دانشجویان رشته عمران - آبفای دانشگاه عباسپور
کلاس فعال و منسجم
اینم انواع فیلترها با شکل و توضیح ولی به زبان انگلیسی
Types of Filters
We will discuss two types of filters below - the slow sand filter and the rapid sand filter. The pressure sand filter is essentially a rapid sand filter placed inside a pressurized chamber while the diatomaceous earth filter is not commonly used in treatment of drinking water.
The history of water treatment dates back to approximately the thirteenth century B.C. in Egypt. However, modern filtration began much later. John Gibb's slow sand filter, built in 1804 in Scotland, was the first filter used for treating potable water in large quantities. Slow sand filters spread rapidly, with the first one in the United States built in Richmond, VA, in 1832. A set of slow sand filters adapted from English designs was built in 1870 in Poughkeepsie, NY, and is still in operation.
A few decades after the first slow sand filters were built in the U.S., the first rapid sand filters were installed. The advent of rapid sand filtration is linked to the discovery of coagulation. By adding certain chemicals (coagulants) to turbid water, the material in the water could be made to clump together and quickly settle out. Using coagulation, clear water for filtration could be produced from turbid, polluted streams.
By the end of the nineteenth century, there were ten times as many rapid sand filters in service as the slow sand type. Currently, slow sand filtration is only considered economical in unusual cases.
The diatomaceous earth filter was developed by the U.S. Army during WWII. They needed a filter that was easily transportable, lightweight, and able to produce pure drinking water. The diatomaceous earth filter is used in smaller systems, but is not commonly part of water treatment plants.
Slow Sand Filter
The slow sand filter is the oldest type of large-scale filter. In the slow sand filter, water passes first through about 36 inches of sand, then through a layer of gravel, before entering the underdrain. The sand removes particles from the water through adsorption and straining.
Unlike other filters, slow sand filters also remove a great deal of turbidity from water using biological action. A layer of dirt, debris, and microorganisms builds up on the top of the sand. This layer is known as schmutzdecke, which is German for "dirty skin." The schmutzdecke breaks down organic particles in the water biologically, and is also very effective in straining out even very small inorganic particles from water.
Number of slow sand filters operating in each state as of 1991. (Sims)
Since rapid sand filters are the primary filtration type used in water treatment in the United States, we will discuss this filter in more detail.
A diagram of a typical rapid sand filter is shown above. The filter is contained within a filter box, usually made of concrete. Inside the filter box are layers of filter media (sand, anthracite, etc.) and gravel. Below the gravel, a network of pipes makes up the underdrain which collects the filtered water and evenly distributes the backwash water. Backwash troughs help distribute the influent water and are also used in backwashing (which will be discussed in a later section.)
In addition to the parts mentioned above, most rapid sand filters contain a controller, or filter control system, which regulates flow rates of water through the filter. Other parts, such as valves, a loss of head gauge, surface washers, and a backwash pump, are used while cleaning the filter.
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