What are good solutions for high ammonia nitrogen levels in wastewater treatment? Thank you

What specific components are they,,,

Our company has a large equalization tank where wastewater is stored for 10 days to half a month, while being aerated at the same time. In the effluent indicators, the ammonia nitrogen content has decreased significantly. :lol

It was stripped off under alkaline conditions; in principle, this is not allowed, and it is not recommended

There are various methods for removing ammonia nitrogen, and the biological method is generally cost-effective. Processes such as A/O, A2/O, SBR, CASS, and oxidation ditches all have good capabilities for removing ammonia nitrogen, with the optimal removal rate exceeding 98%.

Air stripping: Under alkaline conditions (pH > 10.5), ammonia nitrogen in wastewater exists primarily in the form of NH3 (Figure 20-2). By ensuring thorough contact between the wastewater and air, the volatile NH3 in the water will transfer from the liquid phase to the gas phase, thereby removing ammonia nitrogen from the water. The stripping tower is filled with wooden or plastic strip packing; air flows in from the bottom of the tower, while wastewater falls from the top of the tower to a collection tank at the bottom. The main factors affecting the efficiency of ammonia stripping are: (1) pH value. Generally, the pH value is raised to 10.8–11.5 ； (2) Temperature: As the water temperature decreases, the solubility of ammonia increases, resulting in a reduced stripping efficiency. For example, the ammonia removal rate is 90–95% at 20°C, while it drops to around 75% at 10°C, which poses difficulties for the operation of stripping towers in winter ； (3) Hydraulic load: An excessive hydraulic load (m3/m2·h) will disrupt the water flow conditions necessary for efficient stripping, thereby creating a water curtain ； If the hydraulic load is too low, the packing may not be properly wetted, resulting in poor operation and the formation of a dry tower. The general hydraulic load is 2.5 to 5 m3/m2·h ； (4) Air-to-water ratio: For a given tower height, increasing the air flow rate can improve the ammonia removal rate ； However, as the air flow rate increases, the pressure drop also increases, so there is a limit to the air flow rate. Generally, the gas/water ratio can range from 2500 to 5000 (m3/m2) ； (5) Packing configuration and height Since repeated splashing of water and the formation of water droplets are key to ammonia stripping, the shape, size, spacing, and arrangement of the packing all have an impact on the stripping efficiency. Generally, the packing spacing is 40–50 mm, and the packing height is 6–7.5 m. If the packing spacing is increased, a greater packing height is required ； (6) Scale control: Packing scale (CaCO3) significantly reduces the treatment efficiency of the stripping tower. Measures to control scaling include flushing the scale layer with high-pressure water ； Add scale inhibitors to the influent water: Use air stripping with little or no CO2 (such as recycled exhaust gas for ammonia removal) ； Plastic packing materials that are less prone to scaling are used in place of wood and similar materials. Ammonia removal by air stripping can achieve a removal rate of 60–95%. The process is simple, the treatment performance is stable, the capital and operating costs are low, and it can handle high-concentration ammonia-containing wastewater. However, at low temperatures, the stripping efficiency is low; scaling in the packing often severely hinders operation; and the stripped ammonia causes secondary pollution to the environment.

