In the water treatment process, which filter material is least efficient in the filtration operation?

In the context of water treatment, conventional sand filters are known for their effectiveness at removing suspended solids and some microorganisms, but they can be less efficient compared to more advanced filtration techniques. Sand filters operate primarily through mechanical straining, sedimentation, and adsorption processes, which can lead to a higher chance of breakthrough when dealing with very fine particles or certain contaminants.

In comparison, dual filters and mixed filters can utilize a variety of media and layers that enhance the removal of different sizes and types of particles. Membrane filters employ a physical barrier that can effectively eliminate even smaller particles, including viruses, providing a high efficiency level that far surpasses that of conventional sand.

Thus, conventional sand filters can be considered the least efficient option in this context, especially when fine filtration or higher purity of water is required. The advancements in filter technology have made alternatives such as dual, mixed, and membrane filters much more effective in modern water treatment processes.