The correct answer is D) Remove small amounts of oil from large amounts of water. An engine room bilge oily-water separator is designed to remove small amounts of oil from the larger volumes of water that accumulate in the engine room bilge. This is important to comply with regulations that prohibit the discharge of oily bilge water directly overboard, in order to prevent pollution of the marine environment. The separator uses physical and chemical processes to extract the oil from the water, allowing the cleaned water to be safely discharged. The other answer choices are incorrect because they do not accurately describe the primary purpose of an oily-water separator, which is to remove oil from water, not the other way around.