Removal of ammonia nitrogen from wastewater: Nitrogen in wastewater often exists in the form of nitrogen-containing organic compounds, ammonia, nitrates, and nitrites. Biological treatment converts most organic nitrogen into ammonia, which can then be further converted into nitrates. Currently, there are four nitrogen removal processes in use: biological nitrification and denitrification, selective exchange adsorption by zeolite, air stripping, and breakpoint chlorination. 　　 I. Biological nitrification and denitrification (biological nitrogen removal method) (1) Biological nitrification: Under aerobic conditions, the process by which ammonia nitrogen is oxidized into nitrite nitrogen and nitrate nitrogen through the action of nitrite bacteria and nitrate bacteria is known as biological nitrification. The reaction process of biological nitrification is: NH4+ + 2O2 = NO3- + 2H+ + H2O. From this equation, it can be seen that (1) during the nitrification process, 4.57 g of oxygen are required to convert 1 g of ammonia nitrogen into nitrate nitrogen ； (2) H+ is released during the nitration process, which consumes the alkalinity in the wastewater; for every 1 g of ammonia nitrogen oxidized, 7.1 g of alkalinity (expressed as CaCO3) is consumed. The main factors affecting the nitrification process are: (1) pH value – the nitrification rate is fastest at a pH of 8.0–8.4 at 20°C. Since the pH decreases during the nitration process, lime must be added when the alkalinity of the wastewater is insufficient, in order to maintain the pH above 7.5 ； (2) Temperature: The nitration rate is faster at higher temperatures. The optimal water temperature for nitrite bacteria is 35°C; their activity drops sharply below 15°C, so it is advisable to maintain the water temperature at least at 15°C ； (3) Sludge retention time: The growth rate of nitrifying bacteria is very low, with a maximum specific growth rate of 0.3–0.5 d-1 (at a temperature of 20°C and pH of 8.0–8.4). To maintain a certain amount of nitrifying bacteria in the tank, the sludge retention time must be greater than the minimum generation time of these bacteria. In actual operation, it is generally advisable to set it to >2, or >2 ； (4) Dissolved oxygen: Oxygen serves as the electron acceptor in biological nitrification, and too low a concentration of it hinders the progress of this process. Generally, in the aeration tank of the activated sludge process, to carry out nitrification, the dissolved oxygen level should be maintained at 2–3 mg/L or higher ； (5) BOD load: Nitrifying bacteria are a type of autotrophic bacteria, whereas BOD-oxidizing bacteria are heterotrophic bacteria. If the BOD5 load is too high, heterotrophic bacteria with higher growth rates will reproduce rapidly, preventing the autotrophic nitrifying bacteria from gaining dominance and thus reducing the nitrification rate. Therefore, to ensure adequate nitrification, the BOD5 load should be maintained below 0.3 kg(BOD5)/kg(SS).d. (II) Biological denitrification: The process by which NO2--N and NO3--N are reduced to N2 under anaerobic conditions, through the action of facultative denitrifying bacteria, is called denitrification. The electron donors (hydrogen donors) in the denitrification process are various organic substrates (carbon sources). Taking methanol as a carbon source as an example, its reaction equation is: 6NO3− + 5CH3OH → 5CO2 + 4H2O + 3N2 + 6OH−. As can be seen from this, during the biological denitrification process, not only can NO3−-N and NO2−-N be reduced, but organic matter can also be oxidized and decomposed. Main factors affecting denitrification: (1) Temperature. The effect of temperature on denitrification is greater than that on other biological wastewater treatment processes. Generally, it is advisable to maintain a temperature of 20–40°C. In cold winters, measures such as increasing the sludge retention time and reducing the load can be taken to maintain good denitrification performance ； (2) pH value: The pH value during the denitrification process should be maintained between 7.0 and 8.0 ； (3) Dissolved oxygen: Oxygen has an inhibitory effect on denitrification. Generally, the dissolved oxygen level in denitrification reactors should be kept below 0.5 mg/L (for the activated sludge process) or below 1 mg/L (for the biofilm process) ； (4) Organic carbon source: When the wastewater contains sufficient organic carbon source and BOD5/TN > (3–5), no external carbon source is required. When the carbon-to-nitrogen ratio in the wastewater is below this value, additional organic carbon must be added. Methanol is commonly used as the added organic carbon. Considering the additional consumption of dissolved oxygen by methanol, the amount of methanol added is generally three times that of NO3--N. Furthermore, microbial death can also be utilized ； The portion of organic carbon released after autolysis is known as the \"internal carbon source,\" but this requires a long retention time for the sludge or a low load rate, so that the microorganisms are in the stationary or decline phase of their growth curve; as a result, the volume of the tank must be increased accordingly. II. Zeolite-based selective exchange adsorption: Zeolite is a silicoaluminate whose chemical composition can be expressed as (M2+, 2M+)O·Al2O3·mSiO2•nH2O (where m = 2–10 and n = 0–9). Here, M2+ represents divalent cations such as Ca2+ and Sr2+, while M+ represents monovalent cations such as Na+ and K+. It is a weak-acid type cation exchanger. In the three-dimensional structure of zeolites, there are regular pore structures and cavities, which endow them with excellent properties such as sieving effects, selective ion exchange and adsorption, thermal stability, and shape stability. There are many types of natural zeolites, and the one primarily used for removing ammonia nitrogen is offretzeite. The exchange selectivity order of offretite for certain