Ceramic media are used for a nearly limitless variety of filtration jobs. We recently reported on a clay-based material for water purification applications in the developing world and a potential filter material that actually expands under pressure but currently lives only in a laboratory.
Today we have news of another organization using a decidedly low-tech approach to promoting health and safe drinking water in developing countries, as well as a ceramic-based filter membrane material that can handle tough applications from wastewater treatment to drinking water filtration.
The former is PureMadi, an organization put together by students and faculty at the University of Virginia (Charlottesville) to bring clean water to people in developing countries. We covered the PureMadi story in some detail (including a video interview with UVA professor of civil and environment engineering and PureMadi founder James Smith) back in February. The organization promotes use of simple water filters produced by local labor using clay, sawdust, and water. Its goal is to develop standardized filter factories that can be replicated throughout the developing world.
On the industrial side of filtration, from LiqTech International Inc., Ballerup, Denmark, comes news that its silicon carbide filtration technology has been certified for drinking water applications by NSF International, a public health and safety organization based in Ann Arbor, Mich. According to the company, SiC filter elements can now replace sand filters, cartridge filters, and traditional polymer/ceramic membranes in applications ranging from removal of precipitated salts from ground water, removing organic suspended solids and humic acid from surface water, and filtration of sea water before desalination.
The company says in a technical paper (pdf) on its website that its filter membranes are produced entirely from SiC, resulting in chemical resistance over the entire pH range, temperature resistance to 800˚C, porosity of approximately 45 percent, and the highest flux of any filter material. According to the paper, the filtration membrane is formed on the walls of parallel flow channels by slip casting, then drying and sintering to ensure bonding with the carrier material. Exact composition of the slip depends on desired pore size and distribution, and the filters can be produced with pore sizes from 0.04–10 μm.
Liqtech can produce filter elements up to 172 mm in diameter and 1,500 mm long, with filtration areas up to 37 m2 per element. In addition to drinking water, applications for the monolithic SiC units include filtration of oily wastewater and industrial process water; chemical, pharmaceutical, and biotech filtration; and the food and beverage industry.
According to the company, SiC’s chemical and temperature resistance allow its application where polymer filters would not be usable. “In durability tests performed on SiC membranes exposed to 1N sodium hydroxide at 90°C for several hundred hours and to 60 percent sulfuric acid at 90°C, only negligible degradation was observed,” the technical paper says. The filters also tolerate chemical cleaning and sanitation and even steam sterilization. Liqtech also manufactures SiC filter elements for diesel particulate emissions as well as SiC kiln furniture.