What comes to mind when you hear the phrase “clean tech”? Advanced, complex water or wastewater treatment facilities? Extensive wind energy farms? Clean rooms where solar panel technology is constructed? Hybrid fuel cars?
What about a PVC or concrete pipe 39-48” long, 16” in diameter containing a layer of fine sand over gravel?
Patent number 5,993,672, “Slow sand filter for use with intermittently flowing water supply and method of use thereof,” was granted on November 30, 1999 to David Manz of Calgary, Canada, and assigned to University Technologies International Inc., the technology transfer arm of the University of Calgary. The patent is classified as 210/744, which places it with inventions dealing with level sensing aspects of liquid purification or separation technologies.
Claim 1 of the patent states:
“A method of operating a slow sand filter for use with an intermittent supply of water, the filter including a container, filter material partially filling the container and having a top, a water inlet above the filter material and a water outlet within the filter material, the method comprising the steps of:
supplying an intermittent flow of water to the container; and
maintaining the water level in the container above the top of the filter material even when there is no flow of water through the slow sand filter at a maintenance level that is selected such that (1) water falling onto the water in the container does not disturb a schmutzdeuke layer formed on the top of the filter material and (2) the schmutzdeuke will survive even when there is no flow of water through the container for at least 24 hours.”
A “schmutzdeuke layer”? What in the world (at least we assume it is not alien) is that? “Schmutzdecke” is a German word that translates as “dirty layer.” If you look in the Background and Summary of the Invention section of the patent (which follows the claims), Manz defines the “schmutzdeuke layer” as a biological layer that forms at the top of sand when the sand is immersed in flowing water for several days. The schmutzdeuke is formed from various organisms such as algae, plankton, diatoms, protozoa and bacteria. It entraps and partially digests and breaks down organic matter container in the raw water passing through the filter. The organic matter accumulates on the schmutzdeuke and simple inorganic salts are formed. At the same time, inert suspended particles in the raw water are removed mechanically. You can see this reddish-brown layer if you have a sand-filtered aquarium. Think of it as a living version of a coffee filter.
Slow sand filters are effective in removing bacteria, parasites, Giardia cysts, Cryptosporidium oocysts and viruses from water. In fact, sand filters might be a major component of the water treatment plant that provides your drinking water if you are on a municipal water system. While bacteria, parasites and viruses may be killed or rendered inactive with disinfection, dormant cysts and oocysts are very resistant to disinfection unless the disinfectant is administered very intensively. Slow sand filters may be used to supply clean water directly for consumption or may be used to supply water for further treatment, such as by reverse osmosis and ultra-filtration, both of which processes require quite clean water to begin with.
Manz’s invention, by providing a static water level above the sand layer, allows the biosand filter to be used in situations where the water supply is intermittent (the biological filter layer dies if it dries out), such as wilderness cabins, third-world countries, and disaster settings.
Simple technology, such as this one in patentECO’s Water Index, can be clean.
