Ammonia nitrogen wastewater treatment method summary, after reading decisively collected!

Ammonia nitrogen wastewater treatment has many methods, such as break point chlorination method, chemical precipitation method, ion exchange method, blowing off method and biological deamination method. These technologies can be divided into two categories: physical and chemical method and biological denitrification technology. biological nitrogen removal method

The process of microbial removal of ammonia nitrogen needs two stages. The first stage is the nitrification process, the process of converting ammonia nitrogen into nitrite nitrogen and nitrate nitrogen under aerobic conditions. The second stage is the denitrification process, the nitrate nitrogen and nitrite nitrogen in the sewage are reduced to nitrogen by denitrifying bacteria (heterotrophic and autotrophic microorganisms are found and many species) under anaerobic or hypoxic conditions. In this process, organic substances (methanol, acetic acid, glucose, etc.) are oxidized as electron donors to provide energy. Common biological nitrogen removal processes can be divided into three categories, namely, multi-stage sludge system, single-stage sludge system and biofilm system.

multi-stage sludge system

This process can get quite good BOD5 removal effect and nitrogen removal effect, its disadvantages are long process, many structures, high infrastructure costs, the need for additional carbon source, high operating costs, a certain amount of methanol residue in the water.

single-stage sludge system

The forms of single-stage sludge system include pre-denitrification system, post-denitrification system and alternate working system. Pre-denitrification biological denitrification process, commonly referred to as A/O process Compared with the traditional biological denitrification process, A/O process has the advantages of simple process, less structure, low infrastructure cost, no need for additional carbon source, high water quality and so on.

Post-type denitrification system, because of the lack of organic matter in the mixed liquor, generally requires artificial carbon source, but the effect of nitrogen removal can be higher than that of the front-type, theoretically close to 100% of nitrogen removal. The biological denitrification process of alternating work is mainly composed of two series tanks. By changing the direction of inlet and outlet water, the two tanks operate alternately under anoxic and aerobic conditions.

The system is still essentially an A/O system, but it uses alternate work to avoid the reflux of the mixture, so the nitrogen removal effect is better than the general A/O process. The disadvantage is that the operating management costs are relatively high, and the computer-controlled automatic operating system must generally be configured.

biofilm system

The anoxic tank and the aerobic tank in the above A/O system are replaced by a fixed biofilm reactor to form a biofilm denitrification system. There should be mixed liquor reflux in this system, but there is no need for sludge reflux. Two sludge systems adapted to denitrification and aerobic oxidation and nitrification reactions are stored in an anoxic aerobic reactor.

physicochemical nitrogen removal

Physical and chemical nitrogen removal commonly used physical and chemical methods are folding point chlorination method, chemical precipitation method, ion exchange method, blowing off method, liquid membrane method, electrodialysis method and catalytic wet oxidation method.

fold point chlorination

The discontinuous point chlorination method is a kind of oxidation method for treating ammonia nitrogen wastewater, and a chemical treatment method for removing ammonia from water by reacting ammonia and chlorine in water to generate nitrogen gas. This method can also play a bactericidal effect, and at the same time make a part of the organic matter inorganic, but after chlorination treatment of residual chlorine in the effluent, should be further dechlorination treatment.

Add hypochlorous acid HClO to the water containing ammonia. When the pH value is near neutral, the following main reactions are gradually carried out with the addition of hypochlorous acid:

NH3 HClO→NH2Cl H2O①

NH2Cl HClO→NHCl2 H2O②

NH2Cl NHCl2 → N2 3H 3Cl-③

When the ratio of chlorine dosage to ammonia nitrogen (Cl/N for short) is below 5.07, type ① reaction is carried out first to generate monochloramine (NH2Cl), and the concentration of residual chlorine in water increases. Then, with the increase of hypochlorous acid dosage, monochloramine reacts according to type ② to generate dichloramine (NHCl2), and type ③ reaction is carried out at the same time, and N in water is removed as N2.

As a result, the residual chlorine concentration in water decreases with the increase of Cl/N. When the Cl/N ratio reaches a certain value or more, the residual hypochlorous acid (I. e. free residual chlorine) due to unreacted increases, and the concentration of residual chlorine in water increases again. The minimum value is called discontinuous point (habitually called folding point). At this time, the Cl/N ratio is 7.6 according to the theoretical calculation; in the wastewater treatment, the Cl/N ratio should be 7.6 higher than the theoretical value, usually 10, because the chlorine reacts with the organic matter in the wastewater. In addition, when the pH is not in the neutral range, trichloroamine is more produced under acidic conditions, and nitric acid is produced under alkaline conditions, and the denitrification efficiency is lowered.

Under the conditions of pH value of 6~7, 10mg of chlorine per mg of ammonia nitrogen and 0.5~2.0h of contact, the removal rate of ammonia nitrogen is 90% ~ 100. Therefore, this method is suitable for low concentration ammonia nitrogen wastewater.

