Phosphorus is the root cause of eutrophication of water bodies. Although the phosphorus content of urban sewage is very low, its water discharge is extremely large. If the water is directly removed without treatment, it will seriously pollute the water environment. Phosphorus is an essential nutrient for the organism and is not toxic by itself. But when a lot of other phosphorus and copper nutrients are discharged into the water together, the problem arises. The large amount of algae growth imbalances the ecological balance of the water body, leading to eutrophication of the water body, and the consequences are very serious.

       1. Calcium removal by phosphorus In the phosphorus removal by precipitation method, the chemical precipitation agent mainly has aluminum ion, iron ion and calcium ion. The equilibrium constant of hydroxyapatite formed by lime and phosphate is the largest, and the phosphorus removal effect is the best. Adding lime to the phosphorus-containing wastewater, the calcium ions react with the phosphate to form a precipitate. The reaction is as follows: 5Ca2++7OH-+3H2PO4-=Ca5(OH)(PO4)3↓+6H2O(1) Side reaction: Ca2++ CO32-=CaCO3↓(2) The equilibrium constant of the reaction (1) is KS0=10-55.9. From the above reaction, it is known that the phosphorus removal efficiency depends on the relative concentration and pH of the anion. It can be seen from formula (1) that phosphate reacts with calcium ions under alkaline conditions to form calcium hydroxyphosphate. The reaction tends to be complete with increasing pH. When the pH is greater than 10, the phosphorus removal effect is better, and the effluent phosphate can be ensured. The standard reaction of salt mass concentration <0.5mg / l (2) that calcium ions react with carbonate in wastewater to form calcium carbonate, which is very important for calcium phosphorus removal, not only affects the calcium dosage, but also produces calcium carbonate. It can be used as a weighting agent to help condense and clarify sewage. The first-stage reaction and precipitation in the above process are mainly zinc removal, control ph=8.5-9.0, adding polyaluminum chloride, the second-stage reaction and precipitation are mainly calcium removal by phosphorus, control ph=11～11.5, effluent After the neutralization, the discharge or reuse of the effluent water quality reaches the first level standard.

       The key technology of calcium dephosphorization is to use calcium chloride or lime as a chemical, using a mechanical mixing reactor and a high efficiency inclined tube precipitator to control the appropriate amount of reaction, mixing strength, precipitation surface load and reaction pH.

       2. Slag is a solid waste generated in the process of iron and steel smelting. It is mainly composed of oxides such as CaO, FeO, MnO, SiO2, Fe2O3, P2O5, Cr2O5 and Al2O3. It has many excellent properties, and each component contained in it can be The experimental study of this method is to add 200mL of simulated phosphorus-containing wastewater and a certain amount of slag in several plug-type bottles, put them on a shaker, and shake at room temperature for a certain time to make the adsorption reaction reach equilibrium and then filter. Then, the concentration of phosphorus was tested on the supernatant, and the adsorption amount and phosphorus removal rate on the adsorbent were calculated by comparing the initial concentration and equilibrium concentration of phosphorus in the solution. The research shows that: 1) With the increase of the amount of slag, The removal rate of phosphorus also increases, but the adsorption amount decreases. 2) The adsorption amount increases with time at the beginning, but when the adsorption time is longer than 2h, the adsorption amount tends to be stable. 3) The adsorption amount varies with the concentration of phosphorus in the wastewater. Increasing and increasing 4) The effect of temperature on the adsorption of slag is very small 5) The pH value of the solution has an important effect on the adsorption effect. When the pH is 7.56, the removal rate of phosphorus is the highest.

       Therefore, when the phosphorus-containing wastewater is treated by the method, when the concentration of phosphorus in the waste liquid is 2 to 13 mg/L, the amount of slag is 5 g/L, the pH is 7.56, and the adsorption time is 2 h, the removal rate of phosphorus can reach More than 99%, the concentration of residual liquid is also lower than the national emission standard, and the method is safe and reliable, and will not cause secondary pollution.

       Third, add lime

       Adding a large amount of lime to the phosphorus-containing wastewater, adjusting the pH to 10.5 to 12.5 to form hydroxyapatite, the precipitate is stable, and the equilibrium constant is large. The equilibrium constant of Ca10(OH)2(PO4)6 is 90, which is larger than that of aluminum salt and iron salt. 3 to 4 times the phosphate precipitate. The larger the equilibrium constant is, the more stable the precipitate is, the better the sedimentation effect is, the dephosphorization is more thorough, the solid-liquid separation effect is also good, and the treatment of phosphorus-containing wastewater is completely up to standard, P≤0.5mg/L.

       Adding lime to increase the pH value of the wastewater to remove phosphorus, and also make the petroleum and CODcr in the wastewater co-precipitate and purify, and the wastewater can reach the standard discharge.

Fourth, phosphorus-containing wastewater treatment process

       In the process design of phosphorus-containing wastewater treatment, electrolytic polishing wastewater, chemical polishing wastewater and other wastewater are uniformly flowed into the wastewater regulating tank. Dissolve lime (CaO mass fraction ≥ 80% ~ 90%) powder into the dosing tank, use the pump to input the wastewater in the conditioning tank into the reaction tank, add the drug before the pump, and then add PAM (polyacrylamide) 0.5 ~ l. 0mg/L, after 10~15min, the coagulation reaction flows into the inclined tube sedimentation tank, and the supernatant is filtered after pH adjustment, and the qualified efflux is detected. The lower slag liquid is input into the sludge concentration tank, concentrated, and then dried by pressure filtration to remove the dry slag.

       All kinds of waste liquids are returned to the wastewater conditioning tank for reprocessing.