The coagulation principle of the water treatment process of the sewage treatment plant mainly involves the aggregation process of colloids and tiny suspended solids in the water. By adding chemicals to the water, the colloid particles that are difficult to precipitate in the water are destabilized and aggregated to form larger flocs, which are finally separated from the water by means of precipitation or clarification. Below I will analyze and explain the coagulation principle and its role.

I. Stability theory of mixed colloids

1. The double-layer theory of colloidal particles is involved in the coagulation process. The core of the colloid is a particle composed of multiple atoms or molecules, called a colloid nucleus. The surface of the colloid nucleus carries a layer of ions, which attract heterotype ions around the particles to form bound counterions and free counterions. Since the ions adsorbed on the surface of the colloid nucleus are more than the counterions in the adsorption layer, the colloid particles are negatively charged, while the micelles are electrically neutral. There are electrostatic repulsion and van der Waals attraction between colloid particles. When the distance between colloid particles is at a certain distance, these two forces will make the colloid particles approach each other, eventually leading to aggregation.

2. The stability of colloids in water treatment mainly involves the characteristics of colloidal particles to maintain a dispersed and suspended state in water for a long time, and the aggregation stability caused by eliminating electrostatic repulsion. The stable existence of colloidal particles is closely related to their double-layer structure. A layer of ions with the same charge is adsorbed on the surface of the colloid nucleus, called the potential ion layer. These potential ion layers attract a layer of ions with opposite signs, forming the so-called "diffusion layer". The stability between colloidal particles is mainly maintained by the structure of these two layers. 

II. Coagulation Double Layer Theory

1. Double layer structure: The stability of colloidal particles comes from their double layer structure, which is composed of negatively charged colloidal cores and surrounding positively charged counterions. This structure generates electrostatic repulsion between colloidal particles, thereby maintaining a stable suspension state.

2. Potential: The zeta potential in the double-layer structure is a key parameter for colloid stability. A high zeta potential means that the repulsion between colloid particles is strong and the colloid is more stable; conversely, a low zeta potential is conducive to the coagulation of colloids.

III. Coagulation kinetic stability

1. Brownian motion: Colloidal particles are affected by Brownian motion due to their small size, which makes them move irregularly and at high speed in water and difficult to settle due to gravity.

2. Particle size effect: Smaller colloidal particles are hit less often per unit time, and the forces generated cannot offset each other, so they appear to be in a state of continuous suspension in water[^5^].

IV. Interaction in water

1. Van der Waals attraction: There is always van der Waals attraction between colloidal particles, which is inversely proportional to the distance between particles. The closer the distance, the stronger the attraction.

2. Electrostatic repulsion: The double-layer structure of colloidal particles leads to electrostatic repulsion between particles. The magnitude of this force is affected by the zeta potential and the ionic strength in the solution.

V. Coagulation destabilization mechanism

1. Compression of double electric layer: by adding electrolytes with high-valent counterions, the counterion strength in water is increased, the thickness of the diffusion layer is reduced, and the zeta potential is reduced, so that the colloid is destabilized.

2. Electrical neutralization: by adding electrolytes such as iron salts and aluminum salts, the charge of the potential ions on the surface of the colloid is neutralized by generating complex ions, the zeta potential is reduced, and the colloid is coagulated.

VI. Flocculation mechanism

1. Adsorption bridging: polymer flocculants form adsorption bridges between multiple colloidal particles through chain molecules, promoting the aggregation and flocculation of colloidal particles.

2. Entanglement and coiling: by adding high-valent metal salts (such as iron and aluminum salts), insoluble hydroxide precipitation is quickly generated, and the colloidal particles or fine suspended matter are removed together.

VII. Sedimentation and dynamic detection

1. Coagulation and sedimentation: By adjusting pH, adding appropriate coagulants, optimizing the mixing and flocculation process, ensuring the maximum destruction of colloid stability and achieving efficient sedimentation.

2. Dynamic monitoring: Real-time monitoring of water quality changes and zeta potential during treatment, adjusting the type and dosage of coagulants as needed to ensure that the final water quality meets the standards. Brownian motion and charge action in water treatment are important scientific principles in the coagulation process, and they play a key role in the aggregation and precipitation of colloidal particles.

In summary, it can be seen that Brownian motion and charge interaction play a vital role in the coagulation process of water treatment. Through the in-depth understanding and application of these two basic principles, the coagulation process can be optimized and the water quality treatment effect can be improved. This not only helps to ensure the safety and hygiene of drinking water, but also has important significance for environmental protection and water resource reuse. Therefore, in-depth research and mastery of these basic principles will have a profound impact on improving the overall level of water treatment technology. The stability of colloids in water treatment involves many aspects, including double electrical layer structure, kinetic characteristics, interactions in water and destabilization mechanisms. In actual water treatment processes, by reasonably selecting coagulants, controlling operating conditions and combining efficient flocculation and precipitation technologies, the stability of colloids can be effectively destroyed to ensure water supply safety. In order to further optimize the water treatment effect, it is recommended to strengthen the real-time monitoring of water quality dynamics and flexibly adjust the treatment strategy according to changes in water quality.