Alabama Grade II Water Operator Practice Test

Reverse osmosis is a water purification process that relies on a specific type of membrane known as a semi-permeable membrane. This membrane allows certain molecules, particularly water, to pass through while blocking the passage of larger molecules and impurities such as salts, bacteria, and other contaminants.

The effectiveness of reverse osmosis is largely due to the ability of the semi-permeable membrane to create a barrier that only permits the desired solvent—in this case, water—to move from an area of higher concentration to an area of lower concentration when pressure is applied. This selective filtration process is essential for producing clean, potable water from sources that may contain undesirable substances.

In contrast, a permeable membrane would allow all substances to pass through without restriction, while a non-permeable membrane would not allow any substances to pass, thus not facilitating the purification process at all. Composite membranes, while they can be involved in some advanced filtration systems, still fall under the category of being semi-permeable. Therefore, identifying the membrane used specifically in reverse osmosis as a semi-permeable membrane emphasizes its capacity for selective filtration, which is crucial for the efficacy of the process.