Water filtration is the process of removing undesirable chemicals, biological contaminants and suspended solids from contaminated water.
Most water is disinfected for human consumption (drinking water), but water purification may also be designed for a variety of other purposes, including fulfilling the requirements of medical, pharmaceutical, chemical and industrial applications.
Various filtration methods exist to accommodate different requirements, most common being:
- Physical processes such as filtration trough a media bed, sediment & carbon filtration with cartridges’ and membrane filtration
- Chemical processes such as disinfection by addition of chlorine, chlorine dioxide or ozon
- Physico-chemical processes such as treatment of coagulation, flocculation followed by sedimentation (floc removal by solid/liquid separation)
Water purification’s goal is the reduction of unwanted elements including suspended particles, parasites, colloids, bacteria and viruses.
Sediment filtration is one of the most basic water treatment options available. This type of filtration is accomplished by mechanically removing solid matters from a fluid stream by trapping particles in a solid media. Sediment filters can be divided in 2 groups depending on the mean of retention used: Depth filter cartridges and surface filter cartridges.
This filtration method uses a bed of activated carbon to reduce contaminants and impurities through chemical adsorption and potentially physical filtration when under carbon block form.
Each particle/granule of carbon provides a large surface area/pore structure, exposing the maximum amount of contaminants to the active sites within the filter media. Thus, 450 g of activated carbon contains a surface area of approximately 40 hectares.
Activated carbon works via a process called adsorption in which polluting molecules in the fluid are trapped inside the pore structure of the carbon substrate. Active carbon filters are most effective at removing chlorine, sediment when under carbon block form, volatile organic compounds (VOCs) emitted by pesticides for instance, taste and odor from water. They are not effective at removing minerals, salts, and dissolved inorganic compounds.
Membrane filters are widely used for filtering both drinking water and sewage. For drinking water, membrane filters can remove virtually all suspended particles larger than 0.0001-0.1 µm or even reduce dissolved matters’ concentration.
Membrane filters are an effective form of tertiary treatment when it is desired to reuse the water for industry, particularly for beverage preparation (including bottled water), for limited domestic purposes, or before discharging the water into a river that is used by towns further downstream.
Below are 2 examples of membrane filtration:
Ultrafiltration (UF) is a membrane filtration process where the inlet water is pushed into a hollow fiber membrane, where each fiber is perforated by millions of pores of 0.01-0,1 µ size. Any non-dissolved element bigger than the pore size of the membrane will be physically retained by the membrane. Water, as well as all dissolved maters will pass through the UF membrane.
UF can be used for the removal of particulates and macromolecules from raw water to produce potable water. It has been used to either replace existing secondary (coagulation, flocculation, sedimentation) and tertiary filtration (sand filtration and chlorination) systems employed in water treatment plants or as standalone systems in isolated regions with growing populations.
Industries such as chemical and pharmaceutical manufacturing, food and beverage processing and waste water treatment employ ultrafiltration in order to recycle water or add value to later products. Blood dialysis also uses ultrafiltration.
- REVERSE OSMOSIS
This method uses mechanical pressure, applied to an impure solution to force pure water through a semi-permeable membrane. Reverse osmosis is theoretically the most thorough method of large scale water purification available, although perfect semi-permeable membranes are difficult to manufacture and maintain. Unless membranes are well-maintained and proper pre-treatment is set up, algae and other life forms can colonize the membranes and scale or other sediment may reduce or even clog the membrane.