Water filtration has been present throughout recorded human history. There are records of water filtration as far back as 2000 BC. Human bodies consist of 70% water and therefore need water — potable water — to sustain them. Historically, civilizations were constructed around bodies of water, but the water was not always ideal for human consumption. This lack of potable water catalyzed the development of water purification and water filtration technologies. These ancient water treatment technologies included boiling water, placing hot instruments into the water before consumption, and introducing water to unrefined sand and charcoal filters.
Media filters are used to reduce the level of suspended solids (turbidity) in incoming feed water. Suspended solids consist of small particles such as silt, clay, grit, organic matter, algae and other microorganisms. Incoming feed water that is high in suspended solids can cause a high-¬‐pressure drop and reduce the effectiveness of downstream filtration equipment such as reverse osmosis membranes and ion exchange beds.
Media filters typically contain multiple layers, with a supporting (non-filtering) layer of gravel at the bottom. The lighter medias will be on top and the heavier garnet will remain on the bottom. The filter media arrangement allows the largest dirt particles to be removed near the top of the media bed with the smaller dirt particles being retained deeper and deeper in the media.
This allows the entire bed to act as a filter allowing much longer filter run times between backwash and more efficient particulate removal. Multi-Media Filters can remove particulates down to 5-10 microns. To put this in perspective, the width of a human hair is around 50 microns.
Activated carbon “GAC” is made from raw organic materials (such as coconut shells or coal) that are high in carbon. Heat, in the absence of oxygen, is used to increase (activate) the surface area of the carbon; therefore, these filters are sometimes referred to as “charcoal” filters. The activated carbon removes certain chemicals that are dissolved in water passing through a filter containing GAC by trapping (adsorbing) the chemical in the GAC.
GAC is commonly used in drinking water treatment to adsorb synthetic organic chemicals and natural organic compounds that cause taste and odor, color, and can react with chlorine to form disinfection byproducts. Adsorption is both the physical and chemical process of accumulating a substance at the interface between liquid and solids phases. GAC is an effective adsorbent because it is a highly porous material and provides a large surface area to which contaminants may adsorb.
It is very important that the type and concentration of contaminants, and average water use, be known in order to determine the correct size and components of the system. All treatment systems require proper installation and periodic maintenance. Eventually, the ability of the GAC to bind and remove chemicals is used up and the GAC needs to be changed.
How often the GAC should be changed needs to be based on contaminant levels and water use. While some filters may last for several years if contaminant levels and/or water use are low, higher levels or use may require more frequent change-outs. A GAC filter system is used to remove semi-volatile and volatile organic compounds (SVOCs and VOCs), such as constituents of gasoline, heating oil, and chlorinated solvents, from polluted drinking water.