Water purifiion
They are washed by using air to first loosen the sand and then water, at an up wash rate of 32 m/h, to wash away all the collected dirt. Filters are covered to exclude light to less than 25 lux to prevent algal growth on the filters. After filtration, the water has a residual turbidity of 0,5 NTU or less. The filter backwash water is treated to remove organics, heavy metals, bacteria and .