The main pollutant in waste water discharged from a petroleum refinery is oil (b

The main pollutant in waste water discharged from a petroleum refinery is oil (both in free and emulsified form). Free oil is removed by

Water filtration rate in a slow sand filter ranges from __________ litres/m 2 /h

Water filtration rate in a slow sand filter ranges from __________ litres/m 2 /hr.