The thickness of the base material on which filter media are supported is 30-75cm.

Introduction:
In the field of chemical engineering, filter media are commonly used in various processes to separate solids from liquids or gases. These filter media are typically supported on a base material, which provides structural integrity and acts as a support for the filter media. The thickness of this base material is an important parameter that affects the performance and efficiency of the filtration process.

Importance of the base material thickness:
The thickness of the base material plays a crucial role in determining the overall effectiveness of the filtration process. It affects the capacity of the filter to hold the filter media firmly in place, prevents media migration, and allows for the proper flow of the fluid through the filter.

Optimal thickness range:
The correct answer to the given question is option 'C' - 30-75cm. This range of thickness is considered to be optimal for supporting the filter media. Let's understand why:

1. Structural integrity: The base material should have sufficient thickness to provide structural integrity to the filter. Thicker base material ensures better stability and prevents deformation or collapse of the filter during operation.

2. Preventing media migration: The base material should be thick enough to prevent the filter media from migrating or being washed away by the fluid flow. This ensures that the filter media stay in place and effectively capture the desired particles.

3. Uniform flow distribution: The thickness of the base material also affects the flow distribution of the fluid through the filter. A thicker base material allows for better distribution of the fluid flow, ensuring uniform filtration and preventing channeling or bypassing of the fluid.

4. Optimal pressure drop: The thickness of the base material influences the pressure drop across the filter. A thicker base material can accommodate a larger volume of fluid, resulting in a lower pressure drop. This is important to maintain efficient filtration without excessive energy consumption.

5. Handling and maintenance: The thickness of the base material should be practical for handling and maintenance purposes. A thickness range of 30-75cm strikes a balance between providing sufficient support and ease of handling during installation, replacement, and cleaning of the filter media.

Conclusion:
In conclusion, the thickness of the base material on which filter media are supported is typically in the range of 30-75cm. This range ensures structural integrity, prevents media migration, allows for uniform flow distribution, and provides optimal pressure drop. It also considers practical aspects of handling and maintenance.