Slow sand filter for use with intermittently flowing water supply and method of use thereof

A slow sand filter apparatus capable of being operated intermittently comprising:

• a container having an upper portion and a lower portion;
• a water inlet in the upper portion of the container, the water inlet being connected to a supply of water;
• a first layer of filter material in the lower portion;
• a second layer of filter material above the first layer filling at least the lower portion of the container, the second layer of filter material having a top surface below the water inlet;
• a schmutzdeuke layer on the top surface of the second layer of filter material;
• a perforated diffuser below the water inlet and above a water maintenance level, the water from the water inlet passing through the perforations in the diffuser before reaching the top of the water maintenance level and the underlying second layer of filter material;
• a water outlet in the lower portion of the container below the top surface of the second layer of filter material;
• and
• a water level maintenance device which maintains water in the upper portion of the container at a maintenance level between about 1 cm and 8 cm above the top surface of the schmutzdeuke layer and the second layer of filter material, the maintenance level device comprising
• a first water level detector to detect an upper water level in the container;
• a second water level detector to detect a lower water level in the container;
• and
• a programmed microprocessor connected to receive signals from the first and second container water level detectors and to provide signals to a water inlet control means, so that the water maintenance level is maintained between (1) a water maintenance level that is sufficiently deep that water falling from the water inlet through the diffuser onto the top of the water in the container does not significantly disturb the schmutzdeuke layer;
• and (2) a water maintenance level that is sufficiently shallow that oxygen from the air above the water level can diffuse through the water and reach the schmutzdeuke layer so that the schmutzdeuke layer is maintained in living condition even when there is no flow of water through the water inlet.