As the name implies, a flocculant is a chemical used to coagulate substances dispersed in water. Colloidal particles contained in raw water are agglomerated with a flocculant　and removed by filtration　or precipitation.

Inorganic clay such as silt　and mud is typical as colloidal particles contained in river water　and groundwater, but in the case of groundwater, organic substances such as iron hydroxide　and humic substances dispersed by the combination of colloidal silica in raw water　and iron. Also exists as colloidal particles. These cannot be physically removed by anthracite, filtered sand　or even the Ferrorite series, so they will flow into the treated water. Therefore, the flocculant is injected in front of the filtration tower,　and by adjusting the pH, the flocculant is grown as a bridge to the particles that can capture the colloidal particles with the filter material,　and the particles are electrically neutralized　and filtered. Prevents outflow to water.
There are various coagulants used in tap water, but mainly aluminum sulfate (sulfuric acid band), polyaluminum chloride (PAC) aluminum-based coagulants,　and ferric chloride, ferric polysulfate,　and iron such as polysilica iron. It is divided into two types of systems flocculants.
Generally, polyaluminum chloride (PAC), which is inexpensive, easy to handle,　and has high cohesiveness, is used, but in recent years there is concern about the relationship between aluminum　and the occurrence of Alzheimer’s disease, so if the injection amount of the cohesive agent is appropriate. For example, aluminum does not flow out into the treated water, so it is necessary to know the appropriate injection amount of cohesive agent in advance.

There are various coagulants used in tap water, but mainly aluminum sulfate (sulfuric acid band), aluminum chloride coagulant of polyaluminum chloride (PAC)　and iron-based coagulants such as ferric chloride, ferric sulfate　and polysilica iron. It is divided into two types of coagulants: inorganic coagulants.
Polyaluminum chloride (PAC), which is inexpensive, easy to handle,　and highly cohesive, is generally used. In recent years, there are concerns about the relationship between aluminum　and the occurrence of Alzheimer’s disease, but if the injection amount of the coagulant is appropriate, aluminum will not flow out into the treated water, so grasp the appropriate injection amount of the coagulant in advance. Must be done.

● Polymer flocculant
In addition to inorganic flocculants, there are also polymer flocculants that aggregate flocs into larger flocs by cross-linking action. Polymer flocculants are also called polymers　and are available in anionic, cationic　and nonionic systems. Polymer flocculants are mainly used for wastewater treatment. In addition, except for some parts, it is not approved for water supply,　and because the flocs are highly viscous, it is not suitable for filtration using a filter material. Therefore, except for the coagulation sedimentation treatment of some water purification plants, Not used in tap water.

● Aggregation mechanism
Inorganic clay such as silt　and mud is typical as colloidal particles contained in river water　and groundwater, but in the case of groundwater, organic substances such as iron hydroxide　and humic substances dispersed by combining silica　and iron in raw water are also available. It exists as colloidal particles. These cannot be physically removed by anthracite, filtered sand　or even the Ferrorite series, so they will flow into the treated water. Therefore, a flocculant is injected in front of the filtration tower to electrically neutralize it,　and by adjusting the pH, the flocculant is grown as a bridge to particles that can capture colloidal particles with a filter medium,　and the flocs are filtered. This will prevent it from flowing out into the treated water.
When performing precipitation treatment　or pressure flotation treatment, inorganic flocculants alone are not sufficient, so polymer flocculants are used to further aggregate flocs.