Abstract: A treating system comprising a horizontal zigzag flow or vertical zigzag flow treating tank having a plurality of chambers constituted by horizontally or vertically dividing the inside of the tank by partitions and connected to one another in a horizontal or vertical zigzag fashion and having filter media installed in each chamber in a standing or lying position, or a treating system having independent chambers connected with one another where treating substances flow in an alternate fashion of downward and upward flows and is discharged from the last chamber and having filter media installed in each chamber in a standing position, said filter medium comprising a core element and a number of thin tapes of synthetic resin extending radially around the core element.The treating efficiency of the system may be increased by connecting an automatic gas-lift stirring device which performs stirring of the contents of the treating tank using methane gas generating in the treating tank.