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There are many different methods of industrial water filtration, with different types being used in different industries. Nearly every method can be categorized into two categories: water purification or water filtration. Water filtration systems are the most commonly-used variety of industrial water filtration, since most wastewater is not a result of a chemical process. Some of the different types of industrial water filtration include general solid removal, skimming, and using filters. Wastewater purification generally includes oxidation, distillation and reverse osmosis.
Wastewater can be comprised of many different contaminants that make it unsafe to consume or use, such as harmful bacteria, mineral deposits, chemicals, or in many cases, human and animal waste. The latter has its own sub-category known as sewage, which is one of the most frequently-processed and treated forms of wastewater. Sewage treatment plants use both filtration and purification processes to produce "sludge" waste used for fertilization purposes and environmentally-friendly liquid waste, respectively.
Removing solids from water can be relatively simple, with nothing more than sedimentation, a form of basic filtering where the solids come in contact with a barrier in which water can pass, such as a membrane- being necessary. This is useful for removing larger solids, such as stones of varying sizes, sludge, or, in some cases, sand. Removing solid waste can become difficult, however, when the contaminants are very small or have little effect on the wastewater's density. As a result, other forms of filtration are employed, such as using very fine filters and membranes, along with other techniques such as flocculation, a chemical process where smaller particles are suspended in a liquid in the form of flakes.
Another form of industrial water filtration involves the removal of oil and grease, which is done through a process known as skimming. Since oil and grease cannot bond or mix with water, they float to the top, allowing a skimmer coupled with a pump to remove the surface oil, resulting in clean water. The most common type of skimming device is the American Petroleum Industry (API) oil-water separator, which is designed in accordance with API standards for the purpose of removing oil and grease from water. While a skimming device may remove the desired amount of oil, some situations require water to undergo a filtering or chemical process to make it as pure as possible.
One of the most common forms of water filtration is known as slow sand filtration, where un-purified water is passed through multiple layers of sand and sediment, each of which has a different level of coarseness. Water begins at the top layer, which is the coarsest of all the layers, and typically consists of gravel. As the water moves down from layer to layer, different-sized physical contaminants are naturally removed. The bottom-most level is the finest layer, and it filters out a vast majority of any small objects. After this process, the water is almost entirely pure.
Filtration methods cannot always filter out everything, as some contaminants are too small, or in other cases, chemically-bonded to the water. As a result, water purification methods are often employed after filtration. A widely-used form of water purification is distillation, where a liquid is evaporated and then condensed in a separate container. This not only kills any bacteria or parasites in the same way a boiling process would, but also completely removes solid contaminants, such as salt, dirt and other deposits.