A waste liquid treatment apparatus with enhanced treatment capacity for a pre-treatment facility of a liquid radwaste treatment system for a nuclear power plant. The waste liquid treatment apparatus includes: a water tank into which a waste liquid is introduced and from which filtered permeated water is discharged; a waste liquid introduction section through which waste liquid is introduced into the water tank; submerged membranes annularly disposed and spaced apart from each other for filtering foreign substances from the waste liquid; a permeated water suctioning section suctioning the filtered water of the waste liquid and discharging the filtered water outside the water tank; an air supplying section supplying compressed air to the submerged membranes to remove foreign substances; and a porous support plate supporting the submerged membranes.