Water filters have a long history as a method of water purification, beginning as early as 2000 b.c. in ancient Egypt. Filtration has evolved from the simple Hippocratic sleeve of ancient Greece, made from cloth, to the complicated solid block carbon and multimedia water filters currently on the market. Water filtration is now the premier method of water purification, removing more water contaminants, more efficiently, than any other technique.
Filtration is the process of removing solids from a fluid by passing it through a porous medium. Coarse, medium, and fine porous media have been used depending on the requirement. This filter media blocks passage of contaminants through physical obstruction, chemical adsorption, or a combination of both processes. Material construction of the filter media varies widely according to the nature of contaminants needed to remove.
The filtration rate depends on the effective size of the bedding and the water velocity through the filter. The flow required for filtration can be achieved using gravity for the residential application or pressure for the commercial and industrial application. In pressure filtration, one side of the filter medium is at higher pressure than that of the other so that the filter plane has a pressure drop.
Every filtration unit construct of the following major components -.
Physical water filtration
Also called Sedimentation, which is the deposition by settling of a suspended material, which refer to it as total suspended solids or TSS, it consist of tiny insoluble particles in water that include grit, silt, clay, ferric iron and other precipitates. Suspended material often adheres to the surface of RO membranes and interferes with the passage of water through the membrane which result in:
Membrane fouling, particularly the first elements of the first stage
Increased pressure drop, thereby causing lower flows
Greater pump discharge pressure used to overcome fouling, thereby leaving less pressure to drive the water through the membranes
Frequent cleanings and unplanned downtimes
Sedimentation is accomplish generally in two different filter type according to its application and required purity level.
Sand & multimedia vessel:
For commercial & industrial application
For high purity and residential application
Sand & multimedia filtration
Sand & multimedia filtration Systems also known as depth filters or turbidity filters, usually utilized for commercial & industrial application contain one or more types of media and gravel under-bedding. The gravel is used as a support to keep smaller Medias out of the distribution system and to stop channeling of water.
It is single-media filters use graded silica san media, to remove suspended solids like algae & Microorganisms from water. The filter medium consists of a multiple layer of sand with a variety in size and specific gravity and same density , where larger grains lay toward the bottom of the filter bed and finer grains lay at the top of the filter bed. When water flows through the filter, the suspended solids precipitate in the sand layers as residue and the water of free suspended solids flows out of the filter. When the filters are loaded with particles the flow-direction is reversed, in order to regenerate it. Smaller suspended solids have the ability to pass through a sand filter, so that secondary filtration is often required.
A multimedia sand filter is similar in operation to a conventional sand filter, but instead of using a single layer of filter sand, it use 3 layers of anthracite, sand and garnet. These are often the media of choice because of the differences in mass between the materials. Garnet is by far the heaviest per unit volume, sand is intermediate while anthracite is the lightest. The idea behind using these three media of differing densities is that anthracite media, with the largest particle size, will stratify on top following backwash while the intermediate size media (sand) will settle in the middle and garnet, the heaviest but having the smallest particle diameter, will settle to the bottom.
This filter media arrangement allows the largest dirt particles to be removed near the top of the media bed with the smaller and smaller dirt particles being retained deeper and deeper in the media. This allows much longer filter run times between backwash and much more efficient dirt or turbidity removal. Sand filters typically remove particles down to 25-50 microns while a well-operated multi-media filter may remove particles from 10-25 microns.
The Deep Bed Multimedia principle offers a higher degree of filtration, longer filtration cycles and lower backwash water consumption than obtained from conventional sand filters or dual media filters.
By operating the filters at higher than normal operating pressures, we are able to promote extremely fine particle size removal; typically 5-microns and better.
The differing media layer depths and particle sizes also allow for far higher solids holding capacity without turbidity leakage.
The solids retention abilities of multimedia sand filters allow them to be operated at high filtration velocities, which result in reduced installation space and capital costs.
A multi-media filter is operate in the same manner as a sand filter, where It has three different operation that it performs. The head controls these functions and they are as follows-
Service – During service (filtration) the water is directed down through the filter media where the particles in the water are trapped. Once the water has reached the bottom of the tank, it returns to the top of the tank through the distributor.
Backwash – Once the filter bed becomes blocked with dirt, a pressure drop across the system indicates that the filter should be backwashed. On automatic systems, backwashing is controlled by a timer or water usage or differential pressure switch. During backwash the head will direct water down through the distributor and up through the media. To stir up the filter bed and float off the suspended particles. The water that leaves the top of the tank is directed to the drain. The various layers of media retain their stratification because each material has a different density.Because of the comparative weight of the filter media, only the dirt will be lost during backwash.
On manual systems, operator intervention is required to put the filter into backwash
Rinse – Once the media has been backwashed, it is rinsed by again sending water down through the media and then to drain. This will rinse any lose material at the bottom of the bed and in the riser to drain. Once rinsed, the filter will return to service
Multi-media filters are frequently operated at loading rates of 3-8 gpm per square foot of surface area and must be backwashed at 12-15 gpm per square foot to adequately lift and loosen the bed
Economical and efficient, Multi-Media Filters can be equipped for manual, semi-automatic, or full-automatic operation. Regardless of the set up, only limited technical expertise is required for operation. Multi-Media Filters will integrate into a complete water treatment system without expensive custom field engineering and programming.
Cartridge filters are preferable for systems with contaminations less than 100 ppm, that means with contamination levels less than 0.01% by weight and can be realized as surface or as depth-type filters. For concentrations that are heavier contamination applications than 100ppm, cartridges are normally used as final polishing filters, and some other method should be initially used instead of cartridge filters.
Depth-type cartridge filters capture contaminations through the total thickness of the medium, while in surface filters (usually made of thinner materials like papers, woven wire cloths) particles are captured at the surface of the filter.
Cartridge filters are also designed disposable, which means that they have to be replaced when the filter is clogged.
Fiber Filters: can be made of a variety of materials. Wound string or cord, polypropylene, polyester, cellulose, glass fiber, and cotton are among the most common
Ceramic Filters: Ceramic filters are much like fiber filters and use a process where water is forced through the pores of a ceramic filtration media. This provides mechanical filtration only. This type of filter can reduce asbestos fibers, cysts (if the pores are one micron or smaller), some bacteria (with pore sizes in the 0.2 – 0.8 micron range**) and other particulate matter.
Water filters, because they do not require the costly energy sources of reverse osmosis and distillation, provide a source of relatively inexpensive, purified water. Also, water filters waste very little water, as compared to reverse osmosis and distillation systems.