How is a slow sand filter “cleaned”?
Cleaning methods include wet harrowing, (described above in faq 19) or physically removing the top 2 or 3 centimeters of sand (usually done on larger filters with the water level significantly reduced). DO NOT “BACKWASH” A SLOW SAND WATER FILTER ( force water to flow backwards – up through the sand from the bottom drain at any pressure – high or low ). In a biological sand filter (slow sand water filter), the top few centimeters of sand contain living organisms and a biological mat. The biological mat thickens and small particles are trapped in and on top of this mat. This is what slows down the flow. If you backwash the filter you will mix all the debris throughout the filter as gravity allows the material from the top to settle down throughout the depth of the sand and this will plug the filter for good. Unlike a rapid sand filter, backwashing disrupts and may very well destroy the biological component and the physical structure of the lower layers of a biological sand filter. There
Cleaning methods include wet harrowing, (described above in faq 19) or physically removing the top 2 or 3 centimeters of sand (usually done on larger filters with the water level significantly reduced). DO NOT FORCEFULLY “BACKWASH” A SLOW SAND WATER FILTER ( force water to flow backwards – up through the sand from the bottom drain at any pressure – high or low ). There are some filter designs that use a cleaning method similar to backwashing, but the flow does not disrupt the sand layers and the design has been carefully engineered, tested and shown to be functional. Simply hooking up a pressurized water source to the bottom of a biological sand water filter and forcing water backwards through the filter ( as shown on several youtube videos) is not the same thing and will most likely destroy the filter. In a biological sand filter (slow sand water filter), the top few centimeters of sand contain living organisms and a biological mat. The biological mat thickens and small particles are
