It has been almost one month since we were in Orlando for the Water Quality Assn. Convention & Exposition, and we keep thinking back to our...
Ceramic filter technologies remove pathogens and improve water quality
Nearly two centuries after Henry Doulton invented it, the ceramic water filter continues to be manufactured by the millions. It plays a significant role in the provision of clean, safe water throughout the world.
The filter elements are produced using modern manufacturing techniques to provide a hollow, porous ceramic that is fired at temperatures in excess of 1,830°F. They are most often made from diatomite, which in its raw state is a chalky, fine-grained, low-density material.
Diatomite contains a high percentage of silica, has a cellular nature, and is characterized by a porosity of around 80%. Most people think of ceramics as brittle, but the way the shaped diatomite is sintered, often with organic binders and lubricants, aids densification and produces a strong final component.
The smaller the pore size in the filter wall and the more tortuous the path the water must follow, the more effective the particle removal process. Ceramics have a small, complex, interconnected pore structure — sometimes down to 0.2 µ — making them ideal for the job.
Furthermore, major manufacturers such as Fairey Industrial Ceramics, which has been producing the Doulton range for 187 years in the U.K., are able to accurately control this pore structure, thus ensuring product consistency. Ceramic filters are chemically inert, so they can be used right away or brought out of storage after many years, and will perform with identical effectiveness.
When it comes to the fired ceramic tubes, there are two established shapes: the candle and the cartridge, designed in such a way that the water passes from the outside to the inside.
Ceramic candles are formed with a domed, closed end at the base and are open at the top. The open end is closed off with a food-grade plastic mount, which enables the candle to fit into a filter housing.
By contrast, ceramic cartridges are formed with both ends open, which also are closed off with plastic mounts. The mount at the base is completely closed, while the one at the top has an opening through which the filtered water flows after it has passed through the ceramic.
In both configurations, ceramic tubes offer a rigorous two-stage filtration process — surface filtration and then depth filtration — in order to trap particles and pathogens.
In surface filtration, particles larger than the pore cannot pass through, and smaller particles hitting the pore at the same time collide, adhere and form a bridge. Additionally, due to inertial mass, particles do not automatically follow the water flow through the pores anyway, and can collide with non-porous areas of the tube wall and be held there.
Particles that do penetrate the ceramic wall then are subjected to depth filtration. This works in three ways. Particles much smaller than the pores are intercepted within the ceramic wall, because the water is forced to flow through a complex series of labyrinths. The path through the filter has many sharp angles due to the complicated ceramic structure, so particles become trapped within it.
Secondly, as with bridging on the surface, small particles can combine to form clusters large enough to become trapped in dead-end cavities.
Thirdly, dispersion forces cause other small particles to become attracted to the ceramic and simply adhere to it in a process known as adsorption.
The versatility of ceramic filters also can be enhanced when used in tandem with special water treatment cartridges. Typical examples would be prefilters, to prevent premature clogging of filters in high-sediment areas; limescale reduction cartridges, for hard water areas; and fluoride reduction cartridges, which help reduce both natural and added fluoride.
In addition to removing dirt particles, ceramic filters have been shown via independent test results to be effective against pathogenic bacteria, microbial cysts and heavy metals. At the same time, they leave the oxygen and trace mineral content unchanged, resulting in a clean, fresh taste.
All around the world, wherever consumers rely on untreated water supplies, stored water or simply only have access to polluted water, people face potentially fatal disease through the ingestion of pathogenic bacteria.
Added to that is the danger posed by waterborne microbial cysts — resistant to chlorine treatment — that cause stomach and intestinal problems, including potentially life-threatening diarrheal disease. The size of the threat cannot be underestimated: Globally, diarrheal disease kills 800,000 children every year.
When it comes to pathogenic bacteria, ceramic systems can filter out the organisms and parasites that cause cholera, typhoid fever, cryptosporidiosis, amoebic dysentry, colibacillosis, schistosomiasis and more. Additionally, more than 99.99% of microbial cysts are removed.
Other undesirables elements in water also can be eliminated. Chlorine affects both the taste and odor of water, but is easily addressed with the addition of activated carbon to the ceramic filter. Where lead contamination is an issue, the inclusion of an ion exchange resin effectively deals with the problem.
The Case for Ceramic