How to select the dosing place of chemical phosphorus removal agent?

Chemical dephosphorization process can be classified according to the adding place of chemical agent. In practice, the commonly used methods are Pre-dephosphorization process, synchronous dephosphorization and post dephosphorization.

The characteristics of the pre-dephosphorization process are that chemicals are added to the grit chamber, the inlet channel (pipe) of the primary sedimentation tank, or the venturi channel (using eddy current). Generally, it needs to set up a device to generate eddy current and supply energy to meet the needs of mixing. The corresponding precipitated products (bulky flocs) are separated by sedimentation in the primary sedimentation tank. If biofilter is used in biological section, ferric salt agent is not allowed to be used to prevent damage to filler (yellow rust).

The Pre-dephosphorization process is more suitable for the reconstruction of existing wastewater treatment plants, because only chemical phosphorus removal measures are added at the front end of the existing process. Through this process, not only phosphorus can be removed, but also the load of biological treatment facilities can be reduced. The common chemical agents are lime and metal salt. The residual phosphate content of 1.5-2.5mg/l after Pre-dephosphorization can fully meet the needs of subsequent biological treatment for phosphorus.

Synchronous phosphorus removal is the most widely used chemical phosphorus removal process, accounting for about 50% of all chemical phosphorus removal processes abroad. The process is to add chemicals into the effluent of aeration tank or the inflow of secondary sedimentation tank. In some cases, chemicals are added into the influent of aeration tank or return sludge channel (pipe).

At present, it has been determined that simultaneous chemical phosphorus removal can be used for activated sludge process and biological turntable process, but it is still worth discussing whether the agent can be added into the secondary sedimentation tank for biological filter process.

Post dephosphorization is a two-stage process, in which precipitation, flocculation and flocculation are separated in a facility separated from biological treatment. Generally, chemical agents are added to a mixing tank behind the secondary sedimentation tank, and flocculation tank and sedimentation tank (or air flotation tank) are set behind it.

Lime water emulsion can be used in the post removal phosphorus removal process for receiving water, which is not strict. However, the pH value of the effluent must be controlled, such as neutralization by CO2. Air flotation tank can remove suspended solids and total phosphorus better than sedimentation tank, but the operation cost is higher because of the constant air supply.

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