2.5 ¡Á 10–13, ammonium magnesium phosphate (MAP) can be generated and removed. Ammonia nitrogen in wastewater. Mu Ganggang and others used the method of adding MgCl2 • 6H2O and Na2HPO4 • 12H2O to industrial wastewater with high ammonia nitrogen concentration to form ammonium magnesium phosphate precipitation to remove the high concentration ammonia nitrogen. The results show that under the conditions of pH 8.91, molar ratio of Mg2, NH4, and PO43- is 1.25: 1: 1, the reaction temperature is 25 ¡ã C, the reaction time is 20min, and the precipitation time is 20min, the ammonia concentration can be 9500mg / L was reduced to 460mg / L, and the removal rate was above 95%.
Because the content of magnesium salts in most wastewaters is relatively low compared to phosphate and ammonia nitrogen, although the generated magnesium ammonium phosphate can be used as agricultural fertilizer to offset part of the cost, the cost of adding magnesium salts has still become the main factor limiting the implementation of this method . Seawater is endless and contains a lot of magnesium salts. Kumashiro et al. Studied the crystallization process of magnesium ammonium phosphate using seawater as a source of magnesium ions. Brine is a by-product of salt production, which mainly contains MgCl2 and other inorganic compounds. Mg2 is about 32 g / L, which is 27 times that of seawater. Lee et al. Used MgCl2, seawater, and brine as Mg2 sources to treat pig farm wastewater with ammonium magnesium phosphate crystallization. The results show that pH is the most important control parameter. When the endpoint pH is ≈9.6, the reaction can be completed within 10 minutes. . Due to the imbalance of N / P in the wastewater, compared with the other two Mg2 sources, the salt brine has the same phosphorus removal effect and the nitrogen removal effect is slightly worse.
5.Chemical oxidation method
A method for removing ammonia nitrogen by direct oxidation with strong oxidant. Inflection point chlorination is the use of ammonia in water to react with chlorine to generate ammonia gas deamination. This method can also play a sterilizing role, but the residual chlorine generated will affect fish, so facilities for removing residual chlorine must be installed.
In the presence of bromide, ozone and ammonia nitrogen will react like the following inflection points:
Br- + O3 + H + → HBrO + O2
NH3 + HBrO → NH2Br + H2O
NH2Br + HBrO → NHBr2 + H2O
NH2Br + NHBr2 → N2 ↑ + 3Br- + 3H +
A continuous aeration column with an effective volume of 32L was used to conduct experimental research on synthetic wastewater (600 mg / L of ammonia nitrogen) to investigate the effects of Br / N, pH, and initial ammonia nitrogen concentration on the reaction to determine the most ammonia nitrogen removed and the least NO3- Optimal reaction conditions. It was found that NFR (ratio of effluent NO3--N to ammonia nitrogen in the feedwater) was linearly related to Br- / N in logarithmic coordinates. When Br- / N> 0.4, the ammonia nitrogen load was 3.6 ～ 4.0kg / (m3 • d ), NFR decreases when the ammonia nitrogen load decreases. When the effluent pH = 6.0, NFR and BrO--Br (toxic by-products) were the least. BrO--Br can be decomposed quantitatively by Na2SO3, and the dosage of Na2SO3 can be controlled by ORP.
6.Biochemical combined method
The physical and chemical methods will not be restricted when the ammonia nitrogen concentration is too high when treating high-concentration ammonia nitrogen wastewater, but the ammonia nitrogen concentration cannot be reduced to a sufficiently low level (for example, below 100 mg / L). Biological nitrogen removal is inhibited by high concentrations of free ammonia or nitrite nitrogen. In practical applications, a combined biochemical method is used to perform physicochemical treatment on wastewater containing a high concentration of ammonia nitrogen before biological treatment.
