Used either on a standalone basis or as part of a multi-stage treatment process, the main purpose of water filter systems is to remove any particulate matter present in the liquid. In a typical multi-stage operation, any solid particles that were sufficiently large and dense would have been removed by sedimentation assisted, perhaps, with the addition of chemical flocculants or coagulants in order to include any additional particles held in colloidal suspension. A much cruder form of filtration, known as screening, is used to remove very large items, such as discarded bottles and branches.
Anyone, who may have studied chemistry for matric, will be likely to recall class experiments in which a simple glass funnel lined with a disc of porous paper was used to separate some coloured precipitate from the liquid in which it was formed. However, while of no consequence to the experiment, the filtrate would not have been pure water, but was certain to contain any soluble products of the precipitation reaction, and possibly even micro-organisms, since these are far too small to be removed by such basic water filter systems.
Like the paper, in their simplest form, filtration media rely on physical properties alone, acting much like a miniature colander. This means the quality of the filtrate obtained is based purely on the size of the tiny holes or spaces in their structure. They need to be sufficiently small to retain the particles present in the source liquid. Advances in the related technology and in the manufacture of specialised filtration membranes have led to a new breed of water filter systems that also use chemical and biological properties, and possess the ability to perform separations at the molecular level. Nevertheless, both the conventional and more advanced technologies have found numerous applications, not just in the fields of industry and commerce, but also in the home and in the great outdoors.
For large scale filtration, such as that undertaken at a municipal treatment plant, the primary filtration medium employed is often sand or a mixture of sand with various aggregates. As the liquid passes between the grains of sand, any insoluble particles present adhere to their surface, and a clear filtrate is formed. In water filter systems of this type, the filtrate will then be removed and subjected to further treatments in order to produce water of drinkable quality.
At the other end of the scale are the devices used to keep swimming pools free of suspended solids. While most modern installations also depend upon so-called sand filters, some older models also use bags woven from fabric for this purpose. When these materials become too clogged with trapped particles, they may then be back-washed in order to expel the waste.
Even more compact are the water filter systems commonly connected to domestic supplies, and designed to remove any residual chemical content, such as chlorine, which some users feel makes domestic tap water less palatable for culinary purposes. This type of device will generally employ granular, activated charcoal, microporous ceramics or membranes, or some combination of these as the filtration medium. For ease of installation, they are designed to be compatible with the existing plumbing fitments.
When far from the nearest tap, and limited in one’s capacity to carry reserves, it is often necessary to drink from natural sources. For military personnel on a mission, or hikers simply enjoying a weekend in the bush, there are now portable water filter systems. Dirty water is hand-pumped through the device, which then extracts any solids present along with live and encysted bacteria, and protozoa that could otherwise cause serious illness. The potable filtrate is collected in an attached container, ready for use.
In a number of instances, it is dissolved compounds within the liquid that need to be removed, and so, physical filtration methods are of no use. Instead, it is common practice to pass liquids through layers of special resins with the ability to attract any unwanted cations and anions, and replace them with hydrogen and hydroxyl ions, which then form more water. Ion exchange resins are widely used in the pharmaceutical and food and beverage industries to provide water of exceptional purity.
Though not a water filter system in the strictest sense, reverse osmosis is now an important technology for the removal of chemical compounds, and has replaced distillation as the method of choice in desalination plants. Wherever water quality is essential, consult Watericon for an innovative solution.