How to Regulate the Size and Density of Flocs in Sewage Treatment to Improve Flocculation Performance

In modern sewage treatment processes, coagulation is one of the crucial technologies for enhancing water quality. Among them, the size and density of flocs in the flocculation stage play a vital role in water treatment performance. By regulating the characteristics of flocs, the efficiency of subsequent filtration and the quality of effluent water can be significantly improved. This article will delve into how to effectively regulate the size and density of flocs in the sewage flocculation stage, thereby enhancing the overall sewage treatment performance.

The core of the coagulation method lies in using chemical agents (such as flocculants) to promote the collision of insoluble particles, thereby forming larger and heavier particles for subsequent sedimentation or filtration. During this process, the polymers produced by the hydrolysis of flocculants form adsorption bridges with tiny solid particles, causing the particles to aggregate and form flocs. However, to achieve effective coagulation and flocculation, the size and density of flocs need to be regulated within a certain range.

The type and properties of flocculants are crucial for flocculation performance. When designing a sewage treatment scheme, it is necessary to select suitable flocculants to meet the requirements of specific water quality. Common flocculants include aluminum salts, iron salts, and high-molecular polymers. The solubility, reaction rate, and molecular structure of these flocculants in water directly affect the formation and characteristics of flocs.

For example, after hydrolysis in water, aluminum salt flocculants (such as aluminum sulfate) can effectively form polymers with adsorption bridge properties. These polymers can quickly adsorb surrounding fine particles and promote their aggregation into larger flocs. However, insufficient or excessive addition of flocculants will lead to unsatisfactory flocculation performance, so reasonable adjustment is essential.

In the flocculation process, the collision between particles is a key link in floc formation. The probability of collision is not only related to physical properties such as water flow velocity and mixing method but also affected by particle size. Larger particles tend to come into contact with smaller particles, while smaller particles may not collide effectively with other particles due to their fast movement speed. Therefore, enhancing the collision probability is of great importance.

To improve collision performance, methods such as mechanical stirring or bubble introduction are often used to create a suitable reaction environment. However, it should be noted that excessively strong stirring will break the formed flocs, leading to a decrease in flocculation efficiency. Therefore, it is particularly important to regulate the mixing intensity, time, and method to achieve optimal flocculation performance.

The growth rate of flocs is an aspect that requires special attention in the regulation process. If flocs grow too fast, especially when their specific surface area decreases sharply, small particles may lose the opportunity to collide with large particles, thereby affecting subsequent flocculation and sedimentation performance. In addition, flocs that grow too slowly will result in poor sedimentation in the sedimentation tank; even if some particles reach the size required for sedimentation, their insufficient density will lead to a decline in effluent water quality. Therefore, moderate growth of flocs is particularly important.

Water quality parameters such as pH value, temperature, and salinity of the water body also affect the performance of the flocculation process and directly influence the formation and stability of flocs. An appropriate pH value can optimize the performance of flocculants, enabling them to achieve optimal hydrolysis performance in water and thus ensuring the smooth progress of the flocculation process.

For instance, under normal circumstances, the optimal flocculation pH range for aluminum salts is 6-8. Within this range, aluminum salts can be completely hydrolyzed and effectively form polymers, thereby improving flocculation performance. Conversely, excessively low or high pH values will cause the instability of aluminum ions, affecting flocculation performance. Therefore, during sewage treatment, water quality should be monitored regularly and relevant parameters adjusted to maintain the optimal flocculation state.

In sewage treatment, the dosage of flocculants should be reasonably designed according to the characteristics of water quality, and the optimal dosage should be determined through experiments. This process can be realized through small-scale tests, laboratory research, and on-site verification. It should be noted that insufficient flocculant dosage will lead to incomplete coagulation, while excessive dosage will result in resource waste and secondary pollution of effluent water. Therefore, it is particularly necessary to establish an appropriate monitoring mechanism and feedback adjustment system to dynamically adjust the dosage of flocculants.

Considering the impact of particle collision, the adoption of different mixing methods (such as combining rapid stirring and slow stirring) can effectively improve mixing efficiency. Rapid stirring can ensure that flocculants are in full contact with particles and promote their collision, while slow stirring is conducive to preventing the formed flocs from being broken. In addition, the introduction of new mixing and separation technologies such as dissolved air flotation and inclined plate sedimentation can improve sedimentation efficiency and treatment performance.

Regularly monitor and adjust water quality parameters of sewage, such as pH value, temperature, and dissolved oxygen, to ensure that the treatment is carried out within the optimal range. In particular, the use of regulators (such as acidic or alkaline regulators) to control the pH value of the water body can promote the effective dissolution and hydrolysis of flocculants.

Optimize the design of sedimentation tanks; a slow flow rate and appropriate residence time can both improve the sedimentation efficiency of flocs. The use of advanced filtration equipment, such as membrane filtration and sand filtration, can further improve the quality of effluent water and reduce the concentration of suspended solids. At the same time, a reasonable arrangement of the sequence of sedimentation and filtration can significantly improve the operating efficiency of the entire water treatment system.

Regulating the size and density of flocs is a key link in the sewage treatment process and is of great significance for enhancing water quality. By optimizing flocculant dosage, improving mixing methods, controlling water quality parameters, and enhancing the sedimentation and filtration stages, the efficiency of sewage treatment can be effectively improved, and better effluent water quality can be achieved....