The stripping-hypoxic-aerobic process was used to treat landfill leachate with high concentration of ammonia nitrogen. The results show that when the stripping conditions are controlled at pH = 95 and the stripping time is 12h, the stripping pretreatment can remove more than 60% of the ammonia nitrogen in the wastewater, and then treat the ammonia nitrogen (from 1400mg / L) after anoxic-aerobic biological treatment. (Reduced to 19.4 mg / L) and the removal rate of COD> 90%.
Horan et al. Used a biological activated carbon fluidized bed to treat landfill leachate (COD: 800-2700mg / L, ammonia nitrogen: 220-800mg / L). The results show that when the ammonia nitrogen load is 0.71 kg / (m3 • d), the nitrification removal rate can reach more than 90%, the COD removal rate can reach 70%, and all the BOD is removed. http://euhowblog.com
Using lime flocculation and precipitation air blow-off as a pretreatment method to improve the biodegradability of leachate, adding an adsorbent (powdered activated carbon and zeolite) to the subsequent aerobic biochemical treatment tank, found The removal efficiency of COD and ammonia nitrogen in the adsorbent at 0 ～ 5g / L increased with the increase of the adsorbent concentration. For the removal effect of ammonia nitrogen, zeolite is better than activated carbon.
Membrane-bioreactor technology (MBR) is a new and efficient wastewater treatment system formed by organic combination of membrane separation technology and traditional wastewater bioreactor. MBR has high treatment efficiency, the effluent can be reused directly, the equipment has less battlefield area, and the remaining sludge amount is small. The difficulty lies in maintaining a large flux of the membrane and preventing leakage of the membrane. Li Hongyan and others used an integrated membrane bioreactor to study the nitrification characteristics of high-concentration ammonia nitrogen wastewater. The results show that when the ammonia nitrogen concentration in the raw water is 2000 mg / L and the volume load of the ammonia helium in the feed water is 2.0 kg / (m3 • d), the removal rate of ammonia nitrogen can reach more than 99%, and the system is relatively stable. The specific nitrification rate of activated sludge in the reactor was basically stable at about 0.36 / d in half a year.
7. Traditional biological nitrogen removal method
The traditional biological nitrogen removal technology started in the 1930s and was really applied in the 1970s. Since the initiation of Barth's three-stage biological nitrogen removal process, A / O process, sequential batch process and other nitrogen removal processes have been proposed and applied to engineering practice.
Three-stage biological nitrogen removal process
The three-stage biological denitrification process is shown in the figure. This process separates three stages of organic matter degradation, nitrification and denitrification. Each stage is followed by its own independent sedimentation tank and sludge return system. The main function of the first stage of aeration tank is to metabolize and decompose organic matter, and make the organic nitrogen ammonium. The second stage of the nitrification tank mainly performs the nitrification reaction to oxidize ammonia nitrogen, and at the same time, it needs to add alkalinity to maintain a certain pH value. The third stage is the denitrification reactor. Nitrate nitrogen is reduced to N2 under anoxic conditions. A stirring device is installed to make the sludge mixture liquid be a suspended carbon source to satisfy the floating state, and the carbon source required for the denitrification reaction is added.
A / O biological denitrification process
The A / O biological denitrification process is shown in the figure. This process places the anoxic section at the front of the system. The alkalinity generated by the denitrification reaction can slightly supplement the nitrification reaction. In addition, the use of organic matter in raw wastewater as a carbon source in the denitrification reaction in the anoxic tank can reduce the need for supplementary carbon sources or not. Through the internal circulation, the nitrate nitrogen produced by the nitrification reaction is transferred to the hypoxic pond for denitrification reaction. The oxygen in the nitrate nitrogen serves as an electron acceptor, which provides the respiration and life activities of the denitrifying bacteria, and completes the denitrification process.
In the A / O biological nitrogen removal process, the reflux ratio of the nitrating solution has a great effect on the nitrogen removal effect of the system. If the reflux ratio is controlled too low, sufficient nitrate nitrogen cannot be provided for the reaction, resulting in incomplete nitrification, which will affect the denitrification effect; if the control is too high, the contact time between the nitrifying solution and the denitrifying bacteria will be shortened, thereby reducing Nitrogen removal efficiency. Therefore, in the actual operation process, it is necessary to control the appropriate reflux ratio of the nitrating solution so that the nitrogen removal effect of the system reaches an optimal level.
