Rapid 'dry' sand filter

The 'dry' rapid sand filter is a container with sand. The water is spread over the sand with sprinklers. Because oxygen is added to the water the iron and manganese will oxidise and turn into flakes. These flakes are captured by the sand. The ammonia in the water is removed with the help of bacteria. A ventilation system is used to pull "fresh" air through the sand to provide enough oxygen to the bacteria.
The filter nozzles let the water through but not the sand. If the filter is full of "dirt" the filter is stopped. With water and air the filter is back-washed and the dirt is deposited in a settling pond.