We are offering sand filters with automatic back wash options. the sand filtration removes the suspended solids from the effluent coming from the secondary clarifier. During filtering operations the retained solids cause an increase of head losses; when apre-set value is achieved (usually 1.0 bar) backwashing with filtered water automatically takes place. Due to the weight of filtered solids, washing with water isnt enough to clean the filter media properly, so the backwashing is normally performed with both water and air.