Sequencing batch denitrification process (eg CASS)
Compared with the A / O process, the sequential batch denitrification process has different operating modes, but it is basically the same as the A / O biological denitrification process in terms of the denitrification reaction mechanism. Sequential batch process is a batch operation mode, using an independent reaction tank instead of the traditional A / O biological denitrification reactor composed of multiple reaction zones with different functions. Sequential batch denitrification process realizes an anoxic / aerobic environment by alternating time, replacing traditional anoxic / aerobic space, and has attracted the attention of researchers because of its simple structure and flexible operation. And research.
7.New biological denitrification method
In recent years, a number of new denitrification processes have appeared at home and abroad, providing a new way for the denitrification treatment of high-concentration ammonia nitrogen wastewater. There are mainly short-range nitrification and denitrification, aerobic denitrification and anaerobic ammonia oxidation.
Short-range nitrification denitrification
Biological nitrification and denitrification is the most widely used method of denitrification. Since a large amount of oxygen is required in the ammonia nitrogen oxidation process, the aeration cost becomes the main expense of this nitrogen removal method. Short-range nitrification and denitrification (denitrification by oxidizing ammonia nitrogen to nitrite nitrogen) can not only save the oxygen demand for ammonia oxidation but also save the carbon source required for denitrification. Ruiza et al. Used synthetic wastewater (simulating industrial wastewater containing high concentrations of ammonia nitrogen) to determine the best conditions for nitrite accumulation. In order to achieve nitrite accumulation, pH is not a key control parameter, because when the pH is 6.45 to 8.95, all nitration generates nitrate, and when pH <6.45 or pH> 8.95, nitrification is suppressed and ammonia nitrogen is accumulated. When DO = 0.7mg / L, 65% of the ammonia nitrogen can be accumulated in the form of nitrite and the ammonia nitrogen conversion rate is above 98%. When DO <0.5mg / L, ammonia nitrogen accumulation occurred, and when DO> 1.7mg / L, all nitration occurred to form nitrate. Liu Junxin et al. Carried out a comparative analysis of the effects of nitrous glass type and nitric acid type nitrogen removal in high-concentration ammonia nitrogen wastewater with low carbon-nitrogen ratio. The test results show that nitrite-based denitrification can significantly improve the total nitrogen removal efficiency, and the load of ammonia nitrogen and nitrate nitrogen can be nearly doubled. In addition, factors such as pH and ammonia nitrogen have important effects on the type of nitrogen removal.
The pilot test results of short-range nitrification and denitrification treatment of coking wastewater show that the average concentrations of COD, ammonia nitrogen, TN, and phenol in the effluent are 1201.6, 510.4, 540.1, and 110.4 mg / L, respectively. The removal rates were 197.1, 14.2, 181.5, 0.4 mg / L, and the corresponding removal rates were 83.6%, 97.2%, 66.4%, and 99.6%, respectively. Compared with the conventional biological nitrogen removal process, this process has a higher ammonia nitrogen load and can improve the TN removal rate at lower C / N values.
2. Anaerobic ammonia oxidation (ANAMMOX)
Anaerobic ammonia oxidation (ANAMMOX) refers to the process in which ammonia nitrogen is directly oxidized to nitrogen using nitrite as the electron acceptor under anaerobic conditions.
The biochemical reaction formula of ANAMMOX is:
NH4NO2- → N2 ↑ 2H2O
ANAMMOX bacteria are obligate anaerobic autotrophs, so they are very suitable for the treatment of ammonia nitrogen wastewater containing NO2-, low C / N. Compared with the traditional process, the process of denitrification based on anaerobic ammonia oxidation is simple, does not require additional organic carbon sources, prevents secondary pollution, and has a good application prospect. There are two main applications of anaerobic ammonia oxidation: the CANON process and the combination with moderate temperature nitrosation (SHARON) to form the SHARON-ANAMMOX combined process.
