Minimum number of filter beds in the slow sand filter:
The correct answer to this question is option 'B' which states that the minimum number of filter beds in the slow sand filter is 2.

Slow sand filtration is a water treatment process that uses a bed of sand to remove impurities and contaminants from water. Filter beds in slow sand filters are designed to promote the growth of a biological layer called the schmutzdecke, which acts as a filter to remove pathogens, suspended solids, and other pollutants from the water.

Slow sand filters are typically constructed with multiple filter beds for several reasons:

1. Efficiency: Having multiple filter beds increases the overall treatment efficiency of the system. Each filter bed goes through a series of processes, including sedimentation, filtration, and biological activity. By having multiple filter beds, the water passes through a greater surface area, allowing for more thorough filtration and treatment.

2. Redundancy: Multiple filter beds provide redundancy in case one of the beds needs maintenance or repair. If one filter bed becomes clogged or damaged, the other filter beds can continue to operate, ensuring uninterrupted water treatment.

3. Flow distribution: Having multiple filter beds helps to distribute the flow of water evenly across the filtration system. This prevents preferential flow and ensures that each filter bed is utilized effectively, maximizing the treatment capacity of the slow sand filter.

4. Flexibility: Multiple filter beds allow for flexibility in operation and maintenance. For example, one filter bed can be taken offline for cleaning or maintenance while the others continue to operate, minimizing the impact on water treatment operations.

In summary, the minimum number of filter beds in a slow sand filter is 2. This ensures efficient treatment, provides redundancy, helps distribute flow evenly, and allows for flexibility in operation and maintenance.