Technical analysis of chemical removal of phosphorus

Basis of chemical phosphorus removal

The removal of phosphorus has two processes: chemical phosphorus removal and Biochemical disposal of phosphorus. The latter one is a relatively economical method of phosphorus removal. However, because the phosphorus removal process is currently not guaranteed to reach the requirements of 0.5mg/L water outlet standard, as we must need to meet the stable water output standards, chemical phosphorus removal measures are often taken into practice.

Chemical phosphorus removal is completed by chemical sinking. Chemical sinking refers to salt that is dissolved with inorganic metal salt agents to sewage, and it forms non -dissolving granular after mixing with dissolved in sewage, such as phosphate mixed Sexual substances, this process involves the transfer process, the reaction equation is shown below. In fact, after the chemical agent is dosed, the sewage is not only a sinking response, but also a chemical flocculation reaction, so the difference between chemical sinking and chemical flocculation must be distinguished.

The sewage sinking response can be simply understood as: the dissolved substance in the water, most of which are the process of converting ion-like substances into non-soluble granular forms, and flocculation is a small non-soluble solid object. So the flocculation is not the process of metastasis.

In the sewage purification process, flocculation and sinking analysis are extremely important, but flocculation is used to improve the precipitation effect of the sedimentation tank, while sinking is used for removal of dissolved phosphorus in sewage. If the converting phase of the sinking process is used, after adding dissolved metal saline agents to the sewage, the dissolved phosphorus transition into non -soluble metal salts on the one hand will also produce non -soluble nature at the same time Hydroxide (depending on the pH value). On the other hand, with the increase of sinking analysis objects and smaller non -soluble solid objects accumulated into a large non -soluble solid, stabilize the stable collagen, and through the speed gradient or diffusion process Contact generate flocculation. Finally, through the solid -liquid separation steps, the purified sewage and solid liquid concentration (chemical sludge) are obtained to achieve the purpose of chemical phosphorus removal.

Type of chemicals for phosphorus removal

According to the basis of chemical sinking response, in order to generate phosphate compounds, flocculants used for chemical phosphorus are mainly metal salt chemicals and calcium hydroxide. After many high valence metal ionic agents are added to the sewage, they will combine with soluble phosphorus ions in the sewage to generate difficulty dissolved compounds. For economic reasons, metal salt agents used for phosphorus are mainly FE3+, Al3+and FE2+salt and lime. These potions are used in the state of solution and suspension. The divalent iron salt can be used only when the sewage contains oxygen and can be oxidized into a trivalent iron salt. FE2+In fact, in order to be added to the aeration sand pool in order to be oxidized or added to the aeration tank with a synchronous sinking analysis process, the effect is the same as using Fe3+, and the reaction type is like the two formulas below.

Because the condemnation reaction competes with the reaction between metal ions and OH ion, so you should pay attention to the metal ion weight for various metal salt products, and the reaction type is like the two other formulas as shown below.

Metal hydroxide will form a large piece of flocculant, which is beneficial to the flocculation of sinking products. At the same time, it will also adsorb colloidal substances and fine suspended particles. It should be noted that the sinking removal in the chemical sinking response for the purpose of chemical phosphorus removal is secondary. However, the condensation of organic collagen and suspension in the flocculation during separation is a decisive process.

The sinking effect is affected by the pH value, and the solubility of metal phosphate is also affected by pH. The best pH range of iron salt is 5.0 ~ 5.5, and the aluminum salt is 6.0 to 7.0, because the dissolution of FePo4 or AlPo4 within the above pH value range is the least. In addition, the use of metal salt agents will also bring benefits to sewage and sludge treatment, such as reducing the sludge index of sludge, which is conducive to biogas desulfurization.

Due to the increase in metal salt agents, the content of CL-or SO2-4 ions in the sewage treatment plant is increased. If the sinking pharmaceutical solution contains sour, it is necessary to pay special attention.

After adding metal salt agents, it will reduce the alkali of the sewage accordingly, which may adversely affect the purification. When using iron sulfate in the synchronous sinking process, the effect of reaction on nitrification must be considered.

In addition, if the sludge of the sewage treatment plant is used for agriculture, the impact of aluminum or iron load on agriculture must be considered when using metal salt drug removal.

Here, we summarize all the suitable chemical salts for the disposal of phosphorus