The CANON process is a method for simultaneously removing ammonia nitrogen and nitrite using completely autotrophic microorganisms under oxygen-limited conditions. From the perspective of the reaction form, it is a combination of the SHARON and ANAMMOX processes in the same reactor. . Meng Lei et al. Found that the leachate treatment plant of the Xiaping Solid Waste Landfill in Shenzhen has a dissolved oxygen control of about 1 mg / L, ammonia influent <800 mg / L, ammonia nitrogen load <0.46 kg, NH4 / (m3 • d) Under the conditions, the SBR reactor can be used to realize the CANON process. The ammonia nitrogen removal rate is> 95%, and the total nitrogen removal rate is> 90%.
Studies by Sliekers et al. Show that both the ANAMMOX and CANON processes can work well in stripping reactors and achieve high nitrogen conversion rates. The dissolved oxygen is controlled at about 0.5 mg / L. In the stripping reactor, the nitrogen removal rate of the ANAMMOX process reaches 8.9 kgN / (m3 • d), while the CANON process can reach 1.5 kgN / (m3 • d).
4. Simultaneous nitrification and denitrification
According to the traditional biological denitrification theory, the denitrification pathway generally includes two stages of nitrification and denitrification. The two processes of nitrification and denitrification need to be carried out in two isolated reactors, or alternately caused by hypoxia and recovery in time or space. In the same reactor in the oxygen environment; in fact, in earlier times, in some activated sludge processes without obvious anoxic and anaerobic stages, people have observed the non-assimilation loss of nitrogen multiple times. The disappearance of nitrogen has also been observed several times in the aeration system.
In these processing systems, nitrification and denitrification reactions often occur under the same processing conditions and in the same processing space. Therefore, these phenomena are called simultaneous nitrification / denitrification (SND). The current representative process for simultaneous nitrification and denitrification is MBBR.
Traditional denitrification theory believes that denitrifying bacteria are facultative anaerobic bacteria, whose respiratory chain uses oxygen as the terminal electron acceptor under aerobic conditions and nitrate as the terminal electron acceptor under hypoxic conditions. Therefore, if the denitrification reaction is performed, it must be in an anoxic environment. In recent years, the phenomenon of aerobic denitrification has been continuously discovered and reported, and has gradually attracted people's attention. Some aerobic denitrifying bacteria have been isolated, and some can perform aerobic denitrification and heterotrophic nitrification at the same time (such as Tpantotropha.LMD82.5 isolated and screened by Robertson et al.). In this way, real synchronous nitrification and denitrification can be achieved in the same reactor, which simplifies the process and saves energy.
Sequential batch reactors treat ammonia nitrogen wastewater. The test results verify the existence of aerobic denitrification. The aerobic denitrification and denitrification capacity decreases with the increase of the dissolved oxygen concentration of the mixed solution. When the dissolved oxygen concentration is 0.5 mg / L, the total The nitrogen removal rate can reach 66.0%.
Continuous dynamic experimental research shows that for high-concentration ammonia nitrogen leachate, the total nitrogen removal string of the aerobic denitrification process reached by ordinary activated sludge can reach more than 10%. The rate of nitrification reaction decreased with the decrease of dissolved oxygen concentration; the rate of denitrification reaction increased with the decrease of dissolved oxygen concentration. The kinetic analysis of nitrification and denitrification showed that simultaneous nitrification and denitrification with the same nitrification rate and denitrification rate occurred when the dissolved oxygen was about 0.14 mg / L. Its rate is 4.7mg / (L • h), the nitrification reaction KN = 0.37mg / L; the denitrification reaction KD = 0.48mg / L.
During the denitrification process, N2O is generated as a greenhouse gas and new pollution is generated. The related mechanisms have not been studied in depth. Many processes are still in the laboratory stage and require further research to be effectively applied to actual engineering. In addition, processes such as full autotrophic denitrification and simultaneous nitrification and denitrification are still in the experimental research stage and have good application prospects.