The phosphorus in sewage comes from the phosphorus containing organic matter in domestic sewage, synthetic detergent, industrial waste liquid, agricultural chemical fertilizers and pesticides and the excreta of various animals. The direct discharge of these sewage without treatment will cause great harm to our environment, and the effect of polyferric sulfate for sewage phosphorus removal is better. In wastewater phosphorus removal treatment, the main treatment methods are divided into two categories: one is microbial phosphorus removal method with low cost and high effect, and the other is fast, convenient and efficient chemical phosphorus removal method. Microbial phosphorus removal method mainly uses microorganisms such as phosphorus accumulating bacteria, while chemical phosphorus removal method uses chemicals as phosphorus removal agent for a series of chemical treatment. Among the chemicals, metal salts such as aluminum sulfate, polyaluminium chloride, ferric chloride and polyferric sulfate are used as phosphorus removal agents. In particular, polyferric sulfate is increasingly used in wastewater phosphorus removal instead of other chemicals.
Polyferric sulfate is an improved high molecular iron salt polymer. In the phosphorus removal treatment of sewage as phosphorus removal agent, the dosage is less and the amount of sludge is less than that of ordinary PFS and other similar agents. Compared with ordinary Polyferric, its content reaches 11% ~ 13%, especially in the phosphorus removal of wastewater, and its dosage can be reduced by 50%.
Phosphorus removal and dosing scheme of polyferric sulfate wastewater
1. It is added in front of the pre sedimentation tank. In other words, the product is applied to pretreatment. Here, not only the phosphate in the raw water can be treated, but also the suspended substances in the water can be adsorbed and settled. However, it also increases the amount of sludge formed, removes a large number of insoluble organic substances, affects the subsequent microbial denitrification and biological phosphorus removal, and increases the difficulty of sludge treatment.
2. It is added to the secondary sedimentation tank as a coagulant to dissolve it. After the polymer product is dissolved, the phosphate in the water is coagulated, and then the deep phosphorus removal treatment is carried out through air flotation or sedimentation filtration separation. Adding polymeric iron here not only has high phosphorus removal rate, but also has strong adsorption capacity for other suspended substances in water. However, compared with the biochemical method, this method increases the dosage of chemicals and produces more sludge, and it is necessary to set a final sedimentation tank to ensure the normal operation of the subsequent filtration system.
3. Conduct simultaneous phosphorus removal treatment with microorganisms, that is, add it to the end of biochemical aeration tank. The residual phosphorus after biochemical phosphorus removal shall be treated. Through the previous biochemical phosphorus removal treatment, this addition method can not only digest the organic phosphorus in the water, but also convert the metaphosphate and soluble phosphorus in the water into orthophosphate, and then add polymerized ferric sulfate for phosphorus removal treatment, and its treatment effect can reach above the discharge standard. This method can greatly reduce the dosage of phosphorus removal agent, improve phosphorus removal efficiency, improve sludge sedimentation performance and reduce phosphorus removal cost.
It can be seen that when polyferric sulfate is used as phosphorus removal agent for wastewater phosphorus removal treatment, it shall be added to the end of biochemical aeration tank as far as possible, or added to secondary sedimentation tank for emergency treatment.