The position, method and dosage of PFS are introduced. Polyferric sulfate is a kind of macromolecular flocculant, which plays the main roles of coagulation, dephosphorization and decolorization in water. In addition to its own quality, it is also affected by the pollutant content, water temperature, pH and other factors. The other is its dosing position, which will not only change its main role, but also affect the subsequent purification treatment.

　　Dosing position of PFS in wastewater treatment

　　1. Like other coagulants, PFS can be added in front of the primary sedimentation tank of wastewater treatment, and the adding direction can improve the removal rate of COD and suspended solids in wastewater.

　　2. However, in the aeration tank, between the aeration tank and the secondary sedimentation tank (in the connecting pipeline or channel), these two dosing positions are helpful to improve the dissolution rate and mixing effect of coagulants such as PFS under the action of aeration.

　　3. After biochemical treatment. This is because it is difficult to deal with the soluble phosphorus, and microorganisms transform the soluble phosphorus to improve the phosphorus removal rate, and will not cause damage to the biochemical system.

　　The dosage of PFS is as follows

　　When polyferric sulfate is used, liquid polyferric sulfate is usually prepared into 10% - 50% aqueous solution (it can be directly added when the turbidity of source water is high), solid polyferric sulfate is prepared into 10% - 30% aqueous solution, and then the prepared solution is put into according to the best conditions and dosage according to the specific situation, and the best coagulation effect can be obtained after full stirring.

　　The dosage of PFS can be determined according to the different turbidity of raw water. Generally, the dosage of PFS is 30-50kg per thousand tons for turbid water (turbidity is 100-500mg / L). The dosage of PFS for high turbidity industrial sewage of non drinking water can be appropriately added.

　　Different purposes, different dosing positions:

　　1. In order to remove phosphorus as the main purpose, in different effluent total phosphorus can be added to the iron position is different, phosphorus content is relatively small, can be added to the primary sedimentation tank. When the relative phosphorus content is relatively high, coagulant is added to the effluent of the secondary sedimentation tank for filtration treatment. When there is no biochemical tank, flocculant can be added directly.

　　2. In order to remove COD as the main purpose, such as in papermaking wastewater treatment, it is generally added to the secondary sedimentation tank or after biochemical treatment.