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Design specifications for chemical phosphorus removal process!

来源:环保工程师 作者: 阅读:2808 网友评论0 Updated: 2019-09-26 12:48 Source: engineer of environmental protection: Read: 2808 2010 0 comments

There are two processes for chemical phosphorus removal: biological phosphorus removal, biological phosphorus removal is a relatively economical phosphorus removal method, but because the phosphorus removal process can not guarantee the stability to meet the requirements of 0.5mg / l effluent standard, so To reach a stable effluent standard, chemical phosphorus removal measures are often required to meet the requirements. Therefore, in the outdoor drainage design code GB50014-2006 (2014 edition), the following provisions have been made for chemical phosphorus removal design: 1. Provisions on the scope of application of chemical phosphorus removal.

The Total Phosphorus Discharge Standard stipulated in the "Emission Standards for Pollutants Discharged by Urban Sewage Treatment Plants" GB 18918: When the level A standard is reached, the sewage plant constructed before December 31, 2005 is 1mg / L, starting from January 1, 2006 The sewage treatment plant is 0.5mg / L. Generally, after biological phosphorus removal in urban sewage, it is difficult to meet the latter standard, so chemical phosphorus removal can be supplemented to meet the requirements of effluent water quality.

Enhanced primary treatment can remove most of the phosphorus in sewage. The test of Shanghai Bailonggang Sewage Plant showed that when the dosage of FeCl3 is 40mg / L ~ 80mg / L, or the dosage of Al2 (SO4) 3 18H2O is 60mg / L ~ 80mg / L, the phosphate and phosphorus concentration in the water The removal rates are 2 mg / L to 9 mg / L and 0.2 mg / L to 1.1 mg / L, and the removal rates are 60% to 95%.

During the anaerobic treatment of sludge, the filtrate of the dehydrator and the supernatant of the concentration tank, etc., under the anaerobic conditions, a large amount of phosphorus-containing substances are released into the liquid. If it is returned to the sewage treatment system, it will cause The vicious cycle of phosphorus in the sewage treatment system, so phosphorus removal should be carried out first, and chemical phosphorus removal should generally be used.

2. Provisions on pharmacy dosing points.

With the bioreactor as the boundary, dosing in front of the bioreactor is pre-dosing, dosing after the bioreactor is post-dosing, and dosing in the bioreactor is simultaneous dosing. Subsequent additions are multi-point additions.

The pre-dosing point is in the raw sewage, and the formed sediment is eliminated together with the primary settling sludge. The advantage of pre-dosing is that it can also remove a considerable amount of organic matter, so it can reduce the load of biological treatment. The post-addition point is that after the biological treatment, the formed sediment is separated by another solid-liquid separation device. The effluent quality of this method is good, but additional solid-liquid separation facilities need to be added. The simultaneous feeding point is in the outlet pipe of the primary sedimentation tank or the biological reaction tank, and the formed sediment is removed together with the remaining sludge. Multi-point dosing points are dosing agents at places such as settling tanks, biological reaction tanks, and solid-liquid separation facilities, which can reduce the total dosage and increase the flexibility of operation. Due to the influence of pH, lime cannot be used as a coagulant. Where nitrification is required, attention should be paid to the effects of iron and aluminum on nitrifying bacteria.

3. Regarding the types, doses, and dosage points of the medicaments, it should be determined according to the test.

Because the quality of sewage water and environmental conditions are different, it is appropriate to determine the best type, dose and dosage point based on the test.

4. Provisions on chemical phosphorus removal agents.

Aluminum salts include aluminum sulfate, sodium aluminate, and polyaluminum, among which aluminum sulfate is more commonly used. Iron salts include ferric chloride, ferrous chloride, ferric sulfate, and ferrous sulfate, among which ferric chloride is the most commonly used.

When aluminum salt or iron salt is used to remove phosphorus, mainly insoluble aluminum phosphate or iron phosphate is generated, and the dosage is directly proportional to the total phosphorus in the sewage. It can be used for the front, back and synchronous dosing of biological reaction cells. Ferrous salts need to be oxidized to iron salts first to obtain the maximum phosphorus removal effect. Therefore, it is generally not used as a coagulant added at the back. When pre-dosed, it is generally added to an aerated sand tank. So that the ferrous salt is rapidly oxidized to the iron salt. When lime is used to remove phosphorus, Ca5 (PO4) 3OH precipitates, and its solubility is related to pH. Therefore, the amount of lime required depends on the alkalinity of the sewage, not the phosphorus content. Lime as a coagulant cannot be used for simultaneous phosphorus removal, only for front or rear phosphorus removal. After the lime is used for pre-dephosphorization, the pH value of the sewage is high, and the pH value needs to be adjusted before entering the biological treatment system. When the lime is used for post-dephosphorization, the treated effluent must be adjusted to meet the discharge requirements. Phosphorus removal from the anaerobic phosphorus release pond of sludge or the phosphorus-rich supernatant produced during sludge treatment. With lime to remove phosphorus, the amount of sludge is much larger than that of aluminum or iron salts, so it is rarely used. Adding a small amount of anionic, cationic or anionic cationic polyelectrolyte, such as polyacrylamide (PAM), as a coagulant, is beneficial to the coagulation and precipitation of dispersed free metal phosphate flocs.

5. Regarding the dosage of aluminum salt or iron salt as coagulant.

Theoretically, trivalent aluminum and iron ions react with equimolar phosphoric acid to form aluminum phosphate and iron phosphate. Because the components in sewage are extremely complicated and contain a large amount of anions, aluminum and iron ions will react with them, thereby consuming the coagulant. According to experience, the molar ratio should be 1.5 to 3.

6. Provisions on the amount of sludge to be considered.

More sludge is produced during chemical phosphorus removal. When aluminum salt or iron salt is used as coagulant, the amount of sludge will increase by 40% to 75% in front; the amount of sludge will increase by 20% to 35% in the latter; 15% to 50%. When lime is used as the coagulant, the amount of sludge is increased by 150% to 500% in the case of pre-dosing, and the amount of sludge is increased by 130% to 145% in the case of post-dosing.

7. It is stipulated that the equipment in contact with corrosive substances shall take anti-corrosion measures.

Ferric trichloride, ferrous chloride, ferric sulfate, and ferrous sulfate are all very corrosive; aluminum sulfate solids are not corrosive under dry conditions, but aluminum sulfate liquids are very corrosive, so do this Regulations.

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