cations is: K+, NH4+ > Na+ > Ba2+ > Ca2+ > Mg2+. Taking advantage of the strong selectivity of offretite for NH4+, an exchange adsorption process can be used to remove ammonia nitrogen from water. Exchanged and adsorptively saturated pumice can be reused after regeneration. The pH value of the solution has a significant impact on the ammonia removal by zeolites. When the pH is too high, NH4+ is converted to NH3, weakening the exchange adsorption effect ； When the pH is too low, the competitive adsorption of H+ increases, which is unfavorable for the removal of NH4+. Generally, the optimal pH value for the inlet water is between 6 and 8. When treating municipal wastewater with total ammonia nitrogen content of 10–20 mg/L, the effluent concentration can be reduced to below 1 mg/L. The water volume during penetration is approximately 100–150 bed volumes. The working exchange capacity of zeolites is approximately 0.4×10-3 n-1 mol/g. Zeolites saturated with adsorbed ammonium can be regenerated using 5 g/L of lime milk or saturated lime water. The amount of regeneration liquid is approximately 3–5% of the amount of water to be treated. Studies have shown that adding 0.1 mol of NaCl to the lime regeneration solution can improve the regeneration efficiency. To address the scaling issue in lime regeneration, a 2% sodium chloride solution is also used as the regeneration fluid, in which case a larger amount of this fluid is required. The high-concentration ammonia-containing waste liquid discharged during regeneration must be treated. The treatment methods include: (1) air stripping – the NH3 removed by stripping is either vented or absorbed by H2SO4 to be used as fertilizer ； (2) Steam stripping: The condensate is an 1% ammonia solution, which can be used as fertilizer ； (3) Electrolytic oxidation (electrochlorination): Oxidatively decomposes ammonia into N2. III. Air stripping: Under alkaline conditions (pH > 10.5), ammonia nitrogen in wastewater exists mainly in the form of NH3 (Figure 20-2). By ensuring thorough contact between the wastewater and air, the volatile NH3 in the water will transfer from the liquid phase to the gas phase, thereby removing ammonia nitrogen from the water. The stripping tower is filled with wooden or plastic strip packing; air flows in from the bottom of the tower, while wastewater falls from the top of the tower to a collection tank at the bottom. The main factors affecting the efficiency of ammonia stripping are: (1) pH value. Generally, the pH value is raised to 10.8–11.5 ； (2) Temperature: As the water temperature decreases, the solubility of ammonia increases, resulting in a reduced stripping efficiency. For example, the ammonia removal rate is 90–95% at 20°C, while it drops to around 75% at 10°C, which poses difficulties for the operation of stripping towers in winter ； (3) Hydraulic load: An excessive hydraulic load (m3/m2·h) will disrupt the water flow conditions necessary for efficient stripping, thereby creating a water curtain ； If the hydraulic load is too low, the packing may not be properly wetted, resulting in poor operation and the formation of a dry tower. The general hydraulic load is 2.5 to 5 m3/m2·h ； (4) Air-to-water ratio: For a given tower height, increasing the air flow rate can improve the ammonia removal rate ； However, as the air flow rate increases, the pressure drop also increases, so there is a limit to the air flow rate. Generally, the gas/water ratio can range from 2500 to 5000 (m3/m2) ； (5) Packing configuration and height Since repeated splashing of water and the formation of water droplets are key to ammonia stripping, the shape, size, spacing, and arrangement of the packing all have an impact on the stripping efficiency. Generally, the packing spacing is 40–50 mm, and the packing height is 6–7.5 m. If the packing spacing is increased, a greater packing height is required ； (6) Scale control: Packing scale (CaCO3) significantly reduces the treatment efficiency of the stripping tower. Measures to control scaling include flushing the scale layer with high-pressure water ； Add scale inhibitors to the influent water: Use air stripping with little or no CO2 (such as recycled exhaust gas for ammonia removal) ； Plastic packing materials that are less prone to scaling are used in place of wood and similar materials. Ammonia removal by air stripping can achieve a removal rate of 60–95%. The process is simple, the treatment performance is stable, the capital and operating costs are low, and it can handle high-concentration ammonia-containing wastewater. However, at low temperatures, the stripping efficiency is low; scaling in the packing often severely hinders operation; and the stripped ammonia causes secondary pollution to the environment. IV. breakpoint chlorination: This is a method in which an excess of chlorine or sodium hypochlorite is added (above the \"breakpoint\", see Chapter 14) to completely oxidize ammonia in wastewater into N2. The reaction can be expressed as: NH4+ + 1.5HOCl → 0.5N2 + 1.5H2O + 2.5H+ + 1.5Cl-. As can be seen from this reaction equation, the theoretical amount of chlorine required to reach the breakpoint is 7.6 kg/kg(NH3-N), while the actual amount needed is between 8 and 10 kg/kg(NH3-N). If the reaction is carried out at pH 6–7, the dosage of reagent can be minimized. The contact time is generally 0.5 to 2 hours. Strict control of pH and chlorine dosage can reduce the formation of harmful chloramines (such as NCl3) and chlorinated organic compounds during the reaction. The breakpoint chlorination method achieves a removal rate of 90–100% for ammonia nitrogen, offers stable treatment performance that is not affected by water temperature, and requires low capital costs. But its operating costs are high ； Residual chlorine and chlorinated organic compounds must be post-treated.

Under alkaline conditions, stripping in a stripping tower yields excellent results.