Introduction and application of high ammonia nitrogen wastewater treatment

Nitrogen exists in various forms such as organic nitrogen, ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3--N) and nitrite nitrogen (NO2--N) in wastewater, and ammonia nitrogen is one of the most important existing forms.

Ammonia nitrogen in wastewater refers to nitrogen in the form of free ammonia and ionic ammonium, which mainly comes from the decomposition of nitrogen-containing organic matter in domestic sewage, industrial wastewater such as coking and synthetic ammonia, and farmland drainage. There are many sources of ammonia nitrogen, and the emission concentration changes greatly.

Ammonia nitrogen wastewater mainly comes from chemical fertilizer, coking, petrochemical, pharmaceutical, food, landfill and so on. A large amount of ammonia nitrogen wastewater discharged into water not only causes eutrophication of water, causes black and odor of water, increases the difficulty and cost of water treatment, and even produces toxic effects on people and organisms.

The general formation of ammonia nitrogen wastewater is caused by the co-existence of ammonia and inorganic ammonia. Generally, the main source of ammonia nitrogen in the wastewater whose pH is above neutral is the joint action of inorganic ammonia and ammonia water. In the acidic condition, the ammonia nitrogen in the wastewater is mainly caused by inorganic ammonia.

There are two main types of ammonia nitrogen in wastewater, one is ammonia nitrogen formed by ammonia water, the other is ammonia nitrogen formed by inorganic ammonia, mainly ammonium sulfate, ammonium chloride and so on.

Treatment of ammonia nitrogen in wastewater

Air blow off

A method of separation using the gas-liquid equilibrium relationship between the concentration of ammonia nitrogen in the gas phase and the concentration of ammonia nitrogen in the liquid phase under alkaline conditions. It is generally believed that the blowing is related to the temperature, PH and gas-liquid ratio. Under the condition of gas, water in 3000:1, ammonia nitrogen treatment effect in 70-75%, cannot one-time ammonia nitrogen wastewater discharging standard, the multistage blowoff need heating, power at the same time, covers an area of big, blow out the ammonia nitrogen, because of the large gas water ratio cannot be recycled, ammonia nitrogen emissions cannot achieve the odorous pollutants discharge standard GB14554-93 ammonia secondary emission standard.

Direct evaporation

Multi-effect evaporation and MVR evaporator were used to concentrate ammonia nitrogen wastewater directly, so that the ammonia nitrogen in the wastewater was crystallized in the form of ammonia salt. In general, the wastewater that needs biochemical treatment under the condition of high COD and high ammonia nitrogen must be treated by evaporator. The steam and power consumption required for evaporation are large, and the investment is large. The effluent ammonia nitrogen is still in the range of 200-1500mg/ L, and further deamination is needed before it can be entered into the subsequent biochemical system.

Degassing membrane

Using the principle of degassing film, ammonia nitrogen wastewater after alkali is fed into one side of the membrane, and sulfuric acid solution is on the other side. The free ammonia on one side of ammonia nitrogen wastewater is continuously absorbed into ammonium sulfate solution by sulfuric acid on the other side through the membrane. After continuous absorption of ammonia nitrogen wastewater to meet the discharge standards. Degassable film has high requirements on the pretreatment of ammonia nitrogen wastewater and the organic matter in wastewater. Due to the absorption of sulfuric acid, the influent ammonia nitrogen concentration should not be too high, usually no more than 500 mg/ L. Therefore, this technology is rarely used in China due to the various restrictions of influent conditions and the uncertainty of membrane service life technology.

Zeolite, ion exchange technology

Zeolite or ions are used for ion exchange of ammonia in wastewater, so that ammonia nitrogen in wastewater can be discharged to the standard. This technology is generally combined with biochemical BAF technology to treat ammonia nitrogen wastewater with ammonia nitrogen concentration below 50 mg/ L.

The application of zeolite deamination must consider the regeneration of zeolite, usually there are regenerative liquid method and incineration method. When the incineration method is used, the ammonia gas produced must be treated. This method is suitable for the treatment of low-concentration ammonia nitrogen wastewater, and the content of ammonia nitrogen should be 10-20mg /L.

Oxidation method, magnesium ammonium phosphate method

Sodium hypochlorite is used to oxidize ammonia nitrogen. Due to the high cost of oxidation, ammonia nitrogen wastewater treatment technology is rarely used. Adding phosphoric acid and magnesium oxide in a certain reaction proportion is also because the concentration is difficult to control, the operation cost is high, and the ammonia nitrogen wastewater treatment process is rarely used.

Steamed ammonia method

Steam is used to heat the wastewater, so that the ammonia in the wastewater is separated and cooled at high temperature and ammonia water is formed. The bubble hood and float valve are used as the inner parts of the column to make the steam contact with the wastewater with high ammonia nitrogen. The remaining ammonia water in the coking industry is mostly distilled ammonium process. The steam consumption of the ammonia process is large, and the ammonia nitrogen effluent is generally 300 mg/ L.