Daily Question 2016.7.21 (EIA Discussion): 3 Wealth points for replies, plus 5 Wealth points for correct answers (multiple-choice question)

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This post was last edited by Zhang Xiaopeng on 2016-7-21 09:28. 96. Among the following methods, those that utilize density differences to remove pollutants from wastewater are ( ). A. Oil separation B. Filtration C. Air flotation D. Reverse osmosis. Answer: AC. Explanation: The basic principle behind using oil separation tanks and sedimentation tanks to treat wastewater is the same; both methods take advantage of the difference in specific gravity between suspended solids in the wastewater and water in order to achieve separation. Air flotation is a water treatment device that uses a dissolved air system to generate a large number of tiny bubbles in water; these bubbles allow air to attach itself to suspended particles in the form of highly dispersed microbubbles, resulting in a density lower than that of water. The principle of buoyancy is then utilized to cause these particles to float to the surface, thereby enabling solid-liquid separation. Filtration is a process used to separate insoluble solids from liquids. For example, the filtration of crude brine is a filtration-based method used to remove the solid impurities present in table salt. Reverse osmosis: Also known as reverse osmotic separation, it is a membrane separation process that uses pressure differences as a driving force to separate the solvent from a solution. It is called reverse osmosis because it goes in the opposite direction of natural osmosis. By taking advantage of the different osmotic pressures of various materials, a reverse osmosis pressure higher than these osmotic pressures can be used – that is, the reverse osmosis method – to achieve separation, extraction, purification, and concentration.