Method for separating pollutants from liquid

Claim 1

In a method for filtering wherein liquid comprising a suspension or emulsion to be filtered is supplied to a zone of particle filter medium forming a filter bed, the liquid being filtered flows, during the filtration thereof, in an upward direction through the filter bed and is discharged from the filter bed as filtrated liquid phase, and wherein the filter medium during the filtration flows in a downward direction through the filter bed in counter-current to the liquid being filtered, past the inflow of the liquid and thereafter is transported separated from the filter bed to a wash path for washing the dirty filter medium during flow along the wash path in counter-current to a wash liquid, whereupon the washed filter medium is returned to the filter bed zone to its top surface, at least a part of the filtrated liquid phase which is discharged from the filter bed zone is maintained above this zone as a zone of filtrated liquid phase in direct contact with the filter bed zone, and said counter-current washing of the dirty filter medium along the wash path takes place during flow of the dirty filter medium in counter-current to a portion of said filtrated liquid phase utilized as wash liquid, said portion of said filtrated liquid phase being supplied to the wash path from said zone of filtrated liquid phase, the improvement comprising adding to the liquid to be filtered chemicals facilitating at least one of the processes of precipitation and flocculation, continuously directing the liquid containing the chemicals from the chemical addition location directly to a zone of moving particulate filter material forming the filter bed, absent intermediate passage through any flocculation tank and absent intermediate passage through any sedimentation basin, passing the liquid containing the chemicals through the filter bed to provide at least one of the precipitation and flocculation processes within the moving particulate material of the bed.