Introduction:
In the process of water treatment, one of the primary objectives is to remove suspended impurities from the water. Sand filtration is a commonly used method for this purpose. The effectiveness of sand filtration depends on various factors, including the size and surface area of the sand grains.

Explanation:
1. Sand size:
The size of the sand grains used in the filtration process plays a crucial role in the removal of suspended impurities. Smaller sand grains provide a larger surface area for the impurities to adhere to, resulting in more efficient removal. On the other hand, larger sand grains have less surface area, making it difficult for the impurities to be trapped and removed. Therefore, in order to remove finer suspended impurities, smaller sand grains are preferred.

2. Surface area of sand grains:
The surface area of the sand grains is directly proportional to the efficiency of the filtration process. Finer sand grains have a larger surface area compared to coarser sand grains. When water passes through the sand bed, suspended impurities come into contact with the sand grains, and their removal occurs through processes such as sedimentation, straining, and adsorption. A larger surface area of sand grains provides more opportunities for impurities to attach and be removed. Thus, smaller sand grains with a larger surface area are more effective in removing finer suspended impurities.

3. Sand depth of the bed:
The depth of the sand bed in a filtration system also influences the removal of suspended impurities. A deeper sand bed allows for a longer contact time between the water and the sand grains, facilitating the removal of impurities. However, a narrow sand depth can limit the contact time and reduce the efficiency of impurity removal. Therefore, a deeper sand bed is preferred to enhance the removal of finer suspended impurities.

Conclusion:
In summary, the removal of finer suspended impurities in water treatment processes is facilitated by using smaller sand grains. Smaller sand grains provide a larger surface area for impurities to adhere to, increasing the efficiency of their removal. Additionally, a deeper sand bed enhances the contact time between water and sand grains, further improving the removal process.