ANS:D - ultrafiltration.

Ultrafiltration is a type of membrane filtration process used to separate suspended solids and solutes of high molecular weight from a liquid, typically water. It operates on the principle of size exclusion, where a semi-permeable membrane with very fine pores allows solvent molecules (such as water) to pass through while blocking larger solute particles. Here's how ultrafiltration works:

1. Membrane: Ultrafiltration employs a semi-permeable membrane that contains microscopic pores. These pores are sized to allow the passage of water molecules and small solutes while blocking larger particles such as suspended solids, bacteria, viruses, and macromolecules.
2. Pressure: Pressure is applied to the liquid being filtered to overcome the osmotic pressure and drive the solvent (usually water) through the membrane. This pressure forces the liquid through the membrane, while the larger particles and solutes are retained on the upstream side of the membrane.
3. Separation: As the liquid passes through the membrane, contaminants larger than the pore size of the membrane are effectively removed from the liquid stream. The purified liquid, now free of suspended solids and high molecular weight solutes, exits on the other side of the membrane.

Ultrafiltration is commonly used in various applications, including water treatment, wastewater treatment, food and beverage processing, pharmaceutical production, and biotechnology. It is particularly effective for removing colloidal particles, proteins, bacteria, and other contaminants from liquids. Ultrafiltration offers several advantages, such as high efficiency, low energy consumption, and the ability to operate at relatively low pressures compared to other membrane processes like reverse osmosis.