Water Filtration Systems and their Uses
While the originators may not have fully understood its action, the concept underlying modern water filtration systems has its roots in Ancient Greece. The physicians of that time considered boiled and filtered water to be not merely cleaner but also healthier. However, lacking any knowledge of microorganisms and their role in disease, they had only empirical evidence to support their belief.
Thanks to Antonie van Leeuwenhoek‘s early microscope, and the subsequent discoveries by Pasteur, Koch, and others, we are now well aware of those invisible lifeforms that threaten our health. More importantly, we have successfully developed new and improved water filtration systems that can eliminate bacteria and various other water-borne health hazards.
Initially, filtering meant little more than removing any visible suspended solids present in a liquid and was achieved by passing it through a cloth. This simple filter medium was able to trap particles larger than the gaps between the cloth fibres while everything else passed through, including those microscopic germs. Today, the underlying idea remains the same, but filter media and their performance have improved by orders of magnitude.
In most cases, the relative efficiency of water filtration systems depends on the pore size of the filter media they employ. In practice, the pores can sometimes be quite large, as in the devices known as strainers. Strainers are used as a preliminary step in water treatment plants to remove larger pieces of debris from the incoming raw source. Typically strainers are made from perforated metal or wire mesh.
Sand and gravel beds have long been a means to remove finer particles and are now joined by more effective granular materials such as charcoal and anthracite. However, the development of water filtration systems capable of retaining microscopic particles, including bacteria, viruses and even molecules, has undoubtedly been the most significant advance in this field.
Modern filter media have pore sizes ranging from a few microns to thousandths of a micron. Based on that size, the media can be classified as either microfiltration (0,05 to 5 microns), ultrafiltration ( 0,001 to 0,05 micron) or nanofiltration (0,008 to 0,01 micron) products. While each of these is able to capture microorganisms to varying degrees, ion-exchange and reverse osmosis (RO) are the only water filtration systems capable of removing molecules. However, ion-exchange resins rely on electrochemical forces to retain ions selectively. By contrast, RO utilises synthetic, semipermeable membranes with a pore size of around 0,0001 microns, small enough to trap aqueous salts and metal ions.