The actual amount of chlorine required for treatment depends on the temperature, pH and ammonia nitrogen concentration. Oxidation of ammonia nitrogen per mg sometimes need 9~10mg chlorine break point, chlorination treatment of effluent before discharge generally need to use activated carbon or SO2 for anti-chlorination, in order to remove the residual chlorine in the water. Although the chlorination process reacts quickly and requires less equipment investment, the safe use and storage of liquid chlorine are required to be high, and the processing cost is also high. If the use of hypochlorous acid or chlorine dioxide generation device instead of liquid chlorine, will be safer and operating costs can be reduced, the current domestic chlorine generation device chlorine production is too small, and expensive. Therefore, the chlorination method is generally applicable to the treatment of water supply, and is not suitable for the treatment of large water and high concentration of ammonia nitrogen wastewater.

chemical precipitation method

Chemical precipitation method is to add a certain chemical agent to the water, react with the soluble substances in the water, and generate salts that are difficult to dissolve in water, and the formation of sediment is easy to remove, thereby reducing the content of soluble substances in water. When PO43-and Mg2 + ions are added to wastewater containing NH4 +, the following reactions occur:

NH4 ++ PO43-+ Mg2 + → MgNH4PO4 ↓ ④ generates MgNH4PO4 precipitates that are hardly soluble in water, thus achieving the purpose of removing ammonia nitrogen in water. The common precipitants used are Mg(OH)2 and H3PO4, the suitable pH value range is 9.0~11, and the mass ratio of H3PO4/Mg(OH)2 is 1.5~3.5. When the concentration of ammonia nitrogen in wastewater is less than 900mg/L, the removal rate is above 90%, and the sediment is a good compound fertilizer. Because the price of Mg(OH)2 and H3PO4 is more expensive and the cost is higher, it is feasible to treat high concentration ammonia nitrogen wastewater, but the method adds PO43-to the wastewater, which is easy to cause secondary pollution.

ion exchange method

The essence of ion exchange method is the exchange reaction of exchangeable ions on insoluble ionic compounds (ion exchangers) and other same-sex ions in wastewater. It is a special adsorption process, usually reversible chemical adsorption. Zeolite is a natural ion exchange material, its price is much lower than that of cation exchange resin, and has selective adsorption capacity for NH4-N, with high cation exchange capacity. The cation exchange capacity of pure mordenite and clinoptilolite is equivalent to 213 and 223mg of material per 100g (m.e) on average.

However, the actual natural zeolite contains impure substances, so the exchange capacity of zeolite with higher purity is not more than 200m.e per 100g, generally 100~150m.e. As an ion exchanger, zeolite has special ion exchange characteristics. The selective exchange sequence of ions is:

Cs (Cs)>Rb (Rb)>K (K)>NH4 >Sr (Sr)>Na (Na)>Ca (Ca)>Fe (Fe)>















>

>

>

>
>

> al [+]> Mg [+]> Li [+].

In engineering design and application, the pH value of wastewater should be adjusted to 6~9, and heavy metals have no influence on the whole. Alkali metal and alkaline earth metal have influence except Mg, especially Ca has greater influence on the ion exchange capacity of zeolite than Na and K. Zeolite adsorption must be regenerated after saturation, to use the regeneration liquid method, combustion method is rarely used. The regeneration liquid mostly uses NaOH and NaCl. Because the wastewater contains Ca2, the removal rate of ammonia by zeolite is irreversibly reduced, so supplement and renewal should be considered.

blow-off method

The blow-off method is to adjust the wastewater to alkaline, then air or steam is introduced into the stripper, and the free ammonia in the wastewater is blown off to the atmosphere through gas-liquid contact. By introducing steam, the temperature of the wastewater can be increased, thereby increasing the ratio of ammonia to be blown off at a certain pH value. When using this method to treat ammonia, it is necessary to consider that the total amount of free ammonia emitted should meet the atmospheric emission standards of ammonia to avoid secondary pollution. Low concentration wastewater is usually blown off with air at room temperature, while high concentration wastewater from steelmaking, petrochemical, chemical fertilizer, organic chemical industry, non-ferrous metal smelting and other industries is usually blown off with steam.

liquid film method

Since the discovery of emulsion liquid membrane by Li Nianzhi in 1986, the liquid membrane method has been widely studied. Many people think that liquid membrane separation method may become the second generation of separation and purification technology after extraction method, especially suitable for low concentration metal ion purification and wastewater treatment process. The mechanism of removing ammonia nitrogen by emulsion liquid membrane method is as follows: ammonia nitrogen is NH3-N easily dissolved in the oil phase of membrane phase, and it migrates from the outside of the membrane phase with high concentration through the diffusion of membrane phase to the interface between the inner side and the inner phase of membrane phase, and reacts with the acid in the inner phase of membrane. The generated NH4 is insoluble in the oil phase and stable in the inner phase of membrane. Driven by the difference of ammonia concentration between the inner and outer side, ammonia molecules continue to adsorb through the membrane surface, permeate diffusion migration to the inner membrane phase desorption, so as to achieve the purpose of separation and removal of ammonia nitrogen.

electrodialysis method

Electrodialysis is a membrane separation technique that uses a voltage applied between a pair of yin and yang membranes to remove dissolved solids from an aqueous solution. A DC voltage is applied between the yin and yang permeable membranes of the electrodialysis chamber. When the water passes through multiple pairs of anion and cation permeable membranes, ammonium ions and other ions pass through the membrane and enter the concentrated water on the other side under the influence of the applied voltage. Set in the concentrated water, thus separated from the inlet water.